Submillimeter Wave Astronomy Satellite
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Submillimeter Wave Astronomy Satellite |
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| SCIENCE OBJECTIVES By observing spectral lines emanating from dense molecular clouds, SWAS will:
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Latest Mission
Information The Science The SWAS instrument is a submillimeter wave telescope that incorporates dual heterodyne radiometers and an acousto-optical spectrometer to investigate the composition of dense interstellar clouds. The instrument weighs 102 kg and attaches to the top of the spacecraft structure as a single module. The total observatory mass is 288 kg. The SWAS mission will operate in a 600 km circular orbit with a 70° inclination. SWAS is a three-axis-stabilized, stellar-pointed observatory with a pointing accuracy of 38 arcseconds and jitter less than 19 arcseconds. The spacecraft will typically point the science instrument at 3-5 targets per orbit. Target selection is constrained so that the solar arrays always face within ±15° of the Sun, except during eclipse. The Principal Investigator will generate the observation timeline and select the navigation guide stars. Using this timeline, the spacecraft, without ground intervention, will "nod" from an on-source target position to an off-source instrument calibration position up to three degrees away under 15 seconds. This nodding occurs approximately every 40 seconds. Attitude control, including pointing and nodding, is accomplished by using three magnetic-torquer coils, one digital Sun sensor, six coarse Sun sensors, four reaction wheels, one magnetometer, three inertial gyros and a high accuracy CCD star tracker. The Attitude Control System (ACS) uses the Spacecraft Computer System (SCS) processor to perform closed loop attitude determination and control. Four deployable, fixed solar panels and one body-mounted panel contain 3.4 m2 of solar cells and provide 230 W of orbital average power that is distributed to the spacecraft and instrument. The orbit average power consumption of the spacecraft hardware is 150 W. The instrument consumes 59 W. The data system for the SWAS mission contains 110 Mbps of bulk memory. It utilizes the MIL-STD-1553 data bus to communicate with the subsystems and the instrument. Instrument data is collected at approximately 12 Kbps average rate. Dual quadrifilar antennas are used for ground communications. The stored data is transferred to the ground at 1.8 Mbps. Commands are uplinked at 2 Kbps.
Author:
Jim Watzin (jim.watzin@gsfc.nasa.gov) |
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