The Compton Spectrometer and Imager
The 2020 Wanaka balloon campaign was canceled this week. Everyone on the COSI team is sincerely thankful for the hard work and kind assistance we received from NASA and CSBF while preparing for the mission. We are proud of what we accomplished and are packing up the hangar knowing that we dedicated everything we had to this iteration of a great instrument.
Thank you to those who follow this blog. We wish the best of health to everyone in these trying times.
After only a week in Wanaka we have unpacked our supplies, successfully tested the proper functionality of each detector, checked our electronics readout, collected low-energy calibration data with Am-241, Co-57, and Ba-133, calibrated our shields, started setting up our power system, and installed our liquid cooling system.
Yesterday, we integrated the cryostat and shields into the gondola and are busy routing the constituent array of necessary power and signal cables. We’re assembling the aspect system for our GPS and will soon proceed with more detector checks, energy calibration data collection, another shields calibration to test performance while integrated, and more. In the near future we’ll perform polarization, depth, and cross-talk calibrations. We will also collect effective area data to study how much of the sky our detector can observe. It’s safe to say we will be busy working towards launch.
Fortunately, we have many people around helping. The current team is me, Brent, Carolyn, Hadar, Jarred, Jimmy, Judy, Nick, and Steve. Thanks to everyone’s hard work and important contributions from CSBF personnel, we’re steadily moving through our checklist.
A timelapse of integrating the cryostat. Thanks to Jarred for shooting and editing the video!
Brent, Steve, Hadar, and I are finally all in Wanaka! Brent and I drove the cryostat from the Christchurch Airport to the Wanaka Airport today. Hadar and Steve arrived in Wanaka earlier this week to hold down the fort and set up our new hangar.
We’re currently monitoring the cryostat 24/7 as it pumps down to near vacuum pressure. We monitor to check that power to the pump hasn’t unexpectedly turned off while we’re pumping. If it does, our UPS (uninterruptible power supply) gives us about 45 minutes to turn on a generator before the batteries run out and the pump turns off. So far, so good.
More importantly, the four of us celebrated our successful reunion with a long-awaited dinner at Ashraf’s. The korma, rogan josh, and naan were delightful, as was the wonderful hospitality we received from the Ashraf’s host who recognized Brent and Steve immediately.
Extracurriculars:
Brent and I made the most of our time waiting in Christchurch for the cryostat to arrive. We toured the Christchurch Botanic Gardens, Riccarton Bush, Akaroa, and the Waipara wine region. I’ve eaten plenty of seafood already, including massive green-lipped mussels and delicious salmon, and have tried NZ toasties, lamb, and the popular Cookie Time packaged chocolate chip cookie. We also pet and fed sheep!
Hadar’s search for the ultimate cheese scone is underway.
The COSI team finished packing its belongings at CSBF earlier this week and tomorrow Brent, Steve, Hadar, and I begin our journeys to Wanaka, New Zealand!
Thank you to everyone in Palestine, TX who made our stay enjoyable, productive, and filled with great memories. Looking forward to picking up where we left off with a lot of hard, but gratifying work as we get ready for flight.
See you on the other side of the world.
P.S. Ashraf’s, we’re on our way. Table for four, please!
Why CSBF?
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.
Integration
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.
On January 5, 2020, Hadar, Nick, and I began our three-and-a-half day drive from Berkeley, CA to the Columbia Scientific Balloon Facility (CSBF) in Palestine, TX. While most of the COSI equipment traveled by truck and the rest of the team by plane, we drove a minivan to Palestine in order to transport the COSI cryostat separately.
Continue readingCOSI is planning to fly again! We plan to fly again in the Austral Fall of (~April 2020) from Wanaka, NZ onboard another Super Pressure Balloon (SPB).
Keep an eye out for news and updates as we prepare our instrument for flight.
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