These linear arrays consisting of 2 x 512 pixels in staggered configuration are based on loophole diode technology with detector electronics on a hybridised detector assembly. Their operating temperatures are 80 K for the TIR and 105 K for the MIR channel respectively.Based on experiences with a airborne laboratory model using a split stirling cooler design the detector assembly was optimised regarding stray-light suppression and power needs to meet the radiometric requirements and to cope with the limited resources of the micro-satellite concept. A detector assembly for military applications (see figure 2) was modified into a space-qualified solution.
The main aspects of the sensor design are:
This system consumes 11 Watts which is a factor of 4 less in comparison to a split cooler concept.
Figure 3 provides the main constructive aspects of the integrated detector cooler assembly.
The design of the flight configuration of the HSRS is driven by strong requirements of the co-alignment stability in the line-of-sight of the MIR to the TIR channel (±0.2 arcmin at duty cycle). It is characterised by the following attributes:
A serious problem of the push-broom sensor, especially in the TIR region is the radiometric stability of the detector elements during the data records which can not be covered by laboratory ground calibration. Hence is it essential to add an in-flight calibration device.
Thus the HSRS has black body units as temperature reference targets in front of the IR-lenses which can be exposed to the complete field-of view at the beginning and the end of the data records. In the passive periods this device serves as protection cover of the optics against contamination and undesirable cool down. The inherent total failure risk is minimised by a separation mechanism that rejects the cover system in the case of emergency.Figure 4 provides the overview of the MIR/ TIR sensor head design and figure 5 gives an impression of the flight hardware completed by thermal control components like radiators and multi-layer insulation.