Magsat

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Magsat
Magsat sketch-1.jpg
Magsat
Mission type Earth observation
Operator NASA / USGS
COSPAR ID 1979-094A
SATCAT № 11604
Mission duration 8 months
Spacecraft properties
Launch mass 158.0 kilograms (348.3 lb)
Start of mission
Launch date 30 October 1979, 14:16 (1979-10-30UTC14:16Z) UTC
Rocket Scout G-1 S203C
Launch site Vandenberg SLC-5
End of mission
Decay date 11 June 1980
Orbital parameters
Reference system Geocentric
Regime LEO
Eccentricity 0.0005741
Perigee 351.9 kilometers (218.7 mi)
Apogee 578.4 kilometers (359.4 mi)
Inclination 96.7488°
Period 93.90 minutes
RAAN 162.3717 degrees
Argument of perigee 301.4198 degrees
Mean anomaly 59.7851 degrees
Mean motion 16.40347862
Epoch 11 June 1980, 02:25:27 UTC[citation needed]
Revolution number 3497
Modeled Earth magnetic fields, data created by satellites with sensitive magnetometers

Magsat (Magnetic Field Satellite, Explorer 61, Applications Explorer Mission-3 or AEM-3) spacecraft was launched in the fall of 1979 and ended in the spring of 1980.[1] The mission was to map the Earth's magnetic field, the satellite has two magnetometers. The scalar (Cesium vapor) and vector (fluxgate) magnetometers gave Magsat a capability beyond that of any previous spacecraft. Extended by a telescoping boom, the magnetometers were distanced from the magnetic field created by the satellite and its electronics. The satellite carried two magnetometers, a three-axis fluxgate magnetometer for determining the strength and direction of magnetic fields, and an ion-vapor/vector magnetometer for determining the magnetic field caused by the vector magnetometer itself.[2] MAGSAT is considered to be one of the more important Science/Earth orbiting satellites launched; the data it accumulated is still being used, particularly in linking new satellite data to past observations.

After launch the payload was brought to an orbit of 96.8° facing the sun as the earth rotated underneath. It was kept in a close earth orbit, with vector magnetometers capable of sensing magnetic fields closer to Earth's surface. The data collected by this satellite allowed a 3D-mapping of the Earth's magnetic interior as never seen before. In combination with a later satellite, Ørsted, it has been an essential component for explaining the current declining state of the Earth's magnetic field.[3][4]

History[edit]

On October 30, 1979 Magsat was launched from pad SLC-5 at Vandenberg AFB in California on a Scout II (101) rocket bearing 97° in a dusk to dawn orbit.[5][6] The spacecraft was placed in an orbit with a perigee of 350 kilometres (220 mi) and an apogee of 550 kilometres (340 mi). After reaching orbit, its telescoping boom was extended outward by 6 metres (20 ft). Two star cameras were used to define the position of the spacecraft relative to Earth. The orbit allowed the satellite to map a majority of the Earth's surfaces except the geographic poles. The satellite decayed from orbit on June 11, 1980.

Critique[edit]

Magsat was not without problems. One of the biggest is that the motion of a metallic object tends to create a magnetic field. One study after the mission found a nonlinear fluxgate response when exposed to fields greater than 5000 mT. The applied field had to be transverse to the axis of the magnetometer.[7] The design was improved by creating a feedback relay over a spherical design.[8] This was the design used on later spacecraft [See:Ørsted (satellite)].

References[edit]

  1. ^ Langel R, Ousley G, Berbert J, Murphy J, and Settle M. The MAGSAT Mission. GEOPHYSICAL RESEARCH LETTERS, VOL. 9, NO. 4, PAGES 243–245, 1982
  2. ^ History of Vector Magnetometers in Space
  3. ^ Hulot G, Eymin C, Langlais B, Mandea M, Olsen N (April 2002). "Small-scale structure of the geodynamo inferred from Oersted and Magsat satellite data". Nature 416 (6881): 620–3. doi:10.1038/416620a. PMID 11948347. 
  4. ^ NASA AND USGS MAGNETIC DATABASE "ROCKS" THE WORLD NASA Web Feature, NASA
  5. ^ Mobley F, Eckard L, Fountain G, and Ousley G. MAGSAT--A new satellite to survey the earth's magnetic field. 1980. IEEE Transactions on Magnetics 16 (5): 758-760.
  6. ^ Vandenberg AFB Launch History. The Space Archive
  7. ^ Acuna, M. H., MAGSAT - Vector Magnetometer Absolute Sensor Alignment Determination. September 1981. NASA technical Memorandum 79648. Goddard Space Flight Center, NASA
  8. ^ Primdahl, F., H. Luhr and E. K. Lauridsen, The Effect of Large Uncompensated Transverse Fields on the Fluxgate Magnetic Sensor Output, Danish Space Research Institute Report 1-92, 1992.