Luke Keller

Luke Keller

Dana Professor, Department of Physics and Astronomy

Specialty:Astrophysics, airborne astronomy, spectroscopy, optical instrumentation, natural science general education
Phone:(607) 274-3966
Office:264 Ctr for Natural Sciences
Ithaca, NY 14850


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Preparing for astronomy with NASA's newest airborne observatory

Posted by Luke Keller at 11:40PM   |  Add a comment
Looking out the window of SOFIA as we taxi across the DAOF runway prior to takeoff on November 18, 2010.

On Thursday, November 18, we took off for the last of the observatory characterization flights. We tested several techniques that we will use to get the first science results in early December. The next time we fly we'll be conducting observations for new astronomical research.

The tests went very well. Follow this link to a short movie of an infrared image of a star taken with FORCAST while in flight. You will notice that the image of the star is two or three pixels across and moves around very quickly. The movie is actually five copies of a two-second clip for a total of ten seconds. The movie was recorded with FORCAST at a frame rate of 400 Hz (Hertz, or frames per second, see my previous post for a few more details). The purpose of this test was to understand telescope vibrations (and how they affect image motion) so that they can eventually be removed or at least minimized. Minimizing vibrations will improve the image quality since most objects we observe with SOFIA will be very faint so we will use long exposure times, which combined with the motion of the telescope will produce fuzzier images.

This and other tests went very well. Our final test included observations of the Orion Nebula (M42 for you astronomers), a region where stars are forming about 1500 light years from Earth. The data look so good that we expect to be able to use them for new astrophysics studies. In other words, SOFIA is ready for astronomy! [Images to come in a future post.]



Posted by Luke Keller at 8:40AM   |  4 comments
Self portrait as we take off on SOFIA

Today we took off on SOFIA for its second flight devoted 100% to measuring and characterizing the performance of the telescope and camera systems. It was very exciting for me to finally fly after working so long on the project. I was in charge of data quality control during the flight. We spent last week conducting line operations (we call them "line-ops"), using the observatory as if we were in flight but actually sitting on the ground. During the line-ops we practiced controlling the movement of the telescope with computer commands issued from the FORCAST camera. Juergen Wolf and his team from DSI and NASA/Ames also tested their new fine diagnostic camera (FDC), which can take visible light images at several hundred frames per second. For comparison, a movie or video camera usually records images 60 times per second. Why so fast? We wan't to "freeze" the star images, which move around in the telescope and camera viewers due to vibrations of the telescope and aircraft. Taking very fast movies in both visible (FDC) and infrared light (FORCAST) will allow the telescope team to understand in detail how the optical and telescope control systems are working. All of our testing so far indicates that the telescope and cameras are ready to go after a few small adjustments. Our first flight devoted to new astronomy (no more testing!) are scheduled for the week after Thanksgiving. 

Take-off time was 5:00 PM (Pacific Time) on Wednesday, November 10. The flight was scheduled to be 10 hours long, enough time for us to fly from LA to London, but instead we flew a back-and-forth flight plan as they did for the first light flight in May. Here's the flight plan from from last night's flight:

SOFIA flight plan

The flight began and ended at DAOF in Palmdale, CA (the white dot at the top of the map). The faint dotted outline in the upper right corner is the coast of southern California and Baja, Mexico. The light blue/green lines are the flight "legs" that add up to the full 10-hour flight plan. Each flight leg is plotted so that SOFIA can observe a particular object in the sky. For this flight the targets were bright stars that we used to test the cameras.

The flight crew including FORCAST team worked hard during the flight. This photo shows the FORCAST team working at the "PI Rack" that contains our camera control computer and the communication system that we use to communicate with one-another during the flight. Everyone wears headphones to reduce noise and enable efficient communication.

FORCAST team working on SOFIA

Our flight was about an hour longer than planned due to a minor problem: the telescope cavity door was stuck open (!!) due to a software glitch. Not a problem for the aircraft or pilots, but they had to slow our descent to allow the telescope mirrors to warm up from -37 C (at our cruising altitude of 42,000 feet) to 1 C on the ground. Landing with a cold telescope would have condensed ice on the mirrors, bad news for a $100,000,000 telescope! As soon as we landed, the aircraft operations engineers fixed the problem and closed the door.
All in a night's work on SOFIA.

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