Summary
NASA’s Jet Propulsion Laboratory has tested a lightweight, fabric-based Vivaldi antenna for the SkyFall Mars helicopters’ ground-penetrating radar. The prototype survived simulated temperature swings and 200 Mars landings without losing signal performance, but it still needs further testing before flight qualification.
NASA’s Jet Propulsion Laboratory has completed an initial test campaign for a lightweight, flexible radar antenna intended for the agency’s planned SkyFall Mars helicopters. The fabric-based antenna is designed to let three rotorcraft use ground-penetrating radar to locate and map shallow subsurface ice.
The prototype survived simulated Martian temperature cycles, repeated flexing and the equivalent of 200 landings without losing radar performance. JPL said the hardware still needs additional testing before it is fully flight-qualified.
Why SkyFall needs a low-flying radar
Orbiting spacecraft can map substantial ice deposits tens of yards below Mars’ surface, but they have limited visibility into the upper several yards of regolith—the layer of broken rock and dust covering the planet. That shallow zone could be particularly important for future astronauts because ice close to the surface would be easier to reach and process into water, oxygen and fuel.
SkyFall’s helicopters are being designed to fly low and slowly while transmitting radar signals into the ground. The radar will operate across an ultra-wide frequency range of 500 to 2,500 megahertz, corresponding to wavelengths from about 60 to 12 centimetres. The longer wavelengths can penetrate several yards into the surface, while the shorter wavelengths can provide more detail about near-surface layers and texture.
Ground-penetrating radar works by transmitting radio signals and analysing echoes returned from boundaries beneath the surface. Changes in the material underground—such as the transition between dry regolith and ice—can produce changes in those echoes that help reveal subsurface structure.
A radar antenna built to bend during landing
A conventional antenna for this frequency range would be about 19 inches (48.3 centimetres) long. That would be impractical on SkyFall because the clearance between the Martian surface and the bottom of the helicopter’s fuselage is only about 6 inches (15.2 centimetres).
The team selected a Vivaldi antenna, a design that can transmit and receive signals across a broad, continuous range of frequencies. Its flat profile can also be formed from flexible, metalized fabric. Engineers reduced the antenna’s size for SkyFall’s shallow surveys, which are planned for depths below 16 feet (5 metres) in dry Martian regolith. JPL says that material blocks radio waves less than Earth’s soil, allowing the radar system to be miniaturised further without sacrificing sensitivity.
The antenna is about one and a half times longer than the helicopter’s legs, so it must bend away during landing and spring back into position after takeoff. Its structure includes polyester and Vectran layers, flexible fiberglass tape springs and a lightweight magnesium mount. The complete assembly weighs about 5 ounces (150 grams).
Prototype survived 200 simulated landings
At JPL’s Environmental Test Laboratory, engineers bent the antenna to reproduce a possible post-flight orientation and exposed it to temperature changes of as much as 170 degrees Fahrenheit (94 degrees Celsius), simulating the Martian day-night cycle. They then flexed it repeatedly to represent dozens of landings.
The team paused the campaign six times to test the antenna in an electromagnetic chamber and check whether its ability to transmit and receive radar signals had changed. During radiofrequency testing, the antenna was inverted to impose stresses greater than those expected under Mars’ roughly one-third Earth gravity.
By the end of testing, the antenna had withstood 200 simulated Mars landings—more than twice the number required for a successful prime mission according to JPL—with no loss of performance.
The next engineering model will undergo vibration testing, deployment in a simulated Martian environment, further signal testing and outdoor trials at JPL’s Mars Yard. SkyFall is expected to launch aboard NASA’s Space Reactor-1 Freedom in late 2028. Each of the three helicopters is planned to carry four instruments, following the aerial operations demonstrated by NASA’s Ingenuity Mars Helicopter.