The Landsat-7 Earth science spacecraft will not be launched in July 1998 as planned, due to necessary changes in the design of the electrical power supply hardware for the spacecraft's main instrument. A new target launch date will be set by NASA officials after completion of instrument thermal vacuum tests scheduled for this July.
During a series of instrument-level thermal vacuum tests beginning in December 1997, a power supply on the Enhanced Thematic Mapper Plus (ETM+) instrument failed twice. ETM+ is Landsat-7's only science instrument. As a result of the most recent failure in January, both internally redundant power supplies were returned to their manufacturer. Completion of vacuum testing will be delayed while the power supplies are being repaired, which will consequently delay the launch.
It is not possible to set a precise new date for the launch from Vandenberg Air Force Base, CA, at this time, according to project managers. NASA will now work with its launch contractor, Boeing, on moving the Landsat-7 launch to a mutually agreeable date.
"We're looking at several options in order to minimize the impact to the launch schedule," said Phil Sabelhaus, Landsat-7 project manager at NASA's Goddard Space Flight Center, Greenbelt, MD. "When we understand precisely why the power supply failed and how long it will take to fix the problem, we'll be able to ascertain the impact to the launch schedule."
The enhanced thermatic mapper was designed and built by Raytheon (formerly Hughes) Santa Barbara Remote Sensing, Santa Barbara, CA. The Landsat-7 spacecraft was built by Lockheed Martin Missiles and Space, with integration of the instrument and spacecraft conducted at the company's facility in Valley Forge, PA.
Landsat-7 is the latest installment in a long history of land remote-sensing spacecraft, spanning over 25 years of multispectral imaging of the Earth's surface, starting with the launch of Landsat-1 in 1972. Landsat-5, launched in March 1984, is still transmitting images to several domestic and international ground stations worldwide.
In particular, the science instrument on Landsat-7 will continue a data base of high-resolution Earth imagery begun in 1982 by the Landsat-4 thematic mapper. As changes occur on the Earth's surface due to natural or human-induced events, scientists will be able to study these recent changes with the aid of the archive of similar imagery. Applications include agriculture, forestry and urban planning.
Landsat-7 will add to the global archive of sun-lit, substantially cloud-free images of the Earth's land surfaces. Approximately one-quarter of the Earth's landmass will be imaged every 16 days, with a emphasis on seasonal changes in vegetation.
Landsat-7 contains several technological improvements over previous Landsat satellites and their instruments. These improvements include better instrument calibration and a solid state data recorder capable of storing 100 individual enhanced thematic mapper images of the Earth. This capability will enable Landsat-7 to update a complete global view of Earth's land surfaces seasonally, or approximately four times per year.
NASA also is developing an advanced land imager instrument and related small spacecraft technology that will enable future follow-on measurements to be made by a sensor that is one-fourth the mass of the enhanced thermatic mapper and uses only 20 percent of the electrical power, while reducing the instrument's cost by 75 percent.
Landsat-7 was authorized by the Land Remote Sensing Policy Act of 1992, which established a joint NASA-U.S. Air Force program. This was superseded by a second Presidential Directive in 1994, that established a joint program between NASA, the National Oceanic and Atmospheric Administration (NOAA) and the U.S. Geological Survey (USGS).
Landsat-7 is part of NASA's Earth Science enterprise, a long-term research program designed to study Earth's land, oceans, atmosphere, ice and life as a total integrated system. Goddard Space Flight Center manages the development of Landsat for NASA's Office of Earth Science in Washington, DC.