On February 11, 2000, the space shuttle Endeavour embarked on its 14th journey into orbit, carrying out the Shuttle Radar Topography Mission (SRTM). This mission was a landmark event in the field of space exploration and Earth sciences, bringing together an international crew and a collaborative effort among multiple space agencies. The mission aimed to obtain the most accurate and comprehensive digital elevation model of the Earth’s surface using advanced radar technology.
The team aboard Endeavour was composed of a diverse group of astronauts from different backgrounds. Commander Kevin Kregel, a seasoned astronaut, led the mission. He was accompanied by Pilot Dominic Gorie, Mission Specialists Gerhard Thiele from the European Space Agency, Janet Kavandi, Janice Voss who served as the payload commander, and Mamoru Mohri from the Japan Aerospace Exploration Agency. This diverse team worked together to achieve the mission’s objectives over an 11-day period.
The primary goal of the SRTM was to collect elevation data on a near-global scale using radar instruments located in the payload bay of the Endeavour. This data was crucial for creating a high-resolution digital elevation model of the Earth, a task that had not been accomplished with such precision before. The mission was a collaborative effort involving NASA’s Jet Propulsion Laboratory, the Department of Defense’s National Imagery and Mapping Agency, and the space agencies of Germany and Italy.
Prior to the SRTM, detailed topographic maps of Venus existed, thanks to the Magellan radar mapping mission, but Earth lacked similar detailed mapping. The SRTM aimed to fill this gap by using radar interferometry, a sophisticated technique that allowed for imaging landmasses at resolutions up to 30 times greater than previously possible. This technique involved the use of two synthetic aperture radar instruments, which had been tested on earlier missions, along with a second receiver antenna mounted on a 200-foot deployable mast.
The preparation for this historic mission began well in advance. NASA selected the crew for STS-99 in October 1998. For Kevin Kregel, who had been an astronaut since 1992, this mission marked his fourth spaceflight. Gorie and Kavandi, selected in 1994, had previously flown together on the STS-91 mission, which was the final Shuttle-Mir docking mission. Janice Voss, selected in 1990, had considerable experience as a mission specialist and payload commander. Mamoru Mohri and Gerhard Thiele were also experienced astronauts, bringing their unique expertise to the team.
The SRTM was an innovative mission that leveraged cutting-edge technology to achieve its objectives. Radar interferometry, the technique used in the mission, involves sending radar signals from multiple locations to create detailed images of the Earth’s surface. The data collected provided an unprecedented view of the Earth’s topography, surpassing previous models in detail and accuracy.
The mission’s timeline was meticulously planned. On December 2, 1999, the space shuttle Endeavour was moved to the Vehicle Assembly Building for integration with its external tank and solid rocket boosters. It was then transported to Launch Pad 39A on December 13. The crew underwent a Terminal Countdown Demonstration Test from January 11-14, 2000, before returning to Houston for final training. They came back to Kennedy Space Center on January 27 to prepare for the launch, which finally occurred on February 11 after two previous attempts.
At precisely 12:43 p.m. EST on February 11, 2000, Endeavour roared into the sky from Kennedy’s Launch Pad 39A. Just 37 minutes later, the shuttle reached its designated 145-mile orbit, allowing the radar instruments to commence their work. Once in orbit, the crew opened the payload bay doors and deployed the shuttle’s radiators. Kavandi and Thiele activated the radar instruments, deployed the 200-foot mast, and conducted initial system checks.
To ensure continuous data collection, the crew operated in two shifts. The red shift, comprising Kregel, Kavandi, and Thiele, began with the initial activation of the radars, while the blue shift, consisting of Gorie, Voss, and Mohri, took over for the first data collection period. The mission required the crew to change data tapes every 30 minutes, resulting in the production of 332 high-density tapes and the collection of data covering 99.96 percent of the planned observations.
In addition to their primary mission objectives, the STS-99 crew engaged in educational outreach through NASA’s EarthKAM program. This initiative allowed middle school students to remotely capture images of Earth using a camera mounted in one of the shuttle’s windows. Managed by the University of California at San Diego, EarthKAM connected with middle schools worldwide via the Internet, enabling students to select Earth targets of interest for photography. During the mission, a record 75 schools participated, capturing 2,715 images of our planet.
The crew also took advantage of their high-inclination orbit to photograph seldom-seen parts of the Earth using handheld cameras. These images provided valuable insights and contributed to our understanding of the planet’s diverse landscapes.
As the mission drew to a close, the crew prepared for their return to Earth. On February 22, they closed Endeavour’s payload bay doors, donned their launch and entry suits, and secured themselves for re-entry and landing. Commander Kregel piloted the shuttle to a smooth landing at Kennedy’s Shuttle Landing Facility, concluding a successful mission that spanned 181 orbits around the Earth in 11 days, 5 hours, and 39 minutes.
The SRTM mission was an extraordinary accomplishment, collecting over one trillion data points and generating 12.3 terabytes of 3-D data. This mission significantly advanced our understanding of the Earth’s topography, providing crucial information for various scientific and practical applications. As Earnest Paylor, SRTM program scientist at NASA Headquarters, noted, the mission was a "magnificent accomplishment," imaging regions of the Earth that had previously been uncharted due to persistent cloud cover.
For more insights and to experience the mission from the crew’s perspective, you can watch a video narrated by the STS-99 astronauts here.
The SRTM mission stands as a testament to the power of international collaboration and technological innovation. It set new standards for Earth observation and laid the groundwork for future missions aimed at exploring and understanding our planet in greater detail.
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