Mars, Venus, Titan - wherever there's air, we can explore by balloon.
- By Joe Pappalardo
- Air & Space magazine, July 2006
(Page 3 of 5)
The balloons also faced competition from a Mars airplane with similar scientific goals, called ARES. Says Hall: "Airplanes and balloons are close to direct competitors," since they both fill the niche between orbiters and surface rovers. ARES survived to the final round of proposals, only to lose to the more conventional Phoenix Mars Lander, which will go on the first Scout launch next year. The airplane's good showing led to additional funding and a higher profile that improves its chances for this year's competition. In contrast, no balloons are likely to be proposed for the 2012 Mars Scout opportunity. Hayati says that if the complexities of entry, deployment, and inflation can be solved for the thin Martian atmosphere, things might change. But for now, the aerostat teams are turning their attention to other worlds. Atmosphere required.
THE SCATTERED BUILDINGS OF the Jet Propulsion Laboratory stand against the San Gabriel Mountains outside Pasadena like a college campus tossed carelessly onto a hillside. New employees live and die by facility maps. After a while they learn to ignore the deer that routinely graze on the sculpted lawns. Harder to ignore are the occasional mountain lion tracks found outside the buildings or between cars in the parking lots.
Jeff Hall's aerostat office is tucked away in a nondescript building that at first blush resembles a trailer. Entering the lab doesn't dispel the impression-it looks like nothing more than a plain rectangular meeting room. But step through a side door and you find the heart of the place, a 1,500-square-foot workshop. Winches, workbenches, soldering equipment, and rolls of balloon material indicate the kind of hands-on work being done here. In one corner, past the sensor payloads and video processing equipment, an undergraduate student attaches straps to a rolled-up trial balloon.
Then there's the fully inflated, 36-foot-long blimp, lashed to a 60-foot table.
This, Hall explains, is the test bed for an aerobot designed to explore Saturn's largest moon, Titan. The Huygens probe's brief look at the cloud-covered moon last year (see "219 Minutes on Titan," Oct./Nov. 2005) whetted scientists' appetite for a more thorough investigation. And Titan's atmospheric density-about four to five times greater than Earth's-makes it better suited than Mars for exploration by lighter-than-air machines. "We're only underdogs on Mars," Hall says.
The test bed is slightly smaller than the actual, 50-foot Titan airship would be. Since 2001, it has flown nearly 20 times in the Mojave Desert, northeast of Pasadena, operated by a pilot on the ground or by the onboard computer. The main objective has been to test a basic autopilot system and a more sophisticated guidance system that determines the balloon's motion from video pictures of the terrain below.
A Titan aerobot will need to be able to react to its surroundings without help from Earth, since radio signals take 70 or 80 minutes to travel one way, and at times Saturn will block direct radio signals altogether. "You just can't joystick it from down here," Hall says.
The prototype has a gasoline engine to fight winds in Earth's atmosphere. The real one would likely have a nuclear power source that could keep the balloon conducting science investigations for as long as six months, and even longer if researchers can slow the rate of gas leakage or replenish the gas.