Editor’s Note: Welcome to ANITA, the Antarctic Impulsive Transient Antenna! From October to December, Katie Mulrey is traveling with the ANITA collaboration to Antarctica to build and launch ANITA III, a scientific balloon that uses the entire continent of Antarctica for neutrino and cosmic ray detection. This is the sixth installment in a series, “Neutrinos on Ice,” documenting that effort.
Launch day finally arrived. The winds were low, and the forecasts were promising for a great neutrino-detecting balloon launch. This was ANITA's sixth attempt at launching. Everyone was more than ready to bid the balloon farewell. Until the balloon and payload are airborne, the scientific team has little to do on launch day. The launch is in the hands of the CSBF rigging, electronics and weather teams.
The balloon is launched from a huge vehicle named “The Boss,” behind which everything necessary for flight is laid out in a long line. First you have The Boss holding the payload on a crane. Next comes a parachute that will be used to bring the payload back down to the ground when the flight is over. Attached to the parachute is the balloon (seen in a pink wrapper in the image above). The balloon is made out of a material similar to a plastic grocery bag, so it is very delicate! Once it is taken out of the wrapper there is no going back, because trying to repack the balloon might cause some damage. We were waiting for the news that the wrapper had been opened. Then we knew launch was immanent.
Only the tip of the balloon is filled with helium. That is enough to lift the two-ton ANITA to 36 kilometers, where it will take data. The entire balloon will inflate to the size of a football field once the balloon rises to lower density atmosphere. Helium is inserted into the balloon through two long plastic tubes that get tied off after the correct amount is added. That balloon can lift the whole payload, so a lot of work goes into keeping it on the ground before the launch.
At launch time, The Boss starts driving the balloon and payload in the direction of the wind. It lets go of the payload and the balloon begins to rise in the air. The timing is very hard to get right! If you hold the payload too long the balloon will pull too hard and could tear. Too early, and you drop the payload onto the snow. Talk about exciting! There was a lot of cheering as we watched the balloon float away.
Now it's data time. There are hard drives on ANITA that are constantly writing data, but we can't access that until the flight is over, and then only if the payload can be recovered. (In some cases the payload will fall into water or be covered with snow, so we can't get it.) We record lots of radio signal data, only a small fraction of which is really a neutrino or cosmic ray. We send down data we think might be really important via satellite. At the beginning of the flight we also have “line of sight” access to the balloon, meaning we can talk directly to the instrument with radio communication before the balloon goes over the horizon. After that we rely solely on satellite communication. ANITA collaborators watch the data stream 24/7 to see if everything working properly. We monitor the temperature of the instrument, voltage and current levels, and plots of the radio data coming in.
If the signals from our 48 antennas match up in the right way, we know we have a neutrino! We spend months after the flight carefully analyzing the data to be sure we know what we saw. ANTIA has almost made one circle around Antarctica. If we are lucky, we might get two more circuits. The more data we collect, the better.
For so long, we thought of ANITA as a mammoth science instrument looming in front of us. It looked so small floating away into the atmosphere. It's amazing that that payload will shed light on the highest energy particles on Earth.