Early one morning, we wake up, attach ANITA to the hoist at the top of the hangar and slowly carry it outside and lower it onto the deck, a piece of plywood in front of our hangar. The BOSS--a vehicle designed specifically for lifting 5000-pound payloads such as ours, attaching them to balloons, and launching them--comes over and picks up ANITA, and slowly drives out to the launchpad.
The launchpad is a 1-mile diameter circle of snow packed by the [NASA CSBF] staff. Another piece of plywood sits out on the snow, the dance floor, and that was where ANITA was headed. The BOSS lowered her down and we started our tests.
The first thing to check was whether we could communicate with our instruments onboard ANITA. Thanks to our friends at CSBF, we have four ways of doing this: through antennas pointed directly at receivers where we are and through satellite links that beam data up to the satellite and then back down to CSBF headquarters in Palestine, Texas, and then back to us via the internet. Some of these connections are faster than others, but it's nice to have a backup way to communicate to the instrument. After a little back and forth trying to get everything setup, we were taking data.
What data were we taking? We hooked up about half of the antennas. The antennas are read out through electronics boards that convert the analog signal to a digital signal. They are fast electronics, that record voltages coming from the antennas every billionth of a second. We also have amplifiers that allow us to read out signals as small as a millionth of volt. This is helpful, because the expected signal from a neutrino is a short electrostatic burst that is attenuated as it propagates hundreds of kilometers from the ice up to the payload.
The day we went out to dance, we pointed another antenna at ANITA. Through this antenna we sent pulses similar to what we expect from neutrinos and cosmic rays. We can check several things with such calibration pulses--how in sync all of the electronics are that read out all 48 antennas and how good our GPS signal is. We also tested another pulser that will be launched on a smaller balloon after we launch ANITA.
We do a lot of this pulsing. In fact, that's what we've spent the last two weeks doing in the hangar. We can pulse directly into the RF channels inside, but we have to go outside to transmit signals from one antenna to the payload, because the hangar would reflect and amplify signals inside too much.
Pulsing is also why I've lately been traveling to Siple Dome and WAIS Divide, places deep in the middle of nowhere. There we can calibrate the instrument free from any other sources of noise, and while the payload is in flight.
The day was a success. We were able to see pulses in all the channels we hooked up, from both the ground antenna and the balloon-borne won. Now we're just waiting for our next big test: the hang test that will qualify us for launch.