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Satellite Missions Catalogue

SkySat Constellation

Jul 26, 2016

EO

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High resolution optical imagers

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Land

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Multi-purpose imagery (land)

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SkySat is the world’s largest fleet of high-resolution imaging satellites, with a total of 21 satellites launched to date, owned by Planet Labs. The main goal of the constellation is to provide high-resolution panchromatic and multispectral imagery of any place on Earth multiple times a day. SkySat-1 and SkySat-2 are called A and B generations, the other 19 satellites are called modernised C generation satellites.

Quick facts

Overview

Mission typeEO
AgencyPlanet
Mission statusOperational (extended)
Launch date21 Nov 2013
Measurement domainLand
Measurement categoryMulti-purpose imagery (land)
Measurement detailedLand surface imagery
InstrumentsSkySat Camera
Instrument typeHigh resolution optical imagers
CEOS EO HandbookSee SkySat Constellation summary

Related Resources

Four satellites of the SkySat Constellation (Image credit: Space Systems Loral)


 

Summary

Mission Capabilities

SkySat Camera is a Cassegrain telescope with a focal length of 3.6 m, with three 5.5 megapixel Complementary Metal Oxide Semiconductor (CMOS) imaging detectors making up the focal plane and able to collect frame imagery, stereo imagery, and video by day and by night.

Each SkySat satellite is three-axis stabilised and agile enough to slew between different targets of interest. SkySat imagery offers various environmental applications, including monitoring agriculture, forestry, and other natural resources, as well as asset tracking, where spacecraft images help customers monitor various facilities for changes. It captures on-demand imagery of targets requested by customers. The resolution of the SkySat satellite imagery and videos is high enough to observe objects that impact the global economy such as terrain, cars and shipping containers. The satellites can capture video clips lasting up to 90 seconds at 30 frames per second.
 

Performance Specifications

The optical imager covers a panchromatic band from 450 - 900 nm achieving a resolution of 0.90 m at nadir. Four multispectral channels are covered by the satellite (Blue 450-515 nm, Green 515-595 nm, Red 605-695 nm, and Near Infrared 740-900 nm) achieving a multispectral resolution of 2 m at nadir. A ground swath of 8 km is covered at nadir, and stereo imaging is supported by the satellite.

The first 15 SkySat satellites are in a sun-synchronous orbit, while the remaining six operate in an inclined, non sun-synchronous orbit, with inclination 53o. These non-sun-synchronous orbits increase the image cadence between 52o northern and southern latitude up to 6-7 times per day on worldwide average, with a maximum of 12 times per day. Depending on the satellite’s specific orbit, the altitude varies from 400 km to 600 km and the sun-synchronous satellites have LTDN (Local Time on Descending Node) of 1030 hours or 1300 hours. 

Space and Hardware Components

SkySat images are compressed with JPEG 2000 and then stored in the 768 GB of onboard storage, or downlinked to the ground station at a rate of 450 Mbit/s. The SkySat fleet is composed of satellite buses with both maneuverableand non-maneuverable capabilities. 
The design life of Generation A and B buses is approximately four years, while Generation C has a design life of approximately six years.

SkySat Constellation

Spacecraft     Launch    Mission Status     Sensor Complement    Propulsion Subsystems    Ground Segment    References

 

SkySat is a commercial Earth observation microsatellite of Skybox Imaging Inc. (Mountain View, CA, USA), licensed to collect high resolution panchromatic and multispectral images of the Earth. 1) 2) 3) 4)  In 2014, Google purchased Skybox Imaging, rebranding it as Terra Bella. Then, in 2017, Planet aquired Terra Bella, with Google maintaining a share in Planet as part of the deal.

Skybox Imaging (Skybox) provides global customers easy access to reliable and frequent high-resolution images of the Earth by designing and building microsatellites and cloud services. By operating the world's first coordinated microsatellite constellation, Skybox aims to empower commercial and government customers to make more informed, data-driven decisions that will improve the profitability of companies and the welfare of societies around the world. Founded in Silicon Valley in 2009 by four graduate students at Stanford University, Skybox is backed by leading venture firms and comprised of internet and aerospace professionals.

Skybox Imaging is looking at two distinct markets for their imagery and video: various environmental applications, including monitoring agriculture, forestry, and other natural resources; and asset tracking, where spacecraft images help customers monitor various facilities for changes. Those plans have won Skybox a significant amount of VC (Venture Capital) funding. In 2012, the company raised $70 million in a Series C round of financing, bringing the total raised by the company to $91 million. Khosla Ventures, Bessemer Venture Partners, Canaan Partners, and Norwest Venture Partners, VC firms who have a significant Silicon Valley presence, have all invested in the company. 5)

Figure 1: The co-founders of Skybox Imaging (left to right): Dan Berkenstock, Ching-Yu Hu, Julian Mann and John Fenwick (image credit: Skybox Imaging) 6)
Figure 1: The co-founders of Skybox Imaging (left to right): Dan Berkenstock, Ching-Yu Hu, Julian Mann and John Fenwick (image credit: Skybox Imaging) 6)

• In May 2013, Skybox announced it has entered into a multi-year, strategic partnership with Japan Space Imaging (JSI), a subsidiary of Mitsubishi Corporation, to provide high-resolution imagery and full motion commercial video to the Japanese market. The agreement, subject to U.S. regulatory approval, will enable JSI to directly task, downlink and receive imagery from Skybox's constellation of microsatellites on a reliable and frequent basis. 7) 8) 9) 10)

• After building its first two satellites, Skybox hired SS/L (Space Systems/Loral) to build the next 13 improved spacecraft and Orbital Sciences Corp. to launch six in late 2015 on a Minotaur-C rocket from Vandenberg Air Force Base in California. Skybox plans to offer customers timely access to still imagery, full-motion video and data services. 11)

- SSC Corp.’s ECAPS division will provide propulsion systems for 12 satellites to be built for imagery services of startup Skybox Imaging, the companies announced March 11. ECAPS (Ecological Advanced Propulsion Systems, Inc., Solna, Sweden), a subsidiary of Sweden-based SSC, was already under contract to supply the propulsion system for that satellite, dubbed SkySat-3, and now has an order for the remaining 12. 12)

- SkySat-3 is expected to be launched in the summer of 2016.

• On June 10, 2014, Skybox announced that it had entered into an agreement to be acquired by Google for US$500 million. The acquisition was completed on August 1, 2014. Skybox is now a subsidiary of Google (Ref. 63).

• In January 2016, Arianespace announced it signed a contract with Skybox Imaging to launch four SkySat minisatellites (SkySat-4 though -7) on a Vega vehicle from Kourou in the summer of 2016, along with PeruSat-1 of the Peruvian Armed Forces.

 

Figure 2: Illustration of the SkySat-1 and -2 microsatellites (left) to the second generation SkySat-3 minisatellite (image credit: Skybox, Ref. 70)
Figure 2: Illustration of the SkySat-1 and -2 microsatellites (left) to the second generation SkySat-3 minisatellite (image credit: Skybox, Ref. 70)

SkySat-3 will be different than SkySat-1, and -2 in these ways:

- smaller pixels

- increased agility to collect more area

- propulsion for orbit stationing.

 


Spacecraft

SkySat-1 and SkySat-2 are microsatellites built and operated by Skybox Imaging that are licensed to acquire high resolution panchromatic and multispectral images of Earth. The spacecraft are three-axis stabilized using an on-board closed-loop control system. Each satellite has a mass of 83 kg and features body-mounted solar panels. The microsatellites feature an aperture cover that protects the imaging payload during launch and initial orbital operations. The cover also hosts the high-data rate antenna of the satellite. The spacecraft will acquire high-resolution images and video of Earth. 13)

Figure 3: Photo of the SkySat-1 microsatellite in the clean room of Skybox Imaging (image credit: Skybox Imaging)
Figure 3: Photo of the SkySat-1 microsatellite in the clean room of Skybox Imaging (image credit: Skybox Imaging)

Spacecraft mass

83 kg (microsatellite)

Spacecraft size (stowed configuration)

60 cm x 60 cm x 80 cm

Spacecraft power

120 W OAP (Orbit Average Power), use of body mounted solar panels

Attitude control accuracy

±0.1º

RF communications

X-band downlink of payload data: 470 Mbit/s
S-band uplink: 16 kbit/s
Onboard data storage capacity: 768 GB

Design life

4 years

Table 1: Parameters of the SkySat-1 and SkySat-2 spacecraft parameters

 

Flight qualification of the star trackers conducted on orbit for the SkySat-1 mission: 14)

The performance of the two ST-16 star trackers, developed at Sinclair Interplanetary,fell initially significantly below expectations. Concerned by these results, engineers at Skybox Imaging (SB), Sinclair Interplanetary (SI) and Ryerson University (RU) embarked on an aggressive and comprehensive flight qualification program to understand the causes of these problems and to re-attain the expected performance targets. Two months later (February, 2014), the the investigative project made the last of a sequence of software, catalog and parameter modifications that have met these goals.

Accuracy

< 7 arcsec RMS cross-boresight, < 70 arcsec RMS around boresight

Availability

>99.9%

Size, mass

59 x 56 x 31.5 mm, ~90 gram

FOV (Field of View)

7:5º (half axis)

Exposure time

100 ms

Catalog

3746 stars

Table 2: Key parameters of the ST-16 Star Tracker
Figure 4: Photo of the Sinclair Interplanetary ST-16 Star Tracker (image credit: SI)
Figure 4: Photo of the Sinclair Interplanetary ST-16 Star Tracker (image credit: SI)

Collaborative relationship: Restoring the star trackers to full function was do-or-die for both Skybox Imaging and Sinclair Interplanetary. Skybox had invested in the spacecraft, and Sinclair in the star tracker product, and neither could afford to fail. While stressful, this unity of purpose was in no small part responsible for timely success. Skybox operations was extremely accommodating in collecting and delivering large quantities of data. Sinclair and Ryerson focused exclusively on this problem for a two month period. In a more relaxed and less motivated environment the necessary advances might not have been made.

In summary, there were many improvements being done to sensor processing on the ST-16 that were necessary to bring the sensor performance back up to their intended specifications. These changes included improvements in the logic for star detection, star measurement, rate estimation, and catalog management. Together the algorithmic improvements yielded higher availability, better accuracy, and much-lower bad-match rate. Although new launches may require a short qualification period to tune calibration and operating parameters, the project expects that the core software is stable.

Figure 5: SkySat-1 and SkySat-2 deployed configuration (image credit: SkyBox Imaging) 15)
Figure 5: SkySat-1 and SkySat-2 deployed configuration (image credit: SkyBox Imaging) 15)

Launch

SkySat-1

The SkySat-1 microsatellite was launched on Nov. 21, 2013 as a secondary payload on a Dnepr launch vehicle from the Dombarovsky (Yasny Cosmodrome) launch site in Russia. The launch provider was ISC (International Space Company) Kosmotras. 16) 17) 18) 19)

The primary payloads on this flight were DubaiSat-2 of EIAST (Emirates Institute for Advanced Science and Technology), a minisatellite of UAE (United Arab Emirates) with 300 kg, and STSat-3, a minisatellite of KARI, Korea (~150 kg).

The secondary payloads on this flight were

• SkySat-1 of Skybox Imaging Inc., Mountain View, CA, USA, a commercial remote sensing microsatellite of ~83 kg.

• WNISat-1 (Weathernews Inc. Satellite-1), a nanosatellite (10 kg) of Axelspace, Tokyo, Japan.

• BRITE-PL-1, a nanosatellite (7 kg) of SRC/PAS (Space Research Center/ Polish Academy of Sciences of Warsaw, Poland.

• AprizeSat-7 and AprizeSat-8, nanosatellites of AprizeSat, Argentina (SpaceQuest)

UniSat-5, a microsatellite of the University of Rome (Universita di Roma “La Sapienza”, Scuola di Ingegneria Aerospaziale). The microsatellite has a mass of 28 kg and a size of 50 cm x 50 cm x 50 cm. When on orbit, UniSat-5 will deploy the following satellites with 2 PEPPODs (Planted Elementary Platform for Picosatellite Orbital Deployer) of GAUSS:

- PEPPOD 1: ICube-1, a CubeSat of PIST (Pakistan Institute of Space Technology), Islamabad, Pakistan; HumSat-D (Humanitarian Satellite Network-Demonstrator), a CubeSat of the University of Vigo, Spain; e-st@r-2 (Educational SaTellite @ politecnico di toRino-2), of Politecnico di Torino, Italy; PUCPSat-1 (Pontificia Universidad Católica del Perú-Satellite), a 1U CubeSat of INRAS (Institute for Radio Astronomy), Lima, Peru; Note: PUCPSat-1 intends to subsequently release a further satellite Pocket-PUCP) when deployed on orbit. 20)

- PEPPOD 2: Dove-4, a 3U CubeSats of Cosmogia Inc., Sunnyvale, CA, USA

MRFOD (Morehead-Roma FemtoSat Orbital Deployer) of MSU (Morehead State University) is a further deployer system on UniSat-5 which will deploy the following femtosats:

- Eagle-1 (BeakerSat), a 1.5U PocketQub, and Eagle-2 ($50SAT) a 2.5U PocketQub, these are two FemtoSats of MSU (Morehead State University) and Kentucky Space; Wren, a FemoSat (2.5U PocketQub) of StaDoKo UG, Aachen, Germany; and QBSout-1, a 1U PocketQub testing a finely pointing sun sensor.

• Delfi-n3Xt, a nanosatellite (3.5 kg) of TU Delft (Delft University of Technology), The Netherlands.

• Triton-1 nanosatellite (3U CubeSat) of ISIS-BV, The Netherlands

• CINEMA-2 and CINEMA-3, nanosatellites (4 kg each) developed by KHU (Kyung Hee University), Seoul, Korea for the TRIO-CINEMA constellation.

• GATOSS (former GOMX-1), a 2U CubeSat of GomSpace ApS of Aalborg, Denmark

• NEE-02 Krysaor, a CubeSat of EXA (Ecuadorian Civilian Space Agency)

• FUNCube-1, a CubeSat of AMSAT UK

• HiNCube (Hogskolen i Narvik CubeSat), a CubeSat of NUC (Narvik University College), Narvik, Norway.

• ZACUBE-1 (South Africa CubeSat-1), a 1U CubeSat (1.2 kg) of CPUT (Cape Peninsula University of Technology), Cape Town, South Africa.

• UWE-3, a CubeSat of the University of Würzburg, Germany. Test of an active ADCS for CubeSats.

• First-MOVE (Munich Orbital Verification Experiment), a CubeSat of TUM (Technische Universität München), Germany.

• Velox-P2, a 1U CubeSat of NTU (Nanyang Technological University), Singapore.

• OPTOS (Optical nanosatellite), a 3U CubeSat of INTA (Instituto Nacional de Tecnica Aerospacial), the Spanish Space Agency, Madrid.

• Dove-3, a 3U CubeSats of Cosmogia Inc., Sunnyvale, CA, USA

• CubeBug-2, a 2U CubeSat from Argentina (sponsored by the Argentinian Ministry of Science, Technology and Productive Innovation) which will serve as a demonstrator for a new CubeSat platform design.

• BPA-3 (Blok Perspektivnoy Avioniki-3) — or Advanced Avionics Unit-3) of Hartron-Arkos, Ukraine.

Deployment of CubeSats: Use of 9 ISIPODs of ISIS, 3 XPODs of UTIAS/SFL, 2 PEPPODs of GAUSS, and 1 MRFOD of MSU.

Orbit: Sun-synchronous near-circular orbit, altitude = 600 km, inclination = 97.8º, LTDN (Local Time on Descending Node) = 10:30 hours.

SkySat-2

The SkySat-2 microsatellite was launched as a secondary payload on July 8, 2014 (15:58:28 UTC) with a Soyuz-2.1b/Fregat launch vehicle of NPO Lavochkin. The launch site was the Baikonur Cosmodrome, Kazakhstan. The primary payload on this flight was the Meteor-M-2 spacecraft of Roskosmos/Roshydromet/Planeta (Moscow, Russia). 21) 22) 23) 24)

Secondary payloads on this flight were:

• MKA-PN2 (Relek), a microsatellite of Roskosmos, S/C developer NPO Lavochkin on the Karat platform (59 kg, study of energetic particles in the near-Earth space environment (ionosphere) including the Van Allen Belts.

• DX-1 (Dauria Experimental-1), the first privately-built and funded Russian microsatellite (22 kg) of Dauria Aerospace, equipped with an AIS (Automatic Identification System) receiver to monitor the ship traffic. 25)

• TechDemoSat-1 of UKSA/SSTL, UK with a mass of 157 kg

• SkySat-2 of Skybox Imaging Inc. of Mountain View, CA, USA, a commercial remote sensing microsatellite of 83 kg.

• M3MSat dummy payload of 80 kg.

• AISSat-2, a nanosatellite with a mass of ~7 kg of FFI (Norwegian Defense Research Establishment) Norway, built by UTIAS/SFL, Toronto, Canada.

• UKube-1, a nanosatellite (~3.5 kg) of UKSA/Clyde Space Ltd., UK.

Orbit of Meteor-M2: Sun-synchronous circular orbit , altitude of ~ 825 km, inclination = 98.8º, period = 101.41 minutes, LTAN (Local Time on Ascending Node) at 9:30 hours.

Orbit of the secondary payloads: Sun-synchronous near-circular orbit, altitude of ~ 635 km, inclination = 98.8º. The MKS-PN2 (Relek) was released first of the secondary payloads into an elliptical orbit of 632 km x 824 km.

SkySat-3

The SkySat-3 microsatellite was launched as a secondary payload on June 22, 2016 (03:56 UTC) aboard a PSLV vehicle of ISRO (PSLV-C34 flight) from SDSC (Satish Dhawan Space Center) SHAR (main launch center of ISRO on the south-east coast of India, Sriharikota). The CartoSat-2C mission was the primary payload on this flight with a launch mass of 727.5 kg. The total mass of all satellites onboard was 1288 kg. 26)

Orbit: Sun-synchronous orbit, altitude = 515 km, inclination = 97.56º.

The secondary payloads (19 satellites) on this flight were:

• SkySat-3, also referred to as SkySat-C1, an imaging minisatellite of Terra Bella of Mountain View, CA, USA. The first satellite of the SkySat constellation with a HPGP (High Performance Green Propulsion System).

• GHGSat, a microsatellite (15 kg) of GHGSat Inc., Montreal, Canada

• BIROS (Bi-spectral InfraRed Optical System), a minisatellite 130 kg) of DLR, Germany.

- BIROS carries onboard the picosatellite BEESAT-4 (Berlin Experimental and Educational Satellite-4) of TU Berlin(1U CubeSat, 1 kg) and release it through a spring mechanism [ejection by SPL (Single Picosatellite Launcher) after the successful check-out and commissioning of all relevant BIROS subsystems]. After separation, it will perform experimental proximity maneuvers in formation with the picosatellite solely based on optical navigation.

• M3MSat (Maritime Monitoring and Messaging Microsatellite) of DRDC (Defence Research and Development Canada) and CSA (Canadian Space Agency).

• LAPAN-A3, a microsatellite (115 kg) of LAPAN (National Institute of Aeronautics and Space of Indonesia) Jakarta, Indonesia.

• SathyabamaSat, a 2U CubeSat of Sathyabama University (1.5 kg), India.

• Swayam, a 1U CubeSat of the College of Engineering (1 kg), Pune, India.

• 12 Flock-2p Earth observation satellites (3U CubeSats) of Planet Labs (each with a mass of 4.7 kg), San Francisco, CA.

Figure 6: The 20 satellites, with the primary payload CartoSat-2C on top) are packaged inside the PSLV’s payload fairing. The number marks the most satellites ever launched by India on a single flight (image credit: ISRO)
Figure 6: The 20 satellites, with the primary payload CartoSat-2C on top) are packaged inside the PSLV’s payload fairing. The number marks the most satellites ever launched by India on a single flight (image credit: ISRO)
Figure 7: Photo of the SkySat-3 minisatellite with a mass of ~ 120 kg and the integrated HPGP propulsion system (red boxes), image credit: Terra Bella
Figure 7: Photo of the SkySat-3 minisatellite with a mass of ~ 120 kg and the integrated HPGP propulsion system (red boxes), image credit: Terra Bella

SkySat-4 to -7

Four SkySat minisatellites (SkySat-4 through SkySat-7) of Terra Bella, secondary payloads to PeruSat-1 (primary payload of the Peruvian Armed Forces), were launched on September 16, 2016 (01:43:35 UTC) on a Vega vehicle of Arianespace from Kourou. 27)

Orbit: Sun-synchronous orbit, altitude = 695 km, inclination = 98.3º.

Secondary payloads:

• SkySat-4 to -7. The four imaging minisatellites of TerraBella (former SkyBox Imaging, Mountain View, CA, USA) are part of this mission. The four secondary payloads are integrated in the upper position atop the VESPA (Vega Secondary Payload Adaptor) dispenser system, and will be released one-by-one during the flight sequence's 40-minute mark, to be followed by PeruSat-1's separation approximately one hour and two minutes later. 28)

The SkySat satellites, each with a mass of approximately 110 kg, will be used to provide very-high-resolution maps of the entire Earth, augmenting the existing three on orbit satellites for new Arianespace customer Terra Bella, a Google company.

Terra Bella’s satellites — SkySat-4, -5, -6 and -7 — separated from the Vega rocket’s upper stage over a ground station in South Korea about 40 minutes after liftoff into an orbit about 500 km above Earth. 29)

Figure 8: Artist’s concept of the four SkySat satellites deploying one after another from the Vega rocket’s upper stage (image credit: Arianespace)
Figure 8: Artist’s concept of the four SkySat satellites deploying one after another from the Vega rocket’s upper stage (image credit: Arianespace)

SkySat-8 to -13

On Oct. 31, 2017 (21:37 UTC), six SkySat minisatellites of Terra Bella (a Planet Labs company) and 4 Dove (Flock-3m) nanosatellites of Planet Labs were launched on a Minotaur-C vehicle of Orbital ATK from VAFB, CA (SLC-576E). The Minotaur-C is an upgraded, renamed version of the Orbital Sciences Taurus rocket. Approximately 12 minutes into flight, the ten commercial Planet spacecraft deployed into their targeted sun synchronous orbit of 500 km altitude. 30) 31)

Orbit: Sun-synchronous near-circular orbit, altitude of ~500 km, inclination of ~97º.

Figure 9: Illustration of the launch sequence (image credit: Orbital ATK) 32)
Figure 9: Illustration of the launch sequence (image credit: Orbital ATK) 32)

The launch was the first time Planet was the primary customer for a launch, having relied on secondary payload accommodations for all its previous launches. That meant that, for this mission, the company was able to choose the orbit and time of the launch, said Mike Safyan, senior director for launch and global ground stations at Planet, in post-launch statement.

“We sent these 10 satellites to an afternoon crossing time of approximately 13:30 hour to further diversify our product offering,” said Safyan. Most remote sensing satellites, he said, operate in morning-crossing sun synchronous orbits, including the company’s other Dove and SkySat spacecraft. “Having the world’s largest fleet of medium and high-resolution assets in both morning and afternoon crossing times enables a dataset never before provided in the commercial market at this scale,” he said. 33)

Figure 10: The six SkySats and four Doves were enclosed inside the Minotaur-C’s payload fairing earlier in October (image credit: FAA/Orbital ATK)
Figure 10: The six SkySats and four Doves were enclosed inside the Minotaur-C’s payload fairing earlier in October (image credit: FAA/Orbital ATK)

SkySat-14 and -15

The SkySat-14 and -15 microsatellites (100 kg each) of the SSO-A rideshare mission of Spaceflight were launched on 3 December 2018 (18:34 GMT) on a SpaceX Falcon-9 Block 5 vehicle from VAFB (Vandenberg Air Force Base) in California, 34)

SpaceX statement: On Monday, December 3rd at 10:34 a.m. PST (18:34 GMT), SpaceX successfully launched Spaceflight SSO-A: SmallSat Express to a low Earth orbit from Space Launch Complex 4E (SLC-4E) at Vandenberg Air Force Base, California. Carrying 64 payloads, this mission represented the largest single rideshare mission from a U.S.-based launch vehicle to date. A series of six deployments occurred approximately 13 to 43 minutes after liftoff, after which Spaceflight began to command its own deployment sequences. Spaceflight’s deployments are expected to occur over a period of six hours. 35)

This mission also served as the first time SpaceX launched the same booster a third time. Falcon 9’s first stage for the Spaceflight SSO-A: SmallSat Express mission previously supported the Bangabandhu Satellite-1 mission in May 2018 and the Merah Putih mission in August 2018. Following stage separation, SpaceX landed Falcon 9’s first stage on the “Just Read the Instructions” droneship, which was stationed in the Pacific Ocean.

Orbit: Sun-synchronous circular orbit with an altitude of 575 km, inclination of ~98º, LTDN (Local Time of Descending Node) of 10:30 hours.

SkySat-16 to -18

Three of Planet’s SkySat Earth-imaging microsatellites are mounted on top of 58 of SpaceX’s Starlink broadband satellites for launch on 13 June 2020 (09:21 UTC) from Cape Canaveral on top of a Falcon 9 rocket, the first secondary payloads to ride to orbit on SpaceX’s commercial rideshare service. The mission, known as Starlink V1.0 L8, launched from Space Launch Complex 40 at Cape Canaveral Air Force Station in Florida. 36)

- The launch of three Planet SkySat spacecraft Saturday will be followed by another Falcon 9/Starlink mission in July carrying Planet’s final three SkySats, capping off the deployment of the company’s fleet of 21 commercial high-resolution Earth observation microsatellites.

- Mike Safyan, Planet’s vice president of launch, said SpaceX’s small satellite rideshare service, which the launch provider announced last year, was “a very attractive offering” to launch the company’s last six SkySat satellites.

- While Safyan would not disclose what Planet paid SpaceX to launch the six SkySats, SpaceX has published pricing for rideshare launch services on its website. The company lists a price as low as $1 million for a 440-pound payload on a rideshare to a polar sun-synchronous orbit.

- “That’s incredibly competitive pricing,” Safyan said. “Coupled with the fact that the Falcon 9 is one of the world’s most reliable and well-flown vehicles out there, and they’re going to a variety of orbits very regularly, makes it a very attractive offering.”

- Safyan said SpaceX provided Planet with parameters to integrate the SkySats on top of a flat-packed stack of Starlink satellites.

- SpaceX deployed the SkySat satellites first, about 13 minutes after liftoff, followed by the Starlink satellites about 39 minutes after liftoff. 37)

- The mission used a Falcon 9 booster that flew two cargo missions to the International Space Station for NASA, the last being CRS-20 in March. The rocket featured a previously flown payload fairing, with one half recovered from the Jcsat-18/Kacific-1 satellite mission in December, and the other from SpaceX’s third Starlink mission, which took place in January.

- SpaceX recovered the rocket’s first-stage for a third time, landing the booster on the drone ship “Of Course I Still Love You” in the Atlantic Ocean.

Figure 11: Three of Planet’s SkySat Earth-imaging microsatellites are mounted on top of 58 SpaceX Starlink Internet satellites for launch on 13 June 2020 (image credit: Planet / SpaceX)
Figure 11: Three of Planet’s SkySat Earth-imaging microsatellites are mounted on top of 58 SpaceX Starlink Internet satellites for launch on 13 June 2020 (image credit: Planet / SpaceX)

- SpaceX recovered the rocket’s first-stage for a third time, landing the booster on the drone ship “Of Course I Still Love You” in the Atlantic Ocean (Ref. 37).

- The launch marks the beginning of the rideshare program SpaceX announced in August 2019, offering regular opportunities for SmallSat operators to hitch rides on Starlink missions.

- SpaceX Lead Manufacturing Engineer Jessie Anderson said the launch contract covering Planet’s three SkySat satellites was signed six months ago. Planet’s Saturday launch, and a second Starlink rideshare scheduled for July will complete the operator’s constellation of 21 SkySats, a fleet that complements Planet’s larger constellation of Dove CubeSats.

- Once all 21 SkySats are in orbit, Planet says it will be able to image locations an average of seven times a day, with some locations seeing up to 12 revisits a day, at 50-centimeter resolution. Planet’s CubeSats collect imagery in 3-5 meter resolution.

SkySat-19 to -21

The world’s largest fleet of high-resolution imaging satellites just welcomed three new satellites to the family. On August 18, 2020 (14:31:16 UTC), SpaceX’s Falcon 9 rocket launched SkySats -19, -20 and -21 on yet another successful Starlink rideshare mission. Much like SkySats 16-18, which were launched by SpaceX on June 13, 2020, SkySats 19-21 were successfully injected into a drop-off orbit of approximately 207 x 370 km with an inclination of 53º. 38)

Figure 12: Three Planet SkySat Earth-imaging satellites (SkySat-19, -20 and -21) accompanied 58 SpaceX Starlink satellites on a Falcon-9 rocket on Launch 11 (image credit: SpaceX)
Figure 12: Three Planet SkySat Earth-imaging satellites (SkySat-19, -20 and -21) accompanied 58 SpaceX Starlink satellites on a Falcon-9 rocket on Launch 11 (image credit: SpaceX)

- Over the next several weeks the SkySat satellites will use their onboard propulsion to boost themselves up to their operational altitude of 400 km, and also begin phasing their orbital plane with respect to SkySats 16-18 in order to maximize coverage and revisit. Thanks to Exolaunch who helped deploy these most recent six SkySats with their CarboNIX deployer rings. These three new SkySats join the 18 others already in orbit and significantly expand our capacity to provide world class, high-resolution images to a variety of commercial, governmental, academic and non-profit organizations.

- SkySats 19-21 are also the final SkySats to be built and launched, completing the campaign of 21 satellites originally planned by the SkyBox team in 2009. Eleven years later, the innovation of the SkySat design and mission remains world-class and continues to move the high-resolution satellite industry forward.

- It’s been a busy few months here at Planet, with both SkySat and SuperDove launches stacking up as the launch industry recovers from the COVID-19 pandemic. Our satellite Mission Operations teams are hard at work bringing all the satellites online, so stay tuned to Planet Pulse and Twitter for more launch and satellite operations updates.

 


Mission Status

• May 13, 2022: Planet SkySat, a part of ESA's Third Party Mission Programme since April 2022, captured a high-resolution image (Figure 13) of the iconic Arc de Triomphe in Paris on 9 April 2022. The arch, also known as the Arch of Triumph of the Star due to its location at the Place Charles de Gaulle, is a symbol of France commissioned by Napoleon I in 1806 to commemorate French military achievements. The image showcases the arch's central position in Paris, marking the western terminus of the famous Champs-Élysées. Planet SkySat's high-resolution satellite imagery, with a 50 cm spatial resolution, provides valuable data for various applications, together with PlanetScope (both owned and operated by Planet Labs). Planet SkySat and PlanetScope are now accessible through ESA’s Third Party Mission programme, benefiting research and industries worldwide. 39)

Figure 13: This striking, high-resolution image of the Arc de Triomphe, in Paris, was captured by Planet SkySat – a fleet of satellites that have just joined ESA’s Third Party Mission Programme in April 2022. The image is also featured on the Earth from Space video programme (image credit: Planet SkySat)
Figure 13: This high-resolution image of the Arc de Triomphe, in Paris, was captured by Planet SkySat. The image is also featured on the Earth from Space video programme (image credit: Planet SkySat)

• August 14, 2020: Planet is expanding its fleet of SkySat satellites with the launch of three new satellites, SkySats 19-21, on August 18 (subject to change). These additions join SkySats 16-18, which successfully launched aboard a SpaceX Falcon 9 in June. While the first 15 SkySats operate in Sun Synchronous Orbits, providing twice-daily coverage of the Earth's surface, SkySats 16-21 will operate in a mid-inclination orbit of 53 degrees, complementing the sun synchronous fleet. This orbit allows for more targeted coverage of the latitude bands where most human activity occurs. By leveraging SpaceX's rideshare program and splitting the payload across two launches, Planet can provide enhanced products to its customers faster than other providers. 40)

Figure 14: SkySat 18 saw the village of Xiguanjing, China and the hills of Inner Mongolia when it first observed Earth on July 18, 2020 (image credit: © 2020, Planet Labs Inc)
Figure 14: SkySat 18 saw the village of Xiguanjing, China and the hills of Inner Mongolia when it first observed Earth on July 18, 2020 (image credit: © 2020, Planet Labs Inc)

• June 9, 2020: Over the past year, Planet has witnessed an increased demand for its SkySat imagery as customers seek timely and precise information, a trend further intensified by the COVID-19 pandemic's limitations on traditional surveying and inspection methods. In response, Planet has introduced three notable releases to enhance its tasking offerings. These enhancements include higher-resolution 50 cm imagery, which provides a more detailed view of changing ground conditions, particularly beneficial for applications like commercial and government mapping. Additionally, Planet has introduced a Tasking Dashboard and API, streamlining the process for customers to request SkySat collections and manage their orders more efficiently. Furthermore, Planet's commitment to rapid response is underscored by the launch of six new SkySats, allowing for up to 12x revisit capabilities in certain locations, enhancing the ability to monitor global events and capture satellite imagery at previously unseen times of the day. These developments align with Planet's mission to democratize access to satellite imagery, serving diverse customer needs across government and commercial sectors. 41)

Figure 17: Screenshot of Planet’s Tasking Dashboard (image credit: © 2020, Planet Labs Inc. All Rights Reserved)
Figure 15: Screenshot of Planet’s Tasking Dashboard (image credit: © 2020, Planet Labs Inc. All Rights Reserved)
Figure 18: The first SkySat image (taken in the morning) and second SkySat image (taken in the afternoon) were collected on May 20, 2020, and show the remains of the Edenville Dam, breached after heavy rainfall over Michigan. The silvery appearance of the water in the morning is due to sunglint, which is the reflection of light directly into the satellite’s telescope (image credit: © 2020, Planet Labs Inc., All Rights Reserved)
Figure 16: The first SkySat image (taken in the morning) and second SkySat image (taken in the afternoon) were collected on May 20, 2020, and show the remains of the Edenville Dam, breached after heavy rainfall over Michigan. The silvery appearance of the water in the morning is due to sunglint, which is the reflection of light directly into the satellite’s telescope (image credit: © 2020, Planet Labs Inc., All Rights Reserved)

• September 4, 2019: ESA and Planet have jointly announced an opportunity for free access to PlanetScope and SkySat data, available until the end of the year, over three European demonstration sites: Demmin, Wilhelmshaven, and Berlin. This initiative, conducted within the framework of ESA's Earthnet program, serves as a data familiarization phase preceding the potential formal integration of PlanetScope and SkySat into the Third Party Missions program. The Demmin test site, situated north of Berlin, is characterized by its agricultural intensity, providing a diverse landscape for remote sensing applications. In Wilhelmshaven, located in the Wattenmeer region, the focus extends to coastal and urban applications, while the Berlin city test area encompasses a densely populated urban environment with varied structures. These sites offer a valuable platform for testing and leveraging Planet's satellite data for Earth observation purposes. 42)

Figure 19: Lacations of the three test stations used by ESA (image credit: ESA)
Figure 17: Locations of the three test stations used by ESA (Image credit: ESA)

• August 9, 2019: The SkySat constellation, comprising 15 optical satellites managed by Planet, offers a range of imagery products, including the SkySat Level 2B Basic Scene, Level 3B Ortho Scene, and Level 3B Consolidated full archive and new tasking products. The SkySat Basic Scene product is provided in an uncalibrated raw digital number format, without correction for inherent geometric distortions, but includes Rational Polynomial Coefficients (RPCs) to enable user-driven orthorectification. Processing levels encompass Analytic (unorthorectified, radiometrically corrected, multispectral BGRN), Analytic DN (unorthorectified, multispectral BGRN), and Panchromatic DN (unorthorectified, panchromatic). In contrast, the SkySat Ortho Scene is sensor- and geometrically-corrected, utilizing DEMs with post spacing ranging from 30 to 90 meters and projected to a cartographic map projection, with accuracy varying by region based on available GCPs. 43)

• August 8, 2019: In the Proceedings of the 33rd Annual AIAA/USU Conference on Small Satellites, which was held at the beginning of this month in Logan, UT, USA, the SkySat Mission Operations team revealed their progress in managing the expanding SkySat fleet, which has grown from one to fifteen satellites in six years. Automation was essential to reduce manual intervention in satellite health and safety maintenance, especially as the constellation size increased rapidly. Automated anomaly response systems removed the need for active monitoring, relying on alert-driven notifications instead. Routine maintenance tasks are also being automated, leading to a three-fold reduction in person-hours per week while increasing on-orbit assets five-fold. This shift in operational posture has eliminated the necessity for 24/7 staffing at a dedicated operations center. Flexibility in ground software systems has been crucial, allowing for incremental automation development and adaptation to evolving mission needs. Building trust and collaboration between operators and software teams has been vital in the successful integration of automation into the operational environment. 44)

• October 25, 2018: SSL, a Maxar Technologies company, has sent two Earth Observation (EO) satellites, SkySat 14 and 15, to Vandenberg Air Force Base for launch on Spaceflight's dedicated rideshare mission aboard a SpaceX Falcon-9. These imaging satellites, featuring 72 cm resolution, are manufactured for Planet, a commercial EO company, and will expand Planet's SkySat constellation, which currently includes 11 SSL-built smallsats. This move enhances SSL's position as a leader in manufacturing innovative small form-factor satellites. Planet's SkySat constellation complements their Dove constellation, making them the commercial imagery provider with the most satellites in orbit. SSL continues to produce more SkySats for Planet, improving delivery cadence and integrating enhancements in its state-of-the-art SmallSat manufacturing facility. 45)

Figure 20: Photo of SkySats-14 and -15 in SSL's smallsats manufacturing facility (image credit: SSL)
Figure 18: Photo of SkySats-14 and -15 in SSL's smallsats manufacturing facility (image credit: SSL)

• June 2018: The SkySat mission operates with two types of satellites: two Generation A (non-propulsive) satellites, namely SkySat-1 and -2, and eleven Generation C (with propulsion) satellites from SkySat-3 to -13. Despite this difference in propulsion, the overall operational concept remains largely consistent. SkySat commissioning involves several key steps, including initial contact and downlink of launch data, utilizing onboard GPS for initial orbit determination, stabilizing the satellite using guidance, navigation, and control hardware, checking the imaging system and deploying the satellite's door, calibrating the satellite and payload, and performing orbit phasing maneuvers. Currently, 13 SkySats are in operation, with continuous imaging activities since the launch of SkySat-1 in 2013. The ongoing optimization of this diverse Earth Observation fleet benefits from the operational expertise gained through Planet's extensive satellite launches and management of its extensive satellite constellation. 46)

Attribute

Generation A

Generation C

Mass

83 kg

110 kg

Dimensions

60 x 60 x 80 cm

60 x 60 x 95 cm

Total ΔV

No propulsion

~200 m/s

Design life

~4 years

~6 years

Revisit (all)

Sub-daily

Constellation (MLTDN)

1 - SkySat 1 (11:00)
1 - SkySat 2 (14:00)

5 - SkySat 3-7 (10:30)
6 - SkySat 8-13 (13:30)

Table 3: SkySat satellite bus details

Mission
Name

Launch
Vehicle

Primary
Payload

Launch
Date

Orbit

Quantity

Launch to
First Light

SkySat 1

Dnepr

DubaiSat-2

21 Nov. 2013

SSO

1

21 days

SkySat 2

Soyuz 2.1b

Meteor M-2

8 July 2014

SSO

1

2 days

SkySat 3

PSLV

CartoSat-2C

22 June 2016

SSO

1

3 days

SkySat 4-7

Vega

PeruSat

16 Sept. 2016

SSO

4

3 days

SkySat 8-13

Minotaur-C

SkySat

31 Oct. 2017

SSO

6

7 days

SkySat-14 and -15

Falcon-9 Block5

SSO-A Spaceflight

03 December 2018

SSO

2

 

Table 4: Launch history of SkySat constellation

 

• May 15, 2018: A year ago, Planet and Google formed a strategic partnership that included the acquisition of Terra Bella, making Google a Planet customer and investor. Since then, the Terra Bella and Planet teams have seamlessly merged with a shared mission and vision. This partnership was put to the test when six SkySat satellites were launched, and now, it is confirmed that these new SkySat satellites are fully operational, with their data available through Planet APIs. This expands the SkySat constellation to a total of 13 satellites, making it the largest high-resolution satellite constellation on the market. This milestone empowers Planet to offer sub-meter resolution imagery of any location on Earth's landmass with twice-daily coverage, all at a fast pace and low cost, enhancing decision-making for its global customer base. The SkySat constellation complements Planet's daily global dataset and offers various delivery formats, including Basemaps compatible with OpenStreetMaps and web mapping tile formats. 47)

• November 1, 2017: Planet has confirmed that its ground team has contacted the SkySat (SkySat-8 to -13) and Dove satellites launched by the Minotaur-C rocket earlier this afternoon, and the spacecraft have entered their planned orbits. This confirms the final phase of the Minotaur-C mission occurred as expected, with a normal fourth stage motor burn and a complete separation of all six payloads. 48)

• September 5, 2017: Six high-resolution SkySat satellites for Planet, constructed by SSL (Space Systems Loral), have arrived at VAFB and are scheduled for launch in mid-October aboard an Orbital ATK Minotaur-C vehicle. These satellites, named SkySat 8 through 13, measure about 60 x 60 x 95 cm and weigh around 100 kg each. They are capable of capturing sub-meter color imagery and up to 90-second clips of HD video at 30 frames per second. Together with the seven SkySats already in orbit, these satellites will significantly enhance Planet's high-resolution imaging capabilities, allowing for multiple imaging passes in a single day. Coupled with Planet's fleet of over 170 Dove satellites and their software analytics platform, this constellation enables timely insights from any location globally. Planet's constellation offers a wide array of data, tools, and analytical services, aiding leaders in various sectors, including business and humanitarian, in solving intricate problems. 49)

• August 10, 2017: Five SkySat satellites equipped with HPGP (High-Performance Green Propulsion) systems were launched in 2016 from two different launch sites. Specifically, SkySat-3 was launched from ISRO's SDSC in India on June 22, 2016, while SkySat-4 to -7 (four satellites) were launched from VAFB in California on September 16, 2016. After separating from the launch vehicle upper stage, each SkySat underwent propulsion system commissioning, a process lasting approximately 8 hours per satellite, depending on ground station contact scheduling. This commissioning involved activating thruster catalyst bed heaters, ensuring uniform heating, and eliminating residual moisture. The HPGP systems are employed for routine station keeping, inclination maintenance, and compensating for drag. As of the publication date, the entire fleet executed forty propulsive maneuvers, including normal operations and subsystem tests. The on-orbit performance of the SkySat HPGP propulsion systems corresponds well with the pre-flight predictions, with detailed information available in Table 5. Additionally, Figure 19 illustrates the as-measured performance of “Thruster B” (fired at 100% duty cycle) on the SkySat-3 satellite for all closed-loop maneuvers performed to date, while Figure 20 displays a comparison plot showing the reactor temperature of Thruster B on SkySat-3 during regular orbit maintenance maneuvers, with the end of each maneuver indicated by a sharp decrease in reactor temperature. 50)

Satellite

Number of maneuvers

Total impulse (as of 1 June 2017

SkySat-3

13

1,732 Ns

SkySat-4

3

57 Ns

SkySat-5

5

150 Ns

SkySat-6

5

269 Ns

SkySat-7

14

317 Ns

Table 5: SkySat constellation propulsive maneuver summary

Legend to Table 5: SkySat-4 is currently being used as the ‘reference’ for maintaining constellation phasing (and has thus required fewer maneuvers than all of the other satellites).

Figure 21: Comparison of On-Orbit Steady-State Performance vs. Pre-Flight Predictions (image credit: ECAPS)
Figure 19: Comparison of On-Orbit Steady-State Performance vs. Pre-Flight Predictions (image credit: ECAPS)
Figure 22: SkySat-3 Thruster B (image credit: ECAPS)
Figure 20: SkySat-3 Thruster B (image credit: ECAPS)

• April 19, 2017: As of April 18, Planet of San Francisco completed its acquisition of Terra Bella, a rival satellite imaging company. Google is now a shareholder in Planet as part of this deal, which was initially announced on February 3. The acquisition included Google taking an equity stake in Planet in addition to a multi-year imagery contract. The deal received regulatory approvals from several federal agencies, including NOAA (National Oceanic and Atmospheric Administration), FTC (Federal Trade Commission), and FCC (Federal Communications Commission), with "early termination" notices issued on March 16. Planet plans to integrate Terra Bella's high-resolution imagery from its SkySat satellites into its own constellation of nearly 150 satellites. A "significant portion" of Terra Bella's employees will continue to work with Planet, and the company will maintain an office in Mountain View, California, where Terra Bella was headquartered. 51)

Figure 23: An illustration of four of the SkySat high-resolution imagery satellites developed by Terra Bella. Planet announced April 18 it has completed its deal announced in February to acquire Terra Bella from Google (image credit: Space Systems Loral)
Figure 21: An illustration of four of the SkySat high-resolution imagery satellites developed by Terra Bella (image credit: Space Systems Loral)

• September 27, 2016: Terra Bella released the first images from the four newest high-resolution imaging satellites, SkySat-4-7, which were successfully launched aboard an Arianespace Vega rocket from French Guiana on September 16, 2016. The following images (Figures 22 and 23) are untuned and uncalibrated. 52)

Figure 24: SkySat-4 image over Google Headquarters in Mountain View, CA on September 23, 2016 (image credit: Terra Bella)
Figure 22: SkySat-4 image over Google Headquarters in Mountain View, CA on September 23, 2016 (image credit: Terra Bella)
Figure 27: SkySat-7 image over Algeciras, Spain on September 23, 2016 (image credit: Terra Bella)
Figure 23: SkySat-7 image over Algeciras, Spain on September 23, 2016 (image credit: Terra Bella)

• September 16, 2016: The launch of SkySat-4, -5, -6 and -7 expanded a growing satellite fleet operated by Google’s Terra Bella company, giving the Silicon Valley firm seven spacecraft fitted with high-resolution cameras that can take rapid-fire pictures many times a second, allowing processors on the ground to string together video clips (Ref. 29). The Terra Bella satellites add to Google’s vast imagery catalog, which help improve popular applications such as Google Maps, according to Luc Vincent, director of GEO imagery at Google.

• August 3, 2016: ECAPS announced that the HPGP (High Performance Green Propulsion) system on SkySat-3 has been successfully commissioned on-orbit and declared fully operational. Commissioning of the HPGP propulsion system was completed approximately 48 hours after launch. All initial data from the propulsion system has indicated nominal performance and the HPGP system is now being used for recurring orbit maintenance operations. 53)

• July 1, 2016: SkySat 3, the third satellite of Terra Bella (formerly Skybox Imaging) has downlinked its first images following its June 22 launch aboard a PSLV (Polar Satellite Launch Vehicle) from the ISRO. The satellite launched with 19 other co-passengers and was released into a sun-synchronous orbit of ~ 500 km. 54)

Figure 28: Chicago’s Soldier Field stadium as seen by SkySat-3, acquired on June 25, 2016 (image credit: Terra Bella)
Figure 24: Chicago’s Soldier Field stadium as seen by SkySat-3, acquired on June 25, 2016 (image credit: Terra Bella)

• March 8, 2016: Google's satellite subsidiary, Skybox Imaging, has been renamed Terra Bella, with a new vision focusing on "pioneering the search for patterns of change in the physical world." While Terra Bella initially launched SkySat-1 two years ago and has since captured 100,000 images, the company now has "more than a dozen satellites under development" set to launch in the coming years. Terra Bella aims to expand beyond satellite imagery by integrating various geospatial data sources, machine learning capabilities, and experts to convert raw imagery into actionable data. New products not reliant solely on satellites are expected to be announced in the coming year. 55)

• August 13, 2015: The Skybox Flight Operator program has been instrumental in the operation of Skybox's microsatellites, SkySat-1 and -2. This program, which involves training college students and recent graduates, has yielded significant benefits for Skybox Flight Operations. It has attracted motivated individuals seeking short-term growth opportunities in satellite operations. The Flight Operations team at Skybox oversees satellite commissioning, maintenance, and overall health, operating 24/7 with two Satellite Controllers (SatCons) responsible for monitoring telemetry, addressing anomalies, and performing maintenance tasks. The intern staffing program, initially launched in 2013, collaborates with local universities, providing aerospace students with hands-on experience in satellite operations. To date, 16 individuals have participated in this program, contributing to the continuous 24/7 operation of SkySat-1 and -2 from Skybox's Mission Operations Center (MOC). 56)

• February 9, 2015: The SkySat-1 and -2 satellites are operating nominally. SkySat-3 was scheduled for launch in the summer of 2015 as a secondary payload aboard a PSLV-XL rocket from ISRO's Satish Dhawan Space Center in India. This satellite, part of a larger plan by Skybox Imaging, aimed to provide high-resolution imagery and full-motion video for commercial purposes. Additionally, ECAPS (Ecological Advanced Propulsion Systems, Inc.) of Solna, Sweden, secured a contract to supply propulsion systems for 12 satellites intended for Skybox Imaging's imagery services. This contract marked the largest-ever order for ECAPS's environmentally friendly High-Performance Green Propulsion system designed for small satellites. Skybox had entered into a contract with Space Systems/Loral (SSL) for the manufacturing of 13 small imaging satellites, with SkySat-3 as the first satellite in this series. Subsequently, ECAPS received an order to supply propulsion systems for the remaining 12 microsatellites. Skybox's ultimate goal was to establish a 24-satellite constellation distributed across four polar orbit planes to offer high-resolution imagery and full-motion video for commercial use. 57) 58)

Figure 29: The Tower of London (bottom center) acquired by SkySat-1 on November 10, 2014 (image credit: Skybox) 59)
Figure 25: The Tower of London (bottom center) acquired by SkySat-1 on November 10, 2014 (image credit: Skybox) 59)
Figure 30: SkySat-1 image of the Helkeim Glacier in Greenland, acquired on Aug. 18, 2014 (image credit: Skybox Imaging) 60)
Figure 26: SkySat-1 image of the Helkeim Glacier in Greenland, acquired on Aug. 18, 2014 (image credit: Skybox Imaging) 60)

• August 1, 2014: On June 10, 2014, Google announced its acquisition of Skybox Imaging, a satellite Earth imaging startup, for $500 million. Google's aim was to utilize Skybox's imaging technology to enhance various aspects, including maintaining the accuracy of Google Maps with current imagery. Furthermore, Google envisioned leveraging Skybox's expertise and technology to advance Internet accessibility and disaster relief efforts, aligning with its longstanding interests in these areas. 61) 62) 63)

• July 10, 2014: Skybox Imaging released the first images from SkySat-2. The project team progressed already through initial commissioning activities. The SkySat-2 system tuning and calibration are expected to continue for several months. SkySat-1 and SkySat-2 operations are conducted from the Skybox MOC (Mission Operations Centerour) on a 24 hour/7 day basis in Mountain View, CA. 64)

Figure 31: SkySat-2 image of Port-au-Prince, Haiti, acquired on July 10, 2014 within 48 hours after launch (image credit: Skybox Imaging) 65)
Figure 27: SkySat-2 image of Port-au-Prince, Haiti, acquired on July 10, 2014 within 48 hours after launch (image credit: Skybox Imaging) 65)
Figure 33: SkySat-1 image of Zayed University in Abu Dhabi, UAE (United Arab Emirates), acquired on Dec. 7, 2013 (image credit: Skybox Imaging)
Figure 28: SkySat-1 image of Zayed University in Abu Dhabi, UAE (United Arab Emirates), acquired on Dec. 7, 2013 (image credit: Skybox Imaging)

• December 11, 2013: Skybox Imaging released the first high-resolution images acquired with SkySat-1. 67)

Figure 35: SkySat-1 image of Beaton Park in Perth, Australia acquired on Dec. 4, 2013 (image credit: Skybox Imaging)
Figure 29: SkySat-1 image of Beaton Park in Perth, Australia acquired on Dec. 4, 2013 (image credit: Skybox Imaging)

 


Sensor Complement

The optical imager covers a panchromatic band from 450 to 900 nm achieving a Pan resolution of 0.90 m at nadir. Four multispectral channels are covered by the satellite (Blue 450-515, Green 515-595, Red 605-695, and Near Infrared 740-900 nm) achieving a multispectral resolution of 2 m at nadir. A ground swath of 8 km is covered at nadir. Stereo imaging is supported by the satellite. The instrument is a staring 2D imaging device. 68)

The satellite acquires high-definition video in its Pan channel with durations of up to 90 seconds in which the satellite can keep looking at the ground target by slewing to compensate for the movement in its orbit. Video is acquired at 30 frames/s with a resolution of 1.1 m at nadir and a minimum FOV (Field of View) of 2.0 km x 1.1 km.

Skybox images are commercially marketed and find application in a variety of monitoring operations, land use planning, environmental assessment, resources management, tourism, mapping and for scientific use.

Spatial resolution

Pan (Panchromatic): 90 cm at nadir
MS (multispectral): 2.0 m at nadir

Nominal swath width

8 km at nadir

Spectral bands

Pan: 450-900 nm
MS: Blue = 450-515 nm
MS : Green = 515-595 nm
MS: Red = 605-695 nm
MS: NIR = 740-900 nm

Video data

Pan,
Duration up to 90 seconds
Frame rate = 30/s
GSD = 1.1 m at nadir
FOV: No smaller than 2.0 km x 1.1 km

Table 6: Specification of the optical imager

Each SkySat satellite is equipped with a Ritchey-Chretien Cassegrain telescope (35 cm ∅) with a focal length of 3.6 m, and a focal plane consisting of three 5.5 Mpixel CMOS imaging detectors. Images are compressed with JPEG 2000 and then stored or downlinked to the ground station. 768 GB of on board storage are available and the data downlink rate is 450 Mbit/s. 69)

SkySat-1and -2 use 3 CMOS frame detectors with a size of 2560 x 2160 pixels and a pixel size of 6.5 µm. The upper half of the detector is used for panchromatic capture, the lower half is divided into 4 stripes covered with blue, green, red and near infra-red color filters. A schematic of the focal plane layout is shown in Figure 30. The native resolution at nadir of the SkySat-1 and SkySat-2 is around 1.1 m. Further satellites will be placed in lower orbits, leading to increased image resolution.

The Raw Video and Frame products contains both a physical camera model and a RPC (Remote Procedure Call) for each individual frame. The interior orientation is given by the location (X,Y,Z) and tilts the CMOS detector planes with respect to the projection center of the telescope. The unconventional interior orientation with 3D rotation of the focal plane with respect to the telescope requires extension of the ordinary frame camera geometry routines.

For the video product, the panchromatic part of a single detector records a video with 30 frames/s while the spacecraft pointing follows the target. Video sequences up to 90 seconds in length can be recorded. The video product can be delivered in different formats, a stabilized Full HD video in MP4 format, where all video frames have been coregistered, and an unstabilized video without coregistration. The video size of both products is 1920 x 1080 pixels. A raw video product with individual TIFF files with 11 bit of radiometric resolution and per frame orbit and attitude parameters and RPCs is also available. The raw video frames are available at the full panchromatic detector area size of 2560 x 1080 pixels.

Figure 36: SkySat-1 focal plane, as projected to the ground (image credit: Skybox, DLR) 70) 71)
Figure 30: SkySat-1 focal plane, as projected to the ground (image credit: Skybox, DLR) 70) 71)

Frame product: In addition to the video product, larger areas can be covered by strips with a swath width of 8 km. These are acquired in a ”pushframe” mode, where all three detectors acquire a highly overlapping video sequence, for example at 40 Hz (Smiley et al.,2014). All pan and multi-spectral images overlapping with a single panchromatic ”master” frames are coregistered and fused using a super-resolution algorithm. During the fusion, a super-resolution process is used to increase the resolution from 1.1 m to 90 cm. Panchromatic, multispectral and several variants of pansharpened images are delivered.

The master images are chosen to have some overlap in the along track direction, and there is a small across-track overlap between detector 2 and detectors 1 and 3 (Figure 31).

As handling and mosaicking of the individual frames is not a straightforward operation for most imagery customers, Skybox will offer an mosaicked Geo product in the future.

Figure 37: Fos sur Mer industrial zone as seen by SkySat-1. The bounding boxes show the individual frames after coregistration and multi-image fusion (image credit: Skybox, DLR)
Figure 31: Fos sur Mer industrial zone as seen by SkySat-1. The bounding boxes show the individual frames after coregistration and multi-image fusion (image credit: Skybox, DLR)

Legend to Figure 31: Fos-sur-Mer is situated about 50 km north west of Marseille, on the Mediterranean coast, and to the west of the Étang de Berre.

With the first civil VHR video products, the SkySat satellites offer very interesting possibilities for future applications. The ”pushframe” architecture and the super-resolution approach reduce the complexity of the SkySat satellites and will allow launch of a constellation with multiple daily visits. A drawback of the constellation is the comparably small footprint of the still and video products, Skybox is thus primarily suited for monitoring applications and not for the mapping of large areas (Ref. 69).

 


Propulsion Subsystems 

The declared goal of Terra Bella, formerly Skybox Imaging, is to provide the world's first coordinated constellation of high-resolution EO satellites. After the successful demonstration of the SkySat-1 imaging performance and the development of the SkySat-2 spacecraft, Skybox Imaging of Mountain View, CA, awarded a contract to SSL (Space Systems/Loral) of Palo Alto, CA in February 2014, to build an advanced constellation of LEO (Low Earth Orbit) satellites for Earth imaging. The contract award helps SSL, which is best known for its high-power geostationary communications satellites, to further expand its capabilities building LEO imaging satellites and solutions. 72) 73)

SSL is building 13 small LEO satellites, each about 60 x 60 x 95 cm with a mass of ~120 kg, to be launched in 2015 and 2016. These satellites, based on a Skybox design, will capture sub-meter color imagery and up to 90-second clips of HD video with 30 frames/s. Once the 13 satellites are launched, Skybox will be able to revisit any point on Earth three times per day.

As part of the agreement, Skybox granted SSL an exclusive license to the satellite design. This provides SSL with a unique platform to address the growing demand for small satellites and related services.

The contract with SSL, a subsidiary of MDA Corp. of Richmond BC, Canada, raises the possibility that Skybox could receive backing from Export Development Canada, the country’s export credit agency, one industry source said. Export credit agency financing has become a major factor in the space industry and often helps determine who wins satellite manufacturing and launch contracts. 74)

One of the critical requirements identified in the evolution towards a constellation was the need for a capable propulsion system. Adding propulsion to future SkySat satellites enables the following capabilities: 75) 76)

• Constellation relative phase management: The compact size of the SkySat platform enables enormous cost savings by utilizing a single launch vehicle to launch multiple spacecraft. However, once on orbit, propulsion will be required to phase the spacecraft within each orbit plane and maintain their relative spacing in the face of orbital perturbations.

• Mission flexibility to better serve the EO market: The commercial EO market is relatively new and evolving. High performance propulsion will enable Skybox to meet market demands for increased resolution, collect volume or spacecraft lifetime by adjusting the spacecraft’s orbits.

• Launch vehicle diversity: High performance propulsion will enable Skybox to take advantage of a wide range of future secondary launch options as they become available, while maintaining tight coordination of one-off launches with the rest of the constellation.

Already in late 2012, Terra Bella, formerly Skybox Imaging, became the first commercial company to baseline the HPGP (High Performance Green Propulsion) technology of ECAPS (Ecological Advanced Propulsion Systems, Inc.) of Solna, Sweden — implementing a propulsion system design with four 1N thrusters in their second generation small satellite platform (~120 kg). The initial propulsion module, to be delivered in 2013, will serve to qualify the system design for use in an entire constellation of small satellites intended to provide customers easy access to reliable and frequent high-resolution images of the Earth.

The selection of the HPGP system of ECAPS, an SSC (Swedish Space Corporation) Group company, resulted from a system study of various propulsion options in support of Skybox’s mission to provide high quality and timely earth observation data from a small satellite constellation. Two key technical requirements for the propulsion system were to provide the maximum ΔV achievable (for continued orbit maintenance and mission flexibility) within a considerably limited internal volume typical of many microsatellites. Additionally, in light of the commercial nature of the project, the overall life-cycle cost was considered to be of utmost importance.

A detailed trade study of various propulsion technologies and vendors was conducted by Skybox during the selection process. The results of that study showed that the HPGP solution selected provides nearly twice the on-orbit ΔV of the more traditional monopropellant systems, at the lowest projected life-cycle cost of the liquid propulsion technologies evaluated.

The higher performance of the HPGP system will give the SkySat constellation of small satellites significantly improved mission flexibility, enabling collection and delivery of higher quality and more timely data to customers. Furthermore, the handling and transportation advantages of the environmentally benign ADN (Ammonium Dinitramide) based LMP-103S monopropellant provide reductions in logistics costs and enable more responsive launch preparation. 77)

Figure 38: Photo of a 1 N thruster of the HPGP propulsion subsystem (image credit: ECAPS/SSC)
Figure 32: Photo of a 1 N thruster of the HPGP propulsion subsystem (image credit: ECAPS/SSC)

SkySat-3 will be the first microsatellite of the SkySat constellation which features an HPGP propulsion subsystem with four 1N thrusters, fuel LMP-103S and refueling of the satellite at the launch base.

During 2013, ECAPS worked to design a complete, compact and “modular” HPGP propulsion system; the first (protoflight) version of which was delivered in 2014. A total quantity of nineteen such HPGP propulsion system modules have now been ordered by Terra Bella, and “assembly line” manufacturing is ongoing at ECAPS – with multiple deliveries accomplished in 2015, and continuing into 2016 & 2017. 78)

As a result of the schedule adjustments that are common within the satellite and launch industries, up to eleven of the aforementioned HPGP modules are currently planned to launch in 2016, on three different launch vehicles; from three different launch sites (on three different continents). Collectively, these launches will represent the “commercial debut” for HPGP technology; with the entry point being a large constellation.

HPGP propulsion system design

As successfully demonstrated in-space on the PRISMA mission of Sweden (2010-2015), HPGP (High Performance Green Propulsion) technology provides numerous benefits over monopropellant hydrazine, including: 32% higher volumetric efficiency and 8% higher mission-average specific impulse, significantly reduced transportation/handling hazards and costs, and greatly simplified/shortened pre-launch operations (Ref. 78).

The PRISMA HPGP propulsion system was the first in-space demonstration of the ”green” storable monopropellant HPGP technology, based on ADN LMP-103S, and was used for providing the required ΔV for the PRISMA main satellite maneuvers, together with the hydrazine system. The PRISMA mission was concluded in May 2015; by which time the HPGP system had been successfully operated in space for five years.

The architecture of the complete HPGP propulsion system developed by ECAPS for the SkySat platform is shown in Figure 33. The system design consists primarily of four 1N HPGP thrusters, three propellant tanks (with expulsion via Propellant Management Devices) connected in series, two service valves, a latch valve, a pressure transducer and a system filter. All of the components selected have flight heritage from previous missions.

Figure 39: The SkySat HPGP system architecture (image credit: ECAPS/SSC)
Figure 33: The SkySat HPGP system architecture (image credit: ECAPS/SSC)

The design and function of the thrusters developed for ADN-based monopropellant blends have several similarities with hydrazine thrusters. The FCV (Flow Control Valve) is a normally closed series redundant valve with independent dual coils. The FCV is manufactured by Moog and has extensive flight heritage. In the HPGP thruster, the propellant is thermally and catalytically decomposed and ignited by a pre-heated reactor. Nominal pre-heating is regulated between 340-360ºC which requires an average power consumption of about 7.3 W per thruster in the PRISMA application. For thermal control, the thruster is equipped with redundant heaters and thermocouples.

Figure 40: Left: The SkySat HPGP system layout; right: The SkySat-3 HPGP flight system (image credit: ECAPS/SSC)
Figure 34: Left: The SkySat HPGP system layout; right: The SkySat-3 HPGP flight system (image credit: ECAPS/SSC)

Importantly, from the standpoint of other companies developing small satellites which will require propulsive capability, ECAPS can offer the existing design (or modified derivatives thereof) as a compact (55 x 55 x 15 cm) “drop-in”/off-the-shelf solution for other customers interested in high performance propulsion at a reduced life-cycle cost.

The nineteen complete HPGP propulsion system modules ordered by Terra Bella represent a total quantity of seventy-six (76) 1N HPGP thrusters. In order to achieve the associated production rates, ECAPS has scaled up its capabilities in the areas of both manufacturing and hot-fire acceptance testing of HPGP thrusters.

Figure 41: Photo of 1N HPGP flight thrusters (image credit: ECAPS/SSC)
Figure 35: Photo of 1N HPGP flight thrusters (image credit: ECAPS/SSC)

In support of increased thruster manufacturing rates, ECAPS has invested in additional vacuum braze stations. Additionally, in order to enable an improved thruster acceptance testing timeline, ECAPS’ Test Stand number2 (TS-2) has been modified to support multiple thrusters simultaneously. The new TS-2 configuration, shown in Figures 36 and 37, permits four (4) 1N HPGP thrusters to be mounted in parallel.

Figure 42: Four 1N thrusters mounted in TS-2 (image credit: ECAPS/SSC)
Figure 36: Four 1N thrusters mounted in TS-2 (image credit: ECAPS/SSC)
Figure 43: TS-2 with multiple 1N thrust balances mounted (image credit: ECAPS/SSC)
Figure 37: TS-2 with multiple 1N thrust balances mounted (image credit: ECAPS/SSC)

SkySat HPGP propulsion modules: As shown in Figure 38, the complete SkySat HPGP propulsion system modules are being manufactured in an “assembly line” manner as well. By implementing standardized procedures and support equipment, multiple systems are able to exist in various stages of production simultaneously – thus streamlining the flow of incoming components into their respective systems, and minimizing the likelihood of key tooling sitting “idle” due to the individual integration schedule of any particular system.

Figure 44: Photo of multiple SkySat HPGP systems in various stages of production (image credit: ECAPS/SSC)
Figure 38: Photo of multiple SkySat HPGP systems in various stages of production (image credit: ECAPS/SSC)

 


Ground Segment

Planet’s Mission Operations team largely focuses on automation to manage nominal operations of the fleet of satellites. Rather than building manual/human processes and then trying to replace them with automation, Planet builds automation first and then iteratively improves it. This workflow has been paramount to operating the large fleet of Dove nanosatellites. 79)

The SkySat Mission Operations (SMO) team is responsible for the safe and stable space segment operations for Planet’s thirteen SkySat satellites. This includes all satellite operations as well as the development of tools, processes, and systems for these operations. SMO supports ground station operations, image collection planning, radiometric calibration, software development, and mission systems engineering. SMO takes ownership of the satellite immediately after launch and is responsible for all commissioning, nominal, maintenance, special, and
contingency operations during the satellite's life. SMO is responsible for maintaining throughput to meet our contractual service obligations, scaling operational capacity while minimizing resource use, and delivering imagery to the data pipeline ground segment.

The SkySat ground system supports satellite commanding and real-time telemetry display, analysis, and trending in a 100% web browser based solution. The majority of planning, analysis, and production tools used operationally are also browser-based. Telemetry storage and computation occurs on centralized servers.

The SkySat Fleet

- The SkySat fleet is comprised of fifteen small satellites capable of sub-meter resolution imagery. Unlike the Dove flock, which provides near-continuous imagery along each satellite’s orbit, the SkySats capture on-demand imagery of targets requested by customers. In addition, while the Doves are 3U CubeSats numbering in the hundreds, the SkySat fleet consists of a few dozen small satellites in the 100 kg range. The SkySat fleet is comprised of satellite buses with both maneuverable and non-maneuverable capabilities. Apart from this difference, the various SkySat buses are largely the same and operate under the same concept of operations.

- The rapidly changing operational needs required to maintain the fleet dictated that the SkySat Mission Operations (SMO) team develop tooling around the ground software, described below. These tools would give the team greater control over features while staying as independent as possible from the deployment of new ground software releases. By decoupling this development, SMO could experiment with various automation strategies while maintaining the inherently stable ground software. The ultimate goal of automation was to minimize the effort required to operate the fleet and maximize the amount of time operators could be absent from the operations center, in a so-called lights-out operational posture.

Ground software and tooling

- The base ground system initially provided to operate the SkySat fleet was a web-based user interface with basic features such as scripted command execution and telemetry monitoring and charting. As the number of satellites in orbit grew and operational needs changed, this base infrastructure acted as the foundation for additional tools built to facilitate SkySat mission operations.

- Scripting Engine: One of the primary features of the ground system allows operators to execute prepared scripts, written in Python. The purpose of this feature was to improve upon on-orbit command execution by allowing for complex logic and telemetry verification. The use of scripts has significantly reduced the occurrence of operator error and as a result increased fleet uptime.

- The first scripts developed were simple wrappers for available command and single-point telemetry checks. In these scripts, operators still adjusted the logical flow of execution via command line prompts. Over time layers were added to the script library, logic became more complex, and the need for operator prompting diminished. Much of this was due to the cumulative experience of both operators and engineers in dealing with anomalies on-orbit.

- Telemetry Monitoring and Charting: Operators are able to create custom screens of telemetry points for monitoring specific aspects of the satellite, as well as chart, in real-time, downlinked telemetry data from the satellite. Historical data is kept in a database to be retrieved for long-term trending of satellite data.

- Additionally, the ground system continuously monitors incoming telemetry against a set of thresholds defined by the satellite engineering team. These violations are then recorded and a visual indicator is presented to the operator for further action.

- Organization and Planning Tools: In order to facilitate executing satellite activities, SMO developed the pass planning tool. With this tool, operators may plan and display which operator-initiated activities would be executed in future contacts for each satellite. Additionally, this tool gathers and displays information about the fleet including what activities a satellite will be performing in upcoming orbits, the location of the satellites, and the health and safety effects of upcoming activities. This organization and planning tool became the foundation for many of the future tools that SMO would build, as it evolved into a one-stop location for all of the data the operations team needed.

Procedural and tasking algorithms

- As the fleet expanded, a multi-prong approach was taken to decouple operator effort from fleet size. This included building upon existing script libraries for automated anomaly response, moving to an alert-driven operational posture, and reducing the burden of planning and executing maintenance activities.

- Automated Anomaly Response: Over time, a set of common anomalies has emerged across the fleet that has lead to a thorough understanding of how to triage and resolve said anomalies. These well-defined responses to known anomalies have been implemented into scripts, which can be executed any time an anomalous state is detected. This development eliminated the need for operators to monitor real-time telemetry in order to respond to on-orbit issues.

- Autonomous anomaly response is an integral part of SkySat operations. Responses to common anomalies are entrusted to automation instead of operator intervention. By laying the foundation of autonomous anomaly response, the operations team was able to transition from focusing attention on one satellite at a time to considering and investigating anomalies at a fleet-wide scale. This enabled the operations team to more effectively manage a growing fleet. By automating the most critical responses, human attention could be more evenly spread between satellites competing for resources.

- Back-orbit Activities: A majority of commanding for all satellites in the SkySat fleet is done procedurally via a timestamped sequence of commands. These sequences are prepared and validated on the ground prior to being loaded to the onboard software for execution. These activities, such as image captures, data downlinks, and maintenance tasks, are typically performed in this manner.

- Some maintenance activities with specific constraints, such as onboard storage cleanup, must be executed when the satellite is not in contact with a ground station. To execute these “back-orbit” activities, a suitable execution time must be found and the sequence of commands must be loaded to onboard software prior to that time. Traditionally these tasks were manually performed by operators, which required a thorough understanding of not only when the satellites would be collecting images, but also the orbital state and satellite attitude. For example, would the satellite be passing through the South Atlantic Anomaly (SAA) and will the satellite be in an unsafe orientation if the activity is performed? Automating this process required defining a clear set of constraints that could then be implemented into the logic for determining the appropriate time to execute an activity. Once a suitable window was generated, the sequence of commands could then be embedded into the upcoming activities performed by the satellite.

Table 3: This table shows a simplified representation of the possible timing of a task that must be done while the satellite is in eclipse, not in the SAA, and not interfering with images or contacts. The final row indicates that there are two blocks near the end of the eclipse period that meet these criteria. If the length of these blocks is sufficient to complete the task, it will be added to the sequence of commands loaded to the satellite for that time frame.
Table 7: This table shows a simplified representation of the possible timing of a task that must be done while the satellite is in eclipse, not in the SAA, and not interfering with images or contacts. The final row indicates that there are two blocks near the end of the eclipse period that meet these criteria. If the length of these blocks is sufficient to complete the task, it will be added to the sequence of commands loaded to the satellite for that time frame.

- Alert and Paging System: One of the greatest enablers of lights-out operations was the development of an alert and paging system. If an anomaly occurs on orbit or within the ground infrastructure, the alerting system generates a summary of information surrounding the event to inform the on-call operator of the incident. Tying the alerts into Planet’s existing ticketing system meant issues could be tracked from discovery to resolution.

- Historically, visual indicators signifying that the value of a specific telemetry point was outside a defined threshold were used by operators to identify an anomalous scenario on-orbit. These, alongside logged messages from the onboard computer, were used by operators to triage and respond to the anomaly. At the core of its design, the alerting system collates related messages and telemetry into a single notification to send to operators.

- The precision and completeness of this information allows operators to develop a plan of action without requiring the depth of investigation needed in the past. Combined with changes to the operational posture, specifically extending the time in which operators must respond to an anomaly, this information enabled operators to work outside the operations center and respond to anomalies when convenient.

Automated operator

- After implementing automated scheduling of back-orbit activities, the last thing operators were responsible for was the planning and execution of activities that required communication with a ground station. These activities require ground services for a number of reasons, such as needing a link for telemetry verification or data exchange. These “in-pass” activities are frequently used for anomaly investigation and resolution, software updates, and nominal maintenance. In order to further reduce the person-hours needed to manually plan these activities, the SkySat Mission Operations team needed an automated workflow to determine what activities needed to be executed. In addition, this workflow needed to schedule the activities and to verify their successful completion.

- With the introduction of a so-called “automated operator”, all non-anomaly planning and scheduling could be handled without operator intervention. Tasks in this system were separated into three categories: default plans, run when no other activity is required; recurring plans, maintenance activities run at a regular interval; and triggered plans, activities that are planned in response to on-orbit conditions. The core functionality of the automated operator is scheduling these activities and verifying their successful execution.

- Default Plans: A majority of contacts across the fleet perform nothing beyond routine satellite health and safety checks. These routine tasks are encapsulated in a single script, removing the need for real-time telemetry verification by operators.

- Before the implementation of the automated operator, the “default script” was scheduled via a temporary workaround added to the pass planning tool. This occasionally led to scheduling conflicts and activities that had been carefully planned by operators could be overwritten without notice. This was an acceptable occurrence when the fleet was smaller, since the time it would take for operators to investigate why an activity did not occur did not interrupt nominal fleet operations. As the fleet grew, it became apparent that the system needed a new way to schedule these default tasks. By centralizing all contact scheduling into the automated operator, there was no longer a requirement for operators to manually ensure that a planned task would not be overwritten.

- In order to not interfere with operators manually planning a contact, the automated operator will only schedule recurring or triggered plans if a default plan was there previously. Human operators still have the authority to schedule and execute activities independently of the automated operator.

- Recurring Plans: There are certain tasks that must be executed at defined intervals as prescribed by the responsible subsystem engineer. Many of these tasks require ground assets and cannot be done while the satellites are not in contact. Some of these include loading updated orbit information or loading software configurations to the satellite. The intervals at which these tasks are executed range from weekly to quarterly.

- The automated operator is responsible for all aspects of these activities, including the following:

a) Tracking the status of all individual activities to determine if a task needs to be scheduled (activity scheduled; activity failed; activity recently completed successfully)

b) Tracking constraints for scheduling (minimum contact duration; ground station exclusions)

c) Tracking templates for activities approved for automated scheduling.

- Triggered Plans: There are certain on-orbit states that are typically dealt with in a well-defined manner. These activities are necessary for performing on-orbit tasks such as routine cleanup of satellite storage and enabling certain subsystem configurations. By defining both the on-orbit state and the necessary response to that state in a script, the automated operator schedules these activities as needed without operator intervention. As with default and recurring plans, these triggered plans are monitored from schedule planning through execution verification by the automated operator.

Personnel and staffing

- Despite the fleet size growing from one to fifteen satellites, staffing has remained relatively constant. This is due to evolving operational postures as well as the growing role that automation has played.

- Traditional Operations: Historically, satellite operations has involved staffing a dedicated operations center 24 hours a day, seven days a week. With the launch of SkySat-1, this was the posture taken, with three operators on console monitoring satellite health and safety. This was then reduced to two personnel when commissioning was complete. Outside of commissioning activities, 24/7 two-person operations (2PO) was maintained until 2017.

- Lights Out and On-call: The transition to on-call operations started with allowing the nighttime operators to monitor the fleet remotely, relying on the paging system to alert of any anomalies that needed operator response. This was referred to as nighttime lights-out operations (NLO). As confidence in the systems grew, nighttime staffing was reduced to one person on-call, with another support engineer available to be contacted as needed. This 24/7, one person on-call stance was eventually extended to include weekends in what is referred to as weekend lights-out operations (WLO). After on-call operations was implemented, operators were in the operations center twelve hours a day on weekdays with the remaining hours covered by on-call personnel.

- The team operated with these twelve-hour on-call shifts until in-office hours were eventually reduced to follow a standard eight-hour workday. Operators who began their shift on a weekday morning would finish their shifts remotely for a total of twelve hours on-shift. Operators assigned to weekend shift conducted shift activities, such as anomaly resolution, remotely.

- Alerting Periods: Despite moving to an on-call, interrupt driven stance, the SkySat Mission Operations team was still faced with the burden of having operators on-call 24/7 to respond to satellite anomalies. As the systems in place matured, the operations team relied on automation to take over more of the responsibilities of responding to night and weekend anomalies. With a growing number of the fleet, overall performance would not be greatly impacted by downtime on a few satellites.

- After the initial deployment of the alert and paging systems, there was a period of time where operators closely scrutinized and double checked that anomalies were being caught as expected. As confidence in the automation among operators reached a sufficiently high level, a change in operational stance was made to allow automation to be the primary response at night. Engineers could then triage anomalies in the morning and take action as necessary. This was the first time where there was a period of the day when no personnel were actively monitoring the fleet. This so-called “muting period” was then extended to 16 hours, turning the on-call period into an extension of in-office hours as opposed to staffing a separate shift.

- As it currently stands, the nighttime on-call period has been completely eliminated, with operators in-office only for a normal workweek and on-call personnel available during the day on weekends. Introducing the automated operator has further reduced human operator effort by covering all routine maintenance tasks. Although on-console for a full day, a typical day sees operators performing on-orbit activities such as anomaly response only a few hours per day.

- The overall reduction in staffing hours to monitor the fleet has reduced from 336 person-hours per week to 96 person-hours per week, with on-console operators spending less than half of their shift fully devoting attention to the fleet. This reduction in staffing occurred in parallel with fully supporting fleet expansion from one to 15 satellites. As stated previously, staffing levels have remained relatively constant. With the reduction in effort required to maintain the fleet, the mission operations team has provided support to other subsystems of the SkySat platform, including flight software, ground software, and manufacturing. The SkySat Mission Operations team has evolved into a group of subject matter experts on many aspects of the SkySat platform. This cross-training has made the level of knowledge related to the SkySat fleet at Planet resilient to changes in the overall team composition. Many members of the team have transitioned to other teams at Planet, specializing in disciplines ranging from electrical engineering to project management. Without the continued improvement in automation and relaxation of the operational posture, these changes would not have been possible.

 


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48) Stephen Clark, ”Live coverage: Minotaur-C rocket launches with cluster of satellites,” Spaceflight Now, Nov. 1, 2017, URL: https://spaceflightnow.com/2017/10/31/minotaur-c-skysats-mission-status-center/

49) ”SSL's Six Planet Smallsats Arrive Safely at Vandenberg AFB for October Launch,” Satnews Daily, Sept. 5, 2017, URL: http://www.satnews.com/story.php?number=425923128

50) Aaron Dinardi, Kjell Anflo, Pete Friedhoff, ”On-Orbit Commissioning of High Performance Green Propulsion (HPGP) in the SkySat Constellation,” Proceedings of the 31st Annual AIAA/USU Conference on Small Satellites, Logan UT, USA, Aug. 5-10, 2017, paper: SSC17-X-04, URL: http://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=3670&context=smallsat

51) Jeff Foust, ”Planet confirms Google stake as Terra Bella deal closes,” Space News, April 19, 2017, URL: http://spacenews.com/planet-confirms-google-stake-as-terra-bella-deal-closes/

52) ”SkySat-4-7 First Light,” Terra Bella Blog, Sept. 27, 2016, URL:  https://terrabellatech.blogspot.com/2016/09/skysat-4-7-first-light.html

53) ”Successful on-orbit commissioning of the SkySat-3 HPGP propulsion system,” ECAPS, August 3, 2016, URL: http://www.sscspace.com/news-activities/all-news-archives/2016/successful-on-orbit-commissioning-of-the-skysat-3-hpgp-propulsion-system

54) Caleb Henry, ”Terra Bella’s SkySat-3 Sends Back First Pictures,” Satellite Today, July 1, 2016, URL: http://www.satellitetoday.com/publications/st/2016/07/01/terra-bellas-skysat-3-sends-back-first-pictures/

55) Emil Protalinski, ”Google rebrands Skybox as Terra Bella, will launch ‘more than a dozen satellites’ over the next few years,” VenturaBeat, March 8, 2016, URL: http://venturebeat.com/2016/03/08/google-rebrands-skybox-as-terra-bella-will-launch-more-than-a-dozen-satellites-over-the-next-few-years/

56) Emma Lehman, Mark Longanbach, ”The Skybox Satellite Operator Intern Program - Benefits and Lessons Learned,” Proceedings of the 29th Annual AIAA/USU Conference on Small Satellites, Logan, Utah, USA, August 8-13, 2015, paper: SSC15-IX-1, URL: http://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=3224&context=smallsat

57) Bhavna Singh, “ISRO to Launch Google’s Satellite for GPS Maps,” IAMWIRE, Feb. 9, 2015, URL: http://www.iamwire.com/2015/02/isro-launch-google-satellite-gps-maps/109633

58) Warren Ferster, “SSC To Provide Propulsion for Skybox Satellite Fleet,” Space News, March 12, 2014, URL: http://spacenews.com/39822news-from-satellite-2014-to-provide-propulsion-for-skybox-satellite/

59) SkySat Gallery, URL: http://www.firstimagery.skybox.com/

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62) Peter B. de Selding, “Google To Buy SkyBox for $500 Million,” Space News, June 10, 2014, URL: http://spacenews.com/40869google-to-buy-skybox-for-500-million/

63) Robert H. Meurer, Peng Hwee Seah, “Global Commerce in Small Satellites: Trends and New Business Models,” Proceedings of the 28th Annual AIAA/USU Conference on Small Satellites, Logan, Utah, USA, August 2-7, 2014, paper: SSC14-I-2, URL: http://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=3017&context=smallsat

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65) http://firstimagery.skybox.com/

66) http://www.firstimagery.skybox.com/2014/7/10/bangor-maine

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70) Byron Smiley, Josh Levine, Alexandra Chau, ”On-Orbit Calibration Activities and Image Quality of SkySat-1,” Proceedings of JACIE 2014 (Joint Agency Commercial Imagery Evaluation) Workshop, Louisville, Kentucky, USA, March 26-28, 2014, , URL: https://calval.cr.usgs.gov/wordpress/wp-content/uploads/14.017_bsmiley-JACIE-2014-final-draft-on-site.pdf

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77) Peter Thormählen, Kjell Anflo, “A Stable Liquid Mono-Propellant based on ADN,” Insensitive Munitions and Energetic Materials Technology Symposium, Tucson, AZ,USA, May 11-14, 2009, URL: http://www.dtic.mil/ndia/2009insensitive/8Asjoberg.pdf

78) Aaron Dinardi, Mathias Persson, ”First Commercial Implementation of High Performance Green Propulsion (HPGP),” Proceedings of the 14th International Conference on Space Operations (SpaceOps 2016), Daejeon, Korea, May 16-20, 2016, URL: http://arc.aiaa.org/doi/book/10.2514/MSPOPS16

79) Rob Zimmerman, Deanna Doan, Lawrence Leung, James Mason, Nate Parsons, Kam Shahid, ”Commissioning the World’s Largest Satellite Constellation,” Proceedings of the 31st Annual AIAA/USU Conference on Small Satellites, Logan UT, USA, Aug. 5-10, 2017, paper: SSC17-X-03, URL: https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=3669&context=smallsat
 


The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: ”Observation of the Earth and Its Environment: Survey of Missions and Sensors” (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (eoportal@symbios.space).

 

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