High-solidity and supersonic tip speed rotor test for Mars rotorcraft

With their ability to rapidly traverse long distances over difficult terrain, rotorcraft have the potential to revolutionize Mars exploration. The Ingenuity helicopter proved the feasibility of rotorcraft operations on Mars, albeit at small scale. To unleash the full potential of rotorcraft on Mars, new rotor technology enabling larger vehicles is required.

High-solidity rotors

Concepts studies for large Mars rotorcraft, including the Chopper rotorcraft concept, have shown that the combination of low atmospheric density and significant volume constraints requires a larger proportion of the rotor disk to be covered by blades than what is typical for terrestrial helicopters [1]. The power performance of such a high-solidity design is critical for the feasibility of large-scale Mars rotorcraft, but it is not yet well-understood, because rotorcraft built for hover or edgewise flight on Earth are universally designed with low solidities. The project will fill this knowledge gap by:

- designing and building a custom high-solidity rotor for Mars applications; and

- testing the power performance of the rotor in Martian atmospheric conditions

Supersonic tip speeds

Mars rotorcraft are currently designed to maintain a strict margin against the speed of sound at the blade tips, even during a worst-case wind gust, on the assumption that drag divergence near the speed of sound could be fatal to the rotorcraft. This assumption may be overly conservative, and relaxing the assumption would have direct benefit in terms of liftable mass. This project will examine this question by spinning the test rotor at near-supersonic speeds and using an external fan to temporarily bring the advancing rotor tips into the supersonic regime. This exploratory effort will shed light on whether current assumptions are overly conservative or not, potentially opening the door to a relaxation of assumptions that would allow for carrying more mass.

[1] H. F. Grip et al., "The Chopper Next-Generation Mars Rotorcraft: Scaling Ingenuity by a Factor 20," Proc. IEEE Aerospace Conference, Big Sky, MT, 2025.

High-solidity rotors

Studies of large Mars rotorcraft, such as the Chopper rotorcraft concept, have concluded that high-solidity rotors are a necessity, due to constrained volumes and low atmospheric densities. The power performance of such rotors, as measured by the rotor Figure of Merit, is unknown but crucial. The project will close this knowledge gap by measuring the actual Figure of Merit on a full-scale representative rotor in representative atmospheric conditions. The result will directly affect the sizing of current large-scale Mars rotorcraft concepts and inform the feasibility of future designs.

Supersonic tip speeds

Tip speed limitations currently constitute a significant limitation on the liftable mass for Mars rotorcraft, because tips are not allowed to approach the speed of sound even temporarily during a worst-case gust. Relaxing this requirement would release significant additional mass. By exploring the supersonic regime under Mars conditions, this project will either (1) verify that the current conservative approach is appropriate; or (2) enable a relaxation of the assumptions and thereby release additional mass.

Rotor design

This project includes the design of new rotor blades optimized for high-solidity rotor in the Mars environment. The blades will be fabricated together with compatible hub, actuators, swashplate and linkages, and this rotor system will be put under test.

Assuming test results are in-line with predictions for power performance, it is expected that future large-scale helicopter rotors can be based around the same blade design with modest adjustments.

This is early/mid-stage (TRL 5) — the most realistic path in is NASA SBIR/STTR, which funds small businesses and research institutions to develop technology aligned with NASA's needs (equity-free, phased funding). Check whether a current SBIR/STTR solicitation topic overlaps with this project's technology area, or contact the project directly (above) to ask.

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