Design Considerations for a Mars Highland Helicopter

Mars is sharply divided into the relatively low-lying northern hemisphere, filled with plains, to the higher-elevation, rugged, southern hemisphere. All landers sent so far to Mars have only landed on the plains of the northern hemisphere. Access to the Martian Highlands would present an opportunity to acquire unique insights into the early geologic history of Mars. But landing on the Martian highlands presents many engineering challenges. A new approach has recently been proposed to consider the use of mid-air deployment, during the final subsonic stages of entry, descent, and landing, of a small rotorcraft from the aeroshell. The rotorcraft would enter a powered descent state (rotors would be spun to full speed at moderate collectives) after aeroshell release until reaching a modest altitude above the ground where the vehicle would pullout to level flight. After completing this initial EDL mid-air-deployment and landing, the rotorcraft, which would be capable of solarelectric recharging, would recharge over the course of a few days until ready for subsequent flight sorties to explore the highlands. This overall vehicle/mission concept is called the Mars Highland Helicopter. The paper will next demonstrate that a key necessary condition – efficient hover and forward flight under the much thinner atmospheric conditions of the highlands (0.01 kg/m3 vs. 0.015 kg.m3 for the Ingenuity Mars Helicopter Technology Demonstrator at Jezero Crater) – is indeed possible. This paper considers a number of EDL release/deployment strategies to minimize deployment aeroloads and maximize controllability during release from the EDL backshell. This mid-air-deployment discussion will be followed by a general analytical treatment of a Mars rotorcraft entering fullypowered descent and then forward flight cruise. 1 Associate Fellow; Aeromechanics Office, NASA Ames Research Center, Moffett Field, CA 2 Robotics Technologist, NASA Jet Propulsion Laboratory, Pasadena, CA 3 Fellow; Aeromechanics Office, NASA Ames Research Center, Moffett Field, CA 4 Member; Aeromechanics Office, NASA Ames Research Center, Moffett Field, CA 5 Member; Aeromechanics Office, NASA Ames Research Center, Moffett Field, CA 6 NASA Jet Propulsion Laboratory, Pasadena, CA 7 NASA Jet Propulsion Laboratory, Pasadena, CA 8 NASA Jet Propulsion Laboratory, Pasadena, CA 9 NASA Jet Propulsion Laboratory, Pasadena, CA 10 Student intern, Ohio State University, Aeromechanics Office, NASA Ames Research Center, Moffett Field, CA 2 Nomenclature AGL Above ground level AMH Advanced Mars Helicopter CONOPS Concept of operations c Speed of sound, m/s CPL Lower rotor power coefficient CPU Upper rotor power coefficient CTL Lower rotor thrust coefficient CTU Upper rotor thrust coefficient D Aeroshell/capsule diameter, m EDL Entry, Descent, and Landing HIGE Hover in ground effect HOGE Hover out of ground effect MHH Mars Highland Helicopter MSH Mars Science Helicopter MHTD Mars Helicopter Technology Demonstrator, aka “Ingenuity” NDARC NASA Design and Analysis of Rotorcraft software tool R Rotor radius, m s/R Rotor-to-rotor vertical spacing ratio with respect to rotor radius sD/R Solar array vertical spacing from upper rotor with respect to rotor radius VD Descent velocity, m/s VTip Rotor tip speed, m/s V Forward flight cruise velocity, m VTOL Vertical takeoff and landing shaft Rotor shaft angle, zero degrees when rotor axes are vertical, Deg. 0.75 Rotor collective, i.e. blade pitch angle at the seventy-five percent radial station, Deg.  Forward flight advance ratio, μ = V V ⁄