More radiation-resistant active pixel sensors for vision-based navigation

Precision planetary landing missions typically rely on the use of vision based cameras as one of the main navigation sensors. The detector choice for such applications can have a dramatic impact on the performance of the unit but also on its development and qualification effort and other key parameters. While most Active Pixel Sensor (APS) products developed for space to date have been optimised either for star tracker applications or for payloads, these typically have slightly differing requirements to navigation cameras.

Due to the low volume of units needed, it is not considered cost effective to develop a bespoke sensor for navigation sensors, as such a new activity with TDE and Jena Optronik, Germany, has assessed the applicability of the latest generation of APS detectors for navigation applications.

This activity could have applications in three areas of navigation: Absolute Navigation (matching visual landmarks with a reference map to estimate a position in a planetary fixed frame); Relative Navigation ( tracking unknown landmarks to estimate a displacement or velocity in a planetary-fixed frame); and Hazard Avoidance (a subsystem identifying hazards in the vicinity of the targeted landing site such as rocks, terrain roughness, shadows or slopes, and providing a guidance solution to re-target the spacecraft towards a safe landing site).

Specifically, it can be applied to landing applications for potential future ESA missions.

The activity is intended to characterise additional detectors to the ones developed by the agency (HAS3 and Faint Star) to help improve not just navigation cameras but also possibly Star Trackers.

It included an assessment of the trade-off between snapshot shutter and rolling shutters and a comparison of potential APS sensors to determine their suitability for space.

Eventually, the Teledyne e2v APS CMOS detector CIS120 (Capella) was selected to undergo the radiation test campaign, which it successfully passed, although it did show some degradation in the Total Non-Ionising Dose test. This detector is expected to be used for several scientific or earth observation missions. Since these tests were run, a new version of the component was produced and was also tested and is expected to give even better results.

T305-404EC closed in 2020.