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Jet-X at MSSL |
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Jet-X - The Hardware |
JETX operates as a stand-alone instrument with simple interfaces to the spacecraft.
The JETX structure is constructed from three carbon fibre tubular sections. The structure contains the instruments and acts as an optical bench, with which to maintain focus and stable alignment of the x-ray mirrors relative to the focal plane detectors and accurate co-alignment between the x-ray telescopes and the attitude monitor. A telescope alignment monitor (TAM) measures the thermal mis-alignments and angular distortion between the mirror and focal plane bulkheads to 5 arcsec accuracy. The structure is under active thermal control by means of a distributed array of heaters and temperature sensors. Heat flows to and from space are controlled by multilayer insulation, and by thermal baffles in front of the x-ray mirrors, and stray light baffles in front of the attitude monitor.
The forward section of the structure has a deployable door, which remains closed until the satellite has reached orbit. A pyrotechnic cutter releases the door latch on command and the door is opened by spring-loaded hinges with dampers. The function of the door is to protect sensitive optical surfaces from contamination and moisture for ground operations and during launch.
The x-ray mirrors are mounted on a bulkhead in the forward section of the structure. The CCD detectors, together with a shutter and a filter wheel mechanism, are mounted on the focal plane bulkhead, which is part of the rear section of the structure. Each CCD is cooled by a passive radiator which is mounted on the outside of the structure and connected to the CCD cryostat by a thermal link. The thermal link is rigidly clamped for ground handling and launch activities and released in orbit to create thermal isolation between the CCD/thermal link assembly and the cryostat structure. Signal processing electronics for the CCDs are also mounted on the focal plane bulkhead.
The instrument incorporates an on-board command and data management electronics with a 60 Mbyte mass memory sufficient to store 24 hours-worth of scientific data. The command and data management system (CDMS) electronics, the 60 Mbyte mass memory and the power converters and power distribution unit are housed in the electronics compartment, which is mounted on the side of the aft section. The CDMS is designed around four identical microprocessors, one for control and data formatting, two for processing events - one for each x-ray telescope, and the fourth in redundancy. All spacecraft and internal interfaces are redundant. On-board software is held in PROMs. All electrical interfaces to the spacecraft, including spacecraft power,timing and commands are in the electronics compartment. Power and commands are routed through the power distribution unit and CDMS, respectively, to the other sub-systems. Heat from electronics units is radiated directly to space via a high emissivity surface on the electronics compartment.
The attitude monitor is mounted on the outside of the forward section, together with a stray light baffle, whose aperture is kept closed prior to launch, by an extension on the JETX door. The drive electronics are integral with the attitude monitor; signals are transferred to the CDMS unit for processing and transfer to the Spectrum-X telemetry.
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