To begin: news of the rotor. When we found out last week that our rotor was not qualified for our gondola’s weight this flight, we returned it to Berkeley for a “pull test.” As the name suggests, the test consisted of gripping the rotor from both ends in a machine and pulling–with 50,000 pounds of force! Yesterday, we learned that the rotor had passed the test without any catastrophic failure, so we can fly without cutting weight. However, the yokes and pins we use to connect the rotor to the balloon above and the gondola below were bent during the test. Accordingly, Berkeley is making new yokes and ordering new pins. Hopefully the rotor will return to us very soon!
Update, 4/30: A closer inspection of the rotor in Berkeley found a cracked component. This is going to impose a significant delay…
As we wait, we’re dealing with lots of odds and ends. On Monday, we got the flight computer interfaced with CSBF’s commanding computers (on the first try!). Daniel has been heroically taping temperature sensors all over the gondola. Alan and I are continuing to debug the flight computer and ground control program. Justin is working on our analysis software. Zhong-Kai is keeping track of the card cages. And Mark is talking to all the CSBF personnel and keeping us on track.
Today the wind was a bit lighter, so we attached the solar panels and pushed the gondola outside (waaaaay outside) to test the solar power system and to calibrate our differential GPS. Both systems performed flawlessly!
Our other task has been to calibrate the efficiency of the telescope. We do this by placing radioactive sources in the field of view of the instrument. These sources emit gamma-ray photons of specific, known energies. Since we know the activity of the sources–the number of photons they emit per second–by placing them at a specified distance and counting how many photons we observe, we can calibrate the efficiency of our telescope. (This is called the “effective area” of the telescope; its maximum is the geometric area of the detectors, which would happen if all photons hitting the detectors were observed.)
Since the efficiency varies with energy and throughout the field of view, we have quite a few calibration measurements to take. We need fairly precise knowledge (~ a few centimeters) of the position of the source relative to the detector for these calibrations, which is hard since the source is several meters in the air! To find the positions, we use a theodolite–a surveying instrument which measures angles. The last few days, I’ve been training the other students to use the theodolite, and we’re all taking turns doing late shifts to take data.
The latest CSBF weather reports indicate that turnaround–the period when the upper atmosphere winds are still enough for long flights–is still about a week and a half away. There’s some definite jockeying for position in the flight queue happening–come on, rotor!