Sunday, December 14, 2014
Today we held an open house in MAPO, the building housing the Keck Array, to show the rest of the station what our telescope looks like and to tell them about the science we are doing. In honor of this event, I think it’s finally time for a blog post containing a tour of the building where I’ve been spending most of my time. In a companion post, I will give an explanation of the science we are doing there.
MAPO (the Martin A. Pomerantz Observatory) is located in the Dark Sector, about half a mile from the main station. The Dark Sector is reserved for astrophysics experiments and the use of radios, wifi, or other sources of electromagnetic radiation that might interfere with our observations is forbidden. DSL (the Dark Sector Laboratory), the building housing BICEP3 and the South Pole Telescope (SPT), is also located in the Dark Sector, as is IceCube (an experiment designed to look for neutrinos). There are several other clusters of buildings surrounding the main station, each with a different scientific purpose. The Quiet Sector minimizes radio communications and vibrations and contains long-term seismic monitoring experiments (there are no earthquake faults nearby, but since the Earth spins about the South Pole this is a good place to monitor global seismic activity and long-term oscillations). The Clean Air Sector is located upwind of the main station and contains climate research experiments and the Atmospheric Research Observatory. Since the wind travels hundreds of miles across open ice before reaching the station, with no sources of human pollution (flights must detour around this area), the air is some of the cleanest in the world. Other types of science done here include meteorology (weather balloons are released from the roof of the main station twice daily) and the study of the aurora.
MAPO was built in 1994, which makes it the oldest building in the Dark Sector. Since then it has housed a number of astrophysics experiments, including several designed to observe the cosmic microwave background. The most recent of these is the Keck Array, the telescope I’m working on. We share the upstairs of the building with HEAT, an astronomy experiment designed to look at dust in our galaxy. The downstairs is occupied by a machine shop, which both Keck and BICEP3 have found very useful this year.
Since its construction, MAPO (like all buildings at the South Pole) has been slowly sinking into the snow. It’s impossible to build foundations on solid rock here, as the ice is thousands of feet deep, so the best engineers can do is design buildings that sit on compacted snow, which slowly subsides under the weight of the buildings and new snow accumulation. Most buildings sit on stilts to prolong their lifetime, but all will have to be replaced eventually before they are buried. MAPO is now twenty years old, so this natural settling is starting to become problematic. The first floor is now several feet below the natural snow level, meaning that the station crew has to work hard to dig it out during the summers. An adjacent building, which housed the CMB experiment VIPER and is no longer maintained, is slated to be removed this year as its entire first floor is buried. In a few years MAPO will be taken down too, before it gets covered in snow completely. In the meantime, the drifts on the upwind side of the building are an impressive sight, rather like a frozen, cresting wave.
Upon entering MAPO, one passes through a small cargo unloading area and then enters the machine shop (which takes up almost all of the first floor). Directly above the machine shop are two rooms, one that we share with HEAT (still called the “AMANDA control room” for the AMANDA neutrino experiment, which stopped taking data in 2009) and the other that serves as the Keck control room. The control room contains computers where we can monitor all of Keck operations (the temperatures of various telescope components, the direction the telescope is pointing, etc.), issue commands to the telescope, and do real-time data analysis. Both rooms also contain lab benches that we use for hardware work when we take receivers out of the telescope mount for upgrades and repairs.
Continuing to the left through the control room brings one to the door to the roof and a long hallway full of storage cabinets. Continuing down the hallway brings one to the mount room – the location of the Keck telescope mount, the helium compressors used to keep the five Keck telescope receivers cold, and a server rack containing the six computers that directly communicate with the telescope. It’s a very noisy, active room – the fans from the computers are always running (the computers themselves generate enough heat to keep the room at room temperature) and the cooling system for each receiver makes a chirruping noise, so the net effect is similar to a chorus of mechanical crickets. We don’t spend much time in here unless we are actively doing upkeep and maintenance tasks. If we do need to access the telescope directly, we can climb up into the mount itself by going up a pair of ladders. The video below shows what this looks like.
After coming back out of the mount room and returning down the hallway, one can proceed up to the roof. This is where the most impressive views of Keck are, along with nice views of DSL, the IceCube control center, and the surrounding Antarctic plateau. The roof also has a crane for heavy lifting and a hatch door that opens into the lab below, which we use to transfer receivers downstairs when we take them out of the mount to work on them.
In order to get a view of Keck, one has to enter the groundshield, an impressive aluminum and plywood construction. (The plywood remains unweathered in the cold, dry Antarctic climate.) Together with the forebaffles attached to the end of each receiver, the groundshield blocks any microwave emission from the ground from contaminating our signal. Its design also traps some of the snow that is constantly blown around by the wind, creating a need for one of the least glamorous jobs assigned to South Pole graduate students – shoveling. The five Keck receivers protrude from a central platform that insulates the inside room-temperature environment from the much colder outside air. This platform can tip sideways and swivel back and forth, to look at different regions of the sky and track our particular field as it rotates around the celestial South Pole (due to the Earth’s rotation). The celestial South Pole is directly overhead, as we are right at the geographic South Pole, so stars never set and we can look at the same patch of sky 24 hours per day, every day, all year round. Since we are looking for a signal that originates outside our own galaxy and we don’t want dust and gas within the Milky Way to overpower this signal, we chose to look at one particularly dust-free patch rather than the whole sky. The telescope scans back and forth to cover this field, over and over (as seen in the video below), and we combine all of this data to produce a map of this region. The longer we observe, the less noise we will have in our map.
The Keck telescope started observations in 2011 and has been collecting data ever since, with annual breaks for summer maintenance. It is funded to continue operating through the end of 2016 (although we hope to operate it through 2017 and beyond). It continues to be a world-class microwave instrument and we hope that its data will continue to produce exciting results for years to come!