In 1835, an article appeared in the Southern Literary Messenger telling the remarkable story of one Hans Pfaall, a bellows-mender from Rotterdam who escaped his creditors by flying a homemade hot air balloon to the moon. The story turned out to be a prototypical bit of science fiction dreamt up by a young Edgar Allen Poe to dupe his readers. The idea of ballooning to the moon or elsewhere in the solar system never took off, probably because it’s impossible. But for a certain group of engineers, flying balloons on other planets isn’t far-fetched at all. In fact, the Russians have already done it. And NASA’s Jet Propulsion Laboratory (JPL) is keeping the tradition alive.
A sprawling campus just north of Los Angeles, NASA’s Jet Propulsion Laboratory was established by the California Institute of Technology in the 1930s. Emerging from the DIY mindset that launched the science of rocketry in this country, JPL was where the first U.S. satellite was designed, the Mariner and Voyager probes were born, and the long-running Mars rovers were built.
In a small cluster of bunkers at the heart of the campus lies JPL’s Mobility and Robotic Systems laboratory. About 100 engineers develop all of the robotic components, from the autonomy software to the mechanical appendages that enable us to explore other worlds while staying safely on terra firma.
In a back room of the laboratory, a white blimp, about 15 feet long, floats above a table, secured by tethers. The blimp doesn’t seem particularly unique, that is until you hear that it’s a prototype for an autonomous nuclear-powered aerobot that could someday explore Saturn’s moon Titan. The blimp would fly below the dense clouds that hide the terrain from orbiting spacecraft, snapping
high-res photos and possibly even scooping up surface samples for onboard analysis.
“Balloons provide a unique observation platform for doing planetary science that you simply can’t do any other way,” says Jeffery Hall, the senior engineer who leads JPL’s aerobot research.
An aeronautical engineer by training, Hall joined JPL in 1997 after graduating from Cal Tech down the road. At the time, he worked on cryogenic technologies for satellites. Then, he says, the funding dried up and he was forced to expand his horizons.
“I’ve always been motivated to figure out how things work, and that inevitably leads you to building stuff for experiments,” he says. “One of the great attractions of balloons is that it’s fairly easy to make them. Then you get to take them outside and fly them around. From an experimentalist’s point of view, they’re fun things to work with.”
The Titan balloon is just one of several very different aerial vehicles that Hall and his colleagues are designing. Each vehicle’s technology is dictated by its ultimate destination. For example, the very thin atmosphere of Mars requires a spherical balloon at least ten meters in diameter to carry just a couple kilograms of scientific instruments.
In one scheme, the balloon package would be released from a spacecraft upon entry into the Mars atmosphere. As the canopy drifts down beneath a parachute, onboard helium tanks inflate the “envelope,” the actual balloon fabric. Once the envelope is filled, the parachute and tanks are cut loose and the balloon settles at an altitude a few miles above the surface. According to Hall, a windblown helium superpressure balloon like this could float around the planet for up to a year, all the while transmitting data back to mission control on Earth.
References:
Archives