NASA, together with DLR of Germany, is close to completing initial envelope expansion tests of the Stratospheric Observatory for Infrared Astronomy (SOFIA) Boeing 747SP – the world’s biggest airborne observatory. I had a chance to inspect the impressive aircraft and its huge infra-red telescope inside NASA's Dryden Aircraft Operating Facility at Palmdale, California on April 20, 2010. The aircraft will cruise at altitudes up to 45,000-ft, above 90-95% of the atmosphere’s infra-red absorbing water vapor, and is expected to provide astronomers with around 1,000 science observation flight hours per year for at least 20 years.
SOFIA is an ex-Pan Am and United 747SP. (all photos and videos Guy Norris)
Flight testing so far indicates a robust platform with no handling vices or flight control issues says NASA. Flying with the 18-ft by 13.5-ft wide curved upper rigid door open, which covers an open cavity nearly 25% of the circumference of the fuselage, test crews report “no vibrations or aeroacoustics in the cavity that will prevent observations being made. The pilots say there are no adverse handling qualities and only minor differences in performance with it down and open.”
The telescope is mounted on the other side of this specially installed pressure bulkhead. The telescope installation weight is 17 tons (34,000 lb).
The cavity door closed and (below) open.
The first clip (below) shows the door opening mechanism and is followed by a brief introduction by Thomas Keilig of the University of Stuttgart’s Deutsches SOFIA Institute.
In the second clip, Thomas provides us with a walk-through description of the telescope (a 2.7m primary mirror IR system with a 2.5m diameter clear aperture), and the associated systems in the massive fuselage-mounted cavity. If you’re confused about how the sliding doors and covers work, click on this link to see a simple explanatory video clip.