BeppoSAX

BeppoSAX was a three axes stabilized satellite, with a pointing accuracy of 1'. The main attitude constraint derived from the need to maintain the normal to the solar arrays within 30° from the Sun, with occasional excursions to 45° for some WFC observations. Due to the low orbit the satellite was in view of the ground station of Malindi for only a limited fraction of the time. Data was stored on-board on a tape unit with a capacity of 450 Mbits and transmitted to ground every orbit during station passage. The average data rate available to instruments was about 60 kbit/s, but peak rates of up to 100 kbit/s can be retained for part of each orbit. With the solar panels closed, the spacecraft was 3.6 m in height and 2.7 m in diameter. The total mass amounts to 1400 kg, with a payload of 480 kg. The primary sub-systems of the satellite are: • The Attitude Orbital Control System (AOCS), that performed attitude determination and manoeuvred and operated the Reaction Control Subsystem in charge of orbit recovering. It included redundant magnetometers, Sun acquisition sensors, three star trackers, six gyroscopes (three of which are for redundancy), three magnetic torquers and four reaction wheels, all controlled by a dedicated computer. The AOCS ensured a pointing accuracy of 1' during source observations and manoeuvres with a slew rate of 10° per min. • The On Board Data Handler (OBDH) was the core for data management and system control on the satellite and it also managed the communication interfaces between the satellite and the ground station. Its computer supervised all subsystem processor activities, such as those of each instrument, and the communication busses. == 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 attojoules (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). On 6 May 1997 one of the three identical MECS units was lost when a fault developed in the High Voltage power supply. The LECS was similar 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 and operated in a "driftless" mode which is necessary to detect the lowest energy X-rays as these would be lost in the low field regime near the entrance window of a conventional GSPC. The LECS data above 4 keV (641 aJ) is not usable due to calibration issues probably caused by the driftless design. The LECS and MECS had imaging capability, whereas the high-energy narrow field instruments were non-imaging. The HPGSPC was also a gas scintillation proportional counter, operating at a high (5 atmospheres) pressure. High pressure equals high density, and dense photon-stopping material allowed detection of photons up to 120 keV (19,000 aJ). The PDS was a crystal (sodium iodide / caesium iodide) scintillator detector capable of absorbing photons up to 300 keV (48,000 aJ). The spectral resolution of the PDS was rather modest when compared to the gas detectors, but the low background counting rate resulting from the low inclination BeppoSAX orbit and good background rejection capabilities meant that the PDS remains one of the most sensitive high-energy instruments flown. ==Gallery==

• BeppoSAX Mission Overview, Astronomy & Astrophysics Supplement Series, Vol. 122, April II 1997, 299-307 • De Kort, N., Ruimteonderzoek, de horizon voorbij, Veen/SRON, 2003 • Low Energy Concentrator Spectrometer (LECS) 0.1-10 keV, A&A Supplement series, Vol. 122, April II 1997, 309-326 • Medium Energy Concentrator Spectrometer (MECS) 0.1-10 keV, A&A Supplement series, Vol. 122, April II 1997, 327-340 • High pressure Gas Scintillator Proportional Counter (HPGSPC), A&A Supplement series, Vol. 122, April II 1997, 341-356 • Phoswich Detection System (PDS) 15-300 keV, A&A Supplement series, Vol. 122, April II 1997, 357-369 • Wide Field Camera 2-28 keV, A&A Supplement series, Vol. 125, November 1997, 557-572 • Piro, L. e.a., ''SAX Observer's Handbook'', 1995 == External links ==