Opening Black Cat

Now that the PolCal team has finished measuring detector polarization angles, it’s the Receiver Team’s job to take apart the camera, fix it up a little, and re-install it.  There’s quite a bit of work involved, and the first step was taking the camera out of the telescope.  Black Cat, the name we affectionately gave the black cryostat that contains the camera, is attached to a massive “optics” cryostat that keeps the ~ 1 meter secondary mirror of the telescope at a cool 10 K.  The entire double-cryostat structure has to be lowered out of the telescope boom and back into the telescope control room so we can get to work on it.

The first thing to do is to detach all of the readout cabling that took oh-so-long to plug in and secure at the end of the last deployment season.  With the cabling out of the way we hook up some chain hoists to the giant cryostat, disconnect the helium refrigerator lines, unbolt the cryostat from the bench in which it sits in the telescope boom, and then slowly and carefully lower it down onto a rolling cart in the control room so we can move it out of the way.

Black Cat still in the telescope boom and readout electronics plugged in.  Time to disconnect all of those cables.

Ready to be dropped out of the telescope!

The cryostat is down!  JT coming down the manlift after grabbing some tools.

All of those electronics have to come down too.  The crates are really heavy so we use the manlift to help out.

Black cat on the ground and warming up.

The readout electronics set up in a rack on the ground so we can monitor the cryostat as it warms up.

The evening we dropped the cryostats into the control room we were walking back for dinner and a plane was landing, which meant we were stuck behind the crossing beacon (we have to walk across the end of the runway to get back to the station so naturally that’s dangerous when a plane is landing or taking off).  We stopped at MAPO, a laboratory where another CMB polarization telescope is operating.  During the winter a huge drift of snow lovingly called MAPO Mountain built clear up to the second floor of the building, leaving a sharp “cliff” edge facing the building.  As we waited for the plane we climbed to the top of of the cliff and slid 20 feet or so on our stomachs down to the bottom.  Lots of fun.

Another CMB scientist at the top of "MAPO Mountain."  Sliding down this winter snowdrift was a lot of fun.

Anyway, back to work!  With the cryostat on the ground we had to let it warm back up to room temperature and bring the pressure up to atmospheric (the cryostat holds a vacuum so air can’t conduct heat from the warmer portions of the cryostat to the cooler portions).  This takes about a day and a half.  By this past Friday we were ready to detach the camera cryostat from the optics cryostat.  The two are held together by some screws and a couple quarter-inch alignment pins.  It’s easiest to pull the cryostats apart when the pins are perpendicular to the ground, and this requires hoisting up the back side of the cryostat a few feet off the ground.  This thing literally ways a ton and is about the size of a VW beetle so it’s an exciting procedure.  Once everything is aligned, we literally pull the camera cryostat off and set it down on a cart of it’s own.

Now the fun really began.  We took off the various radiation shields and exposed the SPTpol camera.  This thing has been sitting at a fraction of a degree above absolute zero since mid-January and now it’s all cozy warm and open for us to look at, which is kind of fun to think about.  The back of the camera is a complicated mess of readout cabling and heat sinking to get each part of the camera successively cooler.  After an hour or so of inspection, cable and thermometry removing, and unscrewing we lifted the camera out of the cryostat and I carried it up the stairs to the clean room where we usually work on it.

A couple of days after starting to warm up, the cryostat is open and we start disconnecting all the readout cabling inside the camera.

The SPTpol camera out of the cryostat and upstairs where Liz and I dismantled it.  First we take off the spider web-like structure on the back side.

The rest of the day was spent methodically dismantling the camera to get to the detector modules at its heart, where we’ll be doing a lot of rework.  One of the 150 GHz modules was acting funny this year and we want to replace it with a spare module.  If you remember we had to install several structures to keep the back of the camera from shaking as the telescope moved and unfortunately we had to remove all of these anti-shaking structures to get to the module we wanted to replace.  Not really difficult work, but it did mean tearing the camera completely apart.  In just a few short hours the camera went from happily installed in Black Cat to being in a hundred pieces in the upstairs clean room.  It’s a little crazy to think that we have this big complicated machine and there’s no instruction manual besides our notes and pictures to refer to when pulling it apart and putting it back together.  A little scary, especially when we want to make sure it works better than last time.  But we designed it and assembled it (multiple times now) so we know exactly how it works and exactly what to do.  Just another day at the office!...

The camera flipped over to the side that accepts light.  We first have to take this filter off.

Next we remove the aluminized mylar blanket that shields the back side of the camera from nasty radio frequency interference.

  

All that's left on the front are a few more filters that define what colors of light the camera accepts.

With the filters off you can finally see the feedhorns.  The seven 150 GHz modules  are in the center.  Surrounding them are 180 individual 90 GHz feedhorns.

Flipping the camera back over we take off the "wedding cake" support structure surrounding it and can start removing the aluminum anti-shaking supports.

The focal plane almost totally dismantled.  We wanted to do work on two of the central modules, but it meant tearing out two more to get to them.  

PolCal

It’s been a busy week and there’s a lot to write about, but this time I’ll focus on all the calibrations that have been taking place.  Our camera is sensitive to both the temperature of the microwave sky and its polarization.  (Polarization is sort of the orientation of light - it’s actually defined as the direction of its electric field).  Since polarization is orientation-dependent we need to know to high precision the orientation of each pixel in the camera.  If we get this “detector polarization angle” wrong then we’ll get the wrong answer for the polarization we measure in the CMB - that’s bad.  And since we’re trying to measure very tiny polarization signals getting the wrong answer, even at a very tiny level, could trick us into thinking we see something in the sky that isn’t there.  Really bad.

To measure the polarization angle of our detectors we made a “PolCal source.”  It’s really just a hot light source behind a grid made of many parallel wires.  The grid defines the polarization of the light coming from the source.  At first the light has no net polarization: there’s about as much light oriented up-down as there is left-right.  The grid acts to block light oriented in a certain way.  Light parallel to the wires in the grid can excite electrons to oscillate in the same direction as the light (up and down the wire) and therefore that light gets absorbed.  Electrons aren’t free to move between wires, so light perpendicular to the wires passes through as it can’t excite the electrons.  The result is light with a well known polarization (perpendicular to the wires in the grid), which is exactly what we need to test our detectors.

The PolCal source is 3 km away from the telescope.  A hot source with a wire grid is behind a giant reflector that bounces power up to the sky.

The station (center) and the telescope (left of center) from the PolCal source.

Our detectors are only sensitive to one light direction - essentially either up-down or left-right.  If the light going through the wire grid is lined up in the same direction as a detector then the detector will pick up the light.  If the light is perpendicular to the direction of the detector then the detector can’t see the light.  You can imagine, then, that if we rotate the wire grid in front of our source we’ll change the intensity of the light the detectors will pick up - maximum intensity when the polarization of the light is lined up with the detector and minimum intensity when the light is 90 degrees out of phase with the detector.  By measuring the strength of light the detectors see as a function of the PolCal source’s wire grid angle we can then fit a simple model to obtain the detectors’ actual polarization angles.  Pretty nifty.  

Here’s a plot of the same type of measurement Jay and I took in the lab before heading to the Pole.  As the angle of our wire grid changes, the strength of the light seen by our detectors is modulated in a roughly sinusoidal pattern.  The red and blue lines are for two different detectors in the same pixel.  By design the angles should be 90 degrees apart and that’s just about what they are in this example.  That’s great, but not every detector plays as nicely as this one, which is why we have to measure all the angles individually.

PolCal measurements we took in the lab.  The strength of the light absorbed depends on the angle of the wire grid in the PolCal source.

There’s been a PolCal team down at Pole for the past three weeks or so making these measurements for as many of the ~1500 detectors in our camera as they can get.  It’s painstaking and difficult work but they did a great job!  It’s a lot harder to do this down at the Pole than it is in our lab in Boulder.  For one, the PolCal source is 3 km away from the telescope and barely off the ground.  That means the detectors are looking through a lot of atmosphere, which dumps a lot of power on them - almost so much that they completely lose sensitivity.  That makes it difficult to understand the signals we’re getting from each detector.  Another complication is pointing - the source is really tiny (so that the power of the light coming from it doesn’t totally blow our detectors out of the water).  A tiny source means you have to be pointing at that source very accurately.  Move off the source just a little bit and the signal strength drops really fast, which can look like a rotation in polarization angle, as in the plot above.  REALLY confusing.  And guess what makes the pointing difficult?  The Sun (among other things).  The Sun will heat one side of the telescope more than the other, which bends and flexes the whole structure changing where the telescope is actually pointing compared to where we WANT to point it.  The PolCal team had to come up with ways around all of these problems and more, but they did and we have excellent data!  Awesome job Ryan, Amy, JT, Tijmen, and Nicholas!

The PolCal team adjusting the source for more observations.

A map of the PolCal source as seen by our detectors.  The light blue strip on the bottom left is the road out to the source.  In this map dark blue is hotter and red is cooler.  Low on the horizon you're looking through a lot of atmosphere, so it's warmer.  The giant reflector in front of the hot source reflects cooler atmosphere from above down into the optical path of the detectors, which is why the reflector is red.

Before the end of PolCal observations I got to go out to the source.  The telescope itself is a kilometer from the station, and the source is a further 3 km.  The station and telescope are little specs on the horizon that far away - makes you really glad for all the cold weather gear as well as the snowmobile we use to get out there because it’s an hour walk one way.  Yuck.  But the really great thing about being that far away from station is that there is absolutely nothing around you.  No buildings, no marker flags.  Just a big, white, empty horizon.  Breathtaking.

An endless blank horizon behind the PolCal source.

Thanksgiving in an Antarctic Wasteland

Saturday was the big station Thanksgiving celebration.  Holidays are always celebrated on the weekends here to give the station crew a second day off (they usually work six days and have Sunday off).  Thanksgiving and Christmas are more special than normal and people often dress up a bit.

Some past and present SPT folks eating some delicious appetizers before dinner .

The food was amazing as always, and it was great to have all the dishes associated with Thanksgiving despite the fact that we're 10,000 miles from home.  Turkey, mashed potatoes, stuffing, green bean casserole... and lots and lots of pie.  Since the galley isn't large enough for everyone to eat all at once there were two seatings and the SPT-ers were all in the first seating.  After having our fill of all the delicious food we headed to the B1 lounge to play some games before heading out to the dance party a little later in the evening.  I learned how to play backgammon, which is really cool, but it took me a while.  I got destroyed several times, but I'm starting to pick up on the strategy.

Brad and Tijmen locked in an epic post-Thanksgiving chess battle, while Amy destroys Jay in backgammon behind them.  She destroyed me too, but Jay and I had never played before...

The weather the evening we celebrated Thanksgiving, with a pretty picture of SPT.  Getting warm!

 Before and after Thanksgiving has been a lot of coding and analysis for me since the camera is still in use.  There's been a number of times I've had to grab data off a computer back home and waiting for the satellite pass can really suck.  But, when the TDRS satellite comes up in the afternoon... well, we all get pretty excited.  With TDRS you can actually check gmail without waiting 10 minutes for your inbox to load.

Best part of the day: start of the TDRS afternoon satellite pass.  30 kB/s  download speeds here I come.

The weather has also been pretty nice the last few days and while the calibration team that arrived before me finishes up their final measurements I went outside to take some pictures when the horizon was so visible.  On days like this it really hits you that there is absolutely nothing out there.  You can see for miles and miles and all that exists is drifting snow.

Jay and I at the Pole marker.

The weather today was incredible.  You really get the sense of how much nothing there is out there.

This is the Last Stop

After four nights in McMurdo, we finally arrived at the South Pole last evening around 8:00 pm.  I don't know what it is, but something about the time I've spent here makes it special.  Of all the places I've lived and seen the Pole and the home I grew up in are most vivid in my mind.  Walking off that plane, seeing the telescope off in the distance... it was like I never left.  It's really great to be back!

Cargo and bags on the LC-130 headed to Pole.  Almost there...

The rest of the SPT crew already down here greeted us outside as is the tradition, and after a round of hugs we headed inside to get our room assignments.  Most of the rooms in station are like the one I had last year - just wide enough for a bed and a tiny desk.  This year, however, we all got rooms in the A1 berthing, which has rooms an extra 3 feet wide or so, along with a much larger desk.  It doesn't sound like much, but that extra space really goes a long way.  I can sit at my desk without concern that if I move in any way (let alone get up from the desk) I'll bump the walls and wake my neighbor.  After the cramped living space last year this feels like flying first class.

A big room in A1.  Lucky!

This year I decided to bring Zazz Malcolm Peribothra Grant with me.  He's a good sea turtle.

My huge desk.  I brought lots of halloween candy to share with folks, and hopefully enough yarn to crochet myself a new pair of slippers.

Once we settled into our rooms we headed to the galley to grab some food.  Dinner ended an hour or so before we landed, but there were plenty of desserts and fresh fruit left over to snack on.  After chatting for a while, I headed to the Science lab where most of the SPT'ers already down here were working hard on a calibration measurement that needs to get done before the receiver team can take the camera apart.  After a bit of an information download and about 5 glasses of water (very important because of the dryness and altitude) I headed to my room to decompress and get some sleep.  Finally made it!

South Pole Station galley.  Nicholas, pictured here, was one of our two winter-overs.

What Antarctica is Supposed to Look Like

Sunday in McMurdo, which means zero chance for a flight out of here.  The plus side to that is we're not checking the monitors and we can go out and see the sights a little bit.  At the start of the day we hitched a ride out to the Long Duration Balloon Facility.  About seven miles from the station, this is where balloon experiments like EBEX and BLAST are assembled and launched.  As I mentioned last time, EBEX is launching for the first time this year, while the newest incarnation of BLAST (BLAST-pol) is also launching.  The brother of BLAST PI Mark Devlin, whom you may have seen a couple years ago on the Colbert Report, made a movie about the experiment's first launch.  Check it out.  A third balloon experiment trying to measure cosmic rays called Super Tiger was also preparing, but I didn't get a chance to talk to any of them.

This is where the balloon experiments are assembled and launched. 

The facility is really made up of several large hangers in which the experiments prepare for launch.  Balloon experiments are totally different beasts.  Instead of a nice stable ground telescope or satellite, balloons have to contend with wind pushing their telescope around, making pointing very difficult.  The camera and telescope are mounted and built in and around gondolas, which are really sophisticated structures designed to stabilize the telescope as it hangs underneath a massive helium balloon 40 km up in the air.  These things have enormous fly wheels that while spinning generate a lot of angular momentum.  As the fly wheel spins in one direction, the telescope wants to spin in the other direction to conserve total angular momentum, so left-right (or azimuth) pointing is controlled by spinning the fly wheel up and down.  There's lot of cool tidbits and technologies like that involved with balloon experiments.  They have similar problems as ground-based projects, but they often have to be far more clever to solve them.  Really cool stuff!

Each balloon experiment is inside one of these hangars.  The gondolas can be swung out on those giant I-beams so tests can be run outside when necessary.

The gondola behind the primary mirror of BLAST-pol.  The camera gets bolted in within the frame.  The lead bricks strapped on are there to keep everything balanced before the camera is dropped in.

The gondola for EBEX.  The primary and secondary mirrors and the camera itself have not yet been installed.  There will also be large sun shades attached as well.  The full structure will barely make it out the hangar doors.

I have more photos of both EBEX and BLAST-pol, but I don't want to post anything too detailed, so I encourage you to look them up.  They're incredibly sophisticated machines and really interesting projects and are worth learning about.  One more photo from the LDB facility, though: one of Mount Erebus.  Still 23 miles away, but it looks like you could just walk out a few hundred yards and climb right up it.  Funny how white featureless terrain can play tricks on you like that.

A view of Mt Erebus from the LDB facility.  Believe it or not, the volcano is still 23 miles away.  This thing is really big...

After dinner we decided to do a quick hike up Observation (Obs) Hill.  It's right outside of town and offers a pretty spectacular 360 degree panorama.  Check out the photos below.  Now THAT's what Antarctica is supposed to look like!  Simply stunning.

A view of the ice runway from the top of Obs Hill.  Soon flights will come in on Pegasus runway, a few more miles out of town since this one will melt through the summer months and eventually be open water until winter hits.  

Does that look like Antarctica is supposed to or what?  Liz and Brad standing at the top of Obs Hill surveying McMurdo below with Castle Rock and Mt Erebus in the background.

McMurdo from the top of Obs Hill.  The blue building is where the galley is, and  the dorms are the brown buildings two rows behind that.

You might recall pictures in front of Scott's hut from last year.  That's located on the small jutting peninsula in the background.

Another shot of the Transantarctic Mountains backlit by the sun.  They're about 45 miles away in this shot.  

Me in front of the cross on top of Obs Hill with the ice runway in the background.   The cross is a memorial to Robert Falcon Scott's crew.  They made it to the south pole nearly 101 years ago, but didn't make it back...

A Few Extra Days in McMurdo

We were originally scheduled to fly out to Pole Friday morning, but a weather delay turned into a cancellation and an extra day in McMurdo.  The weather was fantastic during our scheduled departure time, but there was concern about the weather when the LC-130 was due to come back from dropping us off.  Sure enough, mid-day hit and clouds started rolling in, then some ridiculous winds, in which it surely would have been dangerous to land.  Definitely a good call to keep the plane on the ground.  We're scheduled again for a 9:00 am flight Saturday morning, which should get us into Pole around 12:30 - hopefully just in time to catch the end of lunch.  Since I didn't post them before, here are some photos from my trip into McMurdo.

The C17 that we rode to Antarctica.

Several hours into the flight we reached the edge of the sea ice.

The coast of Antarctica.

The Transantarctic Mountains as seen from McMurdo.

There are three "conditions" for weather here, and all but the "best" condition have limitations on what you can do outside.  Condition 3 is the best weather, and you can go about doing what you normally do, be that work or pleasure.  (There are actually a number of decent hiking trails around camp, but you need to go through a safety training class to do anything but the short walk to Discovery Hut I did last year and I haven't been in McMurdo long enough to catch a class).  But just because Condition 3 is "good" doesn't mean it's great... it's considered Condition 3 whenever 

• The wind speed is less than 48 knots (~ 55 mph)
• Visibility is greater than or equal to 0.25 miles
• Windchill is warmer than -75 degrees F.

Clearly there's plenty of room for Condition 3 to suck.  Now, Condition 2 is worse, and pedestrian traffic is limited to between buildings only.  Being in vehicles is also restricted to those equipped with radios and those fully enclosed.  Condition 2 is called when any of the following happens:

• Winds between 48 and 55 knots (55 to 63 mph) are sustained for at least one minute
• Visibility is reduced to between 100 feet and 0.25 miles, sustained for at least one minute
• Windchill is between -100 and -75 degrees F sustained for at least one minute.

I'm sure you get the idea for Condition 1:

• Winds greater than 55 knots sustained for at least one minute
• Visibility less than 100 feet sustained for at least one minute
• Windchill is less than -100 degrees F sustained for at least one minute.

If it's Condition 1, you aren't even allowed to leave your building.  Not good.  The entire time I've visited McMurdo (last year and this year) the camp has been at Condition 3, but today the road out to the runway and the runway itself dropped to Condition 2.  My bet given my experience walking between the library and the galley at lunch time in camp (which was still in Condition 3) - it was the wind.  It was absolutely howling today.

Having some extra time in McMurdo meant we could hang out with some friends and colleagues from other experiments and participate in a little Mactown nightlife.  Thursday night we headed to the Coffee House, a great place to get some coffee, maybe play a board game or listen to some live music, or just chill with some friends.  We met up with some EBEX folks, who are down in McMurdo for their Long Duration Balloon (LDB) flight.  EBEX is another CMB polarization experiment like SPTpol, but the telescope actually flies on a high altitude balloon.  While floating 40 km high under a huge helium balloon there is much less atmosphere to deal with so it's almost like being out in space... but not quite.  EBEX might sound familiar to some of you - it's the experiment that mysteriously disappeared along with the semi-truck it was in and its driver on its way to Texas from Minnesota earlier this year.  Luckily after a few stress-filled days the truck was found with the experiment still perfectly safe inside, and now it's here getting ready for a 10-14 day trip around Antarctica floating high in the sky.

Friday night was pub trivia in Gallagher's, one of the other places to go hang out after hours.  The trivia was movie themed this time.  There were about 10 teams, but we really only cared about EBEX vs SPT.  EBEX ended up beating us, 57 to 50 points, but we had a couple of good rounds, including a fun one about movies Tom Hanks has been in.  We did pretty well considering.  Anyway, it was a good way to spend an extra night here.

Update:  It's now Saturday afternoon, and our flight was again cancelled for unknown reasons.  There are no flights on Sunday so that means we're here until at least Monday morning.  So, I've attached some pictures, mainly from Christchurch, to take advantage of the reasonably fast internet when I still can.  Enjoy.

A fountain in the botanical gardens, Christchurch.

Really cool tree in the gardens.

Ah, living things...  The only living things I've seen in Antarctica so far this year are people.

I wouldn't mind having a house by this pond.  It even has a duck!

Whoever takes care of these rosebushes knows what they're doing.  ALL of the rosebushes in this garden had ridiculous quantities of buds like this one here.

There were dozens of different colored roses, each with their own unique smell.

A phonolite bomb from nearby Mt Erebus, the southern-most active volcano in the world.  This  was part of a 2 meter hunk of volcanic rock flung 1/2 kilometer from the crater rim.

Haven't seen any live penguins yet on this trip, but here's a stuffed one in display in the Crary Science Lab here in McMurdo.

Christchurch, New Zealand: The Garden City

After about 30 hours of flying and waiting in airports, I arrived in New Zealand yesterday afternoon.  I absolutely love this country.  So beautiful.  It's still mid-spring here and the area mountains recently got some snow, so flying in over the Southern Alps towards Christchurch from Sydney was breathtaking.

Our hotel this year is literally right next door to the Antarctic Center where we're issued all of our cold weather gear, which in turn is a 5 minute walk from the airport.  That's great news for when we have to fly out as we can sleep in a little longer but it's a bit tricker getting to downtown and experiencing the city.  After getting settled in our rooms and taking a quick shower we all grabbed a taxi and headed towards the town where we grabbed a bite to eat and walked around central downtown.  This was the area hardest hit by the big earthquake back in February of 2011.  A significant portion of Christchurch, the South Island's largest city and New Zealand's third-largest city, is still rubble piles and  half fallen buildings that are too dangerous to re-enter.  I spent a few days in town after coming off the ice this past February and more of the city has been torn down than re-built in my time away.  But slowly but surely the town is coming back.  More of the city is open to walk through now, even if businesses and restaurants haven't yet returned.  Shops closed since the earthquake are opening their doors, but many have moved to entirely new locations.

The Cathedral, or what's left of it after the earthquake nearly two years ago.

Bits of damage are everywhere.  And more and more lots are empty as people slowly remove buildings too damaged to repair.

This building was being actively torn down.

Today was our appointment to get our extreme cold weather (ECW) gear.  There were only four of us, and we've all been to the ice before, so it went really fast.  That gave us plenty of time to head into town and do some last-minute grocery shopping for some choice foods we won't be able to get at Pole. For example, I grabbed some dried fruit, nuts, and lots of chocolate while others got avocados and limes.  Before too long even this stash of goodies will be gone...  Anyway, it was a little too early to get dinner at this point so after grabbing some ice cream in the container store retail district built after the earthquake we headed for the botanical gardens, a few blocks out of the central city.  The gardens are just gorgeous and are a great place to go see some color and some life right before heading down to the ice.  There are also lots of ducks, and I love ducks.

This little guy was fearless.  Walked up to within inches of us.

This duck was WAY bigger than it looks here.  I really like ducks.

Some cool flowers in the botanical gardens.

More flowers.

The gardens in the center of Christchurch are gorgeous.  A nice place to go before and after heading to the ice to get your fix of color and life.

After getting our fill of flowers (and I have more pictures of the gardens I'll post soon), we grabbed some food.  This was my last chance to have a really good burger for quite a while so I went for it.  Brad and I both ordered burgers and decided to go that extra mile and get a fried egg on top.  Apparently, however, fried eggs on burgers aren't very common here (though beets are).  Our server was clearly very confused when we ordered it and we weren't exactly sure how the burgers would come out.  Well, they ended up taking the request very literally.  Out came burgers with fried eggs very carefully and lovingly placed on TOP of the bun and all.  We got a good laugh out of that.

We asked for fried eggs on top of our burgers.  It was taken literally.

It's about time I hit the sack.  We have our ice flight to McMurdo tomorrow morning with a check-in time of 6:30 AM.  There are only ten people on the list to fly down, so it's likely going to be a lonely flight with a lot of cargo.  Last year it was pallets of Coke and Coors Light.  Last week some of our colleagues flew down with a helicopter.  Wonder what we'll have this time?  Fingers crossed we don't boomerang!