A conventional antenna for SkyFall's radar frequencies would be about 19 inches long. The helicopter has only about 6 inches of clearance beneath its fuselage.

JPL needed to shrink the antenna without making it useless, then design what remained to survive hitting the ground.

SkyFall, planned as a trio of Mars helicopters, is supposed to use ground-penetrating radar to look for shallow subsurface ice. The radar needs a clear view of the ground. The helicopter also needs to land.

JPL's answer is an antenna made partly like a piece of technical fabric. It bends out of the way when the aircraft comes down, then returns to shape after takeoff so it can work as a radio-frequency instrument again. The prototype recently cleared a test campaign built around repeated landings, temperature swings, and radio-frequency checks.

The interesting ice is awkwardly shallow

Mars already has maps of likely buried water ice. NASA's Subsurface Water Ice Mapping project, or SWIM, combines data from several orbital instruments and observations of impacts that have actually exposed ice. Those maps are useful enough to identify promising regions for future exploration.

The awkward part is the near-surface layer. JPL's current framing is simple: orbiters can map thick ice deposits tens of yards below the surface but are effectively blind to the top several yards of regolith. Other instruments can tell us about the surface or provide indirect clues, but the vertical distribution of very shallow ice remains harder to pin down than a colored ice map might suggest.

SkyFall's ground-penetrating radar is designed for that gap. NASA says it will primarily characterize structures and look for ice from about 0.5 to 3 meters below the surface, with deeper penetration possible under favorable conditions.

That range also matters if humans are expected to use Martian ice rather than simply map it. Water buried tens of meters down is scientifically useful, but far less convenient as a resource than ice within reach of practical excavation. NASA points to water, oxygen, and fuel as possible uses.

The obvious way to improve the shallow measurement is to bring the radar close to the ground. That is where a scientific problem turns into a rather literal packaging problem.

A radio antenna that has to fold when it hits a rock

The required frequency range, roughly 500 to 2,500 megahertz, is what creates the awkward geometry. JPL says a conventional antenna for that range would need to be about 19 inches long and positioned with a clear view downward, more than three times the helicopter's available clearance.

The team chose a Vivaldi antenna, a broad-band design whose flat shape can be cut from flexible metalized material. Because SkyFall only needs to survey the shallow subsurface, and because dry Martian regolith attenuates radio waves much less than terrestrial soil, JPL could reduce the antenna's footprint substantially without sacrificing the sensitivity the mission needs.

JPL has not published the downsized antenna's absolute length. It says only that the finished Vivaldi is still about one and a half times longer than the helicopter's legs, which means it is expected to touch the ground and bend even farther if the aircraft lands on a rock.

The antenna is sheathed in polyester and layers of Vectran, a strong fiber with previous Mars heritage in the landing airbags used by Spirit and Opportunity. Flexible fiberglass tape springs help it recover its shape after bending, while a lightweight magnesium structure attaches the assembly to the aircraft. The whole setup weighs about 150 grams, or 5 ounces.

The same object therefore has two jobs that do not naturally belong together. It has to behave like a flexible mechanical structure when the helicopter lands on uneven terrain, then become a predictable radio-frequency instrument once the aircraft is airborne.

JPL's test campaign checked both. Engineers bent the antenna into a simulated landing position, cycled it through large temperature changes meant to represent Martian day-night conditions, and repeatedly flexed it as though the helicopter were landing again and again. Six times, they interrupted the mechanical testing and carried the antenna back to an electromagnetic chamber to see whether its ability to transmit and receive radar signals had degraded.

After 200 simulated landings, more than twice the number NASA says would be required for the prime mission, JPL reported no loss of performance.

There is still a large gap between a successful prototype campaign and hardware ready for Mars. JPL says the team is now building an engineering model for vibration testing, deployment in a simulated Martian environment, further signal testing, and outdoor trials in the Mars Yard. NASA currently lists SkyFall for a late-2028 launch.

Sources

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Curious Air

Curious Air turns invisible signals around an Android phone into measurements you can inspect: Wi-Fi, Bluetooth, cellular, GNSS, NFC, and device sensors. SkyFall works at a very different scale, but both begin with the same idea: signals become useful when an instrument makes them legible.