When you think of scientific telescopes there’s usually only 2 different types that come to mind. The ones down here on terra firma, with their giant white domes covering their precious mirrors, and the ones up in space like the venerable Hubble Space Telescope. Each of these has is set of benefits and drawbacks, like the ground based ones having massive mirrors and the space based ones not having to deal with our atmosphere. However there’s potential for a telescope that straddles the boundaries of these two types of telescopes, one that’s far above the Earth’s surface but also doesn’t require the heavy energy investment of an orbital craft. Indeed NASA has flown craft like these in the past and they’re now looking to airships to fly the next generation of such telescopes.
Ground based telescopes suffer from 2 major drawbacks related to the atmosphere. The first is the aberrations caused by the shifting atmosphere, the same thing that causes the stars to twinkle at night, which makes precise measurements incredibly difficult. The second is that the atmosphere is great at absorbing a lot of the frequencies of light, specifically infrared, something which we can’t really overcome with special optics or filters. Putting a telescope in space negates these problems but brings with it a whole other set of challenges which is precisely why NASA is looking to develop a sub-orbital telescope concept using an airship as the platform.
NASA has constructed platforms like this in the past, the most notable one of which is SOFIA, an infrared observatory that’s built into the back of a Boeing 747. At its cruising altitude it’s able to see 85% of the total infrared light coming to Earth a considerable amount more than any ground based telescope will be able to see. The primary limit to SOFIA is its endurance time which is around eight hours or so although its capability to be pretty much anywhere in the world does make it incredibly flexible in the operations it can perform. The airship design that NASA is looking to pursue would address this limitation whilst providing some other benefits.
Airships, whilst not being as mobile as their winged cousins, have the advantage of being able to stay aloft in a location for extended periods of time that aircraft simply aren’t capable of doing. For an observatory this provides several advantages such as being able to do longer exposures on targets as well as being able to take advantage of higher bandwidth downlinks to their base sites. There are several engineering challenges that will need to be solved before a viable aircraft will materialize, but it’s certainly within the realms of possibility.
Pending funding of the idea NASA will be funding it X-prize style, looking for designs (and I assume workable craft) that can carry a small or large payload up into the atmosphere. Such programs have proved to be highly successful in the past and I’m sure we’ll see some pretty interesting craft come out of it. Considering that SOFIA is slated to be shut down due to budgetary concerns sometime next year a viable alternative needs to be sought so they don’t introduce more holes in their capabilities. Of course getting an airship with a telescope up in the air before that happens isn’t going to be likely but the sooner the process is started the better.