next previous
Up: BeppoSAXthe wide

2. The satellite and the scientific instruments

2.1. The scientific payload

The configuration of the scientific payload and the energy bands covered by the different instruments are presented in Fig. 1 (click here) and Fig. 2 (click here) respectively. The wide band capability is provided by a set of instruments co-aligned with the Z axis of the satellite (Fig. 1 (click here)), Narrow Field Instruments (hereafter NFI) and consisting of (Table 1 (click here)):

Perpendicular to the axis of the NFI and pointed in opposite directions there are two coded mask proportional counters (Wide Field Cameras, WFC, Jager et al. 1996 and references therein) that provide access to large regions of the sky in the range 2-30 keV. Each WFC has a field of view of tex2html_wrap_inline1140 (FWHM) with a resolution of 5'.

Finally, the four lateral active shields of the PDS will be used as monitor of gamma-ray bursts with a fluence greater than about tex2html_wrap_inline1144 in the range 60-600 keV, with a temporal resolution of about 1 ms.

Each instrument (the four NFI and the two WFC's) is controlled by a dedicated computer which has, in particular, the task of performing on board pre-processing of the scientific data according to the acquisition mode required by the specific observation. The basic mode is the Direct mode, in which each single event is transmitted with the full information. For sources fainter than about 0.3 Crab (tex2html_wrap_inline1148 tex2html_wrap_inline1150 in the 2-10 keV range), the telemetry (see next Section) is sufficient to support this mode for all instruments simultaneously. For brighter sources Indirect modes allow to reduce the telemetry by producing on-board spectra, images and light curves with a large choice of parameters. The scientific data packets produced by each instrument are received by the main on-board processor (see next Section) on the basis of the overall telemetry occupation and instrument priority programmable from ground.


Figure 1: BeppoSAX scientific payload accommodation


Table 1: BeppoSAX instruments

2.2. The spacecraft and the other subsystems

The main characteristics of the spacecraft are presented in Table 2 (click here). BeppoSAX is a three axes stabilized satellite, with a pointing accuracy of 1'. The main attitude constraint derives from the need to maintain the normal to the solar arrays within tex2html_wrap_inline1206 from the Sun, with occasional excursions to tex2html_wrap_inline1208 for some WFC observations. Due to the low orbit (see next section) the satellite will be in view of the ground station for only a limited fraction of the time. Data will be stored onboard 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 is 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 is 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 structure of the satellite consists of three basic functional subassemblies:

The primary sub-systems of the satellite are:


Figure 2: Energy coverage of BeppoSAX instrument

Table 2: BeppoSAX: spacecraft main characteristics

Table 3: BeppoSAX: launch, orbit

next previous
Up: BeppoSAXthe wide

Copyright by the European Southern Observatory (ESO)