Although the description above has made reference to the science instruments, they are not regarded as parts of the spacecraft, X-ray telescope, or science instrument modules. However, when the two focal plane science instruments, the High Resolution Camera and the AXAF CCD Imaging Spectrometer are fixed in the focal-plane positioning assembly in the science instrument module, the overall system is renamed the Integrated Science Instrument Module (or ISIM), and it is in this guise that the module appears on Figures 1 and 2.
The other two science instruments are the High-Energy Transmission Gratings and the Low-Energy Transmission Gratings, which are attached to the X-ray telescope by the support structure assembly.
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