Stratospheric Observatory for Infrared Astronomy

Stratospheric Observatory for Infrared Astronomy
Name	Stratospheric Observatory for Infrared Astronomy
Caption	The NASA Boeing 747 SP aircraft carrying the telescope in flight.
Organization	NASA / German Aerospace Center
Wavelength	Infrared, submillimeter
Built	2007
First light	2010
Decommissioned	2022
Website	https://www.nasa.gov/mission_pages/SOFIA/index.html

Stratospheric Observatory for Infrared Astronomy. It was a joint project of NASA and the German Aerospace Center (DLR) to construct and operate an airborne observatory. Mounted aboard a heavily modified Boeing 747 SP aircraft, it conducted astronomical observations from the stratosphere, above most of Earth's infrared-absorbing water vapor. The observatory's mission concluded in September 2022 after more than a decade of scientific flights.

Overview

The observatory was a unique platform that flew at altitudes between 39,000 and 45,000 feet, placing it above more than 99 percent of the atmosphere's water vapor. This allowed its suite of instruments to access wavelengths of infrared and submillimeter light that are otherwise blocked from ground-based telescopes. Its mobility enabled observations of transient events, such as occultations, and studies of celestial objects best viewed from the Southern Hemisphere. The project was managed at NASA's Armstrong Flight Research Center, while science operations were coordinated by the Universities Space Research Association and the German SOFIA Institute.

Development and history

The concept of an airborne observatory succeeded the highly successful Kuiper Airborne Observatory, which operated from 1974 to 1995. Development began in 1996, with NASA selecting the Boeing 747 SP airframe in 1997. Major modifications, including cutting a large door in the fuselage and installing the telescope assembly, were performed by L-3 Communications in Waco, Texas. The telescope's primary mirror was manufactured by Zeiss in Germany. After extensive testing, including "open door" flight tests, the observatory achieved first light in 2010. It entered full operational capability in 2014 and its mission was extended several times before a final review by the NASA Astrophysics Division recommended its termination, leading to the end of operations in 2022.

Technical specifications

The airborne platform was a Boeing 747 SP aircraft, registration N747NA, originally delivered to Pan Am in 1977. The telescope itself was a reflecting telescope with a 2.5-meter (100-inch) diameter parabolic primary mirror, making it the largest airborne telescope ever built. The mirror was made of Zerodur glass-ceramic by Zeiss. The telescope was mounted in the rear fuselage behind a pressure bulkhead, with a large door that opened in flight to allow observations. A complex system of gyroscopes and mechanical bearings isolated the telescope from aircraft vibrations. The aircraft typically operated out of its base at NASA's Armstrong Flight Research Center in Palmdale, California.

Scientific instruments and capabilities

The observatory hosted a suite of interchangeable instruments developed by international teams. Key instruments included the Faint Object infraRed CAmera for the SOFIA Telescope (FORCAST), a mid-infrared camera and spectrograph. The German Receiver for Astronomy at Terahertz Frequencies (GREAT) was a heterodyne spectrometer for high-resolution spectroscopy in the far-infrared. The High-resolution Airborne Wideband Camera Plus (HAWC+) was a polarimeter for studying magnetic fields in interstellar dust. Other instruments, such as the Echelon-Cross-Echelle Spectrograph (EXES) and the Focal Plane Imager (FPI+), provided versatile spectroscopic and imaging capabilities across its wavelength range from 0.3 to 1600 microns.

Key discoveries and scientific results

The observatory made several landmark contributions to astronomy. It was the first to detect the hydroxyl radical (OH) in the atmosphere of Mars, confirming a decades-old prediction. It provided conclusive evidence of water on the sunlit surface of the Moon, within Clavius crater. Observations of the Orion Nebula with the GREAT instrument revealed the chemical fingerprint of the helium hydride ion (HeH+), the first type of molecule to form in the universe. It also studied magnetic fields in the Whirlpool Galaxy and the Centaurus A galaxy, and observed the aftermath of the New Horizons spacecraft's flyby of Pluto.

Operations and mission profile

Science flights typically lasted 8-10 hours, departing in the evening from Palmdale, California. The aircraft could deploy to temporary bases around the world, including Christchurch, New Zealand, for observations of the southern sky. During flight, astronomers operated the instruments from within the main cabin, communicating with the telescope operators and the aircraft crew. Mission planning was conducted by the SOFIA Science Center at NASA's Ames Research Center. Over its operational lifetime, it conducted nearly 800 flights, with data archived and made publicly available through the SOFIA Data Cycle System and the Infrared Science Archive at the Infrared Processing and Analysis Center.

Category:Infrared telescopes Category:NASA aircraft Category:German Aerospace Center Category:Space telescopes Category:Observatories in California