We came back to Armstrong this week knowing we had a fair bit to accomplish, but feeling that on the whole things were going well and we had a plan to fix what we needed to. 7am on Sunday we re-installed a replacement drier for the one that had broken and caused us so much consternation last time we were here. This is a simple mechanical job normally, but with the full rack installed on the plane already we were working on our knees/stomachs in a small hole between two instrument racks, and with other pieces of equipment in the way we had little room to insert fingers/tools to tighten screw etc. On top of this, the consequences of dropping a screw or washer are huge – you cannot have loose pieces on the plane, as they could get thrown about during turbulence/maneuvers, get into an instrument and short circuit things or get out of the plane door and become FOD (foreign object debris – very dangerous around aircraft since it could fly into the propellers and damage things). Therefore it’s essential to find anything that is dropped. Last time I dropped something while working on the rack on the plane it took 3 of us a couple of hours to find it – and you just have to keep looking until you do, no matter how long it takes. This job that may have taken 20minutes in the lab took us over an hour, in which time the plane got very warm from all the instruments and pumps running inside a closed steel tube for this time. By the end of it we felt like we’d had a core workout in a hot gym or similar.
We also had to replace an RH probe that had broken, this was a lot simpler. The drier takes the sample air we pull from outside and removes the water content. The RH probe then measures the relative humidity of the flow of air to make sure the drier did its job. We switched the whole system back on and were very pleased to see that we had no more leaks and everything was working properly.
We put some calibration aerosol into the system and noticed that one of the UHSASs (Ultra-High Sensitivity Aerosol Spectrometers – measures size distributions of particles between 60nm and 1um) was performing sub-optimally. We determined this was because the optics were dirty. This happens periodically as we sample dirty air through the system and bits accumulate on the lenses that make-up part of the optical detection system.
Having confirmed this was the issue, we pulled the instrument from the rack and brought it down to the lab. I secured everything on the rack – tying off lose cables, closing up any ports now open in the plumbing system – while Aga, my colleague who I work on all the ATom mission stuff with – started getting the instrument ready to clean the optics. This is a tough job – you often make things worse before they get better as you moving things you cannot see about on a tiny lens as you try and clean in – and it feels very random. Once you have the basic technique down it’s just a case of being systematic, patient and persistent, and not losing hope that you’re making everything worse instead of better and would have been better off doing nothing. My main job was therefore, as well as trouble shooting with Aga as she cleaned the lenses, simply providing moral support. This is especially important on day’s where you’ve been working physically hard for 8h, and haven’t yet found time for a lunch break. We took turns grabbing a bit of food and kept working away at the optics. Eventually, we got them clean and the instrument was performing well again.
As we were closing up the instrument, ready to re-install the next morning (aircraft access had already finished for the day), the fire alarm went off. We grab our jackets and exited the hangar into the pouring rain and flooded carpark (southern California is experiencing abnormal levels of rain right now, resulting in mudslides and flooded roads). Thankfully it was just dust on a smoke alarm.
The next day the full aircraft and science crew had to test some EMI (electro-magnetic interference) issues that were presumably coming from an instrument somewhere. This commenced at 7am, and we needed the full rack up and running then, so we headed in to re-install everything at 6am before this started.
EMI testing was strange. The plane was out on the ramp, we started engines and transferred power as in a normal flight, but the stayed on the platform for hours as the crew systematically measured frequencies around different instruments, asked us to turn on and off different parts to track down the problem. Mostly I sat looking out at the very unusual snow hitting the tarmac and completed a paper review I need to submit before leaving the US.
With the changes we’d made to the UHSAS, and other parts we’d replaced we really wanted to do a full calibration before test flight the next day. We figured if we had two full hours it was worth trying to get it. At 4pm exactly we were told the EMI tests were concluded for the day, and we had aircraft access until 6pm. Aga and I leapt into action – bringing out equipment we needed and setting up for calibration. We’ve done this pretty often so we have a pretty efficient procedure now. We got set up in record time and had a notably trouble free calibration. Having worked so closely together over about a year now, Aga and I have very good systems of communication and division of roles, which definitely helps us to be efficient and effective with our time, as well as to enjoy our work together. Having a team of people that it’s easy and enjoyable to work with makes the good days even better, and the hard days easier. I’m constantly grateful for this. We were done and off the plane with 10 minutes to spare!
After 12hours working on the plane, and with a longer (7h) test-flight coming up tomorrow, we were in need of an early night. We drove back to the hotel, cooked up some pasta quickly, readied for the flight and called it a day.
It’s been an intense couple of days – lots of precision work in tricky conditions, over relatively long hours – but it’s been rewarding as we fix problems and get ourselves in a better condition to fly. The deployment is coming up very soon and it’s super exciting.
Now we’ve seen how high value the data from the first deployment is, we’re eager to see how measurements this time will relate to that. It’s an exciting time. One more test flight and then we’re off!