--Douglas Isbell (disbell@mail.hq.nasa.gov), NASA
Headquarters, Washington, DC.
--Allen Kenitzer (akenitze@pop100.gsfc.nasa.gov),
Lynn Chandler, NASA Goddard Space Flight Center, Greenbelt, MD.
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.
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.
"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 space-craft 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 Thematic
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 among 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.