Radiation Susceptibility Trials on COTS Cameras for International Space Station Applications

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1 Radiation Susceptibility Trials on COTS Cameras for International Space Station Applications Massimo Zampato, Roberto Finotello, Roberto Ferrario, Alberto Viareggio (Tecnomare) Sergio Losito (Agenzia Spaziale Italiana)

2 STEREO VISION MEASUREMENT SYSTEM Italian Space Agency (ASI) Proto-Flight qualified model computer vision technologies for the space, design to be integrated with a robotic sensor subsystem computer vision SW libraries for tracking of moving object with realtime pose measurement, based on model based tracking algorithm

3 SVMS functions for Planet Exploration Mission measurement of geometric characteristics and pose of object/structure to allow for inspection and remote manipulation operations geometric measurement of the environment for autonomous navigation in unknown environment of rover or Lander measurement of the soil to create 3D-maps from onboard the rover

4 Tecnomare is endeavouring the space qualification of a suitable off-the-shelf camera Sony ST70. The task includes several issues to be dealt with such as their mechanical validation (vacuum, thermal and vibrations) currently going on at CISAS premises (Padua) and their radiation tolerance validation. Imaging Unit

5 The TID (Total Ionizing Dose) has already been examined at the ENEA Casaccia premises with 60 Co Gamma Rays tests under ESA (European Space Agency) specifications. Radiation Test SEE (Single Event Effects) Considering the reference environmental conditions (ISS), the most important effect is by far related to the trapped proton, being ISS in low orbit. This investigation is however the only one feasible (no heavy ion possible) for a COTS where no delidded component included in the camera COTS itself is available due to the penetration thickness of such ions.

6 TID Test Two Sony cameras have been tested to TID: camera A was to test tolerance to radiations up to fatal failure; to record the highest TID before camera image can no longer be processed by computer vision algorithms camera B was to measure parameter modifications after exposure to the TID level expected for the mission reference time (1 year). Unit Dose Rate TID A 200 Gy hr -1 To failure B 0.6 Gy hr Gy (Si)

7 TID Test Report Camera A Camera A had a first failure at 643 Gy (Si), when the image suddenly became pitch black but the camera video output was still a valid video signal. Next definitive failure occurred at 7820 Gy (Si). The test was considered ended after the first failure according to the test policy.

8 TID Test Report Camera B Camera B withstood the whole test. The images of the reference target (a white PVC sheet) acquired all along the test duration showed a general progressive darkening. Image n TID Mean Grey Level 1 0 Gy (Si) Gy (Si) 71 To analyse and split the CCD radiation spoilage effects from the outer factors, a physical model of the light flux acquired has been elaborated.

9 TID Test - CCD illuminance spectrum Numerical integration of the curves points out an overall difference of 12.3 % in the light flux on the CCD prior and past testing accounting for lens and protective glass darkening λ [nm] 0 krad(si) 3 krad(si) The difference directly measured on the images turned out to be 13.4% accounting for all effects. The gap accounting for the camera spoilage only is then 1.1 % thus leading to the conclusion that the camera underwent no meaningful spoilage due to radiation during the test.

10 TID Test - CCD illuminance Temporal variation Temporal variation of illuminance difference between pixels of a row and corresponding pixels of reference image in light conditions Temporal variation of illuminance difference between pixels of a row and corresponding pixels of reference image in dark conditions

11 Single Event Effect Nominal Mission Integral Flux Maximum Solar Flare Peak Integral Heavy Ion Flux Maximum Solar Flare Orbit-Averaged Integral Heavy Ion Flux Daily-Averaged Internal Proton Integral Flux from Trapped Protons Most frightening SEE: latch-up or gate rupture for MOS devices The ISS mission is however a low orbit mission where the most important effects are by far related to the trapped protons, mostly because they are the more troubling particles as to the semiconductor bulk damages due to their high capability to penetrate and ionize the silicon with respect to other ions having the same energy level.

12 SEE Test Main Steps 1. to determine the relationship between the cross-section versus the particle energy or the linear energy transfer (LET). 2. to integrate the estimated cross-section with the proton energy spectrum provided in the ISS reference documents to determine the MTBF (Mean time between failure) as the reciprocal value of the integrated SEE rate

13 SEE Test Facility The SEE (Single Event Effects) tests are scheduled to take place at the INFN-Legnaro (PD) premises in second quarter of They will be carried out by using the ALPI Van der Graaf accelerator: powered with a voltage of 15 MV net proton energy of about 28.5 MeV (in Tandem configuration) Proton beam is monitored through Faraday cups, suitable for high beam fluxes: ranges from 5x10 10 to 1x10 11 proton/cm 2 -s

14 SEE Test Set-up Sony ST70 COTS camera has been spread over a custom framework in a planar configuration so as to allow the proton beam proton to fully collide with every camera board and circuit.

15 SEE Result Analysis and Design Clues MTBF is basically the inverse of the SEE rate MTBF figure lower than that required by the mission can be improved by wrapping the camera surfaces with a metal cladding whose efficiency is proportional to the atomic number of the used metal. A common solution is to use a tungsten cladding, whose atomic number is pretty high. Tungsten vs Aluminum (under the same shielding effect): 20% lighter 80% thinner

16 Conclusion Final goal: validation of the COTS camera Sony ST-70 for the ASI program SVMS in the reference environmental conditions (ISS) by assessing the device compatibility with the mission requirements according to the expected MTBF determined through the test result analysis. Relevant results from TID tests are: first severe failure of the camera occurs at radiation doses much higher (643 Gy(Si)) than the expected mission level of 25 Gy (Si) camera performances are constant prior, during and past the test at a TID of 30 Gy (Si) with no permanent device impairing Results relevant to SEE are due at the end of second quarter of 2004, past the proton tests at INFN-Legnaro premises.