#Science #scienceNews #satellite #landsat Landsat 4 is the fourth satellite of the Landsat program. It was launched on July 16, 1982, with the primary goal of providing a global archive of satellite imagery. Although the Landsat Program is managed by NASA, data from Landsat 4 was collected and distributed by the U.S. Geological Survey. Landsat 4 science operations ended on December 14, 1993, when the satellite lost its ability to transmit science data, far beyond its designed life expectancy of five years. The satellite housekeeping telemetry and tracking continued to be maintained by NASA until it was decommissioned on June 15, 2001. Landsat 1, then known as ERTA-A, was launched July 23, 1972. The satellite took over 100,000 images of the Earth over the course of its life. Landsat 2 had a similar design, and was launched three years later. Landsat 3, launched in 1978, was the last satellite to have a similar design to Landsat 1, and was the last Landsat to be managed by NASA during the Landsat program. Landsat 4 was the first Landsat to be operated by NOAA. The second generation of Landsat, Landsat 4 and 5, flew in lower orbits than the first three missions. Although they were in lower orbits, they had a higher field of view (FOV) so they had the same swath widths. The new Landsat spacecraft also featured improved instrumentation. The spacecraft was built by GE Astro Space, who would later become Lockheed Martin Missile and Space. It used the MultiMission Modular Spacecraft (MMS) bus developed by Fairchild Industries. The satellite was designed to be fixed by astronauts in space via the Space Shuttle, or taken back to Earth for repairs. It was expected that the shuttles would be able to reach Landsat's relatively far orbit by 1985. Landsat 4's attitude was controlled with hydrazine thrusters. The satellite was constructed with aluminum panels and graphite struts. The spacecraft was three-axis stabilized with reaction wheels. It was powered by three nickel-cadmium batteries (NiCd), which were charged via a single solar array that had one axis of articulation. The solar array produced 1430 W of power. The satellite weighed 4,300 pounds (2,000 kg). Landsat 4 was designed to last a minimum of three years. The satellite communicated to the ground with a direct downlink with the Tracking and Data Relay Satellite System (TDRSS) at 85 Mbit/s on the S-, X-, L-, and Ku-bands. The high gain antenna was extended with a retractable boom. The data used 8 bit quantization. Landsat 4 carried an updated Multispectral Scanner (MSS), used on previous Landsat satellites, and a Thematic Mapper. It had a reflective resolution of 30 meters (98 ft) and a thermal resolution of 120 meters (390 ft). Both were built by Hughes Aircraft. Landsat 4 was the first satellite in the Landsat program to incorporate the Thematic Mapper (TM) sensor. The Landsat TM sensor is able to gather seven bands of data as opposed to the four bands of data collected from the Multispectral Scanner. In addition to having three more bands of data to work with, scientists are able to view the TM data at a much higher resolution than with MSS. Bands 1–5 and 7 each have a spatial resolution of 30 meters (98 ft) while the MSS is only capable of a 57 meters (187 ft) by 79 meters (259 ft) resolution. Band 6 (which is a thermal infrared band) has a maximum spatial resolution of 120 meters (390 ft). The data rate for TM data was 84.9Mbit/s, via an X-band transmitter to modernized ground antennas.