Environmental Testing Campaign: Thermal Days 1 and 2

Good morning from the thermal testing team of PROVE Pathfinder from ESA’s CubeSat Support Facility in Belgium!

On Tuesday (11th April) we arrived on site ready to get our payload out of the oven and start our campaign. Following a safety briefing, we got into clean room attire in a process we’re becoming very familiar with – Gloves, Hairnet, Beardnet (if needed), Gown, Shoe Covers, and finally cleaning with IPA everything that we take into the cleanroom with us. We also needed masks to reduce moisture contamination of the baked-out payload.

Our first action was to remove PROVE Pathfinder from its 40 degree, 52 (ish) hour bake-out.

Figure 1: Our first sight of PROVE in a week
Figure 2: Opening the oven post bake-out

We performed a visual inspection, and then it was time for our post bake-out, pre-TVAC RFT (Reduced Functional Test). The result of this is shown:

Figure 3: Terminal output (condensed) for the pre-TVAC RFT. Both cameras fail to connect and establish an interface.

This unfortunately meant something on each camera was damaged by the bake-out and we needed to investigate further.

We did a connectivity test on the Basler harness and, combined with the visual inspection, we found the issue. In the magnetics adapter. The first image is as we saw the pin, and the second looking back into the pictures taken last week.

Figure 3: Inspection image with highlighted pin of concern
Figure 4: Inspection image following X axis vibration

When pressing the pin to ensure connectivity, the visual camera connected correctly. Our preliminary rationale for this was a crack formed in the solder during vibration, then the low vacuum of the bake-out forced expansion.

Turning to the Tau, we tried several fixes, unsuccessfully and had to resort to removing the aperture plate. On doing this, we were delighted to discover that the issue of the Tau had been resolved. We then put the plate back onto the camera, and the connection issue of this camera continued to be resolved. Following some discussion, our preliminary rationale for this was the cable (which is pretty taut in normal assembly) was displaced as a result of the combination of the vibration testing and the bake-out, leading to the unpredictable connection we observed.

Thus we set about devising a plan to fix our remaining connection issue – the Basler. Since the solution involved soldering outside of the cleanroom, we had to bag the payload up to preserve as much of the bake-out as possible. This looked remarkably like performing surgery – with the payload in an ESD safe bag, a scalpel to open the hole, and yellow Kapton tape to seal the rest of the structure away.

Figure 5: “Surgery” on the payload in preparation for soldering

In fixing the connection, we initially bridged a connection. In fixing this, we managed to dislodge another pin. This was then the end of day one. The start of day two saw us with a plan to fix the outstanding issue, and get the payload into the vacuum chamber. In reseating the pin, one of the small wires from the magnetics IC was detached – we tried to resolder it, not expecting it to work and it didn’t. We also took the precaution of putting the spare payload computer we brought to Belgium into the bake-out oven (along with the PTFE adapter plate we intended to use, to better understand its response to temperature changes).

We then made the unfortunate decision to have to replace the payload computer – to which the magnetics module is attached. This involved several soldering operations, as well as the disassembly of a large amount of the structure.

With everything fully assembled again, we were able to successfully run our software test (this time an FFT (Full Functional Test), since we had replaced a significant amount of the payload).

Figure 10: FFT following changing payload computer. The Basler FFT fails due to cable connection
Figure 11: Basler FFT fixed cable interface after the FFT fixed

With a now fully functional payload, we began to install temperature sensors and mount the payload ready to transfer to the vacuum chamber. We had to swap from the planned PTFE plate to our aluminium plate used for the vibration test due to the faster thermal response time this would have.

Figure 12: PROVE Pathfinder mounted on the aluminium plate, with temperature sensors installed
Figure 13: PROVE Pathfinder in the TVAC chamber, with test harness and test sensors linked to the DAQ system

Following the installation process, and a successful test of each camera, we started the pump-down process to a low vacuum (in the region of 10-2 mbar) which would run overnight – and thus day 2 was concluded.