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By NASA
On Feb. 11, 2000, space shuttle Endeavour took to the skies on its 14th trip into space on the Shuttle Radar Topography Mission (SRTM). The international STS-99 crew included Commander Kevin Kregel, Pilot Dominic Gorie, and Mission Specialists Gerhard Thiele of Germany representing the European Space Agency, Janet Kavandi, Janice Voss, who served as payload commander on the mission, and Mamoru Mohri of the National Space Development Agency (NASDA) of Japan, now the Japan Aerospace Exploration Agency.
During their 11-day mission, the astronauts used the radar instruments in Endeavour’s payload bay to obtain elevation data on a near global scale. The data produced the most complete, high-resolution digital elevation model of the Earth. The SRTM comprised a cooperative effort among NASA with the Jet Propulsion Laboratory (JPL) in Pasadena, California, managing the project, the Department of Defense’s National Imagery and Mapping Agency, the German space agency, and the Italian space agency. Prior to SRTM, scientists had a more detailed topographic map of Venus than of the Earth, thanks to the Magellan radar mapping mission.
The STS-99 crew patch. Official photo of the STS-99 crew of Janice Voss, left, Mamoru Mohri of the National Space Development Agency of Japan, now the Japan Aerospace Exploration Agency, Kevin Kregel, Dominic Gorie, Gerhard Thiele of Germany representing the European Space Agency, and Janet Kavandi. The Shuttle Radar Topography Mission patch. Schematic of the Space Radar Topography Mission payloads including the deployed mast. The mast antenna during preflight processing. NASA assigned the STS-99 crew in October 1998. For Kregel, selected by NASA as an astronaut in 1992, STS-99 marked his fourth trip to space, having served as pilot on STS-70 and STS-78 and commanded STS-87. Gorie and Kavandi, both selected in 1994, previously flew together as pilot and mission specialist, respectively, on STS-91, the final Shuttle Mir docking mission. Voss, selected in 1990, served as a mission specialist on STS-57 and STS-63, and as payload commander on STS-83 and STS-94. NASDA selected Mohri as an astronaut in 1985 and he previously flew as a payload specialist on STS-47, the Spacelab-J mission. Selected as an astronaut by the German space agency in 1987, Thiele joined the European Astronaut Corps in 1998, completing his first spaceflight on STS-99.
The SRTM used an innovative technique called radar interferometry to image the Earth’s landmasses at resolutions up to 30 times greater than previously achieved. Two of the synthetic aperture radar instruments comprising the SRTM payload had flown previously, on the STS-59 Shuttle Radar Laboratory-1 (SRL-1) and the STS-68 SRL-2 missions in April and October 1994, respectively. A second receiver antenna, placed at the end of a 200-foot deployable mast, enabled the interferometry during SRTM.
The SRTM payload in Endeavour’s cargo bay in the orbiter processing facility. Endeavour rolls out to Launch Pad 39A. The STS-99 crew walks out of crew quarters for the van ride to the launch pad. Workers rolled Endeavour to the Vehicle Assembly Building on Dec. 2 for mating with its external tank and solid rocket boosters, and then out to Launch Pad 39A on Dec. 13. The astronauts traveled to Kennedy to participate in the Terminal Countdown Demonstration Test Jan. 11-14, returning afterwards to Houston for final training. They traveled back to Kennedy on Jan. 27 for the first launch attempt four days later. After two launch attempts, the STS-99 mission prepared to liftoff on Feb. 11, 2000.
Liftoff! Space shuttle Endeavour takes to the skies to begin the STS-99 mission. At 12:43 p.m. EST, Endeavour thundered into the sky from Kennedy’s Launch Pad 39A to begin the STS-99 mission. Thirty-seven minutes later, a brief firing of the orbiter’s two engines placed Endeavour in the proper 145-mile orbit for the radar scanning.
The SRTM instruments in Endeavour’s payload bay with the mast holding the second antenna receiver deployed at right. The antenna at the end of the deployed mast. STS-99 astronauts Janet Kavandi, left, Dominic Gorie, and Mamoru Mohri in Endeavour’s middeck. Astronaut Janice Voss in the commander’s seat on Endeavour’s flight deck. Astronauts Kevin Kregel, left, and Gerhard Thiele on Endeavour’s flight deck. Shortly after reaching orbit, the crew opened the payload bay doors and deployed the shuttle’s radiators. Kavandi and Thiele turned on the instruments, deployed the 200-foot mast, and conducted initial checkouts of the radars. The crew split into two shifts to enable data collection around the clock during the mission. After overseeing the initial activation of the radars, the red shift of Kregel, Kavandi, and Thiele began their first sleep period as the blue shift of Gorie, Voss, and Mohri picked up with activation and began the first data takes.
The major crew activity for SRTM involved changing tapes every 30 minutes. The SRTM generated 332 high density tapes during more than 222 hours of data collection and these recordings covered 99.96 percent of the planned observations. Data collection finished on the mission’s 10th flight day, after which the astronauts reeled the mast back into its container in the payload bay.
EarthKAM image of the greater Boston area. The EarthKAM camera mounted in a space shuttle window. STS-99 crew Earth observation photograph of El Paso, Texas, and Ciudad Juarez, Mexico. STS-99 crew Earth observation photograph of the Galapagos Islands. STS-99 crew Earth observation photograph of the greater New York area. STS-99 crew Earth observation photograph of Erg Chech, or sand sea, in the Algerian Sahara. NASA’s EarthKAM program enabled middle school students to remotely take photographs of the Earth using an electronic still camera mounted in one of the shuttle’s windows. The University of California at San Diego houses the control center for EarthKAM, linked with middle schools via the Internet. Students choose Earth targets of interest, and the camera takes photos of that region as the shuttle passes overhead. A then-record 75 schools from around the world participated in the EarthKAM project on STS-99, the camera returning 2,715 images of the Earth.
The STS-99 astronauts also spent time taking photographs of the Earth using handheld cameras and the high inclination orbit enabled views of some parts of the Earth rarely seen by shuttle astronauts.
The six-person STS-99 crew pose for their inflight photo. Kevin Kregel guides Endeavour to a smooth touchdown on the Shuttle Landing Facility at NASA’s Kennedy Space Center in Florida. The STS-99 crew poses with NASA Administrator Daniel Goldin under Endeavour at the Shuttle Landing Facility at NASA’s Kennedy Space Center in Florida. Kevin Kregel addresses the crowd at Houston’s Ellington Field during the welcome home ceremony for the STS-99 crew. On Feb. 22, the crew closed Endeavour’s payload bay doors, donned their launch and entry suits, and strapped themselves into their seats for entry and landing. Kregel piloted Endeavour to a smooth landing on Kennedy’s Shuttle Landing Facility. The crew had flown 181 orbits around the Earth in 11 days, 5 hours, and 39 minutes. Enjoy the crew narrate a video about the STS-99 mission.
Postscript
Final coverage map for the SIR-C radar, indicating 99.96 percent coverage of planned land mass targets, with many areas imaged more than once.
False-color image generated from SRTM data of the island of Oahu. False-color image generated from SRTM data of Mt. Cotopaxi in Ecuador, the tallest active volcano in the world. During the 11-day mission, SRTM collected more than one trillion data points, generating 12.3 terabytes of 3-D data of the Earth. Earnest Paylor, SRTM program scientist at NASA Headquarters in Washington, D.C., called the mission “a magnificent accomplishment.” He cited that SRTM imaged by radar equatorial regions of the Earth previously unmapped due to constant cloud cover.
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Preparations for Next Moonwalk Simulations Underway (and Underwater)
Jeremy Frank, left, and Caleb Adams, right, discuss software developed by NASA’s Distributed Spacecraft Autonomy project. The software runs on spacecraft computers, currently housed on a test rack at NASA’s Ames Research Center in California’s Silicon Valley, and depicts a spacecraft swarm virtually flying in lunar orbit to provide autonomous position navigation and timing services at the Moon. NASA/Brandon Torres Navarrete Talk amongst yourselves, get on the same page, and work together to get the job done! This “pep talk” roughly describes how new NASA technology works within satellite swarms. This technology, called Distributed Spacecraft Autonomy (DSA), allows individual spacecraft to make independent decisions while collaborating with each other to achieve common goals – all without human input.
NASA researchers have achieved multiple firsts in tests of such swarm technology as part of the agency’s DSA project. Managed at NASA’s Ames Research Center in California’s Silicon Valley, the DSA project develops software tools critical for future autonomous, distributed, and intelligent swarms that will need to interact with each other to achieve complex mission objectives.
“The Distributed Spacecraft Autonomy technology is very unique,” said Caleb Adams, DSA project manager at NASA Ames. “The software provides the satellite swarm with the science objective and the ‘smarts’ to get it done.”
What Are Distributed Space Missions?
Distributed space missions rely on interactions between multiple spacecraft to achieve mission goals. Such missions can deliver better data to researchers and ensure continuous availability of critical spacecraft systems.
Typically, spacecraft in swarms are individually commanded and controlled by mission operators on the ground. As the number of spacecraft and the complexity of their tasks increase to meet new constellation mission designs, “hands-on” management of individual spacecraft becomes unfeasible.
Distributing autonomy across a group of interacting spacecraft allows for all spacecraft in a swarm to make decisions and is resistant to individual spacecraft failures.
The DSA team advanced swarm technology through two main efforts: the development of software for small spacecraft that was demonstrated in space during NASA’s Starling mission, which involved four CubeSat satellites operating as a swarm to test autonomous collaboration and operation with minimal human operation, and a scalability study of a simulated spacecraft swarm in a virtual lunar orbit.
Experimenting With DSA in Low Earth Orbit
The team gave Starling a challenging job: a fast-paced study of Earth’s ionosphere – where Earth’s atmosphere meets space – to show the swarm’s ability to collaborate and optimize science observations. The swarm decided what science to do on their own with no pre-programmed science observations from ground operators.
“We did not tell the spacecraft how to do their science,” said Adams. “The DSA team figured out what science Starling did only after the experiment was completed. That has never been done before and it’s very exciting!”
The accomplishments of DSA onboard Starling include the first fully distributed autonomous operation of multiple spacecraft, the first use of space-to-space communications to autonomously share status information between multiple spacecraft, the first demonstration of fully distributed reactive operations onboard multiple spacecraft, the first use of a general-purpose automated reasoning system onboard a spacecraft, and the first use of fully distributed automated planning onboard multiple spacecraft.
During the demonstration, which took place between August 2023 and May 2024, Starling’s swarm of spacecraft received GPS signals that pass through the ionosphere and reveal interesting – often fleeting – features for the swarm to focus on. Because the spacecraft constantly change position relative to each other, the GPS satellites, and the ionospheric environment, they needed to exchange information rapidly to stay on task.
Each Starling satellite analyzed and acted on its best results individually. When new information reached each spacecraft, new observation and action plans were analyzed, continuously enabling the swarm to adapt quickly to changing situations.
“Reaching the project goal of demonstrating the first fully autonomous distributed space mission was made possible by the DSA team’s development of distributed autonomy software that allowed the spacecraft to work together seamlessly,” Adams continued.
Caleb Adams, Distributed Spacecraft Autonomy project manager, monitors testing alongside the test racks containing 100 spacecraft computers at NASA’s Ames Research Center in California’s Silicon Valley. The DSA project develops and demonstrates software to enhance multi-spacecraft mission adaptability, efficiently allocate tasks between spacecraft using ad-hoc networking, and enable human-swarm commanding of distributed space missions. NASA/Brandon Torres Navarrete Scaling Up Swarms in Virtual Lunar Orbit
The DSA ground-based scalability study was a simulation that placed virtual small spacecraft and rack-mounted small spacecraft flight computers in virtual lunar orbit. This simulation was designed to test the swarm’s ability to provide position, navigation, and timing services at the Moon. Similar to what the GPS system does on Earth, this technology could equip missions to the Moon with affordable navigation capabilities, and could one day help pinpoint the location of objects or astronauts on the lunar surface.
The DSA lunar Position, Navigation, and Timing study demonstrated scalability of the swarm in a simulated environment. Over a two-year period, the team ran close to one hundred tests of more complex coordination between multiple spacecraft computers in both low- and high-altitude lunar orbit and showed that a swarm of up to 60 spacecraft is feasible.
The team is further developing DSA’s capabilities to allow mission operators to interact with even larger swarms – hundreds of spacecraft – as a single entity.
Distributed Spacecraft Autonomy’s accomplishments mark a significant milestone in advancing autonomous distributed space systems that will make new types of science and exploration possible.
NASA Ames leads the Distributed Spacecraft Autonomy and Starling projects. NASA’s Game Changing Development program within the agency’s Space Technology Mission Directorate provides funding for the DSA experiment. NASA’s Small Spacecraft Technology program within the Space Technology Mission Directorate funds and manages the Starling mission and the DSA project.
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