Last weekend finally everything was prepared for the thermal chamber test. Previously we made a complete system test at room temperature. Only a minor bug was found at the SD Card handling. The root cause was the lack of free RAM in the microcontroller. We refactored the code and now it is reliable.
During the thermal test we reached -16°C (3.2°F) which is the expected temperature inside the insulation box. We used our GPS signal simulator to provide 'real' GPS signals for the system during test. The test setup can be seen below:
The system was running on batteries (The PSU is for the thermometer of the chamber)
The tests were run:
Cool down test: start at +28°C (82°F), cool down to -16°C (3.2°F) while running
System cool down: system was left at -16°C (3.2°F) for 30mins while not running
'Cold start': start at -10°C (14°F), cool down to -16°C (3.2°F) while running
Warm up: temperature was risen from 16°C (3.2°F) to +28°C (82°F) while running
One bug was found during test:
GPS module was regularly restarted under -6°C (21°F). This is related to the wiring of supply lines and was previously fixed in other sub-systems. The GPS module only failed in the thermal chamber, this bug wasn't caught during tests at room temperature.
We have already found a solution by rerouting the supply lines around the EPS module. We will apply the modifications to the Engineering Model this week. A complete system test will be conducted at room temperature on Wednesday and another thermal test is scheduled before our Xmas break