To ensure a safe landing on Mars, a rover inside an aeroshell has to haul along a bunch of ballast to help it orient itself before and after atmospheric entry. This ballast gets jettisoned at two different points in order to control the aeroshell’s center of gravity and attitude, so it’s very important to have along. But, it’s also useless, in that hundreds of kilograms of mass that you’ve hauled all the way from the surface of Earth out to Mars just gets dumped.
NASA, knowing better than anyone how difficult and expensive it is to send stuff to Mars, has been soliciting ideas on how to do something useful with this balance mass. One brilliant idea that’s taken flight: an airplane.
A micro-sized glider sounds like a good idea to me; it also sounded like a good idea to some NASA engineers and community college students working at NASA Armstrong Flight Research Center in California. That’s why they started developing a prototype of the Preliminary Research Aerodynamic Design to Land on Mars, or Prandtl-m.
Prandtl-m would be a small, foldable carbon fiber aircraft that could fit into the volume of a 3U Cubesat—roughly three 10-centimeter cubes stuck together. Deployed, the aircraft would have a 60-centimeter wingspan, and would weigh about half a kilogram. There’d be no engine: the Cubesat unit would be ejected from the aeroshell, survive the atmospheric entry, and then deploy the glider a few thousand feet above the surface of Mars. The glider would soar for about 10 minutes (giving it a range of about 30 kilometers), and then it would, uh, make aggressive contact with the ground.
While the mission wouldn't last long, Prandtl-m could potentially send back a lot of valuable data, especially if it’s scouting over proposed landing sites for future missions and taking higher resolution images than than is possible from orbit. And since the aircraft is just taking up space that would be used for ballast anyway, there’s very little additional cost or risk involved.
NASA already has a tester version that’s ready to fly. The larger, non-foldable glider, called Prandtl-d, will be dropped from 30,000 meters by a high altitude balloon later this year. Prandtl-d will simulate the flight conditions its successor will face inside the Martian atmosphere near the surface. The hope is that the glider will be able to stabilize itself and achieve level flight. If that works out, the next step will be to see if they can get a glider to do the same thing—except for starting all folded up inside of a 3U Cubesat container. The final test mission under discussion would involve actual launch in a sounding rocket up to 137,000 meters (450,000 feet), followed by a deployment and controlled glide of up to five hours in length.
“If the Prandtl-m completes a 450,000-foot drop, then I think the project stands a very good chance of being able to go to NASA Headquarters and say we would like permission to ride to Mars with one of the rovers," says Al Bowers, NASA Armstrong chief scientist and Prandtl-m program manager. We can expect that to happen between 2022 and 2024.