OPAG, Day 1: Hot-air ballooning on Titan
The next presentation at OPAG was given by Ralph Lorenz and Tom Spilker on a Titan Montgolfiere Mission Study. What's a Montgolfiere, you ask? Maybe you know but I didn't know that it's a hot-air balloon -- hot-air, that is, as opposed to lighter-than-air. In other words, they were describing a possible future mission to Titan in which you would inject a probe that would inflate a balloon with Titan's own atmosphere and then just heat it in order to establish neutral buoyancy. It's an intriguing combination of 21st-century space flight with century-old technology.
Ralph opened the presentation by showing a cute picture that Jonathan Lunine had put together, where he framed one of the side-looking Huygens descent panoramas inside an airplane window. "The airplane window view is what this is really all about," Ralph said. "With Huygens, we essentially had a 3-hour cross-country flight that was cloudy for most of it." A Titan Montgolfiere would give you the airplane window view of Titan for weeks, even months or longer.
"Titan is a very diverse world," Ralph said, "so we don't want to send either a lander or a rover." He showed several of the examples of interesting terrain visible from Cassini RADAR images, and pointed out that most topography on Titan is apparently slight, under a kilometer or so. "If you float a balloon at 2 or 3 kilometers, you're likely to be safely above everything." Furthermore, unlike a lighter-than-air balloon, which must vent limited gas to land and then drop limited ballast to rise, a hot-air balloon can drop simply by not continuing to heat its envelope, then rise by heating it again. Of course you need a heat source, which typically requires the burning of a limited supply of fuel, but the Titan Montgolfiere would use a radioisotope heat source and thus wold be able to go up and down, even sampling the surface for in situ studies.
