LeoLabs commercial ground-based tracking service for small satellites
LeoLabs was founded in 2016 as a venture-funded spinout of Silicon Valley research pioneer, SRI International (Menlo Park, CA), by scientists and space industry veterans committed to securing Low Earth Orbit (LEO). LeoLabs is built on 30+ years of R&D in radar systems and satellite tracking algorithms. The team is rapidly expanding its global radar network and data services platform to help satellite operators deploy their services safely and to empower governmental space agencies with detailed visibility into the LEO ecosystem. 1)
As commercial space ventures and newly-formed space agencies from every corner of the globe compete for their place in the emerging LEO economy, LeoLabs is here to address a new generation of risks and opportunities to preserve LEO for future generations.
The space surrounding the earth is a floating junkyard of stuff moving at high speeds with colossal destructive energy. With thousands of satellites, teams of astronauts, and tons of debris, there are over 14,000 orbital objects bigger than a softball and more than 250,000 larger than a marble. As the LEO ecosystem around our planet gets more congested, the risk of collisions rises, and the need to map the orbits of spacecraft, satellites and space debris grows with every launch.
At LeoLabs, our mission is to secure safe and sustainable operations in space. With our network of ground-based, phased array radars, LeoLabs produces high-resolution data on objects in low Earth orbit (LEO), providing unparalleled support for industries that rely on satellite services.
Background and Overview
LeoLabs demonstrates that small satellites, including 1U CubeSats and smaller, are well-tracked to high accuracy by its worldwide network of phased array radars. With its network of two operations radars (valid as of June 2019), LeoLabs is able to provide high-precision ephemeris services for 1U and sub-1U satellites. Roughly 95% of the time, tracking is maintained to better than 1 km at time of estimation (these uncertainties grow when propagating the states). Approximately 50% of the time, these state estimates are better than 200 meters. The quality of the fitted orbits will improve as new LeoLabs radar sites are brought online. Precision tracking services are provided by LeoLabs as a commercial service to small spacecraft operators. Such services are also valuable for regulatory purposes (where detectability and trackability are concerns), for providing backup tracking should GPS not be available, and for safety enhancements by having smaller covariances in instances of potential conjunctions with other satellites. 2)
Recent years have seen a proliferation of CubeSats sized 1U (10x10x10 cm) or smaller in low earth orbit (LEO). LeoLabs , with its global sensor network and data platform, aims to support operators of small CubeSats such as these in multiple contexts including navigation and SSA (Space Situational Awareness).
High-precision orbital information obtained from the LeoLabs Data Platform 3) has advantages over the more traditional two-line element set (TLE) format, which represent only approximations to the true orbit and may have errors of several kilometers. In addition, high-precision ephemerides include propagated covariances, and measurements (which are used as inputs to LeoLabs’ own orbit determinations) are also made available. Conjunction alerts and assessments (including screening against an input propagation) are also available from LeoLabs, complete with probability of collision calculations and covariances for all involved targets. LeoLabs conjunction screening service allows the user to upload an ephemeris and screen against the catalog, which is especially valuable within the context of risk assessment during mission pre-planning or for on-orbit maneuver planning.
LeoLabs Radar Network
At the core of the LeoLabs Data Platform is a global network of phased array radars. Unburdened by the overhead of mechanical slew times, phased array radars are well suited to tracking dozens of objects simultaneously using a beam that can be reoriented hundreds of times per second. Currently, the LeoLabs network is comprised of two radars—the Poker Flat Incoherent Scatter Radar (PFISR) near Fairbanks, Alaska and the Midland Space Radar (MSR) near Midland, Texas (Figure 1). PFISR uses a more traditional 2-dimensional phased array, while MSR uses a proprietary 1-dimensional design, achieving nearly identical measurement fidelity at a significant reduction to cost and complexity. Together these radars are capable of collecting measurements on a catalog of over 10,000 objects 10 cm in size or greater, with each object passing through a LeoLabs sensor about 1-4 times a day.
Construction of a third LeoLabs radar is currently underway in New Zealand. This radar (also based on 1-dimensional array technology), will operate at a higher frequency and permit the detection of resident space objects (RSOs) as small as 2 cm in LEO. This added capability will allow for the construction of a catalog that integrates small debris, increasing the number of RSOs that LeoLabs can provide data for by an estimated factor of ten.
Figure 1: Locations of LeoLabs radars—a third location is under construction in New Zealand (image credit: Google Maps)
LeoLabs Data Platform
The LeoLabs Data Platform offers data and analyses which enable engagement with the LEO environment at a number of different levels, including:
• Radar measurements
• Object state estimations
• Object propagations
• Conjunction screening and alerts.
This platform is accessible via two primary interfaces: a web-based API (suitable for custom analysis scripts and automation tasks), and a graphically oriented web application (focused on intuitive plots and visualizations of the available data). Some target use cases for the LeoLabs Platform include:
• Regulatory (rendering the LEO environment within the context of national or agency guidelines)
• Backup navigation (to augment or supplement existing on-board or ground based systems such as GPS)
• SSA (as a source of upcoming conjunctions, maneuvers, and orbit change alerts—see Figure 2).
Figure 3: Visualization of objects in the LeoLabs catalog, color coded by how recently they have been tracked (image credit: LeoLabs)
In order to fully characterize the performance of sensors in the LeoLabs radar network, including sensor bias and uncertainty, comparisons to an external source of truth must be made. For these purposes LeoLabs employs data from the International Laser Ranging Service4. The ILRS (International Laser Ranging Service) distributes orbit propagations for targets of interest which are computed by a number of different providers. Since they are derived from laser-based measurements, these propagations are of a high fidelity and suitable to be processed for predicted measurements, which are then used as truth data.
Comparisons to these predicted values are made multiple times a day, deriving the bias and uncertainty which should be associated with the range and doppler measurements made at PFISR and MSR. These parameters are automatically incorporated into measurements provided by the LeoLabs API, and reported in a dashboard on the LeoLabs Platform page. At present, range uncertainties for both radars are typically near 15 meters, with doppler uncertainty near a value of 3 meters per second on PFISR, and 25 cm per second on MSR (see Figure 4).
Orbital state estimations at LeoLabs are achieved via an unscented Kalman filter (UKF). This class of algorithm pairs the computational efficiency of a Kalman filter with the unscented transform (UT), which attempts to more accurately render covariance evolution in nonlinear systems by propagating a set of sample points using the full physical model. Both orbit determinations and propagations provided by LeoLabs make use of the Orekit open source orbital dynamics library 4), with the following forces considered:
• Non-uniform gravity (to degree and order 42)
• Atmospheric drag (using the NRLMSISE-00model)
• Solar radiation pressure
• Third body forces from the Sun and Moon.
Computations of new orbital state estimations are initiated by a transit of the target through a LeoLabs radar, and are performed at most once per hour in a cloud-based computer cluster. For targets in polar orbits new estimations are calculated as often as four times per day. Each estimation is coupled to an eight-day propagation window that looks one day backward from state epoch and seven days forward.
To assess the quality of state estimations, comparisons to ILRS-provided propagations are computed automatically for a 48-hour period centered on state epoch and captured in an internal dashboard (see Figure 5 for a similar but manually-created analysis with longer duration comparisons). Each state estimation is also compared to previous (and, if possible future) estimates in terms of both physical distance and Mahalanobis distance (a multi-dimensional statistic similar to standard deviation). These distance comparisons are viewable on the LeoLabs Platform site for each available state estimation and propagation.
Performance on small satellites
Of particular interest to the SmallSat community is the performance of the LeoLabs Data Platform against targets sized 1U or smaller. A survey of RMS position uncertainties at state epoch for 68 targets with sizes of 0.25U, 0.5U and 1U is shown in Figure 6. The median of the distribution of these values is found to be below 200 meters, with about 95% of all values falling below 1 kilometer.
Only six of the objects in this survey fall in the “sub-1U” category, enabling a detailed time series plot of the evolution of the RMS position uncertainties for these satellites over a one-month interval (see Figure 7). Even under propagation RMS position uncertainties for these targets are usually below 1 kilometer.
In summary, LeoLabs provides a data platform built on top of a global network of phased array radars (including one currently under construction in New Zealand that will enable the creation of a catalog that includes debris down to 2 cm in size). This data platform can provide measurements, orbital state estimations, propagations, conjunction information, and detailed visualizations of objects in the LEO environment.
Information from LeoLabs provides increased transparency to operators over existing sources of information, and is provided via both programmatic (API) and graphics-based (web GUI) interfaces. Performance of LeoLabs systems versus a set of 68 small CubeSats (≤1U) is seen to be favorable, with greater than 50% of epoch RMS position uncertainties falling below 200 meters. Propagated uncertainties of several sub-1U satellites over one month are also largely contained with the same (100 meter) order of magnitude.
Major improvements to both accuracy and precision are expected in the near future, as LeoLabs continues to deploy new radars and refine orbit its algorithms.
Development Status and Operations
• June 16, 2021: LeoLabs plans to expand its global ground network of space-tracking radars to the Azores archipelago, an autonomous region about 1,500 kilometers off Portugal’s Atlantic coast. 5)
- The new S-band phased-array radar, which is scheduled to come online in early 2022, will improve the “timeliness and accuracy” of LeoLabs’ global coverage because the company does not operate radars at similar longitudes, Dan Ceperley, LeoLabs CEO and co-founder, told SpaceNews.
- “The Azores, specifically, is very critical because it offers coverage of the North Atlantic and Europe, giving us the ability to track all the debris and the satellites in that region,” Ceperley said.
Figure 8: Preview of the field of view of the LeoLabs Azores Space Radar. The new radar is designed to extend LeoLabs' radar network to cover new longitudes (image credit: LeoLabs)
- Because the new radar will be capable of tracking objects as small as 2 centimeters in diameter, it also will help LeoLabs keep tabs on small debris.
- “We want to take that small debris off the table in terms of risk to satellite operators,” Ceperley said.
- When evaluating new sites, LeoLabs searches not only for appropriate locations but also for relationships with organizations seeking to play a role in the growing space economy.
- “When we put up a radar, it’s there for 20 years,” Ceperley said. “We like to go places where we’re well aligned, everybody’s excited about space and we can join this growing mix of space companies and endeavors.”
- LeoLabs found that community in the Azores, where the firm is working closely both with the Portuguese Space Agency and the Azores regional government, said Alan DeClerck, LeoLabs vice president of business development.
- The Portuguese Space Agency, established in 2019, is seeking to build a spaceport in the Azores. Portugal also is active in the European Space Agency and the European Union’s space activities, DeClerck said.
- In recent years, ESA leaders have highlighted the threat posed by orbital debris and established a debris mitigation program that includes one of the world’s first active debris removal missions.
- Swiss start-up ClearSpace SA is working under an ESA contract to capture and remove from orbit an Arianespace Vega rocket payload adapter.
- Ceperley sees an important role for LeoLabs data in future debris removal services.
- “With the data we produce, you can highlight the riskiest satellites or pieces of debris up there and either prioritize them to get removed or help a company like Clean Space or Astroscale close the business case for removing those,” Ceperley said.
- LeoLabs licenses data it collects and offers service agreements to satellite operators, government regulators, defense agencies and insurance companies.
- While constructing the Azores Space Radar, LeoLabs will be investing in all those relationships in Europe, Ceperley said. “This radar is a symbolic step into that market,” he added.
• January 1, 2021: It was a banner year for the commercial space industry. Even in the midst of a pandemic and while piling up big economic losses, companies continued to expand into the final frontier. One big milestone: In late May, Elon Musk’s SpaceX ferried two astronauts to the International Space Station, the first time human beings had been sent to orbit on a privately owned spacecraft. Investors have continued to back companies in the space industry, and new technologies were unveiled in 2020 that promise more success in the years to come. 6)
- For these reasons, we have chosen to focus the inaugural Forbes Science Awards exclusively on the commercial space sector. Here are the best and the brightest from the year.
Best Product: Leolabs’ Collision Avoidance
- Space is getting increasingly crowded, and with a number of companies putting constellations of hundreds of satellites into low Earth orbit in the coming years, ensuring that they don’t collide with each other – or an old bit of space junk — is increasingly important. That’s where Menlo Park, Calif.-based LeoLab’s automated collision avoidance system comes into play. The company has multiple radar systems monitoring low Earth orbit, serving as space “traffic cops” for their customers, which include both private companies and government agencies.
• October 14, 2019: LeoLabs, the Silicon Valley space mapping startup, announced Oct. 14, initial operation of the Kiwi Space Radar, the firm’s third space surveillance radar and first with updated technology to track debris as small as two centimeters in low Earth orbit. 7)
- “We founded the company on the promise that we would deliver this technology,” Dan Ceperly, LeoLabs co-founder and CEO, told SpaceNews. “We’re extremely excited to show the technology that we’re going to take around the world.”
- LeoLabs now operates three radars to track spacecraft and debris in low Earth orbit (LEO). The firm’s first two radars, located in Alaska and Texas, are designed to track objects as small as ten centimeters, the size of a single cubesat. U.S. Strategic Command tracks objects of similar size and shares the information through the website spacetrack.org.
- “The Kiwi Space Radar raises the bar on addressing the threat of collisions that have never before been tracked in LEO,” Michael Nicolls, LeoLabs co-founder and chief technology officer, said in a statement. “By operating at a higher frequency than our earlier sensors, the Kiwi Space Radar was designed to track an estimated 250,000 additional objects down to two centimeters in size. These objects account for most of the risk of collisons in space, and Kiwi Space Radar is the first big step towards addressing that risk. It will enable thousands of new satellites to safely use LEO.”
- LeoLabs has completed construction of the new radar on New Zealand’s South Island and is obtaining data for testing and calibration, Ceperley said. By the end of the year, LeoLabs plans to include data from the Kiwi Space Radar in the products and services for its customers.
- The new radar can see objects as small as two centimeters across thanks to electronics that work at a higher frequency, additional structures in the shape of snowboarders’ halfpipes and the extremely smooth surfaces of those structures.
- “In Midland, Texas, there’s one halfpipe,” Ceperly said. “At the New Zealand site, there are four acting as almost two radar systems.”
- LeoLabs plans to have six radars online by the early 2020s. The firm plans to install radars at three additional sites in the next couple of years, Ceperley said, including one near the equator as well as radars “a little bit further north and a little bit further south to give us good coverage of large constellations going into higher inclinations.”
• June 25, 2019: LeoLabs, a space situational awareness startup, has created a tool to help the New Zealand Space Agency (NZSA) continuously monitor satellites in low Earth orbit, LeoLabs and NZSA announced June 25. 8)
Figure 9: Here's a screen shot from the Space Regulatory and Sustainability Platform developed by LeoLabs to help the New Zealand Space Agency track and monitor satellites in low Earth orbit (image credit: LeoLabs)
- The cloud-based Space Regulatory and Sustainability Platform relies on information from LeoLabs’ network of phased-array radars to track satellites in low Earth orbit. The mapping and software platform then analyses the data to ensure satellites launched from New Zealand are complying with licensing rules.
- Companies and government agencies plan to send constellations of dozens, hundreds or thousands of satellites into low Earth orbit in the next few years, prompting concerns the heavy traffic could lead to satellites colliding with one another and create debris clouds.
- “As a launching nation, we have a responsibility to minimize orbital debris and preserve space for future generations,” Peter Crabtree, general manager of New Zealand’s Ministry of Business, Innovation and Employment, which houses NZSA, said in a statement. “Understanding where objects are is the first step towards doing this.”
- Through the Space Regulatory and Sustainability Platform, NZSA can track the position, heading and orbit of individual satellites, view historical orbit records, obtain reports on changes in a satellite’s orbit and receive alerts when a satellite is not complying with its licensing agreement, LeoLabs said in a June 25 news release.
- The New Zealand Space Regulatory and Sustainability platform is the first of its kind, Mike Nicolls, LeoLabs co-founder and chief technology officer, said by email. “However, every space agency and regulatory body engaged in [low Earth orbit] will require a similar baseline of tools and capabilities to perform their own oversight function, and LeoLabs intends to work to create a standard offering for all of these agencies, all based on our core [low Earth orbit] mapping platform,” he added.
- Under the 1967 Outer Space Treaty, nations are responsible for authorizing and continually supervising satellites launched from their territory or their facilities. Rocket Lab began sending satellites into orbit from its New Zealand range in January 2018, two years after New Zealand established a space agency.
- “The mission of the NZSA is to provide leadership and regulatory oversight for our rapidly expanding space sector,” Crabtree said. “Critical to achieving this mission is putting in place the tools and capability to monitor and ensure responsible and sustainable behavior. The Space Regulatory and Sustainability Platform developed with LeoLabs is a significant achievement in this direction and demonstrates current best practices within the commercial space regulatory arena. It also affirms our intent to be proactive in addressing the preservation of space for future generations.”
- In 2018, LeoLabs and the New Zealand Ministry of Business, Innovation and Employment announced a memorandum of understanding to work together on various projects. LeoLabs plans to operate a phased array radar in Central Otago on New Zealand’s South Island. The parties also agreed to cooperate in space-related research and development activities.
- Initially, NZSA will use the new platform to monitor satellites in orbit. In the future, the platform could be enhanced to assess collision risk and predict the location of objects re-entering Earth’s atmosphere, Nicholls said. The platform is “designed to reflect both the operational and the policy-oriented priorities of a regulatory agency, and help them evolve their parameters for compliance and responsible behavior,” he added.
LeoLabs Radar Installations
LeoLabs’ announced April 22, 2021 that two S-band radars in Costa Rica have begun tracking objects in low Earth orbit and delivering data to customers. 9)
Figure 10: LeoLabs' Costa Rica Space Radar is an S-band phased-array designed to detect objects as small as 2 cm in low Earth orbit. With S-band radars operating in New Zealand and Costa Rica, LeoLabs is closing in on its goal of tracking 250,000 objects in low Earth orbit (image credit: LeoLabs)
“The Costa Rica Space Radar completes our coverage of low Earth orbit,” Dan Ceperley, LeoLabs CEO and co-founder, told SpaceNews. “It’s the first radar in our network that tracks objects in low inclination orbits.”
LeoLabs gathers data from six phased-array radars at four sites. The Silicon Valley firm operates a UHF radar in Texas and makes observations with a National Science Foundation radar in Alaska. In Costa Rica, like in New Zealand, LeoLabs operates two S-band radars on a single site to detect and track small space objects.
Having a second S-band radar site “is the key for us being able to track and maintain custody of objects smaller than 10 centimeters,” said Ed Lu, LeoLabs co-founder and vice president of strategic projects.
Since it was founded in 2015, LeoLabs has been mapping spacecraft and debris in low Earth orbit. The firm’s initial radars were designed to pinpoint objects as small as 10 cm. With the Kiwi Space Radar unveiled in 2019, LeoLabs began observing objects as small as 2 cm.
Pinpointing objects at a single point, however, makes it impossible to determine the orbit with high confidence. “When you get a second site, you get a minimal ability to do that,” said Lu, a physicist and former NASA astronaut.
LeoLabs plans to continue to establish radars around the world to provide additional observations, Ceperley said.
When LeoLabs began looking for an equatorial radar site, Lu contacted Franklin Chang-Diaz, another physicist and former NASA astronaut who is also a Costa Rican-American mechanical engineer.
Chang-Diaz agreed enthusiastically.
“I want to bring Costa Rica into the space age,” said Chang-Diaz, CEO of Ad Astra Rocket Co., a Texas-based firm with a subsidiary in Costa Rica. “Costa Rica has all the right ingredients. It’s a stable, educated society in a peaceful country.”
In addition, the LeoLabs project aligns well with “Costa Rica’s interest in environmental stewardship and projects that into space,” Chang-Diaz said. “The environment doesn’t end with our atmosphere. It’s going to extend far beyond that.”
LeoLabs provided all the funding for the Costa Rica Space Radar, which was constructed in less than a year with the support of the Costa Rican government.
Costa Rican officials “helped us make sure that we were able to meet all the local requirements and engage in a positive manner,” Ceperley said. “It’s critical that we develop positive relationships with the local government, with the national government and with the agencies because our intention is for that site to be powering space traffic management for the next 20 years.”
Both Lu and Chang-Diaz said orbital debris tracking and mitigation is vital to the economic development of space. In addition, the former astronauts are concerned about the threat untracked debris poses to people living and working on the International Space Station.
“The number one danger to astronauts aboard the International Space Station has been and is today the risk of orbital debris that is too small to be tracked by the U.S. Department of Defense going through the hull,” Lu said. “The biggest potential impediment to further economic development of space is orbital debris.”
Poker Flat Incoherent Scatter Radar (PFISR)
The Poker Flat Incoherent Scatter Radar (PFISR) is located at the Poker Flat Research Range near Fairbanks, Alaska, owned and by NSF (National Science Foundation) and operated by SRI International. It is a two-dimensional phased array radar consisting of 4096 transmitting and receiving elements. PFISR was built by SRI International on behalf of the National Science Foundation to conduct studies of the upper atmosphere and ionosphere in the auroral zone.
Figure 11: Located in Alaska, this is a UHF radar covering the Northern Hemisphere- operational since 2007 (image credit: LeoLabs)
Midland Space Radar (MSR)
In February 2017, LeoLabs commissioned the Midland Space Radar (MSR), the second radar in its global radar network. MSR is located near Midland, Texas, and operates in the UHF band. MSR is a one-dimensional phased array radar and makes use of LeoLabs' proprietary radar technology. MSR is able to track thousands of objects per hour, and is sensitive to space debris as small as 10 cm in diameter.
Figure 12: LeoLabs uses state of the art, patented phased-array radars to offer the industry’s first commercial collision avoidance and mapping service for LEO (image credit: LeoLabs)
Kiwi Space Radar (KSR)
The Kiwi Space Radar (KSR), located in the Central Otago region of New Zealand, is the third radar in LeoLabs’ global radar network. KSR is an advanced radar based off LeoLabs’ proprietary S-band technology and consists of multiple one-dimensional phased array radar systems. KSR is the first of LeoLabs’ systems in the Southern Hemisphere, and the first of its systems that is sensitive to small, currently untracked space debris.
Figure 13: LeoLabs uses a Phased Array Radar in New Zealand (image credit: LeoLabs)
Figure 14: LeoLabs announced initial operation in 2019 of the Kiwi Space Radar. It is designed to track objects in low Earth orbit as small as two centimeters across (image credit: LeoLabs) 10)
Figure 15: Location of the Kiwi Space Radar in New Zealand (image credit: LeoLabs)
Costa Rica Space Radar
The Costa Rica Space Radar, located in the Guanacaste region of Costa Rica, is the fourth radar site in LeoLabs’ global radar network. It is an advanced radar based off of LeoLabs’ proprietary S-band technology and consists of multiple one-dimensional phased array radar systems. Costa Rica Space Radar is the first of LeoLabs’ systems in an equatorial region, and the first of its systems in the Americas that is capable of tracking small objects down to 2 cm, both satellites and orbital debris.
Figure 16: Photo of the Costa Rica Space Radar which is operational as of April 2021 (image credit: LeoLabs)
• April 22, 2021: LeoLabs, Inc., the leading commercial provider of low Earth orbit (LEO) mapping and Space Situational Awareness (SSA) services, today confirmed "fully operational" status for its Costa Rica Space Radar, effective immediately. This new phased-array radar reinforces LeoLabs' leadership as the premier data and services provider to inform and protect the rapidly expanding commercial and governmental activities in LEO. 11)
- "Only nine months after breaking ground in Costa Rica, it is gratifying to announce full operational status for the most advanced commercial space radar of its kind anywhere on the planet", said Dan Ceperley, LeoLabs co-founder and CEO. "The Costa Rica Space Radar is a critical addition to the global constellation of radars LeoLabs is building, and clearly demonstrates not just our rapid deployment capabilities, but the dramatic increase in data underpinning our LeoLabs services platform."
2) Nathan Griffith, Ed Lu, Mike Nicolls, Inkwan Park, Chris Rosner, ”Commercial Space Tracking Services for Small Satellites,” Proceedings of the 33rd Annual AIAA/USU Conference on Small Satellites, August 3-8, 2019, Logan, UT, USA, paper: SSC19-WKVI-03, URL: https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=4412&context=smallsat
Alex Knapp, ”Forbes Science Awards 2020: Prepare For The
Outer-Space Stock-Market Boom,” Forbes, 1 January 2021, URL: https://www.forbes.com/sites/alexknapp/2021/01/01/
8) Debra Werner, ”LeoLabs and New Zealand announce tool to monitor low Earth orbit activity,” SpaceNews, 25 June 2019, URL: https://spacenews.com/leolabs-and-new-zealand-announce-tool-to-monitor-low-earth-orbit-activity/
9) Debra Werner, ”LeoLabs declares Costa Rica Space Radar operational,” SpaceNews, 22 April 2021, URL: https://spacenews.com/leolabs-declares-costa-rica-space-radar-operational/
11) ”LeoLabs Announces Costa Rica Space Radar "Fully Operational", PR Newswire, 22 April 2021, URL: https://www.prnewswire.com/news-releases/
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 (firstname.lastname@example.org).