Periodically we have reported on NASA’s Innovative Advanced Concepts (NIAC) Program, which seeks out proposals from commercial industries on development of new technologies that will assist in future space missions.
The selected proposals address a range of visionary concepts, including metallic lithium combustion for long-term robotics operations, submarines that explore the oceans of icy moons of the outer planets, and a swarm of tiny satellites that map gravity fields and characterize the properties of small moons and asteroids.
NIAC Phase II awards as much as $500,000 for a two-year study, and the awards allows proposers to further develop their concepts from previously selected Phase I studies. The Phase I studies must demonstrate the initial feasibility and benefit of a concept. Phase II studies allow awardees to refine their designs and explore aspects of implementing the new technology.
NASA selects the projects through a peer-review process that evaluates innovativeness and technical viability. All projects are still in the early stages of development, most requiring 10 or more years of concept maturation and technology development before use on a NASA mission.
One concept that is being developed as a result of the NIAC program is ‘windbots,’ robots that drift on the wind through the skies of a planet like Jupiter.
Recently a team of engineers at NASA’s Jet Propulsion Laboratory in Pasadena, California, wondered if a probe could be buoyant in the clouds of Earth or a distant gas giant planet, like Jupiter.
That team has recently started studying the idea, thanks to a one-year, $100,000 study, funded by the NIAC program. They are studying the feasibility of creating a windbot, The NASA-funded study will systematically investigate how future spacecraft of this kind could stay airborne and harvest energy.
Although no mission is currently scheduled to use windbots, the researchers hope their study will open new avenues for atmospheric science on gas giant planets using high-mobility robotic explorers.
Adrian Stoica, principal investigator for the windbots study at JPL, points to a great example to think about from nature when thinking of the windbot concept: a dandelion seed. “A dandelion seed is great at staying airborne. It rotates as it falls, creating lift, which allows it to stay afloat for a long time, carried by the wind. We’ll be exploring this effect on windbot designs.”
Stoica and his colleagues think that, to stay airborne for a long time, a windbot would need to be able to use energy available in the planet’s atmosphere. That energy might not be solar, because the probe could find itself on the planet’s night side for an extended period. Nuclear power sources also could be a liability for a floating probe because of their weight. But winds, temperature variations and even a planet’s magnetic field could potentially be sources of energy an atmospheric probe could exploit.
As they begin their study, the team suspects the best bet for an atmospheric robot to harvest energy is turbulence – wind that’s frequently changing direction and intensity. The key is variability. High wind velocity isn’t enough. But in a dynamic turbulent environment there are gradients –- differences in energy from high to low –- that can be used.
Embracing turbulence to make power and stay aloft is a departure from the approach taken by conventional aircraft, which carry their own internal power sources and perform best in smooth air. Commercial airliners, for example, cruise in Earth’s stratosphere, where winds tend to be much smoother and flow faster than in the dense air closer to the ground.
The JPL team is starting out by characterizing winds among the clouds of Jupiter to understand what kinds of places might be best for sending a windbot and to determine some of the technical requirements for its design. “There are lots of things we don’t know,” Stoica said. “Does a windbot need to be 10 meters in diameter or 100? How much lift do we need from the winds in order to keep a windbot aloft?”
One thing the team is pretty certain of is that a windbot would need to be able to sense the winds around it in order to live off the turbulence. To that end, they plan to build a simple windbot model as part of their study. The aerodynamic modeling for this type of craft is particularly difficult, so Stoica thinks having a physical model will be important.
The model windbot would be subjected to carefully controlled turbulent airflows to determine how best to design systems that react and reorient the robot to keep it aloft. After that, the team would move on to investigating means, such as electronic sensors, for a windbot to perceive the wind field in the environment around itself. Putting these capabilities together into a functional prototype would be left for a future study.
If the cost of building windbots turned out to be sufficiently affordable, Stoica thinks it would be useful to have multiple units sending back data from different places in a planet’s atmosphere. “One could imagine a network of windbots existing for quite a long time on Jupiter or Saturn, sending information about ever-changing weather patterns,” he said. “And, of course, what we learn about the atmospheres of other planets enriches our understanding of Earth’s own weather and climate.”
In fact, windbots might also come in handy as an additional tool to help scientists understand turbulent weather phenomena on Earth, such as hurricanes, without venturing beyond our planet’s atmosphere. A windbot designed to sense and feed off turbulence might not only survive such hazardous environments, but also transmit valuable data all the while.
Despite its potential, the windbot concept is not without its tradeoffs. The buoyant probe might have to sacrifice travel time in moving to interesting destinations on a planet to simply stay alive –- trading a shorter route from point A to point B to follow the energy available from winds to stay aloft. At other times, when it has sufficient energy, it might be able to head to its destination via a more direct path.
The windbot concept is a long way from being ready to launch to Jupiter, but Stoica and his colleagues are excited to dive into their initial study.