August 20, 2019

24.06.10: SOFIA takes flight.

A unique airborne telescope is now open for business after what has seemed like endless delays. On May 26th, NASA’s SOFIA, or the Stratospheric Observatory For Infrared Astronomy took flight to perform its first nighttime observations of the far infrared sky. And what a long road to flight it’s been… SOFIA was first proposed in the mid-90’s as a joint German DLR/NASA venture. The primary instrument consists of a 2.5 meter telescope (similar in size to Hubble) positioned perpendicular to the fuselage of a 747SP peering out a retractable cut away opening. SOFIA operates at a wavelength of 0.3 to 1600 microns, and at a cruising altitude of 41,000 feet should give diffraction limited views at wavelengths exceeding 15 microns. SOFIA needs this lofty perch to put it above 99% of the Earth’s water vapor absorbing atmosphere; at these altitudes, seeing is typically in the 2″ to 4″ arc second range. The entire project was brought back from the brink several times; in 2006, the plug was nearly pulled by Congress as the package had just neared completion! Even with cost overruns, flying telescopes aboard planes or balloons is still many times cheaper and easier than placing them into space… SOFIA is the logical predecessor of the Kuiper Airborne Observatory, a 0.9 meter IR telescope that flew aboard a modified C-141 cargo transport from 1974-95. Already, SOFIA is showing its stuff on its first observing runs, and is expected to reach a goal of 150 flights a year by 2014. Service life of SOFIA is expected to be 20 years, again far longer than that of any IR-dedicated space based telescope. SOFIA will operate out of NASA’s Dryden Aircraft Operations Facility near Palmdale, California. The 747 is a special performance (designated by SP) edition, capable of long duration flights and a range of 6,600 miles, ideally suited for the SOFIA mission. Of the 45 747SPs built, only 14 remain flying, from those flown by several Middle Eastern VIPs to the one owned by televangelist Ernest Angley (!) These are marked by the distinctive “stubby” or shortened fuselage design built to cut down weight. Doubtless, SOFIA has been the noblest use of this unique airframe yet…but hey, we are biased towards all things astronomical. You’ve come a long way, baby!