WorldView-4 (formerly GeoEye-2)

Spacecraft     Launch    Mission Status     Sensor Complement    References

In June 2014, Digital Globe announced that it received notice from the U.S. Department of Commerce on its application to allow the company to sell its highest-quality and industry-leading commercial satellite imagery. Effective immediately, DigitalGlobe was permitted to offer customers the highest resolution imagery available from their current constellation. Additionally, the updated approvals will permit DigitalGlobe to sell imagery to all of its customers at up to 0.25 m panchromatic and 1.0 m multispectral GSD (Ground Sample Distance) beginning six months after its next satellite WorldView-3 is operational. The launch of Worldview-3 is scheduled for August 2014. ¹⁾

With the launch of WorldView-3, the DigitalGlobe constellation will set a new technological bar for commercial satellite imagery, offering customers the highest available resolution, revisit rate, capacity, and spectral diversity. The company currently operates a fleet of five high-resolution earth imaging satellites. Two of those satellites — GeoEye-1 and WorldView-2 — collect imagery sharper than 0.50 m, and all customers will have access to that imagery at the highest native resolution. WorldView-3 will provide even higher resolution at 0.31 m, and the GeoEye-2 satellite, which is substantially complete, will capture similarly sharp images when it is launched to replace a satellite currently in service or as an expansion to the constellation once warranted by market demand.

Table 1: Some background on the GeoEye-2 / Worldview-4 development program ^{2) 3) 4) 5) 6) 7) 8) 9) 10) 11)}

Spacecraft:

WorldView-4 will be DigitalGlobe's next very high resolution imaging satellite providing high resolution and color imagery to commercial, government and international customers. Lockheed Martin is the prime contractor of the WorldView-4 spacecraft. WorldView-4 will provide map-accurate images with a new, high-resolution camera provided by Harris Corporation. In addition to delivering critical geospatial situational awareness and global security information to intelligence analysts, war fighters and decision makers, commercial users will also benefit from access to imagery from WorldView-4. The satellite is fully integrated, tested and ready for launch call-up. ¹²⁾

Figure 1: Artist's rendition of the WorldView-4 spacecraft (image credit: Lockheed Martin, Digital Globe)

Table 2: Some spacecraft/observation parameters

Figure 2: Photo of the WorldView-4, the world's second 30 cm imaging satellite, taken in July 2016 (image credit: DigitalGlobe) ¹³⁾

Development status:

• August 15, 2016: WorldView-4, which weighs 2,500 kg and stands 5.5 m tall, is "a big telescope with a little satellite wrapped around it," said Walter Scott, founder, chief technical officer and executive vice president of Westminster, Colorado-based DigitalGlobe. ¹⁴⁾

- WorldView-4 has taken an unusually long time to get to the launch pad. Lockheed Martin began building the satellite, originally named GeoEye-2 for GeoEye of Herndon, Virginia, in 2010. After DigitalGlobe and GeoEye merged in 2013, DigitalGlobe proceeded with its planned launch of WorldView-3 and opted to store GeoEye-2. DigitalGlobe renamed the GeoEye-2 satellite WorldView-4 in 2014 when the company announced its 2016 launch.

Figure 3: Photo of the WorldView-4 spacecraft. Employees at Lockheed Martin completing final preparations of the WorldView-4 imaging satellite (image credit: Lockheed Martin)

• On July 28, 2016, the WorldView-4 satellite arrived at VAFB after a 250-mile trip (from Sunnyvale, CA) in a cleanroom-on-wheels. The Lockheed Martin-built WorldView-4 was transported by truck in a special container that mimics the environment of the cleanroom where the satellite was manufactured. ¹⁵⁾

- Prior to shipping, the satellite passed a full suite of environmental, functional and performance tests and was declared ready for integration with the rocket that will carry it to an altitude of 617 km in space.

Figure 4: Photo of the "cleanroom transport" with WorldView-4 aboard leaving the Lockheed facility in Sunnyvale, CA (image credit: Lockheed)

Launch: The WorldView-4 (former GeoEye-2) spacecraft was launched on November 11, 2016 (18:30 UTC) on an Atlas-V 401 vehicle of ULA (United Launch Alliance) from VAFB, CA, SLC-3E (Space Launch Complex-3East). ^{16) 17) 18)}

The launch of WorldView-4 had to be cancelled on the original launch date of September 18 due to an extremely aggressive fire that consumed some 12,000 acres (4840 hectar) across Vandenberg's South Bases. This was considered to be the largest fire in the base' history but, fortunately, the space launch complexes and other facilities remained clear of the destruction. — All of the 200 miles of cabling have now been certified as in order by the 30^th Space Communications Squadron of the US Air Force, and all appears to be a "go" for this delayed and now re-scheduled launch (Ref. 18).

Orbit: Sun-synchronous orbit, altitude = 617 km, inclination = 98º, period = 97 minutes, LTDN (Local equatorial crossing Time on Descending Node) at 10:30 hours, effective revisit time capability ≤ 3 days.

Secondary payloads: ¹⁹⁾

DigitalGlobe has included a CubeSat rideshare program. The CubeSats will be launched by use of ULA's Centaur Aft Bulkhead Carrier that has flown successfully on four previous Atlas V missions. All of the 7 CubeSats manifested for the WorldView-4 mission are sponsored by the U.S. NRO (National Reconnaissance Office) and are unclassified technology demonstration programs. DigitalGlobe is also partnering with California Polytechnic State University, Tyvak Nanosatellite Systems Inc., Lockheed Martin and United Launch Alliance to bring this rideshare program to fruition.

Tyvak Nanosatellite Systems (Irvine, CA) served as the integrator for all seven CubeSats. ENTERPRISE is the fifthNRO mission to utilize ridesharing, but the first in which the organization has partnered with a commercial company to do so. ²⁰⁾

• CELTEE-1 (CubeSat Enhanced Locator Transponder Evaluation Experiment-1), a 1U CubeSat built by M42 Technologies (Seattle,WA) for AFRL (Air Force Research Laboratory). The goal is to test the performance of an ELT (Enhanced Location Transponder) in support of SSA (Space Situational Awareness).

• Prometheus-2 x 2, two 1.5U technology demonstration CubeSats (Block 2) of LANL (Los Alamos National Laboratory). Test of communications between remote field sites and ground station terminals in a store-and-forward environment.

• AeroCube-8C and -8D, two 1.5U technology demonstration CubeSats of the Aerospace Corporation (El Segundo, CA) to test electric propulsion, CNT (Carbon Nanotubes) and solar cell technology.

• U2U (Untitled 2U), a 2U CubeSat of AFRL to demonstrate the EGM (Electron and Globalstar Mapping) experiment.

• RAVAN (Radiometer Assessment using Vertically Aligned Nanotubes), a 3U CubeSat mission funded by the NASA and developed and operated by JHU/APL.

The CubeSats will be deployed after WorldView-4 separation as part of the NRO-sponsored ENTERPRISE mission.

Figure 5: Illustration of the deployed WorldView-4 spacecraft (DigitalGlobe)

Mission status:

• January 7, 2019: Maxar Technologies Inc. today reported that its WorldView-4 satellite experienced a failure in its CMGs (Control Moment Gyros), preventing the satellite from collecting imagery due to the loss of an axis of stability. ²¹⁾

- Efforts are ongoing in conjunction with its suppliers in an attempt to restore satellite functionality, but thus far these efforts have been unsuccessful. At this time, Maxar believes that WorldView-4 will likely not be recoverable and will no longer produce usable imagery. Maxar operations has put the WorldView-4 satellite in a safe configuration and will continue to monitor the satellite's location and health. The satellite was built by Lockheed Martin and the CMGs were provided by Honeywell.

- WorldView-4 was acquired by GeoEye prior to its merger with DigitalGlobe in 2013. It was launched in November 2016 and generated revenues of approximately $85 million in fiscal year 2018. The satellite had a net book value of approximately $155 million, including related assets, as of December 31, 2018. If the satellite is not recoverable, then the net book value will be written off in Q4-2018. Contingency planning and mitigation efforts are underway to assess the use of the Company's other satellites and outside resources to replace imagery collected by WorldView-4 and meet as much of the existing customer commitments and obligations as possible. The Company currently believes it will be able to offset $10 to 15 million of the annual revenue from WorldView-4 and will work to minimize the potential impact on Maxar's financial results in future years.

- The WorldView-4 satellite is insured for $183 million, and Maxar intends to seek full recovery for the loss of WorldView-4 under its insurance policies. The Company will provide further updates on this matter as new information becomes available.

• October 04, 2018: NASA has launched a pilot program to evaluate how Earth science data from commercial small-satellite constellations could supplement observations from the agency's fleet of orbiting Earth science missions. On 28 September, the agency awarded sole-source contracts to acquire test data sets from three private sector organizations. ²²⁾

- NASA's Earth Science Division in Washington issued blanket purchase agreements for the "Private Sector Small Constellation Satellite Data Product Pilot" program. Under these agreements, the agency purchases data sets and related products based on observations derived from Earth-orbiting, small-satellite constellations designed and operated by non-governmental entities.

- "This pilot program is an innovative and efficient way for us to acquire, examine, and evaluate a wide range of private sector Earth observation data," said Michael Freilich, director of NASA's Earth Science Division. "As our very capable NASA research satellite fleet ages and more small satellites are launched by private industry, there are opportunities to leverage the strengths of each into even more complete climate data sets."

- NASA will provide the test data products to NASA-funded researchers, who will examine whether the data help advance the agency's science and applications development goals. The pilot program is designed to determine whether these private sector observations and associated products offer a cost-effective means to augment or complement the suite of Earth observations acquired directly by NASA, other U.S. government agencies, and international partners.

- The contracts were awarded to:

1) DigitalGlobe, a Maxar Technologies company headquartered in Westminster, Colorado, has five very high-resolution Earth imaging satellites (GeoEye-1, WorldView-1, WorldView-2, WorldView-3, WorldView-4) capable of collecting 30 cm resolution imagery.

2) Planet, headquartered in San Francisco, has three satellite constellations (SkySat, Dove, RapidEye) with more than 150 satellites supplying imagery and derived products over the entire Earth at medium and high resolution with high repeat frequencies.

3) SPIRE Global, headquartered in San Francisco, operates a constellation of over 60 Lemur 3U CubeSats collecting radio occultation soundings, aircraft location information and ship reports. GPS radio occultation measurements can be used to sound the atmosphere for temperature, water vapor, and atmospheric pressure.

- These contracts represent the first time that NASA has engaged with commercial small-satellite constellation operators to purchase their data for scientific evaluation. They establish a way for NASA to acquire and examine the data products during the next 12 months. Each contract includes an option for NASA to extend the agreement for an additional four years, for a total value of up to $7 million for each of the three agreements.

- To be considered for participation in this pilot program, companies had to demonstrate they were currently operating a small satellite constellation of no fewer than three satellites in non-geostationary orbit and producing consistent global coverage. Companies also were asked to supply a comprehensive catalog of their data, describing areal coverage, data latency, pricing, and other factors.

- NASA uses the vantage point of space to understand and explore our home planet, improve lives and safeguard our future. The agency's observations of Earth's complex natural environment are critical to understanding how our planet's natural resources and climate are changing now and could change in the future.

• April 22, 2018: DigitalGlobe, a Maxar Technologies company, formerly MDA (MacDonald, Dettwiler and Associates Ltd.), announced today that with the complete integration of DigitalGlobe's WorldView-4 satellite imagery into SecureWatch, the company's powerful, cloud-based geospatial intelligence (GEOINT) platform, customers can now access more of the world's highest resolution satellite imagery. ²³⁾

- WorldView-4's daily imagery collections more than double SecureWatch's daily volume of valuable 30 cm imagery, enhancing defense and intelligence analysts' ability to closely monitor activity in their areas of interest. WorldView-4 collection plans are constantly analyzed and improved to deliver more refreshed 30 cm imagery over the rapidly changing geographies that SecureWatch customers need to make mission-critical decisions with confidence.

- The subscription-based platform will expand further this summer when RADARSAT-2 imagery from MDA, another Maxar company, becomes available. MDA's RADARSAT-2 SAR (Synthetic Aperture Radar) imagery will expand the capacity for analysts to monitor key locations around the world, regardless of weather and light conditions.

- When layering radar and optical imagery together, an analyst can quickly flag areas of change and develop richer situational reports. The planned addition of MDA's RADARSAT-2 imagery into DigitalGlobe's SecureWatch product is yet another example of how Maxar is extending cross-business technology to accelerate innovation and offer integrated solutions to customers.

- "The combination of RADARSAT-2 imagery and DigitalGlobe's optical imagery, with the other enriched data sources within SecureWatch, will create powerful solutions for analysts to maintain situational awareness and achieve mission success no matter what's happening on the planet," said Jeff Kerridge, Senior Vice President and General Manager of DigitalGlobe International Defense and Intelligence.

- DigitalGlobe also celebrates the signing of its 20th SecureWatch defense and intelligence agency customer since launching the product in February 2017. The first 10 customers started using SecureWatch before the end of 2017 and another 10 have also subscribed this year, joining defense and intelligence analysts around the world who rely on complete access to both DigitalGlobe's 18-year, 100 petabyte imagery archive and the over three million square kilometers of fresh high-resolution imagery added daily.

- "DigitalGlobe is proud to be the trusted partner to 20 SecureWatch subscribers, 70% of whom are new to DigitalGlobe, who understand the demonstrated value of allowing us to help hundreds of analysts deliver GEOINT that is rich, accurate and current," added Kerridge.

- New features within SecureWatch are routinely released to improve user experience by putting more GEOINT sources at analysts' fingertips, in addition to the tools to analyze and exploit the data contained within those sources.

• On December 15, 2017 at 15:36 GMT, SpaceX launched the NASA commercial resupply service mission CRS-13 to the ISS on a Falcon-9 FT vehicle from Cape Canaveral SLC-40. - After the launch, SpaceX landed the first stage of the Falcon-9 vehicle upright on solid ground at Cape Canaveral, Florida. SpaceX has now managed to return 20 of its rocket boosters after launch, whether on land or on a floating ocean platform, as part of its effort to re-use instead of jettison costly components. ²⁴⁾

- Worldview-4 of DigitalGlobe was in the right orbital position to capture an image of SpaceX's first stage (Figure 6) in upright position just minutes after its landing at Cape Canaveral (Ref. 25).

Figure 6: WorldView-4, captured this image at 10:49 a.m. EST (15:49 GMT) on 15 Dec. 2017, just minutes after the Falcon 9 first stage booster returned to Earth with a flawless landing. A launch crew can be seen hosing down the rocket (image credit: Matthew Flannery, DigitalGlobe) ²⁵⁾

Table 3: Acquisition of DigitalGlobe by MDA ^{26) 27)}

• September 2017: WorldView-4 Launch and Calibration Timeline: ²⁸⁾

- Launch: 11 November 2016

- First image: 21 November 2016

- Relative radiometric calibration: 03 December 2016

- Geometric camera calibration: 12 December 2016

- Geometric accuracy: 1 February 2017

- Absolute radiometric calibration: 8 February 2017.

• September 2017: DigitalGlobe's Future Constellations: ²⁹⁾

Figure 7: Our future DG constellation will diversify our capabilities (image credit: Digital Globe)

Figure 8: Our DG constellation roadmap will extend our industry leadership well into the next decade (image credit: DigitalGlobe)

• August 15, 2017: Digital Globe today announced that it signed a DAP (Direct Access Program) contract with the Australian Department of Defence. This multi-year agreement will allow the Australian government to access DigitalGlobe's industry-leading commercial satellite imaging constellation to support defense and intelligence missions. The contract is expected to deliver $83.0 million USD in incremental revenue to DigitalGlobe over four years, beginning in January 2018. ³⁰⁾

- As a DAP partner, the Australian Department of Defence will be able to directly task and download imagery in real-time to its ground station from all five DigitalGlobe satellites—including WorldView-4, launched in November 2016, and WorldView-3, launched in August 2014, which are the world's two highest-resolution commercial satellites. The addition of Australia—a key ally of the U.S. and member of the Five Eyes intelligence alliance—expands the global footprint of DigitalGlobe's DAP program and reflects the Australian government's commitment to increase the use of commercial satellite imagery for its critical national defense and intelligence missions.

• April 18, 2017: EUSI (European Space Imaging) announced that the company has launched its new ground station with access to the entire fleet of its WorldView Global Alliance DigitalGlobe partner. The Munich-based company is now able to directly handle five high resolution satellites (GeoEye-1, WorldView-1, WorldView-2, WorldView-3 and WorldView-4). This speeds up the whole process of planning, collection, data downlink and delivery and allows European Space Imaging to quickly deliver satellite imagery products to WorldView Global Alliance customers in Europe, North Africa, CIS (Commonwealth of Independent States) countries and the Middle East. ³¹⁾

- "The capabilities of our new ground station and the direct access to the entire DigitalGlobe satellite fleet start a new era in the availability of highest resolution imagery in Europe. It's a major milestone especially in the 30 cm resolution class", says Adrian Zevenbergen, Managing Director of European Space Imaging. "In 2017, we plan to collect more than two times the entire European land mass with the 30 cm satellite constellation alone."

Figure 9: Sample WorldView-4 image of the Istanbul Airport, acquired on March 29, 2017 (image credit: EUSI, DigitalGlobe)

Figure 10: Sample WorldView-4 image of the Leaning Tower of Pisa, Italy, acquired on March 28, 2017 (EUSI, DigitalGlobe)

• February 6, 2017: The WorldView-4 commercial satellite, operated by DigitalGlobe, Inc., has successfully completed on orbit testing and calibration and started to serve the company's first direct access customer on February 1, 2017. ^{32) 33)}

- WorldView-4, launched on November 11, 2016, becomes the fifth active satellite in DigitalGlobe's constellation of high-resolution Earth observation satellites. The satellite's performance meets the industry-leading quality standards of the WorldView fleet and joins WorldView-3 as the world's only commercial satellites capable of achieving 30 cm native resolution. Imagery with this level of detail enables users to reliably read street markings, distinguish between cars, trucks, and vans, and confidently understand activities of significance, as demonstrated by a recent SkyTruth analysis that used WorldView-3 imagery to document the likely transshipment of fish by Southeast Asian vessels in the Indian Ocean.

- The satellite more than doubles DigitalGlobe's capacity to collect 30 cm imagery, enhancing the company's ability to meet the most demanding commercial use cases, such as complementing aerial imagery collection strategies, and enabling the creation of high-quality, imagery-derived products, such as high-resolution 3D models and near-seamless, country-scale basemaps.

Figure 11: Sample image of Brasilia, the Capital of Brazil, acquired with WorldView-4 on January 11, 2017 (image credit: Digital Globe)

Figure 12: Sample WorldView-4 image of Subi Reef, acquired on Dec. 27, 2016 (image credit: DigitalGlobe)

Legend to Figure 7: Subi Reef (also Zhubi Reef) is a reef in the Spratly Islands of the South China Sea located 26 km southwest of Philippine-occupied Thitu Island. It is occupied by China, and claimed by Taiwan, Vietnam, and the Philippines. It currently falls under the jurisdiction of Nansha islands, Sansha city, Hainan province, China. The atoll measures 5.7 km along its longer southwest-northeast axis, and is up to 3.5 km wide. Its total area including the lagoon and rim of the reef measures 16 km², and the lagoon is up to 22 meters deep. ³⁴⁾

• December 5, 2016: DigitalGlobe has released the first image from the company's WorldView-4 satellite, launched on Nov. 11, 2016. ³⁵⁾

Figure 13: WorldView-4's first public image, taken on November 26, 2016, features the Yoyogi National Gymnasium in Shibuya, Tokyo. The site hosted events during the 1964 Olympic Games and will again host international competition when the games return to Tokyo in 2020 (image credit: DigitalGlobe)

• WorldView-4 is the new companion to WorldView-3, effectively doubling the amount of best-on-the-market imagery with unmatched 30 cm resolution. WorldView-3 is booked by U.S. government contracts. WorldView-4 will enable DigitalGlobe sales to foreign allies and commercial uses like agriculture, mining, land developers and oil and gas firms.

Sensor complement: (SpaceView^TM 110)

SpaceView^TM 110 Imaging System:

WorldView-4 will enable expanded capability in the collection of sub-meter imagery to help solve real-world problems. The Harris SpaceView™ line of optical imaging systems offers a broad spectral range of high-resolution optical payloads. The SpaceView™ 110 solution for WorldView-4 will provide the highest resolution satellite imagery commercially available. ³⁶⁾

The SpaceView^TM 110 payload serves as the imaging payload for DigitalGlobe's WorldView-3 and WorldView-4 satellites. Delivering up to 25 cm panchromatic resolution, SpaceView^TM 110 boasts the most advanced capabilities available from an imaging payload on the market today.

Scanning at 24,000 lines/second, the SpaceView 110 imaging payload is capable of providing an image spanning from London to Paris in just 45 seconds. This feature enables users to understand what is happening over a long distance as soon as possible.

Note: In May 2015, Harris Corp. of Melbourne, FL. acquired ITT Exelis Inc. of Fort Wayne, IN. ³⁷⁾

ITT Corporation of Rochester, N.Y. received a subcontract from Lockheed Martin Space Systems to continue building the imaging system for GeoEye's next-generation Earth-imaging satellite, GeoEye-2, ITT announced on August 31, 2010. ³⁸⁾

On March 1, 2011, ITT announced that it has satisfied a key milestone with the successful completion of the CDR (Critical Design Review) for the imaging system for GeoEye-2. ³⁹⁾

In 2011, ITT Corporation's board of directors approved a plan to separate the company's businesses into three distinct, publicly traded companies. As of Oct. 31, 2011, ITT Exelis is the company involved in C4ISR (Command, Control, Communications, Computers, Intelligence, Surveillance and Reconnaissance) related products and systems and information and technical services. This pertains also to space systems.

In April 2012, ITT Exelis Geospatial Systems has delivered GeoEye's next-generation commercial imaging system for the GeoEye-2 satellite to Lockheed Martin Space Systems Company in Sunnyvale, CA. The instrument provides a GSD (Ground Sample Distance) of 34 cm for panchromatic imagery and 1.36 m for multispectral imagery from an orbit of 681 km. ⁴⁰⁾

WorldView-4 will provide map-accurate images with a new, high-resolution camera provided by Harris Corporation. In addition to delivering critical geospatial situational awareness and global security information to intelligence analysts, war fighters and decision makers, commercial users will also benefit from access to imagery from WorldView-4.

WorldView-4 is a multispectral, high-resolution commercial satellite of DigitalGlobe.The SpaceView 110 instrument has a telescope of 1.1 m in diameter ; it will provide imagery of 31 cm in panchromatic resolution and 1.24 m in multispectral resolution from an orbit of 617 km. ^{41) 42)}

http://content.satimagingcorp.com.s3.amazonaws.com/static/satellite-sensor-specification/WorldView-4-Satellite-Specifications

Table 4: Parameters of SpaceView 110 on WorldView-4

SpaceView 110 features:

- Industry-leading geolocation accuracy (predicted <4 m CE90 without ground control)

- High capacity in various collection modes

- Bi-directional scanning

- Rapid retargeting agility using Control Moment Gyros (>2x faster than any competitor) resulting in superior area and point target collection capability. Time to Slew 200 km: 10.6 seconds.

- Direct access tasking from and image transmission to customer sites

- Daily revisit capability.

Figure 14: GSD (Ground Sample Distance) of the SpaceView 110 imager in relation to orbital altitude (image credit: Harris)

Table 5: Overview of the DigitalGlobe constellation ⁴³⁾

Figure 15: Illustration of the SpaceView^TM 110 instrument (image credit: Harris)

Figure 16: Pictorial view of the DigitalGlobe constellation of high-resolution imagery (image credit: DigitalGlobe)

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URL: http://mailchi.mp/euspaceimaging/worldview
-4-data-now-available?e=2c05008044

32) "WorldView-4 enters service," DigitalGlobe, Feb. 1, 2017, URL: http://worldview4.digitalglobe.com/#/main

33) "WorldView-4 Is Up and Capturing," Satnews Daily, Feb. 6, 2017, URL: http://www.satnews.com/story.php?number=1906185948

34) "Subi Reef," Wikipedia, URL: https://en.wikipedia.org/wiki/Subi_Reef

35) "WorldView-4 first image, " DigitalGlobe, URL: http://worldview4.digitalglobe.com/#/main

36) "SpaceView 110 Satellite Imaging Solution," Harris, URL: https://www.harris.com/sites/default/files/downloads/
solutions/55805_sv110_datasheet_final_digital.pdf

37) "Harris Corporation Completes Acquisition of Exelis," Press Release, May 29, 2015, URL: http://www.exelisinc.com/news/pressreleases/Pages/
Harris-Corporation-Completes-Acquisition-of-Exelis.aspx

38) "ITT awarded contract to build the Imaging System for the GeoEye-2 Earth-Imaging Satellite," August 31, 2010, URL: http://www.geospatial.itt.com/news/news_100831.shtml

39) "ITT's Next-Generation Imaging Payload Passes Major Milestone," March 1, 2011, URL: http://www.geospatial.itt.com/news/news_110301.shtml

40) "ITT Exelis delivers imaging system for next-generation, high-resolution GeoEye-2 satellite," Space Daily, April 11, 2012, URL: http://www.spacedaily.com/reports/ITT_Exelis_delivers_imaging_
system_for_next_generation_high_resolution_GeoEye_2_satellite_999.html

41) "WorldView-4 Data Sheet," Digital Globe, Nov. 15, 2015, URL: https://dg-cms-uploads-production.s3.amazonaws.com/uploads/
document/file/196/DG_WorldView4_DS_11-15_Web.pdf

42) "WorldView-4 Data Sheet," Digital Globe, URL: http://content.satimagingcorp.com.s3.amazonaws.com/static/satellite
-sensor-specification/WorldView-4-Satellite-Specifications

43) "The DigitalGlobe Constellation," DigitalGlobe brochure, 2016, URL: https://dg-cms-uploads-production.s3.amazonaws.com/uploads/
document/file/223/Constellation_Brochure_forWeb.pdf
 

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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