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Explorer: SWAS (SMEX 3)

SWAS (SMEX 3) [NASA]

SWAS (Submillimeter Wave Astronomy Satellite) is part of NASA's Small Explorer (SMEX) program. The scientific objectives of SWAS are to study the chemical composition, energy balance and structure of interstellar clouds and the processes that lead to the formation of stars and planets. Galactic interstellar clouds (e.g., Orion, Taurus, Ophiuchi, and Perseus) and extragalactic sources (e.g., Magellanic Clouds) will be studied. It has a 55 × 71 cm elliptical off-axis Cassegrain telescope with a beam width of 4 arcminutes at its operating frequencies. The submillimeter radiometers are a pair of passively cooled subharmonic Schottky diode receivers, with receiver noise figures of 2500-3000 K.

SWAS will focus on the following spectral lines:

  • Water (H2O) at 556.936 GHz
  • Molecular oxygen (O2) at 487.249 GHz
  • Neutral carbon (CI) at 492.161 GHz
  • Isotopic carbon monoxide (13CO) at 550.927 GHz
  • Isotopic water (H218O) at 548.676 GHz

Detailed 1 degree × 1 degree maps of at least twenty giant molecular and dark cloud cores will be obtained. Each of these maps will be made from a grid of measurements taken at 3.7 arc-min spacings.

SWAS's submillimeter radiometers are a pair of passively cooled subharmonic Schottky diode receivers, with receiver noise figures of 2500-3000 K. An acousto-optical spectrometer (AOS) is being provided by the University of Cologne. The outputs of the two SWAS receivers are combined to form a final intermediate frequency, which extends from 1.4 to 2.8 GHz and is dispersed into 1400 1 MHz channels by the AOS.

SWAS has a 55 × 71 cm elliptical off-axis Cassegrain telescope with a beam width of 4 arc-min at operating frequencies. SWAS is designed to make pointed observations stabilized on three axes, with a position accuracy of about 38 arc-s, and jitter of about 24 arc-s. Attitude information is obtained from gyros whose drift is corrected via a star tracker. Momentum wheels are used to maneuver the spacecraft.

SWAS was shut down in February 2008, but reactivated sevaral times for special observations.

Nation: USA
Type / Application: Astronomy, sub-mm wave
Operator: NASA Goddard Space Flight Center
Contractors: NASA Goddard Space Flight Center (spacecraft), Ball Aerospace (instrument)
Equipment: 55 × 71 cm elliptical off-axis Cassegrain telescope, submillimeter radiometers
Configuration: 3 axis stabilized, 4 deployable, fixed solar panels and one body-mounted
Propulsion: ?
Power: 2 deployable solar arrays, batteries
Lifetime:
Mass: 288 kg
Orbit: 637 km × 653 km, 69.90
Satellite COSPAR Date LS Launch Vehicle Remarks
SWAS (SMEX 3, Explorer 74) 1998-071A 06.12.1998 Va, L-1011, RW30/12 Pegasus-XL

References:

  • NSSDC Master Catalog: SWAS