In touch with the stars
© NASA/DLR
September 2021

In touch with the stars

The flying observatory SOFIA is arguably the most efficient way of looking into space. It combines the far-reaching vision of satellite-based telescopes with the comparably easy maintenance of ground-based observatories, plus very high versatility. At the heart of it is a reflecting telescope with a diameter of 2.7 meters (8.9 feet) and a Schaeffler bearing.
Facts and figures
  • 13.7 km
    (45,000 ft) is the altitude at which SOFIA flies. There, at the lower edge of the stratosphere, 99 % of the water vapor in Earth’s atmosphere is below it and the infrared rays from space can reach the telescope unhindered.
  • 3–4 times
    per week. This is how often SOFIA normally embarks on its observing missions. The flights last 8 to 10 hours. SOFIA’s home base is NASA’s Armstrong Flight Research Center, Building 703, in Palmdale, California. But missions have also departed from New Zealand, French Polynesia and Germany.
  • SOFIA
    flies at Mach 0.7 (870 km/h; 540 mph).
  • SOFIA’s base jumbo jet
    was put into service in 1977 as a PanAm airliner. In 1997, NASA took over the jet. It’s one of only 45 747SP types ever built. The “Special Performance” version with a length of 56.4 meters (185 ft) is 14.6 meters (48 ft) shorter than a standard jumbo jet. As a result of this shrinking, the short version can fly at higher altitudes than any other wide-body jet.
  • approx. €1.5 billion
    is said to be the costs that have been incurred so far for the Stratospheric Observatory for Infrared Astronomy, which is SOFIA’s full name.
  • The former lower passenger cabin accommodates the workstations of the astronomers and an area for guests (a maximum of 30 persons in total). Discernible in the tail section is the bulkhead separating the open telescope area from the cabin, including the telescope’s mounting bracket (blue) and the flange-mounted measuring instrument in front of it
    The former lower passenger cabin accommodates the workstations of the astronomers and an area for guests (a maximum of 30 persons in total). Discernible in the tail section is the bulkhead separating the open telescope area from the cabin, including the telescope’s mounting bracket (blue) and the flange-mounted measuring instrument in front of it © NASA
  • Elizabeth Ruth ist the only woman in SOFIA’s pool of pilots. The NASA employee has been flying the observatory jet since 2016
    Elizabeth Ruth ist the only woman in SOFIA’s pool of pilots. The NASA employee has been flying the observatory jet since 2016 © NASA
SOFIA’s major discoveries
  • In 2017, SOFIA confirms the existence of a solar system that resembles ours. It’s 10.5 light years away.
  • In 2015, thanks to its flexibility, SOFIA is on the spot when, during a rare occultation, Pluto throws a fleeting shadow onto the Pacific, and gathers new findings about the small planet.
  • Astronomers use SOFIA to investigate the magnetic field in the middle of our Milky Way and begin to understand the differences between active and quiet black holes.
  • In 2019, thanks to SOFIA, the existence of the helium-hydride ion in space is proven for the first time. Our entire idea of the evolution of chemical elements and life the way we know it is based on the existence of this type of molecule in the universe.
  • In 2020, SOFIA discovers water bound in the Moon’s surface in an area exposed to sunlight that is 120 °C (248 °F) hot. The amount of water discovered corresponds to the contents of an 0.33-liter (12-oz) can dispersed on a football field.
SOFIA’s heart
In touch with the stars© Schaeffler

The 17-metric ton (18.8-short ton) telescope in the tail section is the most important passenger on board. It was made in Germany.

(1 ) A tri-mirror system (primary mirror diameter: 2.7 m/8.9 ft, weight: 750 kg/1,650 lbs.) that (2) is mounted in a carbon fiber cage captures infrared radiation from space and deflects it to (3) the flange-mounted measuring instrument. Variations between six different instruments are possible, depending on the research purpose. A pressure bulkhead separates from the cabin the mirror elements exposed to the atmosphere. (4) A ring with 24 pneumatic spring-damper elements isolates the mounting bracket of the telescope from the aircraft’s vibrations. The actual bearing (5) is a hydrostatic, spherical plain bearing from Schaeffler (diameter: 1.2 m/3.3 ft, weight: 600 kg/1,323 lbs.). It provides isolation as well and ensures movability. In addition, twelve motor segments help orient and track the telescope so that external disturbance forces are compensated for. The whole interaction works so well that a laser pointer mounted to the telescope could accurately target and hit a coin on the ground from an altitude of 12 kilometers (39,370 ft).