Monday, February 22, 2010
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.
Thursday, February 11, 2010
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.