The instrument module houses a suite of six instruments:

• Wide-Field Imager – WFI
• Hard X-ray Imager – HXI
• X-ray Microcalorimeter – XMS
• High Time-Resolution Spectrometer – HTRS
• X-ray Polarimeter – XPOL
• X-ray Grating Spectrometer – XGS

Sectional view of IXO instrument module. Credit: ESA

Since the X-ray beam from the optics module cannot be folded in the manner typically used in visible-light telescopes, five of the instruments (WFI+HXI, XMS, HTRS, or XPOL) must be rotated into the focus, with only one operating at any given time.

The XGS views X-rays that have been diffracted out of the main beam by gratings, onto a CCD camera at the side of the main focal plane – it operates continuously. The HXI sits behind the WFI and views high-energy X-ray photons that have passed through the WFI's focal plane.

The four instruments / instrument combinations that must operate at the focal point of the main beam will be mounted on a revolving platform with four stops, moved by redundant motors. The movable instruments will have their own fine-focussing mechanisms to allow them to compensate for changes in focus between ground testing and the flight environment.

The XGS CCD camera will have a lateral fine-positioning mechanism so that it can be centred on the X-ray diffraction beam coming from the gratings. The gratings will be located at the end of the fixed telescope structure nearest the service module, or in the service module itself.

All the instruments will be protected from incoming protons in the energy bands of interest by magnets, positioned close to the detectors.

On the platform mounting the movable instruments, the five instruments will need to have electronics boxes housing their signal processing systems – these need to be close to the detectors. Once the sensor signals have been digitised, the data can be sent to additional electronics housed on the underside of the fixed part of the instrument platform. From there the data is sent to the service module for storage and transmission to Earth.

The electronics on the movable instrument platform will be cooled by means of heat-pipe connections to a radiator. The instruments may have their own radiators looking to deep space. The electronics on the underside of the instrument module will also be cooled with heat pipes and a radiator.

A fixed sunshield attached to the instrument module will keep the instruments in shadow at all times. The limitation of spacecraft roll (± 10 degrees) and pitch (± 20 degrees) with respect to the Sun line somewhat simplifies the task of stabilising the thermal environment for the instruments. 

Deployable telescope structure