German-Built Device Received New Reflective Coating

Engineers and technicians from NASA, the German Space Agency and the Deutsches SOFIA Institut recently reinstalled the German-built primary mirror assembly into NASA's Stratospheric Observatory for Infrared Astronomy, or SOFIA, airborne observatory.

Technicians removed the glass mirror from the modified 747SP observatory in April 2008 and transported it to NASA's Ames Research Center in Moffett Field, CA, where it received its reflective aluminum coating in a vacuum chamber in June 2008. The coating, five one-millionths of an inch thick, will be reapplied as necessary during the 20-year life of the program.

"We had completed system tests of our mirror coater but this is the first time we've actually coated SOFIA's mirror. The team and equipment performed flawlessly and the results are magnificent," says Ed Austin, SOFIA science project manager at Ames.

The mirror assembly was transported back to NASA's Dryden Aircraft Operations Facility in Palmdale, CA mid-September, and reinstalled October 8.

"The reinstallation of the mirror is a significant program milestone on the path to science observations with the SOFIA observatory in the summer of 2009," said Bob Meyer, SOFIA program manager at NASA's Dryden Flight Research Center in Edwards, CA.

In coming months, both the telescope and the aircraft's telescope cavity door system will be adjusted, leading to open-door ground operational testing. These activities will be followed by six to eight open-door flight tests next spring to study the handling qualities of the aircraft as air flows over and into the telescope cavity.

The upper rigid cavity door will be opened incrementally at various altitudes to determine the aero-acoustic effects, or buffeting, on the aircraft and telescope systems. NASA and Deutsches SOFIA Institut, or DSI, engineers considered the challenges of aero-acoustic effects on the telescope when designing the cavity system, completing wind tunnel tests and computational fluid dynamics analyses to minimize these effects.

SOFIA's state-of-the-art infrared telescope and some of the observatory's scientific instruments will be tested on the ground in the next few months in preparation for the first open-door test flights.

The optical performance of the telescope system will be checked using the High-speed Photometer for Occultations, or HIPO, science instrument built for SOFIA at the Lowell Observatory in Flagstaff, AZ. HIPO takes images of the sky rapidly at wavelengths the human eye can see. Once HIPO has been used to check the basic characteristics of the SOFIA observatory, the two infrared instruments intended for the first scientific flights will be mounted for more ground observation tests.

After these ground tests are complete, a short series of initial astronomical science flights are planned. During the six scheduled flights, the Faint Object Infrared Camera, or FORCAST, from Cornell University, Ithaca, NY and the German Receiver for Astronomy at THz Frequencies, or GREAT, from the Max Planck Institute for Radioastronomy in Bonn, Germany, will conduct SOFIA's first science observations.

SOFIA incorporates a 2.5-meter diameter infrared telescope in a Boeing 747SP aircraft that will carry the telescope into the stratosphere to conduct astronomical research. The observatory also includes a ground-based science center.

SOFIA is a joint program between NASA and the German Space Agency, Deutsches Zentrum fur Luft-und Raumfahrt or DLR. The SOFIA program is currently managed at NASA Dryden and the aircraft is based at the Dryden Aircraft Operations Facility. NASA Ames manages the SOFIA science and mission operations in cooperation with the University Space Research Association, or USRA, and the DSI.

FMI: www.nasa.gov/sofia, www.sofia.usra.edu