Luke Keller

Luke Keller

Associate Professor and Chair, Department of Physics and Astronomy

Specialty:Optical instrumentation, astrophysics, physics education research
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 2:10PM   |  1 comment
FORCAST (red with gold colored electronics boxes attached) is now installed on the SOFIA telescope. (Photo by George Gull)

FORCAST is now bolted to the telescope assembly on SOFIA! George Gull and Chuck Henderson, assisted by the engineering team at DAOF, have successfully installed the camera system. The process of lifting the instrument from the ground, rolling it onto the aircraft on its cart, and attaching it to the telescope went very smoothly. On Monday they restored all of the electrical cables and Terry Herter joined them as they powered all systems up. Everything is working well. I think it looks smaller on the telescope than it did in the lab, but that's not surprising since it is now attached to a 20-ton telescope!

The next step towards the first-light flight is to align the FORCAST camera optics with the telescope optical system and measure image quality while observing bright stars with the aircraft parked on the ground. Once we complete these so called line-operations (or "line-ops"), we will conduct rehearsals of our in-flight tests and observations. Flight time on SOFIA is very expensive so any work that we can do on the ground, or that we can make more efficient by practicing on the ground, will save us time (and therefore $$) during the flights. I will travel to DAOF next week to help with line-ops and set up the data processing and analysis software that my students and I have developed. I will also prepare for processing the data taken during the first light flight. Looks like FORCAST will be flying soon...

Posted by Luke Keller at 12:53PM   |  Add a comment
FORCAST pointed at the sky, measure the infrared sky brightness. Chuck Henderson at the controls.

SOFIA test flights have been successful and plans are in the final stages now for the "first light flight," the first flight on which we will conduct astronomical observations with a science instrument on the telescope. First light is a major milestone for any observatory; it's usually the first time that the entire telescope-instrument combination are used to gather data that could be used for astronomy (as opposed to data used to test the telescope). 

The SOFIA telescope assembly had it's first light in late 2008 while the aircraft was parked on the ground. For that initial test of the telescope system astronomers used the Lowell Observatory's High-Speed Imaging Photometer for Occultations (HIPO). That test verified that the telescope optics and aircraft observatory systems work together to allow astronomical observations. The FORCAST camera had it's own first light on a ground-based telescope. These tests showed that the FORCAST optical and electronic systems are ready. Last week SOFIA flew with the telescope cavity opens and the telescope tracking system on. Results of those tests showed that SOFIA can track astronomical objects well in flight.

Now it's time to put the SOFIA telescope and FORCAST together and test the performance of the telescope by making infrared images of bright stars. One measurement that we have made in preparation for these observations is to measure the infrared brightness of the sky using FORCAST from the ground with no telescope attached. George Gull and Chuck Henderson made those observations on May 5 and they are now installing FORCAST on the SOFIA telescope for the first time. The next step will be observations with FORCAST and SOFIA from the ground and, finally, the telescope characterization flight tests. Once those tests are completed successfully the plan is to image something that looks a bit more interesting.

FORCAST will be the instrument used for the first light in flight (I like to call it First [F]Light!). Stay tuned for the first astronomical data taken from SOFIA in flight!

Posted by Luke Keller at 3:39PM   |  Add a comment
An infrared image of the author taken with FORCAST in the lab at DAOF.

After several infusions of liquid helium, FORCAST has been running for the past ten days with its infrared detectors at a chilly 4 K (-453 F, -269 C). Why so cold? Infrared light does not carry much energy so our infrared detectors have to be very sensitive. At room temperature or even at the temperature of liquid nitrogen (-321 F, -196 C) the electrons trapped in the detector still have enough thermal energy that the detector cannot distinguish electrons moving around because they are "warm" from electrons moving around because they have just been hit by infrared light. Once the detectors are cooled with the chillier liquid helium, the electrons are very lethargic unless they are illuminated by infrared. So 4 K is the optimal temperature for running FORCAST. We keep the optical components of the camera, including filters, at 77 K (liquid nitrogen)  so that they do not emit infrared light and confuse our observations of warm objects in space. Here's a nice explanation of infrared astronomy.

It's a common misconception that infrared is heat; not so! Infrared is light that our eyes cannot see. Objects that are relatively warm (an astronomer for example) emit a lot of infrared. If you have an infrared camera, you can see the light that people emit--we're walking infrared light bulbs. The image at right is portrait of your's truly taken with FORCAST in the DAOF lab. Notice that my warm skin is bright (high infrared intensity), while my cooler glasses and shirt are darker (low infrared intensity). If you look more closely, you'll see that my nose and beard are cooler than my skin since they appear slightly darker in the infrared image. 




Posted by Luke Keller at 12:25AM   |  Add a comment
The FORCAST camera (left) and supporting electronics and computers assembled in the DAOF lab.

FORCAST is now at the Dryden Aircraft Operations Facility (DAOF). We spent last week making small final adjustments and additions to the instrument, preparing for it's move to the lab at DAOF. By the end of the week all of our equipment was loaded into eight large crates. The FORCAST cryostat--containing the camera optics, filter changing mechanisms, and infrared detector arrays--has its own crate that George designed with two shock-absorbing layers. How do you send a multi-million dollar camera system across the continent? FedEx! FORCAST had its very own truck dedicated to the move, which took two days. The shipment arrived in Palmdale on Monday, February 8. George, Justin, and Chuck flew out to begin unpacking the boxes on Monday afternoon. I arrived on Tuesday afternoon to help assemble the instrument and prepare for cooling the inner optical and electronic systems. I worked with George and Chuck to check for vacuum leaks in the cryostat, then we let the vacuum pump work for a few hours.

Today we are cooling the cryostat to 77 K (-321 F, -196 C) using liquid nitrogen. After "soaking" in liquid nitrogen for 24 hours, we'll cool the system with liquid helium to 4 K (-453 F, -269 C). By Friday, the instrument will be fully assembled, running at its operating temperature (4 K), and ready for testing.


DAOF is an exciting place to work. The lab dedicated to FORCAST is located in the DAOF Site 9 hangar facility and SOFIA is parked about fifty feet away. Here's the view from our door; that's the nose of the 747 staring at us! It's an awesome sight. Very exciting to finally be here with FORCAST. Everything is working well and the USRA and NASA folks have been very welcoming and helpful. At the end of the day we watched as the maintenance crew pushed SOFIA out onto the tarmac for fueling. It will take off tomorrow morning for a test flight.

Posted by Luke Keller at 3:00PM   |  Add a comment
SOFIA flying with its telescope cavity 100% open.

On December 18, 2009, SOFIA made a successful test flight on which the telescope cavity door was opened fully while flying at an altitude of 35,000 feet. This is a huge success for the aircraft teams. That flight was followed on January 15, 2010, by a closed-door flight during which the telescope was "uncaged" and activated for the first time. That means the telescope was freed from it locking mechanism, which keeps the system rigid and motionless during takeoff and landing, and the telescope tracking and control system were tested. The tests were successful, which brings us much closer to the open-door nighttime flights with FORCAST installed!

Here are photos and movies of the open-door flight. Spectacular!

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