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  • kdavis32 3:53 pm on January 7, 2016 Permalink | Reply  

    STO-2 Hang Test and Flight Readiness! 

    Happy New Year from Antarctica! This year is off to a great start. The STO-2 mission had a hang test late on January 1, and passed the flight readiness review January 3. That means we are ready for launch and are just awaiting good weather before we fill the balloon and let go!


    Moving the balloon out away from the hangar to start the hang test. Normally Mt. Eribus would be in the background, but the fog rolled in and made the hang test day very cold and grey out. 

    If you remember from previous posts, the hang test is a test where the payload is picked up by the launch vehicle and hangs freely while the team performs various tests. First of all, the hang test serves as a practice run for getting the instrument off of its dolley in the hangar and connected to the launch vehicle (more on that later). The launch team practices attaching last-minute equipment such as crash pads and filling the ballast (dead-weight) used to maintain a steady altitude during flight. After the payload is flight-ready, the instrument team can take over and run tests from the ground.

    Hang Test pano 2


    STO-2 payload with the solar panels attached. It is ~22 ft tall and ~34 ft wide. 

    One of the most important checks that occurs during the hang test is the communications tests. The gondola uses several antennas that communicate over three different satellite and ground-based network systems. For the first 24-48 hours after launch, the gondola communicates via line-of-sight antennas with the ground based station at the Long Duration Balloon facility. This is the most important form of communication because the data rate is the highest, so we want to try and do all of the commissioning activities while we have line-of-sight (LOS) communication. As the name implies, LOS communication will only work until the balloon mission disappears beneath the horizon, which occurs sometime after the first day of the flight, depending on the weather patterns and wind direction. Some of the activities that have to occur for commissioning is focus the telescope and align our star tracking cameras to the main telescope.

    Hang Test 1


    The STO-2 payload transitioning from the hangar crane to the launch vehicle. 

    The other communication systems on the gondola are antennas that communicate with satellite networks. You can think of them as two systems, one that is high data rate but must be aligned very precisely and does not have 24 hour coverage, and a second system that has continual coverage but has a slower data rate. In general, we use the high data rate to send commands to the gondola to plan and execute our observing strategy. The slower system will be used primarily to return our (compressed!) data down so we can make sure that it looks like what we expect in real time. This is an important system, because otherwise the raw data is stored on the hard drives in the main computer on the gondola which MUST be recovered. This is a risky situation because there is a good chance we may not be able to recover the gondola when it lands. Some of the reasons a gondola may be unrecoverable are if the weather is too bad at the crash site to land a plane safely, if the gondola gets pushed out to sea or lands in a crevasse, or if we loose communication with the gondola entirely and don’t know where it landed.

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    The other main thing to check during the hang test is the pointing, tracking, and stabilization system of the gondola. The gondola must move freely during flight to allow it to point at what we want to study! We also want to keep the gondola steady, which is hard on a free-hanging object because the motion of the telescope causes vibration and pendulation that shake the gondola. To move the gondola we use two reaction wheels and a motorized telescope. The motor causes the telescope to tip vertically, so it swings out of the upright position that  you see in all these pictures. The two reaction wheels are motorized and are controlled by gyroscopes that track the motion of the payload. The motors spin the opposite way that we want to move, and the gondola spins because, as Newton put it, ‘every action has an equal and opposite reaction’.

    One of the problems of using a telescope is that they are designed to be very powerful at detecting light, but you want to have a fairly small field of view so that you can resolve fine details of whatever you are looking at. However, the narrow field of view makes it difficult to know what you are looking at. It would be like getting dropped off in a neighborhood that you know, but trying to figure out where you are but could only look through a straw. To solve this problem, we have installed to cameras on the sides of the telescope, each with a wider field of view. We look at the night sky with these cameras and observe a bunch of stars. A software package then triangulates the distances between the brightest stars in the image which provide a unique location of the night sky in the direction you are looking. This information is only helpful to you though if the telescope and the two star-tracking cameras are pointed in the same direction.

    Hang Test pano 3

    The STO-2 payload sitting on the launch vehicle called The Boss. 


    During the hang test, we use the star cameras to find specific targets and make sure the telescope moves to the correct location. We can also determine if the star cameras and telescope are properly aligned (though all of these things must be re-checked during the commissioning phase of our flight!!). The gyroscopes track the motion of the gondola, and make sure the gondola moves when it is supposed to. They also tell the reaction wheels if there is any jittery motion, and the reaction wheels correct for it.

    Our hang test took place late at night, which was a first for the Columbia Scientific Ballooning Facility. We began our test at 7 PM and didn’t finish until 3 AM the next day. Since there is 24 hours of daylight in Antarctica this time of your, that wasn’t a problem for us, although it was really really cold! Most of the team got interviewed by a National Science Foundation representative. The interview is mostly for the reporter’s notes but the NSF also stores them in their archive.

    Darren interview

    Darren Hayton being interviewed for the Antarctic Sun, a newspaper for the US Antarctic stations. 

    After the hang test was declared a success (and we went home to get some sleep!) we had a flight readiness review. This was mostly a formality going through a checklist of things that still needed to be done before launch. Now that we have everything ready, we are awaiting good launch weather. There hasn’t been a calm enough day to do the launch yet, although we have gone to the hangar to make the preparations. The other balloon payload here, GRIPS, is also trying to launch, and we are behind them in the que. Word on the intranet is that a huge storm will move in on Monday, but there might be a big calm afterwards. Hopefully, the CSBF folks can get both of us launched back-to-back. The double launch has never been done before, but the team is excited to give it a try! Wish us luck!


    • Thane 1:34 pm on January 9, 2016 Permalink | Reply

      Which you luck on the double launch.

  • kdavis32 7:53 pm on December 7, 2015 Permalink | Reply
    Tags: antarctica, , STO-2   

    STO-2 Progress Update 

    The STO-2 mission has been progressing remarkably smoothly (mostly!) as we prepare for launch later this month. The instrument team, APL gondola team, and NASA Columbia Science Ballooning Facility have all been pushing hard to make this mission a success.


    Pointing testing looking at the sun outside the balloon hangar. 


    Chris Groppi assembling an instrument package to run the 4.7 THz camera.

    On the instrument side of things, the Ball dewar that holds our camera pixels was filled with liquid helium last week. We were able to test the camera detectors once this was done, because the camera will only work at these temperatures. We have 100% of our pixels working at all 3 of our target frequencies! We were able to align all of the cameras properly with the optical system and our Local Oscillators (light pumps, which you can read more about in my previous post here) while the dewar was on the work bench. The alignment took several days and several new bolt holes, but we managed to get everything running perfectly in the end.

    One of the things I am helping with is making sure that the camera detectors are pointing straight out of the dewar window and aren’t tilted to the side. One of the easiest ways to do that is to have the camera take a measurement while looking at a hot and cold load in front of the window, and comparing the input power while looking at the two temperature loads. We used the room temperature (~300 Kelvin = 68 F) paddle on a spinning wheel as a hot load and the bottom of a cup of liquid nitrogen (77 Kelvin = -321 F) as the cold load.  This ~400 degree temperature change causes a significant change in power received in the camera, which we use to measure the sensitivity of the camera towards a given direction. We scan the cup and paddle system in front of the window to find where the strongest signal from the cold load is, and determine if that is in the center of the window or not.

    Once the instrument pointing, noise measurements, and alignment had passed our preliminary tests, we moved forward with the next major progress milestone of putting the dewar underneath the telescope. This involves taking the telescope out of the ‘cradle’ or gondola structure and attaching the dewar to the bottom of it, and then putting the integrated system back in the cradle. Once it is attached, the telescope needs to be re-balanced and tested to make sure that it can tilt and swing without any interference. We were all nervous to see the dewar tilt over, but we had no leaks. We had one electrical problem but it was resolved quickly without costing us much time with our schedule.

    naked telescope

    Kate and Jim look over the telescope (left) and cradle (right)

    OMG telescope is naked

    Telescope with the dewar attached underneath. 

    Over the next few days, we will be testing the focusing of our telescope. It is more challenging to focus the telescope than you would expect because the humidity in the atmosphere on the ground absorbs light at the frequencies our instrument can see. We are getting around this problem by using transmitters at a different frequency than our instruments normally use, but can still see.  Also up next will be more pointing and alignment tests, installing the communications packages, installing the solar panels, and another hang test. Stay tuned!

  • kdavis32 9:15 pm on November 19, 2015 Permalink | Reply  

    Why Balloons, and Why Antarctica? 

    The two questions that I get asked about most frequently when describing the STO-2 mission are “why are you putting a telescope on a balloon?” and “why do they need to launch from Antarctica?” These are great questions, but to answer them I need to give you a brief overview of some terminology. You can get a lot of information about the STO-2 mission in my previous blog post here.

    STO balloon fully inflated annotated.jpg

    This is a picture of the STO-1 mission as it was being launched from Antarctica in 2011. The payload looks small in this image, but it is really 21 ft tall! The balloon is as long across as a football field once it is fully inflated.

    The terminology I’ll be talking about is the payload. The payload is the main piece of equipment that is hanging from the balloon, so pretty much everything that launches except the balloon and the parachute. The payload part of the balloon is shown above. The payload has three primary components: the telescope (primary and secondary mirrors sitting within the tube), the instrument (which is the 3 cameras sitting inside the helium tank [dewar], and associated support electronics), and the gondola structure and support packages (the frame of the telescope, the solar panels, navigation cameras, the guidance/communication system, and more).

    STO-2 Hang Test annotated payload

    This diagram shown the different parts of the instrument payload. The telescope is labeled in red, the instrument is labeled in green, and the gondola and major support systems are labeled in white.


    Why Balloons?

    The reason for putting a telescope is the same as why we put them on satellites; you are looking through less air while in space, so the image quality is better.  The atmosphere blocks some of frequencies of light from making it to the ground, so you can’t see that light from the ground. You are probably familiar with this in terms of the Ozone layer of the atmosphere shielding us from the sun’s UV rays, and the terahertz frequencies we observe for the STO-2 mission similarly blocked. Specifically, terahertz light is blocked by water vapor. The altitude our balloon can reach (125,000 ft = 24 miles) is above 99% of the atmospheric water vapor, so we can see the terahertz light shielded from the ground. Even on the driest places on the Earth’s surface, there is too much water vapor in the air to take images over a large region of the sky.

    Another advantage of balloon missions is that they are recoverable payloads. When a satellite has reached the end of its mission, it is either burned up in the atmosphere or sent adrift into deep space. At the end of a balloon mission, the payload is separated from the balloon and returns to Earth on a parachute. A team goes to recover the payload, it gets sent back to the US to make upgrades and fix minor damage that occurs during the landing, and the mission can fly again. The 2 in the STO-2 mission name means that the STO-2 instrument has already flown once before and is on its second flight. The telescope can have different instruments attached to it, and this telescope and gondola structure are on their 6th flight! Previously, the telescope was used for cosmic ray and comet-observing missions. The STO-2 instrument was upgraded and expanded from the STO-1 flight, which flew in 2011. The ability to make quick upgrades and reusing flight-proven hardware is a significant advantage over satellite missions.

    STO1 cut-down

    A picture of the STO-1 payload during the recovery mission. Even though it tipped on it’s side, we were able to re-use almost all of the equipment for the STO-2 flight.

    The final advantage that balloon missions have over satellites is their cost. A satellite mission costs anywhere from a hundred-million dollars to over one BILLION dollars. Balloon missions cost between 1-10 million, depending on the complexity of the payload, mission length, etc. For emerging technology, like terahertz cameras, it makes sense to build and use small-scale balloon payloads to do really cutting-edge science before spending the money to dive into the finer scientific details with large-scale satellites. Balloon missions serve as a great pathway to developing robust technology that can survive the harsh space environment and still achieve the primary science objectives.

    Why Antarctica?

    Now that I have converted you to balloon-spacecraft enthusiasts, I can address the question of why we fly them out of Antarctica rather than out of ASU’s backyard. Believe it or not, the answer has a lot to do with the weather! Space-weather, that is.

    The maximum height the balloon reaches is ~125,000 ft, which is within the stratosphere. The atmospheric pressure at that height is less than 1% of what it is at sea level, but there is still enough air up there to have wind. Near the solstices, June 21 and December 21 each year, the winds at that altitude circle both the Arctic and Antarctic poles. In order for a balloon payload to be recoverable, as discussed above, we want to launch the balloon somewhere with stable weather conditions where we can reliably predict its flight path and plan on where it will land.  Since these polar winds are seasonal, we know approximately when they will occur each year, and can plan accordingly.

    STO1 flight path

    Approximate flight path of the STO-1 mission. The south pole is not in the exact middle of Antarctica, and you can tell where it is from this picture because it is almost exactly in the middle of the red circle! This picture is also pretty cool because you can see how much of the continent is made of permanent ice shelves.

    We also use the circularity of the winds to our advantage.  Since the winds circle the pole, we can launch the payload from a clear site, and wait for the balloon to make one or more rotations and land it near the launch site. You may not think this is important, but when you launch balloons at the poles, there aren’t roads to get to just any point on the continent to go pick up your payload. The outdoors are harsh even in the summer, and the nearest fully-functional hospital is over 1000 miles away. The closer you can land your payload to the station, the easier and safer it is for the recovery team. You can see the flight path of the STO-1 mission in the picture above.

    We launch balloons from Antarctica, but not many get launched from the Arctic. Why? If you look at the picture of Antarctica, what is missing? There aren’t any big towns on Antarctica, in fact, no person lives here permanently. NASA is concerned about the possibility of the balloons landing somewhere unsafe, since once the payload separates from the balloon there is no way to maneuver it for a controlled descent. The northern latitudes are more populous than the southern latitudes, so the risk of the payload causing damage is less in Antarctica. In the Arctic, the flight path of the balloons goes over many countries, some of which have restrictions on what spacecraft they allow to fly over them. Overall, it is safer to launch from Antarctica only.

    Finally, we only launch from Antarctica during the Antarctic summer (which is winter in the northern hemisphere). The main reason for this is because at 77 degrees south, the sun never sets at McMurdo in the summer. This is good for the telescope since it has 24 hour access to sunlight to get collected by the solar panels to power the various systems on the payload. It also makes the payload recovery easier, as well as easier for the scientists and engineers to set everything up.


  • kdavis32 8:10 pm on November 15, 2015 Permalink | Reply  

    Welcome to Antarctica 

    After 4 days of travel, I finally arrived in Antarctica on Friday afternoon. Antarctica is 21 hours ahead of Arizona time (it is on New Zealand time) so it was Thursday evening back in the states.


    Sea-ice as seen from the plane down from Christchurch


    View of the continent from Ross Island. The Ross Ice Shelf is in the foreground.


    Me at LDB with Mt Erebus in the background.

    We left from Phoenix at 6 PM on Monday afternoon. We had a fairly long layover in LAX, and then had a 15 hour flight to Sydney. We had a pretty quick turnaround in Sydney and then flew to Christchurch, NZ. T All said and done, we spent 29 hours in planes or airports, and it because of the 12 hour dateline crossing, we didn’t land until Wednesday afternoon.

    The following morning, we checked into the Clothing Distribution Center for orientation. We all got a final flu shot since they are very concerned with people getting sick out “on the ice”. We also had a computer screening and several safety briefs. After those were done, we went to get our Extreme Cold Weather (ECW) gear issued to us. We tried everything on and packed our bags into bright orange duffels. The ECW gear is a parka nicknamed ‘Big Red’, a pair of snowpants, waterproof boots called ‘bunny boots’, a lighter jacket, a hat and balaclava, goggles, liner gloves and outer gloves, and a fleece pullover and pants. Depending on what your job is, you might not need ALL of that gear, but Bog Red is a must for the cold!

    Friday morning we had to check into the CDC at 5:30 AM, so we caught our shuttle at 4:45 AM. We had another round of safety briefs, and had all of our luggage and ourselves weighed (fun). Then we took a shuttle out to the Spirit of the Medal of Honor, the C-17 taking us down to Antarctica. The C-17 is the second largest US Air Force plane, and is mostly used for cargo. There are only small portals to look out of the plane. The seats are fold-down seats mounted to the sides of the aircraft and face the other side of the plane, not forward. It turns out that the C-17 is such a large aircraft that the ride was actually very smooth. I did get to go up to the cockpit of the plane and take some pictures out of the front windows.


    Arriving in Antarctica. Everybody must wear their outer layers of ECW gear during the plane ride and landing. You can see the white ‘bunny boots’. Most of the plane holds cargo, and there were only ~15 people on our flight, which is small for this time of year.

    The flight takes 5 hours to reach Antarctica. McMurdo station is not actually located on the continent, but is on Ross Island which is the furthest point south accessible by sea. Ross Island is surrounded by a permanent ice shelf (Ross Ice Shelf), which is where the Long Duration Balloon (LDB) hangars are.The plane lands on the ice shelf on regular tires, not on skis. McMurdo has ~1000 people in the summer and ~200 people in the winter. It is the largest of any base in Antarctica. It is 77 degrees south, almost directly underneath New Zealand (2500 miles to the north). It is still another 900 miles down to the South Pole. There is a smaller American base at the Pole, and one on the Antarctic Peninsula underneath Chile/Argentina. The average summer temperature is between 0-25 F, but the wind chill often makes it feel much colder. The South Pole is approximately 10,000 ft in elevation, and so there are gravitationally-driven winds coming off the continent making it very windy most of the time. It will still snow in the summer, although it is much colder, stormier, and snowier in the winter.


    McMurdo station as seen from the tip of Observation Hill. You can see that a lot of the snow melts in the summer. Ross Island is volcanic, ansd so the rocks and dirt are all very dark and absorb heat easily. By the end of January, a lot of the sea ice will melt as well.


    Boarding the Kress transport vehicle after we landed. We take the Kress to the LDB balloon hangar every day as well.


    Glacier on the continent of Antarctica. It was beautifully lit from a part in the clouds.


    Helicopter about to land at McMurdo.

    After we had settled into our rooms, Chris and I took a hike up Observation Hill, which was used by Scott and his crew began their voyage in 1911. There is a cross at the top as a monument to those who perished returning from the south pole during the expedition.


    Panoramic view from on top of Observation Hill.

    The ballooning facility is located ~10 miles from the McMurdo base on the Ross Ice Shelf. It is called LDB for Long Duration Ballooning facility. There are two hangars, each with a different balloon project. There are several other supporting buildings and offices at the camp. The launch pad is behind the hangars and stretches in a circular pattern with a diameter of 2000 ft along the ice shelf. The ice is about 30 yards thick here and is permanent year round, unlike sea ice which is much thinner and recedes throughout the summer. The exact location of the LDB changes slightly each ear as the ice shifts. The buses must traverse a crevasse field on their way to and from base.


    Welcome flags at LDB field location.


    The LDB balloon station. STO-2 is in the right hangar this year. The launch area is behind everything.


    Mt. Erebus as seen from LDB. It is an active volcano, and sometimes you can see ash coming out of the top. While it looks close, it takes nearly a day to reach the base by snowmobile.


    Weddell seal basking in the midnight sun. There is 24 hours of daylight at this time of year in McMurdo. This picture was taken at ~8 PM.

    I am still getting settled into life on the base and preparing for launch. I will post again soon about the progress of the pre-flight assembly.

  • kdavis32 2:39 pm on October 29, 2015 Permalink | Reply  

    STO-2 Mission Overview and Hang Test August 2015 

    I am a graduate student at ASU working on the Stratospheric Terahertz Observatory reflight mission, STO-2. STO-2 is a telescope that hangs underneath a very large helium balloon. The balloon inflates to ~100 meters across and is full of helium gas. The balloon reaches a height of approximately 36 kilometers, which is within the Earth’s stratosphere. The telescope that sits underneath is 0.8 meters in diameter. The STO-2 science objectives are to look at Cold Dark Clouds in the interstellar medium of the Milky Way galaxy. These clouds are thought to further condense into Giant Molecular Clouds, where star formation takes place. Giant Molecular Cloud studies have been ongoing for several decades, but this mission will be one of very few to directly observe the Cold Dark Clouds, and will help us understand how Giant Molecular Clouds form. We will also study how interstellar clouds get disrupted by nearby high mass stars as they give off intense solar wind, and later from supernovas as they die.

    ISM carbon lifecycle

    A diagram showing the lifecycle of gas and dust in the Milky Way. The diagram shows which dominate species of observable chemical transitions are used to study each phase. The STO-2 mission observes CII and NII and OII emission.

    The STO-2 telescope looks at these cloud regions and uses three separate terahertz detectors to record data from these clouds. Each detector is specifically designed to look at photons emitted by different chemical transitions within the Cold Dark Clouds. Together, these three emission profiles help determine important properties of these galactic clouds, including: distinguishing which cloud type we are observing, what the temperature of the cloud is, where the cloud is located within the galaxy (3 dimensionally), how thick the cloud is, how the cloud is moving internally (rotating, expanding, etc), and the what the radiation environment surrounding the cloud is like. This information will lead us to understanding the higher level questions of: what is the complete lifecycle of interstellar gas, study the creation and disruption of star-forming galactic clouds, determine the parameters that effect star formation rate in the galaxy, and provide templates for star formation and stellar/interstellar feedback in external galaxies.

    STO galactic survey region

    The survey region of the STO-2 payload. We will look at a significant fraction of the galaxy which includes looking through the spiral arm and inter-arm regions.

    The STO-2 mission is scheduled for launch from McMurdo Station in Antarctica in December of 2015. Recently, I traveled to Palestine, TX to help with the integration and testing of the STO-2 payload. This test is critical to to ensure that the instrument is balanced and all of the equipment fits into its specified location, make sure that the data collected by the instrument is properly stored by the onboard computers and relayed by satellite to mission control, and to test that that the telescope is properly aligned and can receive satellite pointing commands.

    There are two major ‘teams’ working on the full STO-2 payload. The first is the instrument team, who are in charge of making sure all the receivers are working properly. The receivers we use are Hot Electron Bolometers (HEBs) for our CII and NII emission. These detectors need a lot of support electronics to make them work properly, and so the instrument team is in charge of focusing the light from the secondary mirror onto the detectors, through a series of lenses, mirrors, and windows. We also shine a second, high powered light source created by us onto the HEB detectors, which acts as a light ‘pump’ for our detectors. We call the light pump a Local Oscillator (LO). The HEBs convert the photons from the LOs and the gas clouds into lower frequency electrical signals. The electrical signals get amplified and converted into digital signals, which are read by our spectrometers. A lot of the electrical equipment, especially the HEBs, need to be supercooled to function properly. The camera sits inside a big dewar, which holds liquid helium at 4 degrees above absolute zero. The instrument team is not only responsible for making sure the electronics are properly aligned, they also need to make sure each piece of equipment is kept at its desired temperature.


    Members of the instrument team working on the electronics outside of the dewar during the Hang Test. The dewar is the white tank in the middle-left of the image with a lot of electronics boxes attached to it. We paint everything flight-worthy white to reflect as much sunlight as possible which helps keep it cool.  

    The other team for the STO-2 mission is the telescope team. While the instrument team sets up the receiver system, the telescope team sets up the majority of the structure of the payload as well as a lot of support systems. The telescope team handles the telescope itself, which is the primary and secondary mirrors, sitting along the long gold baffle. They also set up the guidance system, which uses visible light cameras to triangulate which direction the telescope is pointing, and uses gyroscopes and reaction wheels to keep the telescope steady and slew it back and forth to take an image of the cloud regions we study. The telescope gondola has two sets of solar panels to provide power to the telescope subsystems, and we have batteries on-board to store the extra energy. The telescope team is in charge of thermal control for all the equipment that isn’t cooled by the helium tank in the dewar. Finally, the telescope team provides contact to and from the telescope, which allows us to communicate via satellite with the telescope while in flight to check on its stats, upload pointing commands, and collecting the data through mission control.


    The telescope with the dewar attached but before the solar panels are installed. The guidance system has also not been installed underneath the telescope. The gondola pictured here is just shy of 20 ft. tall.

    The hang test is the first time that the instrument and telescope come together and all the electronics are hooked up to each other. The hang test takes place at the Columbia Science Balloon Facility in Palestine, TX. It is a small NASA center where they used to launch balloon missions, but cannot do so any longer now that Palestine is a booming metropolis (heh). You can still go out and see the gigantic launch pad, which is a 1000 ft diameter concrete circle, surrounded by an even wider open space now used for growing hay.


    The CSBF launch pad during the day (lower) and at night (upper). I wanted to include the sunset picture because it was very pretty. It was not as hot in Texas in August as in Phoenix, but it was about 3 times as humid. You can’t see the launch pad as well from these angles, but it is very large and quite pleasant to take a stroll around.


    During the hang test, the entire gondola payload is actually hung from a crane! The test not only tests the hardware system but also the software system, which is very complex, elegant, and designed by the STO-2 team specifically for this mission. The dewar and the telescope are integrated inside a large hanger. On the day of the test, a crane in the hangar lifts the payload to the door, where it is transferred to a separate crane and taken outside. The hanging payload is free to point and rotate, and it can communicate via satellite. Mission control (Houston) send pointing commands to the gondola, and the team can determine if the telescope is pointing correctly. We also take some ‘fake’ data and make sure it is stored and processed correctly. Since things went well, the hang test only took ~ 3 hours. However, there were two straight weeks of 10-16 hour days necessary to get us to that point (and one 22 hour day!). The success of the hang test shows that the mission is prepared to be sent down to Antarctica for launch. The entire system has to be taken apart to be shipped, so all that hard work gets immediately torn apart.


    The STO-2 instrument and telescope teams in front of the complete instrument gondola. Hang test success!


    The gondola only needs to hang by a few feet to be able to swing properly. You can see the back sides of the solar panels in this view, as well as the instrument support package underneath the dewar. The communication antennas are sticking out on the boom at the very top of the payload.

    Davis Groppi STO2 hanging

    Me and my adviser Chris Groppi with the payload. You can see the extent of the instrument better in this view.

  • kdavis32 2:27 pm on May 15, 2013 Permalink | Reply
    Tags: , , ,   

    Characterizing EDGES Radio Frequency Interference 

    Hello LoCo followers! As the avid readers should know, the LoCo team is working on developing a ultra-sensitive radio telescope, EDGES, in order to detect faint emission signals from the very earliest stars and black holes that formed in the universe. Since the signals are so faint, EDGES must be the most sensitive instrument of its kind. However, the high response of the telescope to small signals can be disadvantageous, since there are many other radio sources that can “drown out” the desired signal. Most everyone has experienced this effect as static on a car radio. In this case, the EDGES frequency range actually includes the FM band, and the radio signals that you want to hear in your car is, to us, just like ‘static’ that interrupts your favorite broadcasts! In fact, astronomers call this unwanted interference ‘noise’ even though it is caused by electromagnetic waves instead of sound waves.
    Here at ASU, I am looking at the radio frequency interference (RFI) patterns that disturb our observations of the early universe. In figure 1, you can see a typical plot of the intensity at a given frequency during the course of the day. The X-axis is a plot of frequency, and the Y axis shows time at one minute intervals. A red pixel shows that there was a lot of incoming flux at a given frequency, and blue shows a low level of flux. The large red sphere is actually the radio emission of our Milky Way galaxy. The vertical bands of high flux correspond to radio frequency channels that we humans use for broadcasting. Some of these bands are used for FM radio, some are used for GPS, and others are used for industrial or amateur radio communication (like cell phones or satellite TVs).

    Antenna Temp 2011_315_00_Ta

    The intensity of the RFI signals in these bands changes throughout the day for a wide variety of reasons. I am looking for times when the power is unusually high, and seeing if those events correlate to known environmental phenomenon. For instance, one of Earth’s atmospheric layers is composed of high temperature particles that have been stripped of their electrons and form ions, thus the layer’s name ‘ionosphere’. When a force perturbs this layer, the charges move around in wavelike patterns. Moving electrical charges radiate photons, and the frequency of the radiation is dependent on the frequency that the ions oscillate. If the ions oscillate at radio frequencies, then there will be an increase in radio photons coming from the ionosphere, and the EDGES instrument will record that event. Other RFI sources that cause noise in the data are meteor showers (that perturb the ionosphere), ionospheric clouds, solar flares, and geomagnetic storms.
    The frequency at which radio waves can propagate through the ionosphere is called the critical frequency. Signals at higher frequencies than this escape to space, while signals at lower frequencies
    are reflected back towards Earth. Figure 2 shows a plot of the average critical frequency of the f1 layer of the ionosphere for each day from 2007 to present, which spans the time period that the EDGES instrument has been running. You can see that there are seasonal peaks each year, due to the orientation of the earth’s magnetic field compared to the direction of the sun. I am interested in finding the spikes in the data, to see if there are any peaks in the RFI intensity on those dates.

    RFI 2011_315_00_rfi

    As mentioned above, infalling meteors are known to cause perturbations in the ionosphere. Many of these meteor showers are spectacular to view with the naked eye, but a few are so faint that we only know they are there because of the disturbances they make in the ionosphere that have been recorded by other radio instruments. Figure 3 shows a plot of how many meteors are expected to hit the atmosphere for any given day. They are separated into ‘visible’ and ‘radio’ showers, based on whether they are visible to the naked eye or have been detected by radio instruments only. The X axis runs over one year only, since the Earth only runs into each group of meteors once per year due to our orbit around the sun. The Y axis gives the Zenith Hour Mean (ZHM), which is the total number of events predicted to occur during the hour that the shower has the most meteors.

    Total Expected Radio and Visible

    So far, I have been working on getting the data into a format that will be meaningful to do the comparison between. In the next few weeks I should start to see if there are any of the correlations between the ‘noise’ in the EDGES data and the events that happen in the sky above it. If this is successful, I can use the information to remove the events from the data so the astronomical signal we want to detect will be clearer. Wish me luck!

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