During 2010, SOFIA, the Stratospheric Observatory For Infrared Astronomy – a joint project of the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) and NASA – achieved programme goals and passed milestones at a pace almost as fast as the observatory can fly.
On 8 February 2010, Principal Investigator Terry Herter and his team from Cornell University and Ithaca College, both located in Ithaca, New York State, delivered what would become SOFIA’s first operationally flown instrument, the Faint Object InfraRed Camera for the SOFIA telescope, or FORCAST. This instrument is a mid-infrared camera that records images in the 5 – 40 micron range (5 – 8 microns, 17 – 25 microns, and 25 – 40 microns, depending on the channels or filters selected). For comparison, the human eye sees radiation with wavelengths between 0.4 and 0.7 microns. The instrument was delivered to SOFIA's operations base at the NASA Dryden Aircraft Operations Facility (DAOF) in Palmdale, California, and was quickly set up in one of DAOF’s laboratories. In the laboratory, engineers from the FORCAST team tested the instrument thoroughly to verify its performance before installing it on the SOFIA telescope.
Achieving 'first light'
Once the FORCAST instrument had been tested in the laboratory, it was mounted on the SOFIA telescope and a series of 'line-ops' or ground-based trials on the tarmac, began at sundown on 19 May. From the ground, the telescope tracked the planet Mars and spent a number of hours capturing images of Polaris, the North Star, to check alignment and focus. By 22 May, testing was complete and SOFIA's science staff took the weekend off to rest.
In astronomy, 'first light' is when photons from a celestial object travel down a telescope's tube for the first time. For SOFIA, first light was determined to be the first time a celestial object was imaged in flight – a little different to a ground-based telescope, but an event certainly worthy of celebration. At around 22:00 local time on 25 May, SOFIA took off from Palmdale for its first light flight. While cruising to its flight area, the telescope door was opened to cool the mirrors to a temperature between -30 and -40 degrees Celsius. In the late hours of 25 May, the FORCAST instrument recorded infrared light that had been emitted by the red supergiant star Antares (Alpha Scorpii) 550 years ago.
The observatory’s second target for the evening was Jupiter, which was imaged at wavelengths of 5.4, 24, and 37 microns (24 microns is very hard to see from ground-based telescopes and 5.4 and 37 microns are impossible to see from Earth). The FORCAST instrument looked through the clouds of Jupiter to record heat radiating from the interior of the planet.
Observations of Jupiter were followed by a close look at the galaxy Messier 82 in the constellation Ursa Major. Peering through its obscuring clouds of dust and gas, SOFIA captured images of the star-forming heart of the galaxy, more than 10 million light years away. The first light flight was not only the first time light entered the telescope, but was planned as a demonstration of SOFIA’s stability and versatility, imaging stars, planets and a galaxy on the same flight.
"Looking back on this accomplishment, I could not be more proud of our team in their commitment to the project, their dedication to completing the required flight tests, and meeting the first light milestone on schedule," said NASA SOFIA Programme Manager Bob Meyer. "These tasks had to be completed before SOFIA could pass from being in the testing phase to becoming a flying observatory about to release world-class astronomical science results."
Observatory in operation
After the first light flight, SOFIA entered its 'Short Science' observing phase, which highlights the capabilities of the airborne observatory. The Short Science programme consists of three flights with FORCAST (accomplished at the end of 2010) and three observing flights in spring 2011 with the German REceiver for Astronomy at Terahertz Frequencies, or GREAT, a spectrometer developed by a team from the Max Planck Institute for Radio Astronomy (Max-Planck-Institut für Radioastronomie; MPIfR) in Bonn, lead by Principal Investigator Rolf Güsten. GREAT's first flight on board SOFIA will take place in April 2011. GREAT produces very high-resolution spectra at wavelengths between 60 and 200 microns and has been designed with a beam splitter that enables two channels to be monitored simultaneously.
"GREAT will provide a new opportunity to study the atmospheres of planets, examine the chemical composition of the interstellar medium and will expand our knowledge of circumstellar disks around young stars," said Hans Zinnecker, SOFIA Science Mission Operations Deputy Director, based at the University of Stuttgart. "The international collaboration between GREAT and SOFIA delivers one of the most versatile and unique astronomical instruments available for studying the far-infrared spectrum. In the foreseeable future, GREAT is the only instrument, ground- or space-based, able to collect such data."
In June 2010, SOFIA science staff and interested researchers gathered at the Asilomar Conference Center to discuss the next generation of instruments for SOFIA. Valuable input was received and incorporated into the parameters of NASA's announcement of opportunity for second-generation instruments. Final solicitation for new instruments will take place in mid 2011.
First science flights
SOFIA's first science flight took place on 30 November 2010. FORCAST Principal Investigator Terry Herter was on board leading the collection of data. Celestial targets imaged during the initial science flights included Comet Hartley and star-forming nebulae Messier 42, W3 IRS5 and Sharpless 140.
"SOFIA and its instruments will enable us to see regions of the Milky Way at infrared wavelengths that, at this time, cannot be observed with any other telescope, ground- or space-based," said NASA SOFIA Project Scientist Pamela Marcum. Marcum was on board SOFIA monitoring operations on the second science flight.
In 2011, researchers expect to release scientific results from flights with SOFIA. NASA is planning to issue the final solicitation for new instruments around mid-year, and scientists will have the opportunity to apply for time on SOFIA in late 2011.
During 2011, the SOFIA team will be starting its Airborne Astronomy Ambassadors (AAA) programme, where educators will have the opportunity to participate in science operations with SOFIA researchers..The educators will then share their experience with the public by presenting workshops, training other teachers, and presenting programmes at schools, science centres and to groups within their local community.
Bob Meyer summed up the excitement SOFIA has brought to the astronomical community by saying, "everyone on the SOFIA team has high expectations for this new phase of operations and we anticipate that more valuable and intriguing scientific results will come from our next set of observations."
The SOFIA programme is managed at NASA's Dryden Aircraft Operations Facility in Palmdale, California. The NASA Ames Research Center in Moffett Field, California, manages the SOFIA science and mission operations in cooperation with the Universities Space Research Association (USRA) in Columbia, Maryland, and the Deutsches SOFIA Institut (DSI) in Stuttgart.