The Long Goodbye

Now that the busy polar summer season is over, things have gotten much quieter around here. Although there are just two SPT team members (Zak Staniszewski and Steve Padin) left at pole, there is still tons of work to do! Right now we are busy commissioning the telescope, and thus far everything is progressing well. Here is a shot of the SPT scanning during these early tests:

Be sure to go check out the newly revised SPT Multimedia page where we've uploaded lots of movies and photos from both the test build in the US and construction at pole this season.

Now that February is here, the temperatures at the South Pole Station have begun to drop again, and the station is preparing to close for the winter. Most of the people currently working at the station will fly out within the next couple of weeks, leaving only a core group of "winterovers" here who will stay through the extremely cold and dark months of the Antarctic winter.

The University of Chicago "reflector assembly team", consisting of Tom, Jeff, Joaquin and Ryan, has already left the ice. But many members of the SPT project are still here until the very end of the summer season to work on the receiver, the last few details of the telescope itself, and the software used to control the telescope and interpret the data that we take with it. At the moment, we are busy cooling down the receiver and the secondary optics in order to test how everything works when we put it all together. It's a very busy time, with people working around the clock.

Even though we all tend to be very focused on whatever tasks are currently at hand, everyone in the team finds themselves sometimes just staring at this beautiful telescope and admiring everything that has already been achieved this year. It really is a gorgeous instrument, and it's especially impressive to see how smoothly it moves. From the windows of the indoor laboratories where most of our work is taking place, we can see the last remaining crews who are working on the telescope outside in the cold. To assemble this enormous telescope has taken teams of iron workers, electricians, insulation workers, carpenters, and many other specialists here at the Station and back in the U.S. It's been incredible to be here and see how the whole South Pole Station is pushing for the success of this project.

Before the Chicago reflector assembly team left, we had a chance to take some pictures of them together with the iron workers and telescope specialists who played big roles in the construction of the telescope. Many of these individuals went through the process of test-building the telescope in Texas last summer, and here they are at the completion of the final instrument in one of the harshest places on earth. It's truly a great group of people and they've done an amazing job. All of the rest of us are in awe!

The Gang's All Here!


(Photo credit: John Kovac with Adrian's camera. Click here for a higher-res version.)

For a brief couple of weeks, we have assembled the entire SPT 2006-2007 South Pole Science team --- i.e., every scientist on the SPT project that's coming down this year. As you can see, we're quite a crew:

Lying down: Steve Padin

Kneeling (left to right): Tom Crawford, Kathryn Miknaitis, Tom Plagge, Matt Dobbs, Ryan Keisler

Standing, 1st row (left to right): Ken Aird, Zak Staniszewski, John Carlstrom, Joaquin Vieira, Martin Lueker, Erik Leitch, Jeff McMahon, Adrian Lee

Standing, back row (left to right): Clem Pryke, Steve Meyer, Brad Benson, Bill Holzapfel

Looming, background: The SPT

The Receiver Has Arrived.

The final (and possibly most complex) piece of the great puzzle that is the South Pole Telescope has arrived: The receiver. This is the end of the line for the light gathered by the telescope. Those ancient photons will end their existence being absorbed as heat onto the web of one of the ~1000 ultra-cold (1/2 degree above absolute zero) detectors, sensed as tiny temperature fluctuations by the tiny superconducting thermometer attached to the detector's web, and read out by the SQUID (superconducting quantum interference device) current meter / amplifier coupled to the detector. Computer records of these tiny temperature fluctuations will allow us to reconstruct the small-scale brightness pattern of the Cosmic Microwave Background (CMB) with unprecedented sensitivity, eventually enabling us (we hope) to measure the abundance of distant galaxy clusters through the distortion they imprint on the CMB and use this measurement to constrain properties of Dark Energy.

So we're pretty excited to have the receiver here. And already together and about to undergo some pre-installments tests. Amazing as it may sound (at least, it sounds amazing to me), the crew of newly arrived SPT scientists working on the receiver managed to unpack the receiver, open it down to its guts, install the detectors, close the receiver back up, and get it on the vacuum pump and cooling down within about 48 hours of its (and their) arrival.

(Speaking of which, we should note that we are now about a three times larger group of scientists than we were a few short days ago. Just arrived are: the receiver team of Bill Holzapfel, Adrian Lee, Brad Benson, Martin Lueker, and Tom Plagge (all from UC Berkeley) and Zak Staniszewski (from Case Western); Steve Meyer from Chicago (providing yet more receiver-type expertise and general wisdom); and software mavens Ken Aird and Kathryn Miknaitis from Chicago and Erik Leitch from JPL.)

Assuming that the receiver tests go well, we will be in position to couple it to the cryostat that contains the secondary mirror (which has also arrived at Pole but has not been unpacked and installed yet). And if that goes well, then it's onto the telescope with both of them, and we're off.

That's getting a bit ahead of things, but it's easy to get carried away when things are this exciting. For now, here are some pictures of the receiver and its contents.
(Thanks to Ryan for the pix.)

Adrian Lee working on the receiver focal plane (six wedges of 160 detectors each).


The fully assembled receiver on the pump and cooling down.

The Reflector Is Up.

As promised, the reflector has been placed on the telescope. This is one of the major milestones on the path to first light. It was a complicated two-crane lift (three if you count the one carrying people up to bolt the reflector down), and it was managed beautifully by Raytheon's Eric Nichols and Bill Johnson. As you can see from the mini-gallery below, it went off without a hitch, and we now have a darned impressive looking telescope --- just some testing and a camera away from mapping the sky.

The lift begins.


Docking the flying saucer.


Steve P., Joaquin, and Tim Hughes prepare to enter the belly of the beast (to attach the reflector center hub to the telescope).


As Bill Johnson and Aaron Thompson look on, the last of Steve disappears into the maw.


Ryan, Jeff, and I look on as the crane gently lowers the reflector into just the right place. (Photo credit: Jerry Marty)


The reflector in place, Eric Nichols and Brian Hardin fasten up the bolts that Bill and Aaron can't reach.


The telescope, facing the horizon (grid south), seen from the roof of DSL.


The telescope, facing the horizon (grid east), seen from the roof of DSL.

Tomorrow, we look like a telescope.

Sorry about the long delay between posts. The Christmas and New Year's holidays have taken up most of our free time, but there has been lots of work going on as well. The most exciting news is that after our first round of photogrammetry, analysis by Jeff, and tweaking of the mirror panel positions, the surface of the mirror looks to be within a tenth of a millimeter of bang on, and the path looks clear to getting it significantly better than that. Since then, the mirror has been lifted off the large invar cone that will attach it to the telescope, and the invar cone itself has been lifted and attached to the telescope. And tonight, when the mirror and back-up structure get lifted and attached, we'll have a telescope that looks darn near complete.

Then comes the minor detail of something at the telescope focus to detect the incoming light. Two cryostats and 10 scientists show up later in the week to start that process. Stay tuned.

All the Panels are on the reflector!

(The following is simply a transcription of Jeff's e-mail to the collaboration announcing this milestone.)

Hi all,

Last night we placed the last panel on the bus, and here is the
picture to prove it. The dish may look flat, but that is just the
fish eye undoing its curvature- every indication is that it is very
close to the correct shape. Just wanted to send out a picture so
you can share in our enthusiasm.

-Jeff


ps. The sun dog picture is from right after we finished.

The (almost) fully populated reflector


Auspicious omens in the sky on the occasion of the placement of panel #218

The Telescope & Reflector Begin to Take Shape

A quick disclaimer before today's post: The SPT is not just the primary mirror, and the collaboration does not consist solely of the reflector assembly team. It may seem that way at the moment (at least to readers of this blog), but that will change rapidly as more members of the team --- and more pieces of the instrument --- show up at the Pole. January will bring lots of new faces and much more emphasis on the receiver (i.e., the part of the telescope that actually detects and records the incoming light). But for now, you're going to keep hearing about the telescope infrastructure and the primary mirror.

OK, now back to the post.

Though it may seem slow, the progress on the telescope infrastructure and primary mirror continues --- pretty much on schedule even. A couple of days ago, the first piece of the telescope lower boom (the structure that extends out from the primary mirror and holds the secondary and receiver) went into place, giving the first hint of the scale and final shape of the telescope.

Telescope with part of lower boom


Meanwhile, the reflector assembly folks have spent the last few days in furious panel-placing and -aligning mode. In fact, we're up to a pace of over 20 panels a day placed and aligned to (we hope) less than 100 microns. If we can keep this up, we'll have all the panels placed a few days before Christmas, at which point we spend a couple of days taking care of some wiring and mechanical details, then it's on to testing the surface. The first big test of how well we managed to align the surface will use a technique called photogrammetry. I'll defer a detailed explanation of this process to a later post; for now, it suffices to know that one takes a bunch of pictures with a specially outfitted camera then hands those pictures to an incredibly expensive piece of software that picks out the locations of hundreds of little reflective targets stuck to the mirror surface (and some bigger targets too) and uses that information to determine the exact shape of the mirror surface. You can see the photogrammetry targets (and the progress we've made laying panels) in the picture below. In this photo, Steve P. is using a feeler gauge (a precision set of metal shims) to check the job that Jeff, Ryan, and I did on the latest set of panels. The large metal bars layed across the middle of the reflector are to give the photogrammetry software a known length scale to work with, the foam pads with pressboard on top allow us to walk across the panels, and the shrouded piece of equipment in the center of the reflector is a theodolite (a surveying instrument we use in panel alignment).

Steve checks the alignment job.

Panel Alignment

As of last post, we had assembled the reflector backup structure (BUS) and were ready to start placing reflector panels. The first step was to get the BUS from where we assembled it (next to the airstrip, right where the pieces came out of the LC130 they arrived in) to where the rest of the telescope was going together --- namely the Dark Sector Lab (DSL), about 1km from the South Pole Station. We had assembled it on a sled just for this purpose.

The BUS on the move


At DSL, the BUS was dragged into a large tent built to shelter us from the wind as we worked, and we could begin the prep work needed to place panels. This work mostly fell to Jeff, who is in charge of understanding how one makes an off-axis paraboloid by placing 218 irregular shapes at different heights above an on-axis paraboloid. (If "off-axis" and "on-axis" mean nothing to you, just believe me that this is a crazy idea.) After lots of thinking on Jeff's part and some manual labor by the rest of us, we had seven panels placed in the innermost ring.

Prep work on the BUS inside the tent


Perhaps not surprisingly, how things looked after this initial placement resulted in lots more brainwork by Jeff (with a little help from the rest of us), sniffing out small non-idealities in certain parts of the system that have to be taken into account for everything to fit correctly. After a few iterations of this, panel placement can now begin in earnest.

Just a heads up: although he is several days behind in his publishing, Ryan has been adding posts, photos, and videos to his blog.