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CATSAT (STEDI 3)

CATSAT (STEDI 3) [UNH]

CATSAT (Cooperative Astrophysics & Technology Satellite) carries a suite of three instruments that will simultaneously measure GRB (Gamma Ray Burster)  spectra over the broad energy range from 500 eV to 5 MeV. CATSAT's wide field-of-view and extension of the low energy threshold downward by nearly an order of magnitude into the soft x-ray range for GRBs will allow it to perform important spectral measurements of the prompt emission from GRBs.

CATSAT has one primary and 2 secondary instruments:

  • Soft X-Ray spectrometer (SXR) whose primary function is to measure burst spectra in the soft X-ray region and determine the effective column density to bursts;
  • Hard X-Ray spectrometer (HXR) whose function is to extend the spectral measurements into the hard X-ray region and search for cyclotron features in burst spectra;
  • Directional Gamma-ray Spectrometer (DGS) whose function is to verify the GRB nature of the event, provide broad-band spectral information across the gamma-ray region and search for annihilation features. Additionally, DGS will provide directional information to bursts within 10 using triangulation.

CATSAT is a three axis stabilized satellite which uses a single momentum wheel and magnetic torqueres for attitude control. The orbit and satellite attitude are driven by the requirements of the prime detector instrument (the SXR) to stay at a temperature (-30 deg C) which requires it to view deep space in order for it stay at its operating temperature. To achieve this the top of the spacecraft which houses the SXR must not look at the Sun or Earth. Therefore the Solar terminator orbit was chosen as it always normal to the sun and anti-nadir. Given that the prime constraint is to keep the SXR from viewing the sun the mission is solar pointed with the bottom of the spacecraft being held with a Nadir constraint. The SXR front protective door when in its open state acts as a sun shield which allows the Attitude Control System (ACS) up to 5 degrees of wander before the sun light hits the SXR system.

A terminator orbit offers continuous illumination of the solar panels and enhances power management efficiency. It also allows a nearly 2pi steradian field of view for the soft X-ray detectors free of earth occultations and contaminating background from the Sun. The altitude is a compromise between the minimum backgrounds and particle dose rates from the SAA at lower altitudes and a greater than 1 year useful orbit life.

After launch, UNH will monitor and operate the satellite from the prime Spacecraft Operations Control Center (SOCC) located at UNH in Durham, NH. A secondary SOCC will be located at Leicester University.

It was funded as the third STEDI mission under NASA's Explorer program, but funding has been terminated by NASA because the projected costs unacceptably exceeded the cap. The satellite was nearly completed, but no alternative launch opportunity had been found.

Nation: USA
Type / Application: Astronomy, Gamma rays
Operator: University of New Hampshire, NASA
Contractors: University of New Hampshire
Equipment: SXR, HXR, DGS
Configuration: 3-axis stabilized
Propulsion: None
Power: 2 deployable fixed solar arrays, batteries
Lifetime: +1 year
Mass: 168 kg
Orbit: TBD (500 km - 700 km desired)
Satellite COSPAR Date LS Launch Vehicle Remarks
CATSAT (ex STEDI 3) - not launched

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