NASA’s Hubble Space Telescope is arguably the best-known and most successful observatory in history, providing unprecedented images that have thrilled the public and astronomers for more than 30 years. But even so, there’s nothing particularly special about Hubble. Ultimately, it’s just a large optical telescope that has the advantage of being in space rather than on Earth’s surface. In fact, Hubble was long believed to be no different from contemporary spy satellites operated by the National Reconnaissance Office – it simply points in a different direction.
There are some truly unique instruments in NASA’s observing arsenal, however, and while they may not have the name recognition of the Hubble or James Webb Space Telescopes, they still represent incredible feats of science. ‘engineering. This is perhaps best exemplified by the Stratospheric Observatory for Infrared Astronomy (SOFIA), an airborne infrared telescope built into a retired airliner that is truly one of a kind.
Unfortunately, this unique aerial telescope is also exceptionally expensive to operate; with an annual operating cost of about $85 million, it is one of the agency’s most expensive ongoing astrophysics missions. After twelve years of observations, NASA and their partners at the German Aerospace Center have decided to end the SOFIA program after its current mission ended in September.
With the telescope so close to making its final observations, it seems like the time has come to reflect on this incredible program and why US and German space centers decided it was time to put SOFIA back in the hangar.
eye in the sky
By performing its astronomical observations while flying over the stratosphere at an altitude of approximately twelve kilometers (40,000 feet), SOFIA is literally and figuratively a happy medium between terrestrial and space telescopes. Its operational altitude means the telescope is above the vast majority of atmospheric water vapor that would otherwise prevent certain infrared frequencies from reaching the Earth’s surface, while its ability to be regularly serviced and upgraded gives the kind of scientific flexibility that would normally be associated with a ground-based observatory.
Key to the SOFIA program is an aircraft large enough to carry the telescope, along with its instrumentation and the personnel to operate it, to the altitude required for stable, long-duration flights. In this case, it is a wide-body Boeing 747SP that began its career with Pan Am in 1977.
This special “SP” variant of the iconic 747 was specifically designed to fly longer, faster and higher by removing a section of the fuselage and making other mass-saving modifications. Built in relatively limited numbers specifically for flights between New York and the Middle East, the airframe used for SOFIA is one of only four 747SPs still flying.
Considerable structural modifications were required for the 747SP to carry the 17 metric ton (38,000 lb) telescope, but certainly none more obvious than the large door that can be opened during flight to expose the 2.7m primary mirror (8.8 feet). To prevent a gust of wind when the door is opened, which would introduce unacceptable vibration into the optics, a pronounced “hump” was added to the rear of the fuselage to redirect high-speed airflow before he does not reach the opening. Turbulent air invariably enters the chamber, but this can be compensated for by using the telescope mount, which uses a combination of pressurized oil bearings, counterweights, gyroscopes and magnetic torque motors to stabilize and aim the telescope. ‘instrument.
The SOFIA telescope is by far the largest ever mounted on an airplane, a record that will almost certainly never be broken. Even still, its primary mirror is dwarfed by the 6.5m (21ft) reflector of the James Webb Space Telescope (JWST), NASA’s new flagship infrared telescope that is just days away from commissioning. line. Although it is difficult to directly compare the two observatories and their capabilities, there is no doubt that the JWST represents the future of infrared astronomy. At the same time, SOFIA has been criticized in recent years for the little scientific data it has been able to collect compared to its high development and operating costs.
While the JWST makes SOFIA largely redundant, that doesn’t mean the scientific community won’t mourn its loss. Not only is SOFIA able to observe a much wider range of infrared frequencies, but its unique ability to target the moon directly led to the confirmation in 2020 of water on the lunar sunlit surface. It can also be upgraded over time to make observations with instruments that may not even exist today, when the JWST is too far from Earth to receive the kind of incremental upgrades that Hubble did.
Simply put, there is a valid need for an observatory like SOFIA. But unless NASA finds a cheaper way to build and operate one, this could be a scientific niche that won’t be filled.