A trio of Lens R&D Sunsensors is changing temperature under vacuum at a speed that surpasses that of a real satellite.
The plot shows the temperature profiles achieved for the BiSon Sunsensors in frame of the ongoing ESA life testing qualification and the MAUS Cubesat Sunsensor.
Contrary to common high speed cycling (which is generally performed under a nitrogen atmosphere) these tests are performed under vacuum. This is done in our dedicated Sunsensor thermal vacuum (TVAC) test facility. The facility can hold up to 9 Sunsensors simultaneously and is controlled by a fluid loop controlled hotplate.
Custom developed for Lens R&D by Vacutech (Delft the Netherlands), the VaB facility consists of a small vacuum chamber and thermal controller.
Due to the dedicated design, the unit is capable of cycling from -40°C to +80°C and back in less than 1 hour.
As low Earth orbiting satellites typically take 90 minutes to circle the Earth, this is faster than the rate of change a real satellite would experience. As a result the test can be considered an accelerated life test. The complete qualification will consist of 1000 thermal vacuum (TVAC) cycles between -40°C and +85°C followed by another 1000 TVAC cycles between -45°C and +105°C. Calibrations before during and after the test will serve to show the stability of the sensor performance.
In order to limit the stress on the MAUS (which is specified for qualification at -40°C..+80°C we deliberately limited the thermal contact between the MAUS and the hotplate. This causes the MAUS to trail the BiSon sensors in temperature despite the lower thermal mass. (currently cycling between -33°C and +81°C) It is an interesting experiment to test the resilience of this new member of the Lens R&D Sunsensor family. If the sensor meets the accuracy requirements after this test it is obvious that the sensor is very well suited for use on board of any Cubesat.
The more critical test for the MAUS will come during the second 1000 cycles as these will take the MAUS well beyond its design temperature range. How much is unclear but it would not be unexpected if the high temperature will exceed 95°C during that test. So if it would break it would not be an issue, if it survives the MAUS will probably be the best qualified Cubesat Sunsensor in the world. (both for radiation and thermal cycling)
The MAUS has been TVAC cycled 135 times between -40°C and +80°C before, so the qualification testing was already performed (on the same unit). The qualification thermal cycling will last a number of months. As the VaB can test 9 sensors at once, it was decided to take advantage of the opportunity and have a MAUS qualification unit cycle along with the BiSon sensors during their qualification. (as added proof of quality is never a waste)
For now, the first 500 TVAC cycles have been finished and the forward voltage of the new diodes remains extremely stable as an indication that the sensors will probably still perform as before. The next calibration is foreseen in a couple of weeks so look out for some updates on this post.
ISISpace (www.isispace.nl) has selected the MAUS for their new high reliability core AOCS system. Several Sensors have therefore been designed in already and are awaiting lauch. This means the flight qualification for the MAUS is expected before the thermal cycling is finished ensuring that a radiation hardened Cubesat Sunsensor is available to the market at TRL9 level before Q3/2021.