Highlights of the Project Data Management Plan for the Submillimeter-Wave Astronomy Satellite

This is a summary of a preliminary version of the Project Data Management Plan (PDMP) for SWAS, and subject to slight revision. The PDMP itself will be available on request from the Configuration Management Office of NASA's Small Explorer (SMEX) program (NASA/GSFC, Code 740.0, Greenbelt, MD 20771).

Institutions

SWAS is a NASA-funded mission with the Smithsonian Astrophysical Observatory as the Principal Investigator institution. Co-Investigator institutions are the University of Cologne, University of Massachusetts, NASA Ames Research Center, National Air and Space Museum, Cornell University, and Johns Hopkins University.

Instrumentation

SWAS has one instrument, a two-channel Schottky-barrier diode submillimeter receiver. It has an acousto-optical spectrometer (AOS) with 1450 channels of 1 MHz bandwidth and two continuum detectors, each of 700 MHz bandwidth. SWAS will observe lines of O_2 (487 GHz), C (492 GHz), 13CO (551 GHz), and H_2O (557 GHz) toward dense interstellar clouds in our Galaxy.

Observing Modes

SWAS has a only a few observing modes:

1. Spectral nod - position-switched spectral line observations, where the off-source spectrum is obtained by slewing the spacecraft up to 3 degrees away from the on-source position. Period is 60-120 seconds.
2. Spectral chop - position-switched spectral line observations, obtained using the chopping secondary to switch to an off-source position 10' away from the on-source position, with a 4 second period.
3. Spectral map - obtains a regular grid of spectra in spectral nod mode, with the possibility of multiple on-source spectra per off-source observation. All on-source spectra share the same off-source, reference position.
4. Planetary chop - used primarily for calibration observations of planets; the chopping secondary is used, with a 0.5 second period, and only the continuum detectors are read.
5. Planetary map - same as planetary chop, except a regular grid of positions is observed.

Data Rate and Volume

Data from SWAS will be downlinked to GSFC once or twice per day and will be transferred to SAO via a dedicated digital data link. The lowest level data processing will be performed at SAO; higher-level processing will be shared among the PI and Co-I institutions. About 20 Gbytes of raw data are expected for each 6 months of operation. The corresponding volume of reduced data, largely spectra and maps (see below), is expected to be 200 Mbytes.

Data Products

The data products will fall into three categories: Raw, Level 1, and Level 2.

• Raw data will essentially be time-ordered, consisting of individual 2-second integrations taken with SWAS. An index of the individual integrations will also be produced.
• Level 1 data will consist of flux and frequency-calibrated spectra. For each target observed, spectra will be provided for each 5 minutes of integration, as well as for the overall observation. Baseline subtraction will be performed if it can done in a uniform, non-controversial way. Level 1 data products will also include beam maps, either from ground-based near-field tests or from continuum observations of planets.
• Level 2 data will consist of final co-added spectra of all sources observed, along with derived line strengths, velocities, and widths. Maps will be provided for sources observed in one of the mapping modes.

All data products will be produced in FITS table and CLASS formats.

Data Release Schedule

SWAS will not have a guest investigator program. SWAS data products and documentation will be made publicly available beginning 18 months after launch, when the raw and Level 1 data from the first 6 months of operation are released. Subsequent releases will be made at 6-month intervals, 12-18 months behind the observations. Level 2 data products will be released six months after SWAS ceases operations, or three years after launch, whichever comes first.