SAX, images of the launch

SAX on top of the Atlas on the launching pad (Click for larger view)

The Atlas I launch vehicle, designed and built by Lockheed Martin Astronautics, consists of the Atlas booster with a Centaur upper stage. The Atlas stage will deliver the Centaur/SAX spacecraft to an altitude of approximately 100 nautical miles. The Centaur will use two engine bums separated by a 15-minute coast to place the SAX into a low-Earth, near equatorial, circular orbit where the SAX spacecraft will perform its experiments. SAX will be placed into orbit on the 100th historic Atlas/Centaur launch since Atlas began flying in 1957.

Spacecraft--SAX

The Italian-Dutch Satellite Astronomy X-ray (SAX) is the first X-ray mission that has the capability of observing sources over more than three orders-of-magnitude of energy-from 0.1 to 300 kiloelectron volts (keV)-with a relabvely large area, and a good energy resolution. The instrument complement is composed of a medium-energy (1-10 keV) concentrator/spectrometer, MECS, consisting of three units, a low-energy (0.1-10 keV) concentrator/spectrometer, a high pressure gas scintillation proportional counter (3-120 keV), and a phoswich detector system (15-300 keV), all of which have narrow fields-of-view and point in the same direction. These constitute the Narrow Field Instruments (NFI).

The other capability of the mission is to monitor large regions of the sky with a resolution of 5' in the range 2-30 keV to study long-term variability of sources down to 1-mCrab and to detect X-ray transient phenomena. This is realized by means of two coded operabve proportional counters termed the Wide Field Cameras (WFC) pointing in diametrically opposed directions perpendicular to the NFI.

Finally, the anticoincidence scintillator shields of the PDS will be used as a gamma-ray burst monitor in the range 100-600 keV.

Applications

With its minimum lifetime of two years (extendible to four years), SAX will be able to perform more than 2000 pointings. While the Narrow Field Instruments (NFI) will be the pnme instruments most of the time, the Wide Field Cameras (WFC) will be periodically used to scan the galactic plane to monitor the temporal behavior of sources above 1 mCrab and to detect transient phenomena. Thanks to their large field-of-view, the WFC will also monitor selected objects when the NFI perform their sequence of pointed observabons. The observing program will be held flexible to accommodate Targets Of Opportunity (transient phenomena) for follow-up observations with the NFI. Furthermore the operational capability of SAX will allow acquiring the target within a few hours of its discovery.