Sofia en route to Germany

September 20, 2011

On 17 September 2011 Sofia, the airborne observatory, flew from Palmdale, California to Cologne, Germany. Author Alexander Stirn was on board. This is his log.

Rolf Güsten from the Max Planck Institute for Radio Astronomy, engrossed in his work on board Sofia.

1.30pm CEST: Sofia is carefully towed out of the large hangar at Dryden Aircraft Operations Facility in Palmdale, California. The flying infrared observatory, which is operated jointly by NASA and the German Aerospace Center, has already been airborne 75 times. But today will be something special.

2.00pm: The sun is slowly rising in the Californian desert, which is nine hours behind German time. NASA technicians have begun to refuel Sofia. The converted Boeing 747SP needs exactly 140 tonnes of aviation fuel before it can set off on its first ever flight to Germany. The take-off weight for the journey to Cologne has been calculated to be 361 tonnes. “Don’t worry, Sofia was just as heavy during some of our tests – and everything went OK,” pilot Troy Asher assures us. The refuelling takes about an hour.

4.30pm: Crew briefing. Everyone who wants to fly with Sofia has to attend the meeting. The room on the first floor of the NASA hangar is full of people; around 50 men and women will be on board today’s flight. Yesterday, technicians fitted some extra seats. The radio equipment in the cockpit is also new – otherwise Sofia would not have been able to head for European airspace.

6.43pm: Asher, one of NASA’s most experienced test pilots, switches on the “Please fasten your seatbelt” sign. The jumbo bumps along to the take-off runway.

7.08pm: Eight minutes behind schedule, Sofia gives full thrust on runway 25 at Palmdale Regional Airport. The plane seems heavy, the acceleration sluggish – almost as if it will never end. Finally, the airborne observatory manages to leave the ground. Its route will initially take it due north, almost to the North Pole.

7.16pm: Sofia’s crew and the specialist telescope technicians are wearing beige overalls made of fireproof material, the scientists working with the German instrument Great (German Receiver for Astronomy at Terahertz Frequencies) are wearing blue shirts embroidered with Sofia’s logo. As soon as the pilot, Asher, switches off the seatbelt sign, the two groups mingle with each other: all of Sofia’s take-offs so far have been at night. But now, during the transfer flight to Europe, the engineers and researchers use the remaining hours of daylight to take a few souvenir photos of the Californian desert.

Flight planner Randolf Klein

9.30pm: Sofia enters Canadian airspace. Troy Asher turns the dial of the autopilot slightly and steers the plane onto a new course. The plane is 34 years old, the cockpit is full of switches, knobs and round instruments. A crew of four and a navigator are needed to fly the jumbo jet over the Atlantic. The flight engineer neatly keeps a record of the fuel consumption – with pen and paper.

11.07pm: Waiting for the sunset. Some of those on board are reading, others sleeping or racing cars on their iPad.

0.14am: Almost unnoticed, the crew has opened the flap, which has an area of several square metres and protects the telescope mounted in the rear part of the fuselage during take-off and landing. “If we didn’t know the hatch was open, we wouldn’t notice it,” says Asher. “The aerodynamics engineers have done a fantastic job.”

The cockpit at 2 o’clock in the morning.

0.24am: “A star, we have a star,” shouts telescope engineer Randy Grashuis with delight. Although it is still daylight outside, Sofia’s camera has registered its first heavenly body. Stars are important for getting bearings in the sky, but the main thing is that their light serves as a fixed point which can be used to firmly align the telescope regardless of the movements of the plane.

1.01am: “It’s not looking so good,” comes a voice from the corner where the scientists are sitting. Although we are flying at an altitude of up to 43,000 feet (13.1 kilometres) there is still a relatively large amount of water in the atmosphere. Water vapour is the enemy of the infrared astronomers: it swallows up the interesting frequencies. The water vapour measurements are indicating 35 micrometres, the optimum value at this altitude would be five micrometres. At ground level, in the Atacama Desert, for example, where the air is as dry as dust, the value is more than 300 micrometres.

1.37am: Forty minutes later than expected Sofia provides the first useable spectra. “Good work, Randy,” is the praise from Jürgen Stutzki, a physicist at the University of Cologne and one of the scientific directors of the Great consortium. Ideally, the spiky lines should have a clear hump in their centre. In IC342, the star-forming region being observed today, this curve is very weak, however. “This source is really challenging,” says Stutzki. “It’s really painful.”

2.25am: Time is running out for the astronomers. In barely 25 minutes, southwest of Iceland, Sofia must end its slight left bank which ensures that IC342 remains in the telescope’s field of view. Its path is obstructed by a no-fly zone.

2.43am: “Ten minutes remaining,” radios Mission Director Charlie Kaminski over the plane’s own communication system. Groans.

2.48am: “Five minutes,” says Kaminski. Someone replies: “Oh, oh.”

2.52am: “One minute!” – “My God!”

The airborne observatory has landed in Cologne.

2.53am: Right on time, Sofia steers onto its intended course. The telescope is clamped down. And that’s the end of IC342. “We always come up against the time limit,” says Rolf Güsten, head of the Great project from the Max Planck Institute for Radio Astronomy in Bonn. “But it would be much worse if we ran out of work during the journey.”

5.15am: “Four minutes left.” – “Wow!” With Galaxy M82, the second object on the transfer flight, the astronomers are experiencing the same problems. “It’s a brutal business,” says Urs Graf, a physicist at Cologne University and one of the team which developed Great. “It is therefore all the more important that all observations are precisely planned and specified down to the very last detail.”

6.06am: Mission Director Charlie Kaminski gives the order to close the hatch in the fuselage again.

6.13am: “This is NASA 747 Heavy, say again!” On the deck above, pilot Troy Asher is contending with the dense, completely unfamiliar air traffic over Europe, with the radio equipment and the accents of the air traffic controllers. He finally manages it.

6.49am: The Boeing 747SP makes a hard landing as it comes down to earth on runway 14L at Cologne/Bonn airport. Sofia has arrived in Germany.

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