When it comes to astronomy, large telescopes rule. But if you can get your instrument into space, you bypass the atmosphere that blurs sensitive data. Unfortunately, the cost of launching observatories into space is beyond the budget of most researchers. One possible strategy is to install powerful observatories instruments onto high altitude airships, which can float above most of obscuring atmosphere. The view from the high atmosphere is almost as good as actually being in orbit, and it can be had for a fraction of the price of flying a telescope into orbit.
A recent report written by Robert A. Fesen from the Department of Physics & Astronomy at Dartmouth College, proposes that the time has come for astronomers and funding agencies to seriously consider “lighter-than-air” vehicles for future telescopes. These helium-filled blimps would be capable of reaching high altitudes, and then use solar-powered propellors to maintain a constant position. They could transmit their data back down to Earth for analysis.
Until now, most research into blimps has been by the military and communications companies. The vehicles were seen as a cheaper alternative to satellites, which can cost hundreds of millions of dollars to develop and launch. Furthermore, once launched, satellites are out of reach to make repairs or upgrades. A blimp could be brought back to Earth, serviced, and then launched back into position.
Fesen proposes that a high-altitude airship would be a fantastic platform for astronomy:
… at an altitude of 85 kft an astronomical telescope would experience virtually perfect skies overhead every night with image quality approaching the diffraction limit of the main aperture. An optical telescope with a lightweight mirror just 20-inch in diameter (0.5 m class) with sufficient pointing stability and large CCD arrays could provide wide-field images with FWHM = 0.25 arcsec, making it superior to the imaging system on any ground-based telescope. And it could do it night after night for as long as the platform remained at this altitude. Moreover, such a stratospheric telescope could also provide reliable science support for a host of space-based missions at an estimated cost of a few percent of a conventional low Earth orbit (LEO) satellite.
Some of the challenges that have plagued the military and telecommunications industry to get airships off the ground actually won’t be much of an issue for science. Telescope detectors and CCD arrays don’t require much power. It isn’t an issue of national security if an airship’s power fails and it lands in another country.
The greatest challenges for astronomy will be getting the instrument weights down so a small airship can lift them to altitude, and developing a tracking system that can provide astronomers with the precision they need. Fortunately, these problems are already being worked on for other space-based observatories, like the James Webb Next Generation Space Telescope.
Fesen proposes that the best airship would be a catamaran design, with two blimps connected by bridge where instruments would be attached. It would fly at an altitude of 21 km (70,000 feet), where it could avoid most of the atmosphere, and be positioned at the equator, where it could observe both the northern and southern hemsispheres.