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HawkEye 360 Pathfinder Cluster Mission to identify RFI locations

Spacecraft     Launch    Mission Status     Sensor Complement    Ground Segment    References

HawkEye 360 Inc. of Herndon VA (USA) has developed an innovative combination of classical and novel geolocation algorithms that will enable precise spaceborne geolocation of terrestrial and aerial radio frequency (RF) emitters related to a broad array of business enterprises. In late 2018, the HE360 Pathfinder mission, a formation-flying cluster of three microsatellites, will launch to demonstrate the commercial capability of HE360’s high-precision RFI (Radio Frequency Interference) geolocation technology. The spacecraft will be placed into a sun-synchronous orbit at an altitude of 575 km. 1) 2)

The Pathfinder mission serves to demonstrate the practicality of the geolocation mission and paves the way for a future commercial constellation. Initially, an eighteen satellite constellation (arranged as six clusters of three) is envisioned for commercial, global service. However, the final constellation size and geometry will depend on market factors including the results of the Pathfinder mission.

HE360 selected DSI (Deep Space Industries) of San Jose, CA and major subcontractor UTIAS/SFL (University of Toronto, Institute for Aerospace Studies/Space Flight Laboratory) to design the platform for the Pathfinder mission. DSI is the prime contractor, and the manufacturer of a novel water-fueled electro-thermal propulsion system which will fly on each spacecraft. SFL is responsible for the design and manufacturing all three spacecraft platforms. SFL’s versatile flight-proven 15 kg NEMO (Next-generation Earth Monitoring and Observation) microsatellite bus was selected for the mission. In addition to being a world leader in providing low-cost high-performance small spacecraft, SFL was selected for this mission as it is a pioneer in low-cost precision spacecraft formation flight, a key enabling technology for the HE360 mission. SFL has developed compact, low-cost formation flying technology at a maturity and cost that no other small satellite developer can credibly offer at present. This precise formation control was demonstrated on-orbit by SFL in the highly successful CanX-4/CanX-5 mission in 2014. 3) With 18 successful spacecraft missions on-orbit, SFL’s solutions have demonstrated high reliability and high availability products, which can be depended upon for a wide array of commercial applications. By leveraging SFL’s successful spacecraft platforms and formation flying technology, along with DSI’s pioneering innovations and next-generation propulsion systems, the mission will deliver unparalleled performance in smaller, affordable satellites.

The Mission:

Clearly understanding the world around us is becoming more important than ever. Many of the big problems we face as a society require solutions that contextualize the world around us. This applies directly to the RF domain. HawkEye 360 is capitalizing on the explosive growth of RF signals and their application to tracking assets. Opportunities and applications that arise from this high-precision radio frequency mapping and analytics technology are enormous and appeal to a broad array of business enterprises and government users. The mission is filling a void by bringing a level of visualization to a domain that has historically only been understood by governments. For example, the ability to locate and characterize RF signals across many bands from space will allow regulators, telecommunications companies and broadcasters to monitor spectrum usage and to identify areas of RFI. In the field of transportation, RF signals transmitted from the air, ground or sea could be precisely monitored. The system may also be used to expedite search and rescue operations by quickly pinpointing activated emergency beacons.

RF geolocation as it pertains to this mission means the identification of a terrestrial signal emitter’s location through signal processing and analysis of the received signal at one or more remote observation platforms. In this case, the observation platforms are the three HE360 spacecraft in the Pathfinder cluster. Hereafter the spacecraft will be referred to as “Hawks” and individually as Hawk-A through Hawk-C.

As an example of the utility of the technology which will be made available by this mission, consider an AIS detection case. There are 21 different types of AIS (Automatic Identification System) messages, many of which include the maritime vessel’s location provided by the vessel’s GPS receiver. Many existing satellites decode or receive this information and use the embedded geolocation data for commercial or national purposes.

Unfortunately, it has been demonstrated that AIS data is not universally reliable. It is fairly easy for individuals, such as pirates or illegally operating fishing fleets to “spoof” their AIS emissions, effectively changing the GPS positions they report to make it look as if they are somewhere other than where they actually are or simply changing their identifier. Furthermore, bad actors with less technical capability frequently turn off their AIS transceivers - “going dark” and disappearing from port and satellite AIS data feeds while engaging in criminal activities. HE360 will demonstrate that independent geolocation of AIS and other signals is possible without having to trust potentially false data in the transmissions. In the event that an AIS transmitter is disabled, other well-known signals commonly transmitted by ships can be substituted to maintain position knowledge of an emitter when traditional AIS-receiving satellites would lose contact.

The three Hawks will fly in formation, with co-visibility of a large number of terrestrial emitters at any one time. Pairs of satellites or the entire trio may intercept the same transmission when the transmission originates from the common footprint of the intercepting satellites. The satellites will synchronize clocks using GPS receivers, and these same GPS receivers will stabilize the PLLs (Phase Locked Loops) governing the tuning frequency in the satellites’ digitizing RF tuner payload.

Signals will arrive at the three receivers at separate times corresponding to different slant ranges between the satellite and the emitter. Signals will arrive at different apparent center frequencies corresponding to velocity components in the direction of the signal’s path of travel from the transmitter to the receiver (Doppler effects). Comparing time-of-arrival (TOA) and frequency-of-arrival (FOA) measurements between pairs of receivers serves as a basis for discovering the position of the transmitter using multilateration. GPS receivers provide precise estimates for the position and velocity of the receivers, furnishing the remainder of the information required for multilateration.




Spacecraft

The HE360 Pathfinder mission employs the versatile flight proven NEMO platform of UTIAS/SFL. This state-of-the-art microsatellite bus has been employed by a wide range of commercial and government users, and depended upon in applications and business models which would only allow for a high-performance high-reliability yet affordable platform. Indeed, the NEMO bus has been selected by the Norwegian government for the NORSAT-1, -2, and -3 satellites (scientific, maritime AIS, VDES, and radar applications), the Indian government for NEMO-AM (aerosol monitoring), and GHGSat Inc. for the GHGSat Constellation (greenhouse gas emissions monitoring). The platform supports a full suite of heritage SFL subsystem hardware. The NEMO platform is configurable, with many design aspects tailorable, if needed. The NEMO-platform itself builds upon the extensive heritage gained from SFL’s widely used GNB (Generic Nanosatellite Bus). By leveraging heritage designs and experiences gained through many cumulative years of on-orbit operation, the cost, schedule, and risk associated with the Pathfinder mission was significantly reduced. 4)

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Figure 1: Artist's rendering of the HE360 Pathfinder Platform (image credit: UTIAS/SFL)

The HE360 Pathfinder platform is essentially a 20 x 20 x 44 cm form factor with an additional ~7 cm high ‘mezzanine’, with a launch wet mass of 13.4 kg. Similar to spacecraft designed to the CubeSat standard, four launch rails interface with the separation system and guide the spacecraft during ejection from SFL’s XPOD separation system. An external view of the Pathfinder spacecraft is shown in Figure 1. The bus structure is predominantly lightweight magnesium, with careful arrangement of structural components to provide high mechanical margins. The structural concept of the spacecraft is a dual tray based design, as shown in Figure 2. Most of the platform avionics are clustered towards the +Y end of the spacecraft. This allows for integration and harness design ease, and offers considerable payload accommodation volume.

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Figure 2: Internal layout of the HE360 Pathfinder (image credit: UTIAS/SFL)

As the spacecraft carries a sensitive RF payload, EMI (Electromagnetic Interference) mitigation was an important consideration in the design. The spacecraft was segregated into three distinct RF zones: i) the payloads isolated within their enclosures, ii) the balance of the platform, and iii) the environment external to the spacecraft. The zones were setup by creating boundaries, essentially Faraday cages, which would significantly attenuate noise. This was accomplished by:

• The use of RC-filtered connectors, sized to reject signals above a design cut-off frequency

• The use of conductive gaskets to ensure DC and RF seals across all interfaces of the Faraday cages

• Strict aperture control, to significantly attenuate RF noise, but yet still comply with spacecraft venting requirements. This is particularly important for the spacecraft exterior, as strict aperture control was enforced to prevent transmission of noise which may otherwise be picked up by the payload receive antennas.

The Pathfinder spacecraft employs a single-string design that results in a compact, low mass spacecraft. The power architecture is based on SFL’s modular power system (MPS), which generates power from the body mounted high-efficiency triple-junction solar arrays, and uses a 12 V lithium ion battery for energy storage. A solar array and battery regulator (SABR) unit within the MPS provides peak power tracking functionality to optimize power generation. The MPS also provides power conditioning to generate 3.3 V and 5 V regulated buses in addition to the unregulated 12 V bus, as well as load switching and protection against off-nominal voltage and current events.

C&DH: The command and data handling architecture is centered on two SFL-designed on-board computers (OBCs), which interface to the uplink and downlink radios and all other spacecraft hardware. One OBC is nominally designated as the house keeping computer (HKC), and is responsible for telemetry collection, routing packets to and from the radios, payload operations, and execution of time tagged commands. The second OBC is designated as the attitude determination and control computer (ADCC) and is responsible for polling attitude determination sensors, running the estimation and control algorithms, and commanding actuators. Both computers are cross-connected to all on-board hardware, providing a level of redundancy. In this configuration, either computer can take on the tasks of the other if required.

RF communication: Primary telemetry and command is provided in S-band and UHF, respectively. A SFL UHF receiver is used to provide the uplink channel at a fixed 4 kbit/s data rate. A variable data rate SFL S-band transmitter, which can operate between 32 kbit/s and 2048kbit/s (scaled on-the-fly), in either BPSK or QPSK modulation and 0.5 rate convolutional encoding, is used on the downlink. The platform is also equipped with dedicated high-data rate payload links: uplink in S-band, downlink in X-band and cross-link to other satellites in S-band. The X-band transmitter is capable of 3 – 50 Mbit/s usable data rate. The transmitter uses OQPSK (Offset Quadrature Phase Shift Keying ) and a ½ rate convolutional encoding FEC (Forward Error Correction) scheme. A high-rate S-band uplink is implemented within the payload SDR itself, with a LNA (Low Noise Amplifier) positioned between the radio and the body-mounted patch antenna. A SFL S-band inter-satellite link, although not required for the mission, is integrated to demonstrate the capability to perform the geolocation calculations entirely on orbit. In this scenario, information must be exchanged between the satellites so that all measurements reside on a single spacecraft where the geolocation problem can be solved.

ADCS (Attitude Determination and Control Subsystem): The ADCS employs six sun sensors, a three-axis magnetometer, and a three-axis rate sensor for attitude determination. Attitude control is achieved through three vacuum core magnetorquers and three reaction wheels. Orbit position and velocity measurements are sampled by a L1/L2 GPS receiver and active antenna. Several modes of attitude control are available including de-tumble (for initial stabilization after kick-off from the launch vehicle), inertial pointing, nadir tracking, align-constrain, and ground target tracking. This system allows for 2σ pointing accuracy with only 2.1º and 4.2º error in sunlight and eclipse respectively.

Propulsion system: DSI (Deep Space Industries) is providing a novel electro-thermal propulsion system that uses liquid water as the working fluid, significantly reducing integration and launch risks relative to other market options of similar performance. The unit has a qualified specific impulse (Isp) of 182 seconds, giving it exceptional performance with comparison to a typical cold-gas system. Conversely, while it has a lower Isp than newly available low-power electric propulsion systems, the higher thrust means that DSI’s system can be used quasi-impulsively. This reduces the time required for maneuvers. Electric propulsion systems also typically utilize high voltage power supplies or RF-amplifiers that produce wide-band RF noise, which is detrimental to the RF payload. The propulsion system on Pathfinder has a ΔV of 96 m/s, though, the system features an easily expandable propellant tank, allowing for simple propellant volume tailoring. The water propellant needs to stay liquid at all times. The thermal design of the spacecraft passively maintains the propellant in a liquid state, but auxiliary heaters are positioned to augment this in an emergency.

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Figure 3: Image of the electro-thermal propulsion system (image credit: DSI)

The Formation:

SFL has a strong history in the development and implementation of technologies and algorithms aimed towards operational formation flying missions. The CanX-4 and CanX-5 spacecraft were the first nanosatellites to demonstrate autonomous formation reconfiguration and control with a control error of less than one meter (Ref. 3). This was enabled by a real-time relative navigation algorithm based on carrier-phase differential GPS techniques, which was shown to have a typical RMS error of better than 10 cm. In addition, the drift recovery and station keeping (DRASTK) software was developed and used successfully to design and implement a guidance trajectory for rendezvous following initial spacecraft separation from the launch vehicle, and to maintain a coarse along-track separation in a passively safe relative configuration by appropriately phasing in-plane and out-of-plane motions. 5) It is with this proven track-record of success in applied formation guidance and navigation that SFL is uniquely positioned to implement these techniques operationally for the HE360 Pathfinder mission.

The baseline orbit for the Pathfinder mission is a circular Sun-synchronous orbit with an altitude of 575 km and a local time of descending node of 10:30 hours. In the target formation, the three spacecraft are equally spaced along-track by 125 km. The middle spacecraft has its right ascension of the ascending node (RAAN) adjusted such that it has a 20 km peak-to-peak out-of-plane oscillatory motion, whose maxima are achieved at the equator. For a RAAN-offset orbit, the formation becomes co-linear at the maximum and minimum sub-latitudes of the cluster, which occurs near the northern and southern polar regions. The reduced geolocation precision in the polar regions is tolerable since the human population and activity in this region is limited. Also, the payload data will be downloaded to X-band earth stations in this region frequently. No inclination difference is desired, due to the large cost in maintaining this formation owing to the required RAAN corrections. This formation provides a good balance between ground target viewing geometry for geolocation of RF signals, and fuel cost of formation initialization and maintenance. The quasi-nonsingular mean orbital element set from [6] is adopted in this work for several reasons. First, this parametrization results in an intuitive geometric representation of the formation design variables given its relationship to the solutions of the Hill-Clohessy-Wiltshire equations of relative motion. Second, the equations of relative motion are significantly simplified, so formation guidance and control tasks can be moved onboard more easily. Finally, the use of orbital elements easily lends itself to analysis of “mean” or averaged relative motion, such that short-period and long-period oscillations are ignored and only linear drift in the formation is controlled. The quasi-nonsingular elements cannot be used in equatorial orbits, but this is not considered a detriment since such orbits are not beneficial to HE360 from a ground-coverage perspective.

The required formation control is 5 km (1σ), which must also be tolerant to 1 week ground station outages. The guidance, navigation, and control strategies selected can be implemented on-board the spacecraft, however at present control maneuvers are to be computed on the ground and uploaded to each spacecraft given the relatively coarse formation-keeping requirement. This strategy removes the complexity and risk in implementing autonomous relative navigation and control where it is not warranted. The target mission duration is two years, with a stretch goal of three years. Over this time, only two of the three spacecraft shall be actively controlled. From a power perspective, the spacecraft are constrained to applying orbit control maneuvers at least 45 minutes apart.

Conceptually the formation control strategy is broken down into two phases: formation initialization, and station keeping. Following a two-week commissioning period for the spacecraft systems, the initialization phase is expected to last approximately six weeks. During initialization two of the three spacecraft are maneuvered into the target formation – exactly which two depends on the initial relative configuration upon separation from the launch vehicle. It is expected that all three spacecraft will be deployed approximately five minutes apart from SFL’s XPOD separation system, each at a velocity of roughly 1.8 m/s in an uncontrolled direction relative to the local orbital frame. Given the GPS telemetry from each spacecraft, a guidance plan can be simulated for each permutation of controlled spacecraft. The spacecraft pair leading to minimum fuel consumption will be selected as the controlled spacecraft going forward. The total initialization phase is broken down into sub-intervals (ΔTinit), during which roughly 85% of orbits are allotted for control, while 15% are reserved as maneuver-free periods for the purpose of orbit determination used as input for the next initialization window.

The guidance law during formation initialization is based on 6), where the fuel-optimal reconfiguration from some initial state to a final desired state is framed as a problem of minimizing the net total change in the differential mean orbital elements. This is possible since incremental changes in the orbital elements can be equated to impulsive thrust maneuvers (i.e., instantaneous changes in velocity). The guidance plan generates a set of waypoints in differential mean orbital element space from the current time to the desired initialization time in ΔTinit intervals. The waypoint at the start of the next sub-interval is used as the target during the current control period.

The set of control maneuvers during each initialization sub-interval is computed using the method of Roscoe et al., which exploits a duality between the continuous and discrete time optimal formation reconfiguration problem in order to iteratively solve for a set of maneuver locations and magnitudes that result in a minimum-fuel maneuver plan to reach the target waypoint at the target time. 7) This control strategy is augmented to enforce a minimum time-spacing between maneuvers, and to prevent maneuvers from being planned inside configurable “no thrust” windows, which are specified by operators as a set of intervals.

The station keeping guidance law is designed to keep the spacecraft within a designated control window while keeping the spacecraft passively safe using the eccentricity/inclination vector separation concept. 8) The station keeping phase is conceptualized as a long period of no control (the drift period; approximately 1 week), followed by a short window within which the control maneuvers occur (the control period; approximately 4 orbits). The strategy is motivated by 9), whereby during each control window the active spacecraft targets a specific differential semi-major axis which will cause a drift from one side of the control window to the other. Likewise, the relative eccentricity vector is adjusted such that it will be parallel with the relative inclination vector half-way through the drift period, which maximizes safety during the drift period. The relative inclination vector is simply readjusted to its target value during each control period, since there is no drift desired here. The long drift period is allowable because control maneuvers are expected to be infrequent, owing to the fact that all spacecraft will mirror their attitudes thus minimizing the impact of differential drag on the formation. A side-benefit of this strategy is maximizing the time spent performing payload observations. 10)

The formation control simulations are performed with the aid of Systems Tool Kit (STK). The orbit model includes an EGM2008 gravity model of degree and order 30, third-body perturbations due to the Sun and moon, solar radiation pressure, and atmospheric drag with a Jacchia-Roberts atmospheric density model. Thrusts are modeled as impulsive with a mean error of zero and a standard deviation of 5%. A thrust timing error with standard deviation 10 seconds is applied as well. Thrust minimum impulsive bit and saturation effects are also accounted for, as well as attitude control errors with standard deviation of 2º.




Development status of the HawkEye 360 satellite series

• July 16, 2020: HawkEye 360 Inc., the first commercial company to use formation flying satellites to create a new class of radio frequency (RF) data and data analytics, today announced it has successfully completed environmental testing of its second cluster of three satellites. This significant milestone for HawkEye Cluster 2 clears the way to prepare for launch, which is scheduled for late 2020. — HawkEye Cluster 2 will join the company’s first cluster of satellites that were launched in December 2018, doubling the size of HawkEye 360’s constellation. This is the first cluster in a series of next generation satellites that will improve revisit rates and bring increasingly robust RF data insights to US and international customers to inform their decision-making processes. 11)

- HawkEye 360 has five more clusters of satellites fully financed and under development for launch in 2021 and early 2022. This growing constellation identifies and precisely geolocates a broad set of RF signals from emitters such as VHF marine radios, UHF push-to-talk radios, maritime radar systems, AIS beacons, L-band satellite devices, emergency beacons and more. HawkEye 360 processes and analyzes this data using proprietary algorithms and machine-learning tools to deliver actionable insights to customers.

- HawkEye Cluster 2 features significant advancements:

a) Improved Capability: The satellites contain a new and improved software-defined radio (SDR) that can tune to a wide range of frequencies and gather higher-resolution signal data to deliver quality results to customers.

b) Greater Accuracy: With powerful updated on-board computing, the satellites can process data at a faster rate, leading to increased geolocations with an even greater degree of accuracy, so customers receive the best possible RF geospatial intelligence.

c) Simultaneous Collection: The satellites can simultaneously collect multiple signals over a single region for enhanced analytics that help customers make more informed decisions.

- “HawkEye 360’s investment to advance the field of space-based RF geoanalytics isn’t just about defense and intelligence missions, but it’s also about protecting our global commons by identifying and tracking illicit activities such as illegal fishing, human trafficking, and animal poaching,” said HawkEye 360’s Chief Executive, Officer John Serafini. “In just 18 months, our first cluster has tracked 20 million geolocations and signals of interest to feed growing demand from civil service and defense clients around the world. The successful environmental testing of our HawkEye Cluster 2 satellites brings us one step closer to our goal of a fully operational constellation that will transform invisible signals into insights that make the world a safer place.”

- HawkEye 360 built the RF payloads, which UTIAS/SFL ( Space Flight Laboratory) integrated into the satellite bus. SFL conducted the environmental testing efforts, which included vibration, thermal vacuum, and electromagnetic interference testing. These tests simulate the environment the satellites will encounter in space. The next step is to prepare the satellites for launch integration.

- “HawkEye 360’s investment to advance the field of spaceborne RF geoanalytics isn’t just about defense and intelligence missions, but it’s also about protecting our global commons by identifying and tracking illicit activities such as illegal fishing, human trafficking, and animal poaching,” said HawkEye 360’s CEO, John Serafini. “In just 18 months, our first cluster has tracked 20 million geolocations and signals of interest to feed growing demand from civil service and defense clients around the world. The successful environmental testing of our HawkEye Cluster 2 satellites brings us one step closer to our goal of a fully operational constellation that will transform invisible signals into insights that make the world a safer place.”

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Figure 4: HawkEye Cluster 2 satellite undergoing thermal vacuum testing (Photo: UTIAS/SFL)

- “Each new cluster increases HawkEye 360’s capacity to collect more data that we can then process, analyze and deliver as relevant and robust data insights,” said HawkEye 360’s Chief Operating Officer, Rob Rainhart. “The highly advanced HawkEye Cluster 2 satellites can capture multiple signal layers at once to create a more accurate and detailed visual of activity and then bring that data down in a shorter period of time for our customers’ benefit.”

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Figure 5: Successful testing of new satellites paves the way for faster, more robust data collection and intelligence (image credit: UTIAS/SFL) 12) 13)

• December 19, 2019: The U.S. FCC (Federal Communications Commission) gave HawkEye 360 the approvals it needs to launch and operate 15 additional satellites for radio-frequency mapping from low-Earth orbit. The license, issued Dec. 10, permits HawkEye 360 to launch up to 80 satellites over 15 years in order to maintain a constellation of 15 operational spacecraft. 14)

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Figure 6: Hawkeye 360 plans to operate a constellation of 18 satellites in six clusters to pinpoint the origin of radio frequency signals (image credit: Hawkeye 360)

- Herndon, Virginia-based HawkEye 360 has three pathfinder satellites in orbit today, and 15 more under construction by the Space Flight Laboratory at the University of Toronto Institute for Aerospace Studies. The FCC said the first three satellites will not count towards the 15 since they were authorized under an experimental license.

- Rob Rainhart, HawkEye 360’s chief operating officer, said the new FCC approval positions the company to operate six clusters of three satellites — enough to pinpoint radio signals with revisit rates of 30 to 50 minutes.

- ”It’s right in line with our business plan and gives us time to coordinate beyond that as the markets change,” he said in a Dec. 18 interview.

- HawkEye 360 asked the FCC to defer further evaluation of a filing the company submitted in January to begin laying the regulatory groundwork for an expanded constellation of 80-operational satellites.

- Rainhart said HawkEye 360 chose to take a piecemeal approach to licensing, focusing first on near-term needs instead of trying to coordinate spectrum for a potential larger constellation.

- “We don’t see any issues coordinating those remaining satellites,” he said. “It’s just something we chose not to do in the short term to get up to that full constellation.”

- Rainhart said HawkEye 360 doesn’t have a timetable for an 80-satellite constellation. The company has contemplated constellations of various sizes, he said, but has always had a baseline configuration of 18 satellites.

- There’s absolutely opportunities in the future to grow that much larger than that,” he said. “But we have time to work on that and pre-coordinate that, and we have time to design that.”

- HawkEye 360’s next trio of satellites is scheduled to launch in 2020 on an Indian Polar Satellite Launch Vehicle, Rainhart said. Those satellites, and the 12 others HawkEye 360 has under construction, will all have more power, payload volume and capacity than the company’s first three pathfinder satellites, he said.

- HawkEye 360 flies its satellites in clusters of three, keeping them in tight formation to geolocate signals. Its satellites can detect signals from radars, handheld devices, satellite terminals and other transmitters, enabling the company to identify activity patterns in maritime, defense and other sectors. The company has raised more than $100 million, and counts the National Reconnaissance Office among its customers.


Launch: Three HawkEye 360 (HE360) microsatellites (13.4 kg each) were launched on 3 December 2018 (18:34 GMT) on the SSO-A ”dedicated rideshare” mission of Spaceflight Industries with a SpaceX Falcon 9 Block 5 vehicle from VAFB, CA. 15) 16) 17)

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Figure 7: A Falcon 9 rocket lifts off on 3 December 2018 (18:34 GMT) from Space Launch Complex 4-East at Vandenberg Air Force Base, CA (image credit: SpaceX)

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. 18)

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, LTDN (Local Time of Descending Node) of 10:30 hours.

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Figure 8: Artist’s illustration of the SSO-A mission’s free flyers separating from the upper stage of SpaceX’s Falcon 9 rocket (image credit: Spaceflight Industries)




Mission status

• June 25, 2020: HawkEye 360 Inc., the first commercial company to use formation flying satellites to create a new class of radio frequency (RF) data and data analytics, today announced that the company’s flagship RFGeo product can now map an expanded catalog of marine navigation radar signals to further improve global maritime situational awareness. With this update, HawkEye 360 introduces the first S-band radar signal and quadruples the number of X-band radar signals in the company’s library. HawkEye 360 can now cover the most used frequencies for X-band magnetron-based radar systems, providing a more comprehensive view of maritime activity. 19)

- “We’re addressing critical gaps in Maritime Domain Awareness by revealing an entirely new data layer for vessel monitoring,” said John Serafini, Chief Executive Officer, HawkEye 360. “We’re excited to introduce our first signal in the S-band frequencies. By expanding our signal catalog, we’re not just collecting new and diverse RF data sets, we’re providing actionable intelligence to support the increasing number and scale of our customers’ missions.”

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Figure 9: New HawkEye 360 Radar Signals Delivers Comprehensive Maritime Awareness (image credit: HawkEye 360)

- Vessels continuously operate marine radars to safely navigate from point to point and avoid nearby obstacles, making them an excellent means to track vessels that have otherwise ceased AIS transmissions and gone dark. Commercial vessels 300 gross tonnage or larger are required to be equipped with X-band radars (9 GHz). The largest vessels also carry S-band radars (3 GHz) to penetrate deeper through rain or fog. Each new signal improves HawkEye 360’s ability to develop vessel profiles. This data helps clients identify dark vessels that might be involved in illicit activities, such as smuggling or illegal fishing.

- “Our customers need to maintain accurate and consistent visibility of vessels,” said Alex Fox, Executive Vice President for Business Development, Sales and Marketing, HawkEye 360. “Vessels are continuing to evade AIS detection to conduct illicit activities, making it difficult for organizations to identify and monitor their behaviors. We’re able to provide unique data sets that enable our customers to keep their finger on the pulse of vessel activity.”

- HawkEye 360’s RFGeo identifies and geolocates RF signals collected by HawkEye 360’s proprietary satellite constellation. RFGeo is the first commercially available product offering global spectrum awareness across a broad range of radio signals. In addition to the newly announced signals, RFGeo can independently geolocate marine VHF marine radios, UHF push-to-talk radios, L-band mobile satellite devices, EPIRB (Emergency Position Indicating Radio Beacon) marine emergency distress beacons, and vessel Automatic Identification Systems (AIS). HawkEye 360 is continually adding signals to the catalog to broaden the reach of RF identification across land, sea, and air domains.

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Figure 10: HawkEye 360 geolocates S-band marine navigation radars from vessels off the coast of South Africa (image credit: HawkEye 360)

• March 3, 2020: HawkEye 360 Inc. today announced that a model of its Pathfinder satellite has been transferred to the Smithsonian’s permanent collection and will be displayed in a future gallery at the National Air and Space Museum in Washington DC. This comes one year after HawkEye 360’s Pathfinder satellites were formally commissioned into service to geolocate RF signals. 20)

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Figure 11: Photo of the HawkEye Pathfinder satellite (photo credit: HawkEye 360)

- “It’s an incredible honor for the Smithsonian to select our Pathfinder satellites for its collection,” said John Serafini, Chief Executive Officer, HawkEye 360. “Small satellites are changing what we can achieve in space, and we’re excited to be on the cutting edge of that revolution. We hope that our satellites inspire the next generation of talented minds.”

- HawkEye 360’s cluster of three satellites have successfully geolocated over eleven million RF signals in the past year. This data enables a safer world by supporting many applications, such as finding dark ships that may be engaged in smuggling or illegal fishing.

- “The Pathfinder is an excellent representation of how small satellites are transforming the space industry,” said James David, curator in the Space History Division at the National Air and Space Museum. “We look forward to displaying this commercial RF signals satellite, a first-of-its-kind, to help tell the story of the space age.”

- The Pathfinder satellite is scheduled to go on display when the National Air and Space Museum’s renovation is completed, slated for 2025. The Smithsonian is the world’s largest museum, education and research complex. The National Air and Space Museum is one of 19 museums that make up the Smithsonian.

- HawkEye 360 is fully funded to deploy an additional five clusters, to reach a total of 18 satellites in orbit by the end of 2021. HawkEye 360 is currently building a second cluster of satellites, set for launch in fall 2020.

January 20, 2020: HawkEye 360 Inc., the first commercial company to use formation flying satellites to create a new class of radio frequency (RF) data and analytics, today announced that it has formed a strategic partnership with Airbus, a global leader in the aerospace and defense industry. Through the partnership, Airbus and HawkEye 360 will deliver high-impact geospatial intelligence solutions not currently available. Both companies can leverage the platforms and services of the other partner to address client mission needs. 21)

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Figure 12: The companies HawkEye360 and Airbus will leverage RF signal data and satellite imagery capabilities to create fused geospatial intelligence solutions (image credit: HawkEye360, Airbus)

- “Airbus is an exceptional partner and investor as we develop and deliver our vision for the future of space-based RF data and analytics,” said John Serafini, Chief Executive Officer, HawkEye 360. “Together with Airbus, we will be able to build sophisticated products and services that intelligently leverage a more comprehensive range of data than previously commercially available.”

- This partnership enables HawkEye 360 and Airbus to fuse complementary data sets to maximize value to customers. Airbus will distribute HawkEye 360’s RF data and analytics across Europe to augment its maritime, defense, and intelligence products. HawkEye 360 will offer Airbus’ earth observation optical and synthetic aperture radar (SAR) products jointly with its RF solutions to serve defense and intelligence customers.

- “HawkEye 360 is a pioneer in space-based RF data and analytics and an ideal partner in our mission to improve global situational awareness for our defense, security, and civil customers,” said François Lombard, Director of the Intelligence Business for Airbus Defence and Space. “I look forward to deploying these innovations to serve the growing needs of our customers.”

- “The world’s first EO, SAR, and RF commercial constellation offers unique capabilities, such as a tip-and-cueing Multi-INT system for unprecedented global situational awareness,” said Alex Fox, EVP of Business Development, Sales and Marketing, HawkEye 360. “Integrating these analytics will provide customers valuable insights to execute more informed decisions. We are excited about the business opportunities this unique relationship will bring for both Airbus and HawkEye 360.”

- Airbus was among the investors who participated in HawkEye 360’s $70 million Series B funding in August 2019. The Committee on Foreign Investment in the United States (CFIUS) provided approval for Airbus to close its investment transaction Jan. 8. The Series B funding enables HawkEye 360 to build and launch the full commercial satellite constellation and develop a full line of RF analytic products.

• December 19, 2019: The U.S. FCC (Federal Communications Commission) gave HawkEye 360 the approvals it needs to launch and operate 15 additional satellites for radio-frequency mapping from LEO (Low Earth Orbit). The license, issued Dec. 10, permits HawkEye 360 to launch up to 80 satellites over 15 years in order to maintain a constellation of 15 operational spacecraft. 22)

- Herndon, Virginia-based HawkEye 360 has three pathfinder satellites in orbit today, and 15 more under construction by the SFL (Space Flight Laboratory) at UTIAS (University of Toronto Institute for Aerospace Studies). The FCC said the first three satellites will not count towards the 15 since they were authorized under an experimental license.

- Rob Rainhart, HawkEye 360’s chief operating officer, said the new FCC approval positions the company to operate six clusters of three satellites — enough to pinpoint radio signals with revisit rates of 30 to 50 minutes.

- “It’s right in line with our business plan and gives us time to coordinate beyond that as the markets change,” he said in a Dec. 18 interview.

- HawkEye 360 asked the FCC to defer further evaluation of a filing the company submitted in January to begin laying the regulatory groundwork for an expanded constellation of 80-operational satellites.

- Rainhart said HawkEye 360 chose to take a piecemeal approach to licensing, focusing first on near-term needs instead of trying to coordinate spectrum for a potential larger constellation.

- “We don’t see any issues coordinating those remaining satellites,” he said. “It’s just something we chose not to do in the short term to get up to that full constellation.”

- Rainhart said HawkEye 360 doesn’t have a timetable for an 80-satellite constellation. The company has contemplated constellations of various sizes, he said, but has always had a baseline configuration of 18 satellites.

- “There’s absolutely opportunities in the future to grow that much larger than that,” he said. “But we have time to work on that and pre-coordinate that, and we have time to design that.”

- HawkEye 360’s next trio of satellites is scheduled to launch in 2020 on an Indian PSLV (Polar Satellite Launch Vehicle), Rainhart said. Those satellites, and the 12 others HawkEye 360 has under construction, will all have more power, payload volume and capacity than the company’s first three pathfinder satellites, he said.

- HawkEye 360 flies its satellites in clusters of three, keeping them in tight formation to geolocate signals. Its satellites can detect signals from radars, handheld devices, satellite terminals and other transmitters, enabling the company to identify activity patterns in maritime, defense and other sectors. The company has raised more than $100 million, and counts the National Reconnaissance Office among its customers.

• December 11, 2019: HawkEye 360 Inc., the first commercial company to use formation flying satellites to create a new class of radio frequency (RF) data analytics, today announced it has been awarded a contract for a commercial RF survey study from the National Reconnaissance Office (NRO). Through the contract, HawkEye 360 will examine the integration of commercial RF capabilities and products into the NRO’s geospatial intelligence architecture. 23)

- “This award from the NRO will further our efforts to make our RF data readily accessible to serve the U.S. government,” said John Serafini, Chief Executive Officer, HawkEye 360. “We believe our satellites can complement traditional government systems, introducing a commercial signals capability that is easy to access and share in support of mission needs.”

- Under the study contract, HawkEye 360 will perform assessments, demonstrations, and analysis to validate that commercial RF survey, ordering, cataloging, and data products can integrate into the NRO architecture. These demonstrations will support the review and enhancement of commercial processes for the development of an end-to-end management system.

- HawkEye 360 launched its initial three satellites in December 2018 to globally identify and geolocate a broad range of RF signals. Since achieving commercial operation in April 2019, HawkEye has been working closely with customers to test and bring multiple products to market.

• November 8, 2019: HawkEye 360 Inc., the first commercial company to use formation flying satellites to create a new class of radio frequency (RF) data analytics, today announced that Advance has become the company’s largest shareholder after successfully purchasing Allied Minds’ minority stake. Additionally, Advance has committed to investing $15 million of primary capital into HawkEye 360’s previously announced Series B funding, subject to regulatory approval, and will replace Allied Minds on the company’s board of directors. 24)

- “This shift from Allied Minds to Advance reaffirms our heritage as an American owned, operated, and headquartered corporation, which we know to be essential for leadership in the emerging RF sensing market,” said John Serafini, Chief Executive Officer, HawkEye 360. “Allied Minds was a critical, early institutional investor for HawkEye 360 and we’re proud to have delivered an excellent return to them.”

- HawkEye 360 was founded as one of Allied Minds’ portfolio companies in 2015. On Nov. 6, 2019, Allied Minds’ shareholders voted in favor of selling its shares in HawkEye 360 to Advance. The transaction, which closed today, represents the first significant exit for an institutional investor within the new space industry in the last five years.

• October 4, 2019: HawkEye 360 Inc., the first commercial company to use formation flying satellites to create a new class of radio frequency (RF) data analytics, today announced that the RFGeo product can now map an expanded catalog of signals to address new markets such as border security or anti-poaching efforts. RFGeo identifies and geolocates RF signals collected by HawkEye 360’s satellite constellation. It is the first commercially available product offering global spectrum awareness across a broad range of radio signals. 25)

- “We are excited to introduce an expanded signal catalog to address new markets as we rapidly scale the company after closing our Series B funding,” said Alex Fox, Executive Vice-President for Sales and Marketing, HawkEye 360. “We continue to innovate and rapidly advance our capabilities as the world leader in the emerging space-based RF data and analytics market. These new signals deliver a more comprehensive view of the world to improve the utility of our RF analytics.”

- With this update, HawkEye 360 expands beyond VHF and X-band to include the first RFGeo signals in the UHF and L-band frequencies. In the UHF band, RFGeo is now mapping signals for push-to-talk radios commonly used across land. Through mapping these types of radios, HawkEye 360 can help clients uncover anomalous behaviors for applications such as finding cross-border smuggling operations or poaching activities in nature preserves.

- “Our homeland security customers need affordable services to monitor and secure the borders,” said Tim Pavlick, Vice President of Product, HawkEye 360. “They need timely insights to identify activity and security threats. For example, there are almost 6,000 miles of land border between the continental United States, Mexico, and Canada. HawkEye 360’s unique data and analytics will help our customers maintain better visibility along this border.”

- This RFGeo release includes two additional feature updates:

a) VHF 70 Enhanced – Vessels often program a Maritime Mobile Service Identity (MMSI) code into their digital VHF marine channel 70 broadcasts. HawkEye 360 uses a proprietary process to extract the MMSI identifier, making it possible to match a VHF signal with a specific vessel.

b) RFGeo Catalog – Since February, the HawkEye 360 satellites have collected millions of data points. Customers can now place orders to access archived geospatial data. This data set is useful for developing a richer understanding of patterns of life.

- The RFGeo product launched commercially in April of this year. In addition to the newly announced signals, RFGeo can independently geolocate marine X-band radar, marine VHF radio channels 16 and 70, EPIRB marine emergency distress beacons, and vessel Automatic Identification System (AIS). HawkEye 360 is continually adding signals to the catalogue to broaden the reach of RF identification across land, sea, and air.

• April 4, 2019: HawkEye 360 Inc. today announced that it has launched RFGeo, a first-of-its-kind radio frequency (RF) signal mapping product. RFGeo uses the unique data generated by the HawkEye Constellation of space-based RF sensing satellites to identify and geolocate RF signals, providing a new global geospatial data layer. RFGeo is the company’s first commercially available product. 26)

- “With the launch of RFGeo, HawkEye 360 is now fulfilling customer orders,” said HawkEye 360 Chief Executive Officer John Serafini. “Through RFGeo, customers will access the powerful RF analytics generated by our satellite constellation so they can gain a more comprehensive view of the world. We are much more than just a data source. HawkEye 360 is bringing truly compelling RF analytics to the market, further cementing our position as an exciting and fast-growing leader in the new space field.”

- Although RF signals are ubiquitous, there has never before been a commercially available product that can independently locate, process and track a broad range of signals. RFGeo will initially support identification and geolocation of maritime VHF radio channels, marine emergency distress beacons and vessel Automatic Identification System (AIS) signals. In the coming months, HawkEye 360 will expand the signal catalog to support more applications. Mapping RF signals will provide valuable insights for many markets, such as defense, border security, maritime, emergency response and telecommunications.

- “RFGeo provides our customers with a new view of activities on Earth using the RF spectrum,” said HawkEye 360 Director of Product Brian Chapman. “We are enabling customers to link RF signal geolocations from our RFGeo product to events occurring around the world. RFGeo will help customers monitor RF signals to support a wide range of high-value applications and missions, such as maritime domain awareness.”

- RFGeo is part of HawkEye 360’s core product line for delivering global spectrum awareness. The product simplifies the complexity of understanding RF signals by providing the coordinates and observed characteristics of the identified emitters. RFGeo delivers the RF analytics in a standardized format for loading into common commercial GIS software tools for further analysis.

• February 26, 2019: HawkEye 360 Inc. has successfully commissioned its three Pathfinder satellites and begun geolocating radio frequency (RF) signals. HawkEye 360 satellites fly in a commercially unique formation that independently pinpoints the geographical origin of a wide range of RF signals. Early test results have already demonstrated successful geolocation of VHF Channels 16 and 70, EPIRB (Emergency Position-Indicating RadioBeacon) , and AIS signals as well as identifying marine radar signals. This proprietary source of data enables HawkEye 360 to locate and analyze previously undetected activity, providing new insights for maritime, emergency response, and spectrum analysis applications. 27)

- “We are generating an entirely new data source for important commercial, defense, and intelligence applications around the world,” said HawkEye 360 CEO (Chief Executive Officer) John Serafini. “As the first to be delivering this type of commercial data, HawkEye 360 will help our customers make more timely and precise decisions. Our team has shown unbelievable dedication and passion to reach a new milestone in space technology in just a few short years.”

- In the maritime sector, data gathered by HawkEye 360 can provide visibility for law enforcement into suspicious vessel behavior, giving them better information in their pursuit of illicit activity. Search and rescue efforts can be aided through geolocation of emergency beacons, even when broadcasting incorrect GPS coordinates. HawkEye 360’s spectrum analysis can survey usage of RF bands to maximize communication spectrum and avoid interference.

- “We are thrilled by the breadth of RF data our Pathfinder satellites are gathering from hundreds of miles above the Earth,” said Rob Rainhart, Executive Vice President of Engineering for HawkEye 360. “We’ve achieved much with our early testing and continue to expand the types of signals we can geolocate. It’s exciting to have strong momentum as we prepare to go to market with a full suite of commercially available analytics products over the course of 2019.”

- The company is using the Pathfinder satellites to perform data verification and strategic demonstrations with select customers. These efforts will inform enhancements to the next cluster of satellites currently under development for launch later this year. This next-generation of satellites will broaden the signal range, on-board-processing, and data capabilities as HawkEye 360 expands the constellation to achieve near persistent global coverage.

• January 7, 2019: UTIAS/SFL (Space Flight Laboratory) announced the in-service activation success of the company's three, formation-flying smallsats that were built by SFL under a contract to Deep Space Industries (now integrated into Bradford Space) for HawkEye 360 Inc. 28)

- John Serafini, the CEO of HawkEye 360, said this is the first time a commercial company has used formation-flying satellites for RF detection.

• December 4, 2018: The first moment of first contact with all three of Hawkeye 360's Pathfinder satellites last night! Initial status is good and we'll now begin detailed system checkout. 29)




Sensor complement: (SDR, RF Front-End)

Each spacecraft will have an identical payload, consisting of two high-level components: i) the SDR, comprised of an embedded processor and FPGA resource, and a baseband signal processor, and ii) a custom-RF front-end with antennas, as illustrated in Figure 13.

SDR (Software Defined Radio)

The SDR, flown on the Pathfinder satellites, is comprised of an embedded processor system and three baseband processors. The baseband processor is built around the Analog Devices 9361 product. This is a highly integrated RF transceiver that combines high-speed ADCs and DACs, RF amplifiers, filtering, switching and more on a single chip. The transceiver product is capable of tuning from 70 MHz to 6 GHz, with an instantaneous bandwidth of up to 56 MHz. The 9361 has two receive chains and two transmit chains. Although the device has transmit capability, it is not intended to be used for the receive-only Pathfinder mission. The payload supports three 9361s so that up to three receive channels can be processed simultaneously and on separate frequencies. Although the 9361 has two receive channels, they are tuned via a common local oscillator (LO), which limits the tuning range of one channel to within the instantaneous bandwidth of the other. The embedded processor system is based on the Xilinx Zynq 7045 SOC, which combines a dual-core ARM processor with a Kintex FPGA. The two devices are very tightly integrated on a single chip, which facilitates easy cross-domain switching between the processor and FPGA. This is advantageous for signal processing applications.

HawkEye_Auto1

Figure 13: Simplified block diagram of the sensor complement (image credit: HawkEye Team)


RF Front-End

The HE360 designed custom-RF front end connects to the baseband processors and provides a number of unique, switchable RF paths and antennas to support a range of bands and frequencies of interest. Each switchable path has custom filters, low noise amplifiers (LNA) and even attenuators tailored to a specific band. A low noise block down-converter (LNB) is included to extend the SDR’s frequency range up to Ku-band (~18 GHz). A range of antennas, including quarter-wave dipoles, patches, and wide-band button and horn antennas support the full frequency range, from VHF to Ku-band.

The processor system takes advantage of open-source signal processing software and firmware to maximally mimic desktop SDR products. This allowed ground development to proceed agnostic of the final space hardware and foster adoption of a “fly as you try” philosophy. For the software side, GNURadio will be used. The GNURadio is “a free and open-source toolkit for software radio.” It is widely used in small space projects for ground software processing and may have been used on previous spacecraft in similar embedded environments.

In operation, the payload can be commanded to tune the baseband processor to a center frequency and stream samples at a given sample rate. Nominally, the baseband processor will produce complex (quadrature) samples. The RF front end will also be configured based on the signal of interest. Samples will be conditioned to some extent in the FPGA, including filtering and balancing associated with the ADCs. HawkEye, however, will maximize on-board processing wherever doing so contributes to the bottom line in terms of the product delivered2. 30) Constraints inherent to the mission in terms of downlinking and crosslinking data motivate reducing full-take RF to meta-data surrounding that RF. To accomplish this reduction, user-defined signal processing chains optimized for the embedded platform are implemented.

The payload had gained considerable in-field aerial test experience in parallel with development, building confidence prior to the actual launch of the Pathfinder mission. Indeed, the SDR payloads and receiving antennas were fitted onto three rented aircraft, flown in diverse formations over live RF emitters (including maritime vessels and commercial maritime radar, amongst other targets), yielding RF signal detection and geolocation with unprecedented accuracy.

HawkEye_Auto0

Figure 14: Illustration of the local horizon footprint overlap of the three spacecraft cluster in formation (image credit: HawkEye Team)




Ground Segment

The Pathfinder mission will utilize commercial Earth station services. In April 2018, HawkEye 360 selected Norway’s Kongsberg Satellite Service (KSAT) to provide ground station services for its pathfinder mission. KSAT is a leading provider of ground station communication services to LEO satellites, with a special focus on polar orbits. From its headquarters in Norway, the company has been pioneering the ground segment business for 50 years. Its Svalbard Ground Station, located on 78º North latitude, is the world’s largest commercial ground station that, due to the unique location, provides all-orbit support. 31)

Utilization of the Svalbard ground station will enable fresh and timely data reception of HawkEye 360 data. HawkEye 360 will be using the KSAT Lite product platform, an industry-leading new space network developed by KSAT. The standardized KSAT Lite solution will also enable HawkEye 360 to tie in additional stations in KSAT’s global network to further enhance near real-time delivery of their data product.



1) K. Sarda, N. Roth, R. E. Zee, Dan CaJacob, Nathan G. Orr, ”Making the Invisible Visible: Precision RF-Emitter Geolocation from Space by the HawkEye 360 Pathfinder Mission,” Proceedings of the 32nd Annual AIAA/USU Conference on Small Satellites, Logan UT, USA, Aug. 4-9, 2018, paper: SSC18-II-06, URL: https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=4075&context=smallsat

2) Russ Matijevich, ”Making The Invisible... Visible,” SatMagazine, September 2016, URL: http://www.satmagazine.com/story.php?number=2060893990

3) G. Bonin, N. Roth, S. Armitage, J. Newman, B. Risi, R. E. Zee, “CanX-4 and CanX-5 Precision Formation Flight: Mission Accomplished!”, Proceedings of the 29th Annual AIAA/USU Conference on Small Satellites, Logan, Utah, USA, August 8-13, 2015, paper: SSC15-I-4, URL: https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=3167&context=smallsat

4) Daniel CaJacob, Nicholas McCarthy, Timothy O’Shea, Robert McGwier, ”Geolocation of RF Emitters with a Formation-Flying Cluster of Three Microsatellites,” Proceedings of the 30th Annual AIAA/USU SmallSat Conference, Logan UT, USA, August 6-11, 2016, paper: SSC16-VI-5, URL: https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=3379&context=smallsat

5) Josh Newman, Robert E. Zee, “Drift Recovery and Station Keeping Results for the Historic CanX-4/CanX-5 Formation Flying Mission”, Proceedings of the 29th Annual AIAA/USU Conference on Small Satellites, Logan, Utah, USA, August 8-13, 2015, paper: SSC15-VIII-1, URL: https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=3218&context=smallsat

6) G. Gaias, S. D’Amico, J.-S. Ardaens, ”Generalized Multi-Impulsive Maneuvers for Optimum Spacecraft Rendezvous,” 5th International Conference on Spacecraft Formation Flying Missions and Technologies, Munich, Germany, 30 May 2013, URL: https://pdfs.semanticscholar.org/7c2d/421723cfd75722ddaa987d3d9f4f4727197e.pdf

7) Christopher W. T. Roscoe, Jason J. Westphal, Jacob D. Griesbach, Hanspeter Schaub, ”Formation Establishment and Reconfiguration Using Differential Elements in J2-Perturbed Orbits,” Journal of Guidance, Control, and Dynamics, Vol. 38, No. 9, pp. 1725-1740, Sept. 2015, https://doi.org/10.2514/1.G000999

8) Simone D'Amico; Oliver Montenbruck, ”Proximity Operations of Formation-Flying Spacecraft Using an Eccentricity/Inclination Vector Separation", Journal of Guidance, Control, and Dynamics, Vol. 29, No. 3 (2006), pp. 554-563, https://doi.org/10.2514/1.15114

9) S. D'Amico, ”Autonomous Formation Flying in Low Earth Orbit,” PhD Dissertation, TU Delft, 2010, URL: https://repository.tudelft.nl/islandora/object
/uuid:a10e2d63-399d-48e5-884b-402e9a105c70/datastream/OBJ/download

10) K. Sarda, R. E. Zee, Dan CaJacob, Nathan G. Orr, ”Making the Invisible Visible: Precision RF-Emitter Geolocation from Space by the HawkEye 360 Pathfinder Mission,” Proceedings of the 69th IAC (International Astronautical Congress) Bremen, Germany, 1-5 October 2018, paper: IAC-18-B4.4.1, URL: https://iafastro.directory/iac/proceedings/IAC-18/IAC-18/B4/4/manuscripts/IAC-18,B4,4,1,x42239.pdf

11) ”HawkEye 360 Completes Milestone in Preparation to Launch Second Cluster,” HawkEye 360, 16 July 2020, URL: https://www.he360.com/hawkeye-360-completes-milestone-in-preparation-to-launch-second-cluster/

12) ”HawkEye 360 Completes Milestone in Preparation to Launch Second Cluster,” UTIAS/SFL, 17 July 2020, URL: https://www.utias-sfl.net/?p=3367

13) https://www.he360.com/technology/constellation/

14) Caleb Henry, ”FCC approves HawkEye 360 application for 15 satellites,” SpaceNews, 19 December 2019, URL: https://spacenews.com/fcc-approves-hawkeye-360-application-for-15-satellites/

15) ”HawkEye 360 Announces Successful Launch of First Three Satellites,” HawkEye 360, 3 December 2018, URL: http://www.he360.com/hawkeye-360-announces-successful-launch-of-first-three-satellites/

16) Stephen Clark, ”Spaceflight’s 64-satellite rideshare mission set to last five hours,” Spaceflight Now, 3 December 2018, URL: https://spaceflightnow.com/2018/12/03
/spaceflights-64-satellite-rideshare-mission-set-to-last-five-hours/

17) Stephen Clark, ”Spaceflight preps for first launch of unique orbiting satellite deployers,” Spaceflight Now, 23 August 2018, URL: https://spaceflightnow.com/2018/08/23
/spaceflight-preps-for-first-launch-of-unique-orbiting-satellite-deployers/

18) ”Spaceflight SSO-A: SmallSat Express Mission,” SpaceX, 3 December 2018, URL: https://www.spacex.com/news/2018/12/03/spaceflight-sso-smallsat-express-mission

19) ”New HawkEye 360 Radar Signals Delivers Comprehensive Maritime Awareness,” HawkEye 360, 25 June 2020, URL: https://www.he360.com
/new-hawkeye-360-radar-signals-delivers-comprehensive-maritime-awareness/

20) ”HawkEye 360 Pathfinder Selected for Exhibition in New Smithsonian Gallery,” HawkEye360 Press Release, 3 March 2020, URL: https://www.he360.com
/hawkeye-360-pathfinder-selected-for-exhibition-in-new-smithsonian-gallery/

21) ”HawkEye 360 and Airbus Form Strategic Partnership,” HawkEye360 Press Release, 20 January 2020, URL: https://www.he360.com/hawkeye-360-and-airbus-form-strategic-partnership/

22) Caleb Henry, ”FCC Approves HawkEye 360 Application for 15 Satellites,” SpaceNews, 19 December 2019, URL: https://www.he360.com/fcc-approves-hawkeye-360-application-for-15-satellites/

23) ”HawkEye 360 Awarded Study Contract by the National Reconnaissance Office,” HawkEye360, 11 December 2019, URL: https://www.he360.com
hawkeye-360-awarded-study-contract-by-the-national-reconnaissance-office/

24) ”Allied Minds Completes Sale of HawkEye 360 Stake,” HawkEye360 Press Release, 8 November 2019, URL: https://www.he360.com
/allied-minds-completes-sale-of-hawkeye-360-stake/

25) ”HawkEye 360 Expands Signal Catalog to Address New Markets,” HawkEye360 Press Release, 24 October 2019, URL: https://www.he360.com
/hawkeye-360-expands-signal-catalog-to-address-new-markets/

26) ”HawkEye 360 Launches First Commercial Product – RFGeo,” HawkEye360, 4 April 2019, URL: https://www.he360.com/hawkeye-360-launches-first-commercial-product-rfgeo/

27) HawkEye 360 Begins First-of-its-Kind Commercial Geolocation of Radio Frequency Signals from Space — Identifying and Locating Signals Will Bring Clarity to Previously Undetectable Activity,” HawkEye 360, 26 February 2019, URL: https://www.he360.com
/hawkeye-360-begins-first-of-its-kind-commercial-geolocation-of-radio-frequency-signals-from-space/

28) ”The On Orbit Hawkeye360 Pathfinder Smallsats Activated Successfully by Space Flight Laboratory,” Space Daily, 7 January, 2019, URL: http://www.satnews.com/story.php?number=1268258787

29) ”HawkEye 360,” HawkEye, 4 December 2018, URL: https://twitter.com/hawkeye360/status/1069963687207886851

30) Daniel CaJacob, Nicholas McCarthy, Timothy O’Shea, Robert McGwier, ”Geolocation of RF Emitters with a Formation-Flying Cluster of Three Microsatellites”, Proceedings of the 30th Annual AIAA/USU SmallSat Conference, Logan UT, USA, August 6-11, 2016, paper: SSC16-VI-5, URL: https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=3379&context=smallsat

31) ”HawkEye 360 Selects Norway’s Kongsberg Satellite Service (KSAT) to Provide Ground Station Services for Pathfinder Mission,” HawkEye 360, 18 April 2018, URL: http://www.he360.com
/hawkeye-360-selects-norways-kongsberg-satellite-service-
ksat-to-provide-ground-station-services-for-pathfinder-mission/



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 (herb.kramer@gmx.net).

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