On board the third SOFIA science flight
After the first SOFIA science flight from 30 November to 1 December 2010, yesterday's third flight already had a certain feeling of routine to it. But not for me – the last time I flew with an airborne observatory (KAO, the predecessor to SOFIA) was in July 1987! On the morning of 7 December, the latest updated software packages, with the scientific objectives and the resulting flight plan, were loaded into the onboard computers and the FORCAST instrument was filled with liquid nitrogen and helium. The crew briefing at 1:45 pm briefly went over all aspects of the mission and last minute changes to the schedule, and then we embarked on the aircraft at 2:15 pm.
Everything was packed away – everyone is in responsible for his or her own provisions during the flight. With safety checks to complete, it was 3:25 pm by the time the doors were closed. After the engines started, the telescope, instruments and communications and control systems were thoroughly checked over once more, before SOFIA was ready to take off. Then it was finally time – with 215.000 pounds of kerosene fuel, SOFIA took off at 4:11 pm into the clear Californian evening sky. Over Los Angeles, air traffic control directed us to the southwest, over the Pacific. After just 15 minutes, SOFIA had reached an altitude of 20,000 feet – usually time to open the telescope door to allow the telescope to cool down to ambient temperature. However, on this occasion, clouds prevented this and it was a further 45 minutes before we cleared the top of the cloud cover at 37,000 feet (11.3 kilometres) and the door could be opened. For the next three hours, with our nearly-full fuel tanks, we could not go any higher. But that was good enough for the scientists, since the observation targets had been selected to be able to deliver sufficient infrared radiation to the camera's detectors already at this altitude.
After just a few minutes, the telescope was aimed at the preselected area on sky and tracking precisely. The first object which Terry Herter and his FORCAST instrument team were interested in was Jupiter. They had already observed it during the 'First Light' test flight in May this year. Or, to be precise, they had observed the infrared radiation emitted by the gas giant's cloud bands. Observations by ground-based telescopes in the visible spectrum have detected unusual changes in the bands in recent months, and Herter and his team were eager to see whether their instrument would be able to detect them in the infrared as well. After around 80 minutes of observation they were delighted; they had sufficient data to do a thorough analysis over the following days. After this, the aircraft made a sharp turn; the next observation target was being acquired. Our colleagues from NASA and USRA were sitting in front of their flight plan monitor, following every change in the aircraft’s direction. Since the wind data from the cockpit were also available to them, they were able to correct any deviations from the original plan online.
In the meantime, Holger Jakob, Uli Lamparter and Andreas Reinacher were seated at the telescope control console, eager not miss any incoming data. As colleagues from the German SOFIA Institute, they were on board with the American team to control all the telescope functions, with special responsibility for its stable orientation. When an observation has been completed and the next 'science leg' begins, they have to follow with the telescope as the pilots turn the aircraft onto a new heading for the next flight leg and then fix and centre the new target using the guiding cameras. All this has to be done as quickly as possible, because only then can Herter resume his measurements.
With objects being targeted one after the other, it was soon 7:30 pm; one-third of our fuel had been burnt and SOFIA was able to climb to 43,000 feet (13 kilometres). At this altitude, there is significantly less water vapour to block the infrared radiation from celestial objects. Also, at this altitude SOFIA can manoeuvre without restrictions and fly longer 'science legs'; weaker astronomical sources are also accessible to the telescope. My feet were getting ice cold, my ears buzzing despite being encased in headphones (or perhaps because of them?), the water and sandwiches were no better than what you get on any economy class flight – but the scientists were nevertheless eager to observe their next target, the OMC1 and OMC2 molecular clouds in the constellation of Orion. Terry Herter would like to get a better idea of how new stars and planets form in these clouds of gas and dust. At 11:30 pm, after seven hours of zigzagging over the Pacific, the sea of lights that is Los Angeles appeared to starboard as SOFIA observed another star forming region, known as 'W3' for more than an hour. We 'u-turned' sharply above the 'Four Corners' – where the states of Arizona, New Mexico, Utah and Colorado meet – and as we flew back over Las Vegas we observed the comet 'Hartley 2', which was imaged during a close flyby by NASA's EPOXI deep space probe in early November this year.
At around 2:00 am, now Wednesday, observations had to come to an end, however, since we were running out of fuel. As usual, the scientists pleaded with the pilots for a few more precious minutes of observing time, but then it was over. At 2:03 am, the telescope was locked and the door closed. Everything had gone smoothly and SOFIA started its steep descent. With the aircraft’s noise pointing down, we had a spectacular view of the lights of the greater Los Angeles area. At 2:36 am, SOFIA landed and taxied back to its hangar at the Dryden Airplane Operation Facility (DAOF). However, nobody went home; the iron hand of tradition decrees that every flight is followed (in this case, at 3:30 am) by a debriefing session. This goes over the events of the night; the pilots, flight engineers and telescope operators report on any problems, and the scientists report briefly on their observations.
So, I quickly completed my report and sent it off, drove back to the hotel, hung the ‘Day Sleeper’ notice on the doorknob, switched off the phone (!!) – and went to bed.
The images are from the first science flight, during the night of 30 November to 1 December 2010. Top image and immediately above: View into the cockpit during the preparations. Second image: Pilot Frank Batteas about to enter the aircraft. Third image: SOFIA shortly before the first science flight. All images: NASA.