Landsat 1 (formerly ERTS 1, Earth Resources Technological Satellite) was a modified
version of the Nimbus 4 meteorological satellite. The near-polar orbiting spacecraft
served as a stabilized, earth-oriented platform for obtaining information on agricultural
and forestry resources, geology and mineral resources, hydrology and water resources,
geography, cartography, environmental pollution, oceanography and marine resources, and
meteorological phenomena. To accomplish these objectives, the spacecraft was equipped
with:
- a three-camera return beam vidicon (RBV) to obtain visible and near IR photographic
images of the earth,
- a four-channel multispectral scanner (MSS) to obtain radiometric images of the earth, and
- a data collection system (DCS) to collect information from remote, individually equipped
ground stations and to relay the data to central acquisition stations.
ERTS 1, renamed Landsat 1 in 1975, carried two wide-band video tape recorders (WBVTR) capable of storing up to
30 min of scanner or camera data to give the spacecraft's sensors a near-global coverage
capability. An advanced attitude control system consisting of horizon scanners, sun
sensors, and a command antenna combined with a freon gas propulsion system permitted the
spacecraft's orientation to be maintained within plus or minus 0.7 deg in all three axes.
Spacecraft communications included a command subsystem operating at 154.2 and 2106.4 MHz
and a PCM narrow-band telemetry subsystem, operating at 2287.5 and 137.86 MHz, for
spacecraft housekeeping, attitude, and sensor performance data. Video data from the
three-camera RBV system was transmitted in both real-time and tape-recorder modes at
2265.5 MHz, while information from the MSS was constrained to a 20 MHz rf bandwidth at
2229.5 MHz. The spacecraft was turned off on 6 January 1978, when cumulative precession
of the orbital plane caused the spacecraft to see almost constant sunlight which led to
overheating.
Landsat 2 and 3 were nearly identical satellites to extend the measurements.
