Sandia’s MTI satellite completes its three-year mission
Mission accomplished. The Multispectral Thermal Imager (MTI), the first full satellite and sensor system designed and built by Sandia, has successfully completed its three-year research goals, and the satellite continues to collect imagery for US government agencies, says MTI project manager Max Decker (5743). Not only that, he says, but the satellite has been used in ways that were never anticipated by the design team. The MTI’s telescopic camera captures imagery data in 15 spectral bands that reveal heat or light patterns not visible to the human eye. It does so in levels of radiometric accuracy never previously accomplished from space.
Since its launch just over three years ago, on March 12, 2000, the satellite has orbited the earth more than 17,300 times. (See www.sandia.gov/media/ NewsRel/NR2000/mtsuccess.htm for more about the launch.) Operators at the Sandia/New Mexico ground station have contacted the satellite twice a day, 365 days a year. More than 440 gigabytes of raw imagery data have been downloaded from space, says Max. The goal of the satellite’s three-year research assignment was to demonstrate the feasibility of using the satellite’s unique multispectral imaging technologies for both national security and environmental applications, he says, including treaty monitoring, mapping of chemical spills, studying vegetation health, and more. As planned, the MTI’s imaging camera has collected in some cases more than 50 images of sites outfitted with equipment that allows researchers to compare the imagery data taken from space with data supplied by instruments on the ground — a calibration technique called "ground truthing." "We’ve collected large amounts of data in support of the DOE’s objectives," says Max, "and the results have been shared with the DOE research community."
Research and more
Specifically, the MTI team has fielded a highly calibrated system and worked to understand how to keep it calibrated in space, says Max, a feat that had never before been accomplished to the desired accuracies. The system has repeatedly demonstrated the ability to measure absolute temperatures from space to better than two degrees. It can measure temperature differences to much more precise levels. The MTI team also flew a new kind of linear-array focal plane of three sensor chip assemblies each housing 15 detector arrays. Each detector array looks through a filter that defines its optical capabilities. The three sensor chip assemblies are aligned and mounted on a single focal plane, which is cooled to 75 Kelvin (minus 198 degrees Celsius). The team also demonstrated use of a pulse-tube cryocooler, which kept the components at 75 Kelvin continuously for 30 months. "This is one of the longest continuously running mechanical on-orbit coolers ever fielded," says Max. And they supported the research objectives of the MTI Users Group of more than 100 researchers from 50 national defense and civilian agencies. Among the MTI’s scientific contributions are new understandings of volcanic activity, arctic shelf breakup, and other natural and man-made phenomena. The MTI imaging camera has proven valuable enough that both government and private industry are incorporating similar imaging technology in designs and proposals for future satellites, he says.
A second imager on board the MTI, a Hard X-ray Spectrometer (HXRS) sponsored by the National Oceanic and Atmospheric Association (NOAA) to study solar flares, didn’t quite last three years, says Max. It quit transmitting on Feb. 17, 2003, but managed to accomplish its planned mission first. A letter from NOAA Director Ernest Hildner sent to Sandia praised the Lab’s assistance and called the partnership an unqualified success. "I extend to you … our laboratory’s deep appreciation for [your] substantial assistance and cooperation in making the [HXRS] experiment to view the sun an overall success," he wrote.
The MTI’s mission has not been without problems. Shortly after launch a glitch in the satellite’s on-board power system resulted in unexpected battery discharges that prevented data from being collected and transmitted to the ground station. It raised blood pressures at first, says Max, but the team soon learned to manage its power operations in a way that mitigated the problem. Two other anomalies, a short in one of the satellite’s two solid-state recorders — its computer memory — and a faulty gyroscope forced the team to find other creative workarounds. The MTI’s development and on-orbit operations were funded by NNSA’s Office of Nonproliferation and National Security (NA-22). The satellite and sensor payload were developed by a Sandia, Los Alamos National Lab, Air Force, and industry team led by Sandia.
Exceeding the mission
Now that the mission goals are complete, the MTI has entered a bonus round, of sorts, collecting data on a routine basis for several government organizations. To expedite data processing and improve efficiency, data processing responsibilities were formally transferred from Los Alamos to Sandia in late January, says Max. Sandia is now responsible for all aspects of the MTI system. The satellite currently is gathering about nine images a day, 60 percent of which are requested by other government agencies for research purposes. The other 40 percent are being collected for NNSA labs. A Sandia Spectral Image Processing and Exploitation team led by Jody Smith (5712) is squeezing ever more analysis capability out of the satellite, developing and experimenting with dozens of data processing algorithms and techniques that allow them to see more with existing instruments. The new algorithms are providing new data useful for cloud identification, terrain characterization, change detection, and more, says Max. "What we’re doing now is trying to push the state of the art in spectral analysis tools," he says. "We are experimenting with a lot of ideas." One trick, called "super sampling," involves snapping four images during the time period one image would normally be taken, allowing the team to synthesize images with resolutions four times better than the typical 5 meters of resolution.
The MTI’s fate
This kind of experimentation will continue until the MTI is no longer useful, or until it plunges to earth, whichever comes first, says Max. The satellite is expected to reenter the upper atmosphere in 2009 — or, rather, be captured by the atmosphere — during a solar max (expansion of the atmosphere) that occurs on an 11-year cycle. Already the satellite’s orbit has decayed. Shortly after its launch three years ago the MTI was 590 km high; today it is about 560 km up. In addition, its sun angle has changed, altering the times of day the imager can acquire targets. When it does fall toward earth, says Max, it is expected to burn up and disintegrate before it reaches the ground. "Sandians supporting the MTI program have advanced the state of satellite technology as well as the analysis tools used to exploit the data gathered," says Sid Gutierrez, Director of Monitoring Systems Center 5700. "They should be proud of these major contributions to our national security."