Day 24 (Thursday, March 15)

Yesterday we made the difficult decision to cancel our launch.  Our condition: we have 4-5 working detectors out of seven.  Of these, three survived the cooling accident, and there are concerns that there could be cracks in the readout electronics that may get worse under the vibration of the rocket launch.  There are two new detectors, however, our calibration data for these is minimal (limited to what I could measure in half a day!)  Taking these things into account, it was decided to start over building our detector system from scratch.  This will probably take 3-6 months, so we will try for a new launch in the summer or fall.

I've gotten a lot of questions, so here's some detail of what went wrong in our cooling accident.  We have a cooling regulator that controls the flow of liquid nitrogen to our system.  You can program it to cool to whatever temperature you want.  It knows what the actual temperature is from a temperature sensor inside our system.  Here's the nice part: based on the difference between the actual temperature and the programmed temperature it decides how much nitrogen to allow into the system.  So you can essentially dial in the temperature you want and walk away; it takes care of the rest.  Except, as I found out, you shouldn't do this because it can make a mistake!  It turns out that if the temperature sensor is temporarily disconnected (i.e. if you unplug it and plug it back in) then things go a little haywire and the cooler does not behave properly.  In this case it got confused about what the temperature was and started dumping way too much nitrogen in our system, resulting in much lower temperatures than our system can tolerate.  This actually cracked a couple of components on our detector board, which are not replaceable.  Long story short, we're starting over by building new boards.