NASA develops a flexible, fabric-based antenna for its next Mars SkyFall helicopters that will test for frozen water in the surface layers of the Red Planet.
Three Mars helicopters are getting an antenna built to survive something no ordinary antenna has to withstand: getting landed on.
NASA’s SkyFall mission will fly the aircraft low over the Martian surface, using radar to search the dirt for frozen water that future astronauts could drink, breathe, or burn as fuel.
The problem is fitting a working antenna into six inches of space.
Searching for Mars’ ice with SkyFall
Spacecraft already circling Mars can map thick ice deposits dozens of yards underground. What they can’t see is the top few yards of regolith, the loose mix of broken rock and dust covering the planet.
That shallow layer matters most, because it’s the ice that astronauts could actually reach and process for water, oxygen, and rocket fuel.
Adrian Tang leads SkyFall’s ground-penetrating radar instrument team at NASA’s Jet Propulsion Laboratory (JPL). He said there’s only one way to see ice that close to the surface.
“The only way to detect shallow subsurface ice remotely is to fly close to the ground,” Tang said.
Flying low, he said, “could capture radar images that resolve the fine layering where dry soil gives way to ice, detecting its presence and mapping its extent.”
Six inches of landing room
SkyFall’s radar works across an unusually wide range, from 500 to 2,500 megahertz. That range matches wavelengths of about 24 to 5 inches (60 to 12 centimeters).
The longer wavelengths reach several yards down, and the shorter ones show fine detail near the surface.
A standard antenna for that range would need to be about 19 inches (48 centimeters) long, with a clear view of the ground.
But the fuselage of the Mars helicopters clears the surface by only about 6 inches (15 centimeters) at its lowest point. Engineers needed something that wouldn’t get crushed or knocked loose during landing.
After searching for the right design, the team settled on something called a Vivaldi antenna. It can send and receive signals across a wide band of frequencies, and its flat profile can be cut from flexible, metal-coated fabric.
Peter Gibson invented the shape and named it after the violin, an instrument associated with the composer Antonio Vivaldi, because he thought its curved lines resembled one.
An antenna built to bend
Even the standard Vivaldi shape was too big for SkyFall’s tight clearance. Then the team caught a break. The radar only needed to survey down to about 16 feet (5 meters) into dry Martian dirt.
That dirt blocks radio waves far less than soil on Earth. This meant that the engineers could shrink the antenna even further without losing sensitivity.
Christine Gebara, the mechanical lead for SkyFall’s radar at JPL, explained what that shrinking still leaves behind.
“Although we managed to shrink the antenna quite a bit, it is about 1½ times longer than the helicopter’s legs,” she said.
“That means during landing, the Vivaldi has to bend out of the way – and if it lands on a rock, it bends even further. But when the helicopter takes off again, the antenna must spring back into place for data collection,” she added.
An artist’s concept depicts the three SkyFall Mars helicopters collecting data while flying over the surface of the Red Planet. Credit: NASA/JPL-Caltech. Click image to enlarge.Withstanding repeated bending
SkyFall is expected to make dozens of flights while exploring, so the antenna had to handle repeated deformation pressures without losing its shape in flight.
To survive that bending, engineers wrapped the antenna in polyester and then in layers of Vectran. The same material cushioned the landing airbags for NASA’s Spirit and Opportunity rovers.
Flexible fiberglass strips and a lightweight magnesium frame help the antenna snap back into place after each landing. The whole assembly weighs about 5 ounces (150 grams), a bit more than two violin bows.
Two hundred simulated landings
Paper designs and computer models can only prove so much. Next, the team took the antenna to JPL’s Environmental Test Laboratory to see if it could survive a real mission.
Engineers bent the antenna into a position it might hold after landing. Then they ran it through temperature swings as extreme as Mars gets between day and night, as much as 170°F (94°C).
They flexed it over and over to mimic dozens of landings, pausing six times to check its radio performance in an electromagnetic test chamber.
At one point they flipped the antenna upside down, a position that stresses it more than Mars’ one-third gravity ever would.
By the end of the test campaign, the antenna had endured the equivalent of 200 Mars landings. That was more than double what a full mission would require, and its performance never dropped.
“This test checked every box it was supposed to and answered our biggest technical questions,” Tang said. “While we still have work ahead of us before the antenna is fully flight-qualified, this was a major milestone, and the hardware performed exactly as expected.”
What comes before Mars
The new version still has vibration testing ahead, plus a run through a simulated Martian environment. It also needs signal checks and outdoor trials at JPL’s Mars Yard, a lot built to look like Mars.
SkyFall’s three helicopters, each carrying four science instruments, follow NASA’s Ingenuity Mars Helicopter.
Ingenuity flew 72 times over almost three years and proved that a small aircraft could fly through Mars’ thin air.
Perseverance’s rover team used Ingenuity’s aerial images to plan faster routes and choose where to search for signs of past life.
SkyFall is expected to launch on NASA’s Space Reactor-1 Freedom rocket in late 2028. Nobody yet knows exactly how deep the ice lies under the ground SkyFall will fly over.
Finding out is the antenna’s whole job, and that job starts with surviving the landing.
Details are given in an online article by NASA.
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