The COSI team’s time at CSBF in Palestine, TX is already wrapping up! I wanted to provide an overview of why we temporarily moved our experiment here before heading to Wanaka, New Zealand for the COSI 2020 launch.
The COSI team is able to run the instrument in its full capacity in Berkeley. We routinely study the detectors’ performance, characterize their spectral and noise properties, perform calibrations to benchmark the instrument’s capabilities, repair and improve existing electronics, and develop new analysis techniques for our scientific data. What we do not possess, however, is the ability to fly. For that, we rely on our collaborators at NASA.
Launch success relies on the symbiotic relationship between the COSI team at SSL and the talented teams of scientists and engineers affiliated with NASA who develop the super-pressure, or ultra-long duration, balloon (ULDB) and its underlying systems. The Wallops Flight Facility in Virginia operates NASA’s Scientific Balloon Program and works with CSBF to prepare its balloon payloads for launch.
The primary goal for COSI in Palestine is to pass our “final compatibility check” with CSBF’s technological contributions to the mission. We have spent the past several weeks “integrating” our instrument into its normal, Berkeley configuration and are uniting it with CSBF’s power system, telemetry streams, GPS, solar panels, and more. When both teams are prepared, we will hang the gondola outside with all systems attached to check that they perform as expected and are compatible, hence the name, with each other. Passing compatibility is a significant milestone in the campaign as it brings us one step closer to launching in Wanaka with confidence.
Thermal vacuum test
As I mentioned in my last blog post, Hadar, Nick, and I drove the COSI cryostat from Berkeley to CSBF in order to keep it cold and running smoothly. The first task upon arrival was to check the functionality at flight pressures of two new high voltage filters installed on the cryostat early last year. Electronics are susceptible to voltage breakdowns at low air pressure and by locking the cryostat in CSBF’s thermal vacuum chamber for five days and four nights at approximately 1-2 mbar (slightly lower than our nominal flight pressure of 6-8 mbar) and cold temperatures, we were able to monitor the performance of the new filters in a simulated flight environment. We observed no voltage failures and believe that the cryostat is in good working order for flight.
After the vacuum test we proceeded with calibrations and a variety of integration tasks. With Clio’s help, we performed a more thorough calibration of our shields that revealed position-dependent energy thresholds. Setting these thresholds more accurately will improve the quality of our data collection and our simulations.
We also ramped up high voltage (1000-1500 V) on each of the 12 detectors in the cryostat and verified that their spectra and noise levels matched our expectations from data taken in Berkeley. These measurements were taken “on the bench,” as we call tests done with the cryostat on a table rather than mounted in the gondola, which enabled us to minimize noise through minor adjustments to our then-accessible cryocooler configuration.
Satisfied with the performance of our individual components on the bench, we lifted the cryostat into the gondola with a crane, mounted the card cages that house our read-out electronics, took data comparable to that taken on the bench, installed GPS antenna booms and batteries for our power system, performed a GPS calibration outside on a particularly beautiful day, coordinated with CSBF to prepare telemetry systems, and are currently working through final tasks leading up to compatibility. I can’t possibly list every undertaking, but I can assure you it’s been quite busy around here and we are getting more and more excited as we move closer to launch!
Other COSI activities
We firmly believe in taking necessary breaks from harnessing cables, cutting foam, and testing detectors. Most often these breaks involve food. Sunday brunches at the Queen St. Grille, countless taqueria lunches (and $2 breakfast burritos), dinners at Switch and Pint and Barrel, delicious dinner parties together consisting of chicken piccata, beef bourguignon, roasted vegetables, Blue Bell ice cream, chocolate icebox pie courtesy of Oxbow Bakery & Antiques in Palestine, and more have kept us moving forward. Unfortunately, watching the 49ers lose in the Super Bowl was not as much fun as watching “Mean Girls.” Watching “Joker” also yielded fewer laughs.