Warbirds of Wanaka and COSI Calibrations

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The New Zealand Air Force parked on the apron directly outside the doors of our hangar.

The tiny Wanaka Airport has been buzzing recently. Over the Easter long weekend they hosted the Warbirds Over Wanaka Airshow, which, from the view of our hangar right on the airport apron, was awesome. There were so many amazing planes and skillful pilots, and for many of us, it was our first airshow. We had the hangar doors open to the sunshine and excitement all weekend long and even though we were working most of the time, it was a lot of fun.

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A stunning performance by a team of Yaks.

The Alpine Hangar has been buzzing as well. A lot has happened in the last few weeks. The last update we gave you was the cryostat integration on March 4th and we haven’t given you one since because we’ve been so busy! After we got the cryostat integrated, it took us one more day to get everything else on the gondola up and running so we could start taking calibration data.

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Taking calibration data with COSI (notice the radioactivity sign).

For the majority of our calibrations, we place laboratory gamma-ray sources with known energy lines at precise locations within the field of view of our germanium detectors. Using these measurements we can make sure we fully understand how COSI will behave in space when looking at astrophysical sources. This sounds pretty straightforward, but it involves weeks of measurements with lots of different sources and as many different positions as we have time for. CSBF keeps asking us when we’ll be done calibrating, and the real answer is “never.” One can never have enough calibration data!

One exciting thing to report about our calibrations over the past few weeks is in respects to the polarization calibration. As mentioned elsewhere on this site, COSI, being a Compton telescope, is sensitive to polarization. We don’t have access to a polarized source of gamma-rays, so we have to be a bit more creative. Our usual approach is to create a partially polarized source of gamma-rays by using the Compton scattered photons from a Cs-137 source off of a scintillation detector suspended above COSI. This method works well, but we got some inspiration from POLAR, another Compton telescope (thanks Merlin!), to try a new type of polarization calibration. After tweaking the hardware/firmware/software for a few days, we got it to work! It definitely needs to be mentioned that COSI’s software guru Andreas Zoglauer was able to come to Wanaka for two weeks to help us with the analysis of this data. Thanks Andreas!

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Setting up a new type of polarization calibration. A Na-22 source, which decays via the emission of two coincidence 511 keV photons, is suspended above the instrument. These two photons have correlated polarization and one of them is detected in COSI, while the other is detected by a series of scintillates suspended above.
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The additional scintillators for this new polarization measurement required some extra electronics. McBride spent a few days making some readout electronics for this measurement. You can see from the myriad cables that it was a fairly involved calibration.

The group in Wanaka has also grown significantly over the past few weeks. Mainly, members from Balloon Program Office, with it’s headquarters at NASA’s Wallops facility, have arrived. With there arrival comes more work for CSBF, mainly preparing the balloon for launch. Unlike the traditional zero-pressure balloons that NASA flies, the super pressure balloon has a lot of electronics and valves integrated into the balloon. Quite a bit of work goes into preparing this before launch.

Henry Cathey, one of the main faces behind the super pressure balloons, arrived two weeks ago. We worked with Henry during the COSI’14 campaign from Antarctica.
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Along with Henry and BPO, there are also a few people here from Aerostar, the manufacturers of all of the balloons that NASA flies, including the super pressure. Everyone is involved the in the process of preparing the balloon for launch. Here it is with the top being lifted out of the box. The balloon stays wrapped up in red plastic for protection until right before inflation.

A couple of weeks ago we also had the chance to take COSI outside and try on the solar panels. This was the first time since our fall tests in Palestine, TX, that we’ve had all of our science instrument running concurrently with CSBF’s transmitters/receivers/cameras.

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COSI hanging from the launch vehicle during rotator tests.
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Solar panel mechanical and electrical integration. COSI’16 has almost twice the amount of solar panels that COSI’14 had. The panels are so large and fragile that we take them off before rolling the instrument back into the hangar.

Something that’s very different about balloon launches New Zealand, as opposed to all of the other NASA launch sites, is the community interest. Everyone in town knows about the NASA balloon and when prompted most will start telling you the story of where they were when they saw the balloon ascend last year. The whole community is really excited to be part of something so exciting and unique. Given this, the Balloon Program Office has done a really good job of communicating to the public about the launch and the science we’re hoping to do. One such occasion was when we were invited to give a talk to the Grandview Probes Club. Steve Boggs wasn’t in town yet, so I volunteered. The crowd was really receptive and had great questions.

Talking to the Grandview Probus club about gamma-ray astrophysics.

There also has been a lot of media interest. Boggs, who arrived last week, has already been interview by two national TV channels, in addition to a couple of local newspapers. Check out our News section for the latest.

The COSI team (minus Clio who was doing some PR during Warbirds) and Debbie Fairbrother, the BPO Chief, posing in front of COSI for a local journalist. See the article here.

Looking forward, we’re planning on doing our compatibility test this coming Wednesday. If all goes well, then we’ll be ready to fly! If you followed our blog last year, you’ll know that launch opportunities are weather dependent and the conditions are very stringent for the super pressure balloon. The first possible launch day is April 1st, but the weather doesn’t seem to be cooperating.

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