SAN FRANCISCO — A decade after it was launched as the centerpiece of NASA’s then-nascent Earth Observing System, the U.S. space agency’s flagship Terra satellite remains in extraordinarily good condition with scientific instruments continuing to gather data and enough fuel to remain in orbit for another six years to seven years, according to Marc Imhoff, Terra project scientist at the Goddard Space Flight Center.
“Terra represents a remarkable human achievement, not just scientific and engineering but managerial and diplomatic,” Imhoff told current and former NASA officials gathered Dec. 13 to celebrate Terra’s anniversary during the American Geophysical Union meeting here. Terra, NASA’s first large satellite designed to monitor Earth’s atmosphere, land and oceans, carries instruments built in the United States, Japan and Canada, and involves scientists and engineers working in NASA centers, government organizations, university laboratories, federal laboratories and private companies.
During the design and development process, the Terra program, which was then called the Earth Observing System-AM (EOS-AM), faced numerous obstacles including dramatic budget cuts, extensive program revisions and daunting technical challenges. “All the blood, all the sweat, all the tears, was it really worth it?” asked Piers Sellers, a former astronaut and the first EOS-AM project scientist. “I think it was. Terra and her sisters changed our view of the world. They put flesh on the bones of the concepts and models we have for our changing world.”
Michael King, former EOS senior project scientist, recalled watching Terra’s Dec. 18, 1999 launch with GhassemAsrar, then NASA Associate Administrator for Earth Science. “He told me the future of Earth Science rests with the success of this launch,” King said. “It was a billion-dollar spacecraft on a $110 million rocket, not counting the cost of the instruments and algorithms. We didn’t want to fail and we have not. This worked out very, very nicely.”
All five instruments onboard the 2,300-kilogram spacecraft continue to gather scientific data, although one of the three telescopes on the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) is no longer working. ASTER stopped capturing useful short-wave infrared imagery approximately two years ago, however, the other two telescopes operating in the visible, near-infrared and thermal-infrared regions of the spectrum continue to gather high-resolution images, according to Angelita Kelly, Goddard’s science interface manager for Earth science mission operations.
In addition to ASTER, which was developed by Japan’s Ministry of Trade and Industry, the Terra spacecraft carries four instruments: Clouds and the Earth’s Radiant Energy System built by the NASA Langley Research Center in Hampton, Va.; Multi-angle Imaging Spectro-Radiometer from the Jet Propulsion Laboratory in Pasadena, Calif.; Moderate-resolution Imaging Spectroradiometer (MODIS) provided by Greenbelt, Md.-based Goddard; and the Canadian Space Agency’s Measurement of Pollution in the Troposphere.
“Terra continues to perform very well,” Kelly said. “It is still operating on primary spacecraft components.” One exception Kelly pointed out is a Direct Access System Module which broadcasts MODIS data to 150 sites around the world. When the primary module failed in 2008, the Terra mission operations team switched broadcasts to the redundant module. Terra’s high-gain antenna, which provides the spacecraft’s primary means of relaying scientific data to the ground through the space agency’s Tracking and Data Relay Satellite network, continues to function well, said Eric Moyer, assistant mission director for the Earth Observing System at Goddard.
Although the spacecraft and instruments remain in good health, NASA officials are quick to point out that Terra, which was designed to last five years to seven years, has already spent 10 years in the harsh environment of space. “We have no idea what the future holds, anything could break at any time,” Moyer said. “Right now, fuel seems to be the life-limiting item.”
If the spacecraft continues to function well and does not use up too much fuel dodging orbiting debris, Terra officials are likely to move the spacecraft out of its orbit in 2017. Even then, Terra may be able to continue to operate in a lower orbit for another couple of years, NASA officials said.
Debris may have been responsible for the recent failure of one of Terra’s batteries. Although the cause is still being investigated, one of the spacecraft’s 108 battery cells failed in October. At that time, some of the heaters used to keep other spacecraft batteries warm enough to operate also failed, causing concern among mission officials. Those heaters have since recovered and are working normally, NASA officials said.
