Landsat 2
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Landsat 2 is the second
satellite A satellite or artificial satellite is an object intentionally placed into orbit in outer space. Except for passive satellites, most satellites have an electricity generation system for equipment on board, such as solar panels or radioisotope ...
of the Landsat program. The spacecraft originally carried a designation of ERTS-B (Earth Resource Technology Satellite B) but was renamed "Landsat 2" prior to its launch on January 22, 1975. The objective of the satellite was to acquire global, seasonal data in medium resolution from a near-polar,
sun-synchronous orbit A Sun-synchronous orbit (SSO), also called a heliosynchronous orbit, is a nearly polar orbit around a planet, in which the satellite passes over any given point of the planet's surface at the same local mean solar time. More technically, it is ...
. The satellite, built by
General Electric General Electric Company (GE) is an American multinational conglomerate founded in 1892, and incorporated in New York state and headquartered in Boston. The company operated in sectors including healthcare, aviation, power, renewable energ ...
, acquired data with the
Return Beam Vidicon Return may refer to: In business, economics, and finance * Return on investment (ROI), the financial gain after an expense. * Rate of return, the financial term for the profit or loss derived from an investment * Tax return, a blank document or t ...
(RBV) and the Multispectral Scanner (MSS). Despite having a design life of one year, Landsat 2 operated for over seven years, finally ceasing operations on February 25, 1982.


Background

Landsat 2 (originally designated ERTS-B) was the second Landsat satellite launched. The first, Landsat 1 (originally designated ERTA-1), took and transmitted over 100,000 photos from the two-and-a-half years between the two satellites' launches.


Satellite design


Development

Landsat 2 was manufactured by
General Electric General Electric Company (GE) is an American multinational conglomerate founded in 1892, and incorporated in New York state and headquartered in Boston. The company operated in sectors including healthcare, aviation, power, renewable energ ...
's Space Division in Valley Forge, Pennsylvania. This
satellite A satellite or artificial satellite is an object intentionally placed into orbit in outer space. Except for passive satellites, most satellites have an electricity generation system for equipment on board, such as solar panels or radioisotope ...
was considered an experiment, unlike Landsat 1. Landsat 2 was originally designated as ERTS-B (Earth Resources Technology Satellite-B) and was renamed prior to launch. The satellite was designed to operate for a minimum of one year. The primary objective of the MSS was to acquire global, seasonal data in medium resolution from a near-polar, sun-synchronous orbit. NASA administrator
James C. Fletcher James Chipman Fletcher (June 5, 1919 – December 22, 1991) served as the 4th and 7th Administrator of NASA, first from April 27, 1971 to May 1, 1977, under President Richard M. Nixon, and again from May 12, 1986 to April 8, 1989, under Pres ...
said, "If I had to pick one spacecraft, one space-age development to save the world, I would pick ERTS and the satellites which I believe will be evolved from it later in this decade."


Operation

The spacecraft was tall with a diameter. Two
solar panel A solar cell panel, solar electric panel, photo-voltaic (PV) module, PV panel or solar panel is an assembly of photovoltaic solar cells mounted in a (usually rectangular) frame, and a neatly organised collection of PV panels is called a photo ...
arrays that were long each, with single axis articulation, generated power for the spacecraft. Landsat 2 had a liftoff weight of . The attitude was controlled with three
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thrusters. The satellite transmitted data back to the ground with S-Band and
very high frequency Very high frequency (VHF) is the ITU designation for the range of radio frequency electromagnetic waves ( radio waves) from 30 to 300 megahertz (MHz), with corresponding wavelengths of ten meters to one meter. Frequencies immediately below VHF ...
(VHF) transmitters, at a rate of 15 Mbit/s and 6-bit quantization. The satellite had three-axis fine attitude control with four wheels, which gave it +/- 0.7 degrees of control. The attitude control system also used horizon scanners, sun sensors, and a command antenna. A freon gas propulsion system allowed the satellite to make fine attitude adjustments. Landsat 2 could store 30 minutes' worth of data on two wide-band video tape recorders.


Sensors

As in the case of its predecessor Landsat 1, the satellite's payload included two
remote sensing Remote sensing is the acquisition of information about an object or phenomenon without making physical contact with the object, in contrast to in situ or on-site observation. The term is applied especially to acquiring information about Earth ...
instruments, the
Return Beam Vidicon Return may refer to: In business, economics, and finance * Return on investment (ROI), the financial gain after an expense. * Rate of return, the financial term for the profit or loss derived from an investment * Tax return, a blank document or t ...
(RBV) and the Multispectral Scanner (MSS). The specifications for these instruments were identical to those of the instruments carried on Landsat 1. The data acquired by the MSS was considered more scientifically useful than the data returned from the RBV, which was rarely used and considered only for engineering evaluation purposes. The MSS, built by
Hughes Aircraft Corporation The Hughes Aircraft Company was a major American aerospace and defense contractor founded on February 14, 1934 by Howard Hughes in Glendale, California, as a division of Hughes Tool Company. The company was known for producing, among other produ ...
, was capable of detecting four different
spectral bands Spectral bands are parts of the electromagnetic spectrum of specific wavelengths, which can be filtered by a standard filter. In nuclear physics, spectral bands are referred to the emission of polyatomic systems, including condensed materials, larg ...
: band 4 visible green, band 5 visible red, band 6 near infrared, and band 7 near infrared. Each spectral band had different scientific uses. Band 4 primarily investigated areas of water, with the ability to detect sediment laden areas and areas of shallow water. Band 5 was primarily used to identify cultural features. Band 6 sensed the vegetation boundaries between land, water, and landforms. Band 7 was the most proficient at sensing through atmospheric haze, and identified water and land boundaries, vegetation, and landforms. The scene size for the scanners of the MSS was to , which is the area the sensors could survey per scan. The ground sampling interval of the MSS was to , which is medium resolution. With its three cameras, the RBV was capable of acquiring 3.5 MHz video with resolution in three spectral bands: blue to green (475–575 nm), orange to red (580–680 nm), and red to near infrared (690–820 nm). Besides engineering evaluation purposes, the primary use of the RBV was for cartography of remote areas.


Mission


Launch

Landsat 2 was originally set to launch on January 19, 1975, but an electrical problem with the launch vehicle caused the launch to be postponed. Landsat 2 was launched January 22, 1975 on a Delta 2910 out of Vandenberg Air Force Base in California. The satellite was placed in a sun-synchronous, near-polar orbit with an inclination of 99.2 degrees and an altitude of . Landsat 2 orbited Earth every 103 minutes, totaling 14 times per day. The orbital cycle of the satellite was repeated every 18 days.


Operations

Landsat 2 transmitted its data to several international ground stations. The ground stations were located on six of the seven continents, with the first beginning operations in April 1975 in
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, Canada, and the last to begin operations in December 1981 in Hartebeesthoek, South Africa. The satellite continued operations until February 25, 1982, when it was removed from operations due to a faulty yaw control thruster. The satellite was placed in standby mode on March 31, 1983.


Results

Data received from the satellite is free to the public. There are multiple levels of data available. Level-1 data takes 1–3 days to process, and the user will receive multiple files that they can then piece together to generate an RGB image. Higher level science data can also be requested, which contains data such as surface reflectance. Although the MSS was the most useful instrument on Landsat 2, sometimes the data recorded was anomalous. The
U.S. Geological Survey The United States Geological Survey (USGS), formerly simply known as the Geological Survey, is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, and ...
(USGS) would identify these anomalies and document them. Known issues on the MSS are: banding, coherent noise, data loss, impulse noise, oversaturation, scan correlated shift (SCS), scan mirror pulse, and transmission striping. Transmission striping occurred when data from an individual sensor was lost. Most commonly, multiple data losses occurred simultaneously, resulting in an image with colored bands on it. This form of data anomaly could not be corrected in post processing.


References

{{Orbital launches in 1975 Landsat program Spacecraft launched in 1975 Spacecraft launched by Delta rockets