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BeppoSAX

BeppoSAX was an Italian-Dutch satellite for X-ray astronomy. The satellite structure and control was built by various Italian and Dutch companies, while most of the scientific instruments were developed by the Italian CNR science research institute. The Wide Field Camera's were developed by the Dutch SRON space research institute.

BeppoSAX was named in honour of the Italian astronomer Giuseppe "Beppo" Occhialini. SAX stands for "Satellite per Astronomia a raggi X" or "Satellite for X-ray astronomy".

X-ray observations cannot be performed from ground-based telescopes, since Earth's atmosphere blocks most of the incoming radiation.

One of BeppoSAX's main achievements was the identification of numerous gamma ray bursts with extra-galactic objects. (See the linked article for details.)

Launched in 1996, the expected operating life of two years was extended to April 30, 2002. After this date, the orbit was decaying too rapidly and various subsystems were failing. Final deorbit was planned for 2003.

On April 29, 2003, the satellite ended its life falling into the Pacific Ocean.

Spacecraft characteristics:

Dimensions: 3.6 m high, 2.7 m diameter
Solar cell power: 3 kW
Data generated: 1 GB each orbit (90 min)

Instrumentation

BeppoSAX contained five science instruments:

Low Energy Concentrator Spectrometer (LECS)
Medium Energy Concentrator Spectrometer (MECS)
High Pressure Gas Scintillation Proportional Counter (HPGSPC)
Phoswich Detector System (PDS)
Wide Field Camera (WFC)

The first four instruments (often called Narrow Field Instruments or NFI) point to the same direction, and allow observations of an object in a broad energy band of 0.1 to 300 keV (16 to 48,000 aJ).

The WFC contained two coded aperture cameras operating in the 2 to 30 keV (320 to 4,800 aJ) range and each covering a region of 40 x 40 degrees (20 by 20 degrees full width at half maximum) on the sky. The WFC was complemented by the shielding of PDS which had a (nearly) all-sky view in the 100 to 600 keV (16,000 to 96,000 aJ) band, ideal for detecting gamma ray bursts (GRB).

PDS shielding has poor angular resolution. In theory, after a GRB was seen in the PDS, the position was refined first with the WFC. However, due to the many spikes in the PDS, in practice a GRB was found using the WFC, often corroborated by a BATSE-signal. The position up to arcminute precision - depending on the signal to noise ratio of the burst - was found using the deconvoluted WFC-image. The coordinates were speedily sent out as an International Astronomical Union (IAU) and Gamma-ray burst Coordinate Network Circular. After this, immediate follow-up observations with the NFI and optical observatories around the world allowed accurate positioning of the GRB and detailed observations of the X-ray, optical and radio afterglow.

The MECS contained three identical gas scintillation proportional counters operating in the 1.3 to 10 keV (208 to 1602 aJ) range. LECS was almost identical to the MECS units, expect that it had a thinner window that allows photons with lower energies down to 0.1 keV (16 aJ) to pass through. High background contamination makes the LECS data above 4 keV (641 aJ) unusable. LECS and MECS had imaging capability, whereas the high-energy narrow field instruments were non-imaging.

HPGSPC was also a gas scintillation proportional counter, but high (three atmospheres) pressure. High pressure equals high density, and dense photon-stopping material allowed detection of photons up to 120 keV (19,000 aJ).

PDS was a crystal scintillator (sodium iodide / caesium iodide) capable of stopping photons up to 300 keV (48,000 aJ). The spectral resolution of PDS was rather modest when compared to the gas detectors.