Sometimes you find gold in unexpected places. In this case, it’s from a video about the CH-53 helicopter. The CH-53 Sea Stallion first entered service in 1966. It’s a huge helicopter, capable of lifting immense amounts of weight. All that weight hangs from 6 (or 7 on some models) rotor blades.  The problem was detecting problems with the blades before they grew into a catastrophic failure.

Much like a fixed-wing aircraft wing, the CH-53 rotor blades are designed with a spar as the main structural member.  On early designs, the spar was extruded aluminum. The CH-53D and other variants moved to cold-formed titanium.

All of these blades shared the same problem – detecting tiny cracks in the metal before they grow into blade failure. Detecting cracks turned out to be rather easy. The blades are sealed and pressurized with nitrogen gas. Cracks allow the gas to leak out. A barber pole pressure indicator on the blades allows mechanics to tell at a glance if everything is ok.

That’s all fine and good on the ground, but if a blade begins cracking in the air, the pilots want to know about it immediately. What was needed was something akin to the tire pressure monitoring system on modern cars. A pressure sensor that would turn on a light in the cockpit.  Modern automotive TPMS systems use wireless sensors inside the tire. In the early 60’s though, electronic components were not reliable enough to survive rotating on a helicopter blade. Wiring the sensors through the spinning rotor head using slip rings would be incredibly complex. Expecting wireless electronic components to survive life in a rotorhead would be even more problematic.

The solution turned out to be simple: Throw a little ionizing radiation into the mix. Called IBIS, short for Inflight Blade Monitoring System keeps the CH-53 safe. The magic happens in the same pressure indicator we mentioned earlier. Rather than just a shift from a green to a barber pole indication, the IBIS module also exposes a tiny amount of radioactive Strontium-90.  The Strontium is a beta emitter, meaning its radiation can be detected by a Geiger counter inside the helicopter.  It’s also relatively safe for humans as long as they don’t eat or breathe it in. No batteries, no electronics on the rotor blade. It’s a simple mechanical solution to a difficult problem.

The solution is so elegant it’s still being used today. The newest versions of the CH-53 of fiber optics to detect faults in the newest all-composite blades. The older variants? They’re still going with the nuclear option.

For the first time in more than 30 years, NASA has no firm plans to send any new landers or rovers to Mars. Instead, the agency's near-term focus at the red planet is on aerial drones, a pioneering mode of exploration that didn't seem realistic until a few years ago.

The first real use of drones for science at Mars will come with the SkyFall mission, a fleet of three helicopters set for launch as soon as late 2028. SkyFall's helicopters will ride to the red planet with NASA's Space Reactor-1 "Freedom" mission, which has the primary objective of demonstrating nuclear electric propulsion in deep space.

The launch schedule is aggressive for SR-1 Freedom and SkyFall, projects that didn't even exist in NASA's portfolio six months ago. NASA's plan for the SR-1 Freedom mission, estimated to cost $2.1 billion, calls for repurposing the core module of the canceled Gateway lunar space station into a testbed for nuclear electric propulsion. SkyFall will build on NASA's success with the Ingenuity helicopter, an experimental vehicle that became the first rotorcraft to fly on another world in 2021.

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After the little Mars helicopter Ingenuity blew everyone away with its performance, it was clear that a future Mars mission should involve more helicopters like it, with even more capabilities. The main proposal here is NASA’s SkyFall mission which would involve three autonomous helicopters, capable of searching for resources like water. To this end they would need a ground-penetrating radar system, with the antenna somehow folding away for landings, an idea that JPL is currently testing.

The SkyFall mission is currently penciled in to commence in 2028, following which it will be deployed from the Space Reactor-1 fission reactor-powered spacecraft based around elements of the now discarded Lunar Gateway space station. This obviously poses some uncertainties around when and if this mission will actually take place, but that doesn’t prevent JPL engineers from solving issues with these SkyFall helicopters.

As the antenna for the ground-penetrating radar extends beyond the landing legs, it was crucial that said antenna was flexible enough to simply fold in on itself like fabric. For this they used an existing flexible antenna design called Vivaldi, which was downscaled for the helicopters and subsequently tested to see how many simulated Mars landings it would be able to resist, as well as the effect of the cold nights and warm days.

We’re looking forward to seeing these SkyFall helicopters zip over the Martian surface. Maybe they can even swing by Ingenuity while they’re in the neighborhood.