We students did some real brawn work yesterday–lifting our battery boxes into the bottom of the ebay. It was a tight squeeze, but we got them settled in and strapped down securely. Since the gondola was well-balanced with the added weight in the back, we were free to move on to a much-anticipated task: rotation tests. While we’ve solved the problem that caused our pointing problems on the last flight, we’d really like to be sure that the rotation systems are as stable and repeatable as possible before flight.
As we started wiring up the pointing hardware, though, Steve noticed a problem: the lights on the computer module which drives the servo motor weren’t on. The flight computer indicated the board was working, but flipping the external switches didn’t change the lights’ state as it should. Since we use those switches for flight-line checks–and it’s a crucial module–we needed to figure out what was happening.
Unfortunately, the electronics driving the pointing system were designed by engineers at another university, twenty years ago, and poorly documented. Steve traced through the schematics and pinouts as best he could, and determined that either a small voltage regulator was blown or that the supply voltage wasn’t coming through the backplane. Maybe a cable had been pinched in transit? A bit of testing established that the regulator was fine. Unfortunately, to test the supply voltage we’d have to pull the heavy flight computer case out of the bay–it’s a tight squeeze even without the delicate signal cables lining the side. As I pulled out some of the impeding cables, Steve asked, “I wonder if there might be a switch that controls that power line?” With that, he flipped a heretofore-obscure toggle switch–and the lights came on.
With the “light switch” now appropriately labeled, we were able to pick up the gondola and do rotation tests! All the systems worked flawlessly, and even the fairly crude tests we were able to do in the hangar produced repeatability at the tenths of a degree level–easily better than our needed pointing accuracy.
Overhead, the winds at float are great for flying. On the ground, though, the mighty cyclone is still keeping low-level winds too high for launching. TIGRE might get an opportunity yet this weekend.