The last few days have been so momentous that there hasn’t been a spare moment to post about it. Now that leaves me the challenge of summarizing recent events!
With the total system coming nicely together, we set ourselves a goal of performing a compatibility test with CSBF by the end of the week. Compatibility is the last major task before declaring flight readiness. It involves hanging the balloon gondola from the launch vehicle and performing mechanical, electrical, and communications tests to ensure that all interfaces will work correctly on the flight line. Given the science instrument’s reliance on CSBF equipment for commanding, telemetry, ballast, launch, and cutdown, it is a crucial test for ensuring a successful flight.
With that goal in mind, we set about checking off the final few little items on our checklist. Wednesday morning we rolled outside early to gather a little bit more data from our aspect systems–our differential GPS, our precision magnetometer, and the magnetometer we use to point the gondola relative to the Earth’s magnetic field. Unfortunately, just when we got lined up with our north-south reference, the venerable back tire on the gondola cart exploded!
The CSBF mechanical crew volunteered to find a new wheel for us over lunch, but without the ability to maneuver the gondola, we had to postpone the pointing tests. With that task tabled, we asked the CSBF electronics crew if they could mount the SIP, the electronics package which rides underneath our gondola and handles all of the communications. Despite the extremely short notice, seemingly the entire CSBF crew appeared instantly at our gondola and set to installing the SIP and its many accessories. Installing the SIP occupied most of the rest of Wednesday afternoon, but the task went smoothly and we confirmed that all the interfaces worked flawlessly. One of the advantages of legacy hardware and flight code is that the bugs have been worked out many flights ago!
Wednesday afternoon and Thursday morning we spent on some thankless, tedious, but crucial jobs: tightening all the jack screws on all of the cables not yet firmly connected. While we are testing the system, we leave the cables plugged in through friction alone. Sometimes this causes a cable to work lose and give buggy readings, but it’s far easier to determine that and plug it in again than it is to screw things in and out every time we need to make a small change. Still, it leads to a Augean task at the end. Many of the screws–particularly on the flight computer–are very difficult to access. Others are bent, twisted, or nearly stripped. We got everything fastened eventually, though, so the cables should remain secure for flight.
Two other small tasks proved time consuming. We distributed small temperature sensors throughout the gondola, taking care to place them as on the previous flight. We also installed the mylar solar shields which surround the instrument cradle and deflect the extremely bright visible sunlight at float.
With the SIP in place, yesterday afternoon we were ready to check the final balance of the gondola. One more piece remained to be integrated, though: the SIP cage. This metal frame mounts under the gondola and helps protect the SIP from damage on landing. On our last flight, though, we landed directly upright, and both the SIP cage and the SIP were crushed. When our machinist at SSL rebuilt the SIP cage for this flight, he changed the mounting of the cage as well. Before, it hung on brackets from the bars at the base of the gondola. In an effort to strengthen the gondola and improve the cage’s strength on impact, the new version slides over pegs that stick out the bottom of the gondola frame.
I’ve been worrying about those pegs since I first laid eyes on them. I knew if they bent, we wouldn’t be able to get the SIP cage on, and we’d have precious little chance of repairing the pegs. We’ve taken great care to keep the pegs off the ground and out of trouble, and we’ve been successful. The SIP cage itself has mostly been in storage, out of the way.
Yesterday, though, when we went to slide on the SIP cage, it didn’t fit. The front two tubes were more than an inch out of alignment! Whether due to the heat in the container or pressure in transit, at some point the cage had warped. In an instant, we went from planning for compatibility the next day to being unsure if we’d need to rebuild the cage. Despondent, we went home to sleep on our options.
This morning, we had some lengthy discussions with the CSBF mechanical crew. The approach we converged on was to jack the cage arms outwards with a 4×4 and a hydraulic jack. The original hope was to push the arms beyond our desired length and create a permanent bend, but we quickly found that the cage just sprung back to its original dimensions. Instead, then, the CSBF crew cut a 2×4 to length and wedged it into the arms.
After finishing some tests of the instrument electronics, after lunch we took a deep breath and tried to fit the SIP cage again. We installed tapered tips on the pegs to help guide them in, applied plenty of grease, and then used the gondola weight to lower the gondola onto the cage. Everything came together so smoothly it was hard to remember that there’d been any problems! Elated, we finalized the placement of the ballast hoppers before taking the cage off.
With the problem of the SIP cage solved, we’re now ready for compatibility. Unfortunately, another problem looms: the weather. There have been frequent thundershowers the last few days, and the ground outside the hangar is too wet to drive the crane. Also, since there are more showers in the vicinity we’d run the risk of getting caught out in the rain. So, we’ll hold off on compatibility until probably Monday. It’s no great loss, as the airport is too wet for TIGRE to launch, either! We’re all in a holding pattern, then. We’ll use the time to catch our breath, perform calibrations with our recently-arrived sources, and finalize our observation planning.
On interesting side effect of all this rain: we’re seeing the Todd River in flood a second time!