My collaborators and I are here in Antarctica for one reason: to fly a balloon-borne telescope called SPIDER. SPIDER is designed to observe the cosmic microwave background – the literal glow of the early universe. It is an exceptionally complicated instrument: six telescopes full of microwave optics and superconducting electronics; a massive (1300L) tank of liquid helium to keep it all cold; a motor system to turn and point it during flight; and electronics and sensor systems to monitor and control the whole shebang. It has taken our team seven weeks to prepare it for flight. Below are a few photos and notes from along the way.
Arrival and Unpacking
Even weighing in at 3 tons, SPIDER is incredibly lightweight for what it is and does. It needs to be strong in just the right ways, with lightweight materials (aluminum, carbon fiber, some titanium) and careful engineering design. It is also very large. It thus cannot be shipped to the continent as a unit, but must be largely assembled on-site. This has occupied much of our time since arrival.
LDB camp opened on October 29th (a day early!), with major cargo arriving that day and the next. SPIDER arrived in three sea containers (two 10-foot, one 20-foot) and one large crate for the cryostat itself. The sea containers arrived in Christchurch via ocean-going container ships from Port Hueneme, while the cryostat arrived on a C-17 SAAM flight from McChord Air Force Base. All containers were then carried to Antarctica in October aboard C-17s.
These containers aren’t just SPIDER’s flight hardware and spare parts: we begin the season with an empty high bay, and there are no hardware stores in Antarctica. We thus also need to bring a fully-outfitted lab, with all the tool chests, supplies, electronics, tape, and fasteners we might ever need. This year that even included a small milling machine, 3D printer, belt sander, and much more.
Receivers
SPIDER’s six microwave receivers (telescopes) are the eyes through which it views the early universe. Each needs to be unpacked and carefully prepped for installation into the cryostat. The system takes so long to cool that we have only one chance – get everything right the first time!
Prepping the Cryostat
Cooling the Cryostat
SPIDER’s cryostat is a fancy thermos bottle, designed to maintain a cold interior in warmer surroundings. On November 9th the SPIDER cryostat was complete, and we began to pump it down to vacuum (slowly and carefully, because of delicate membrane filters inside). After a week of this the team filled it with liquid nitrogen, which slowly dragged its interior down to a chilly 77 degrees Kelvin (-321 degrees Fahrenheit) over the next several days. And there we waited for the final fill, with liquid helium, to reach a mere 4 Kelvin (-452 degrees Fahrenheit).
(This is about when I arrived, November 21, after an unexpectedly long stay in Christchurch…)
And there we waited for about 12 days – a few days longer than planned – because our liquid helium had not arrived. To support the SPIDER campaign, NASA arranged to ship 9000 liters of liquid helium to Antarctica – a massive (and expensive!) logistical endeavor. Some logistical problems led the first batch to be delayed. After heroic work by LDB staff and NSF leadership, the dewars started rolling in a few days before Thanksgiving, and we were able to continue cooling. Detector reached operating temperature (0.3 Kelvin) by the end of November.
Gondola Frame
SPIDER is supported on a lightweight (but very strong!) carbon fiber frame, with a reaction wheel to turn it in azimuth and two elevation drive pistons to change its elevation. The cryostat was placed on the frame just before the liquid helium cooldown began.
On December 5th we took it for a brief trip outside to point the detectors at the sky. Beautiful day, and a great occasion for pictures with the team!
Dressed Up and Ready to Go
In flight SPIDER is protected from the intense sunlight at altitude by a large sun shield. This is built of a carbon fiber frame, filled out with foam panels and wrapped in aluminized mylar. The sun shield also supports the various satellite antennas with which we will communicate with SPIDER in flight. SPIDER also has cone baffles atop its six receivers, and aluminized mylar absolutely everywhere for sun protection. Plus a giant solar panel wing, to provide the 2 kW of power SPIDER needs to function.
She’s a thing of beauty, and almost ready to fly!
Jeff Filippini 