Historical rotor designs for Earth and Mars have typically landed at thrust-weighted solidities of ∼0.1-0.15 as a best compromise of performance and weight. Comprehensive analysis predicts that high solidity rotor designs of more than twice this range have the potential to significantly increase the lift capability of future Mars explorers severely limited by packaging and weight. However, there is limited existing experimental data of high solidity rotor designs at representative densities to quantify the efficiency impact and verify models of the aerodynamic environment. Therefore, the Mars Exploration Program (MEP) funded a joint test campaign between NASA's Jet Propulsion Laboratory, NASA Ames Research Center, and AeroVironment, Inc.to validate performance predictions for low- and high- solidity rotor variants at Mars pressures. Experimental setup, test matrix, data processing, data quality, and performance results for the High Solidity Test (HST) campaign are presented and discussed.

The success of the Ingenuity helicopter on Mars has laid the groundwork for rotorcraft becoming a key part of future Mars exploration infrastructure. For this vision to be fully realized it is necessary to scale up Mars rotorcraft technology to a size class where science payloads of multiple kilograms can be carried over significant distances. This paper describes the development of a large-scale Mars rotorcraft concept that can support future standalone missions. It is shown how the challenging flight environment on Mars closes off certain branches of the design space but allows the design of a vehicle with 3-10 kg payload capacity and 3 km daily range.

HeliCAT-DARTS is a high-fidelity rotorcraft dynamics simulator developed for the design and development of rotorcraft for planetary exploration. While initially developed for the life cycle use of the Ingenuity Mars Helicopter mission, the simulator now supports a broad range of rotorcraft configurations and applications. HeliCAT provides a GNC testbed and aerial mobility analysis platform for rotorcraft design, closed-loop flight software development, verification and validation (V&V), and mission operations. This article discusses the design and use of the HeliCAT simulator and results from technology demonstrations and missions.

Integrated simulation capabilities that are high-fidelity, fast, and have scalable architecture are essential to support autonomous vehicle design and performance assessment for the U.S. Army's growing use of unmanned ground vehicles (UGV). The HMMWV simulation described in this paper embodies key features of the real vehicle, including a complex suspension and steering dynamics, wheel-soil models, navigation, and control. This research uses advanced multibody techniques such as minimal coordinate representations with constraint embedding to model complex unmanned ground vehicles for fast mechanical simulations with high fidelity. In this work, we demonstrate high-fidelity dynamics models for autonomous UGV simulations in near real time that can be useful to the U.S. Army for future autonomous ground vehicle dynamics modeling and analysis research.

The sounds of the Ingenuity Helicopter flying in the Martian atmosphere are among the most notable recordings of the microphone on the SuperCam instrument on the Mars 2020 Perseverance Rover. Distinct acoustic signa-tures of the helicopter were recorded on the 4th, 5th, 6th, and 8th flights: prior to this, simultaneous microphone and helicopter operations had not been verified in the testbed, and generally since these early flights the heli-copter has been too far away for its emissions to be detectable given CO2 absorption in the Mars atmosphere.The detected signatures are around 84 Hz and (occasionally) at 168 Hz, at the blade crossing frequency and its first harmonic. Several higher harmonics were prominent in hover tests in short-range recordings in a test chamber on Earth; these are attenuated by CO2 absorption at the 50m-plus ranges on Mars. Doppler shift of the 84 Hz signal can be measured and is consistent with the trajectory measured with Ingenuity's navigation camera and inertial navigation unit, and documented by Perseverance's cameras.A striking feature of the sound recordings is an unanticipated deep modulation of the signals with nulls spaced by around 15-20s, superposed on the simple and expected decline in amplitude with distance. We have evaluated and rejected models of multipath sound interference as requiring implausibly strong near-surface temperature gradients. We find instead that the modulation appears to be the signature of a slight asynchrony between the rotation rates of the two coaxial rotors, such that the blade-crossing azimuth rotates slowly during flight, resulting in a 'lighthouse' sweeping of the radiated sound pattern. Analysis of blade orientations seen in the shadow of the helicopter observed in down-looking navigation images supports this model.

We present the Sample Recovery Helicopter (SRH) element that serves as the primary backup for tube retrieval as part of the Mars Sample Return (MSR) Campaign. SRH was officially incorporated into MSR in July 2022. Concept of operations, aerial and ground mobility, manipulation, avionics, thermal and telecom will be described in the context of SRH's Mission Concept Review held in June 2022. The summarized Concept of Operations (ConOps) of SRH is as follows: 1. SRH would ride along with the Sample Retrieval Lander to Mars and deploy onto the surface. 2. SRH would perform mapping flights to aid in localization during the nominal mission. 3. SRH flies, and lands close to the tube sample depot. 4. SRH drives towards the selected sample tube and acquires it using a manipulator. 5. SRH + sample then take off, fly and land a safe distance from the lander. 6. SRH drives towards the lander and drops the sample tube onto the lander's robotic arm workspace. SRH drives away from the robotic arm workspace. 7. The lander's robotic arm picks up the tube from the ground and places it inside the rocket. 8. Process repeats, go to step 3. No functionality validation or design analysis is included in this work.

The Mars Sample Return Mission (MSR) will carry the next set of Mars helicopters, Sample Recovery Helicopters (SRHs), to the Martian surface. After successfully demonstrating extraterrestrial flight in 2021, Ingenuity has acted as a "scout" for the Perseverance rover while the rover gathers samples of Martian soil. In 2028, the MSR mission will launch a lander and two Ingenuity-sized SRHs to retrieve these samples. These will be the first samples of the Martian surface delivered to Earth. The SRH project will maintain heritage from Ingenuity's design when possible. However, several key changes must be made, including a ground mobility system, a robotic arm for tube manipulation, and the ability to carry the weight of a science payload (the sample tubes). In addition, the onboard software and cameras will be upgraded, and the rotor radius will be increased. Furthermore, new rotor performance and flight dynamics models and thorough characterization of vehicle limits will be required. The new vehicle design will be described, as well as validation and verification efforts to date. Note: The decision to implement Mars Sample Return will not be finalized until NASA's completion of the National Environmental Policy Act (NEPA) process.

Before the Perseverance rover landing, the acoustic environment of Mars was unknown. Models predicted that: (1) atmospheric turbulence changes at centimetre scales or smaller at the point where molecular viscosity converts kinetic energy into heat 1 , (2) the speed of sound varies at the surface with frequency 2 , 3 and (3) high-frequency waves are strongly attenuated with distance in CO 2 (refs. 2 – 4 ). However, theoretical models were uncertain because of a lack of experimental data at low pressure and the difficulty to characterize turbulence or attenuation in a closed environment. Here, using Perseverance microphone recordings, we present the first characterization of the acoustic environment on Mars and pressure fluctuations in the audible range and beyond, from 20 Hz to 50 kHz. We find that atmospheric sounds extend measurements of pressure variations down to 1,000 times smaller scales than ever observed before, showing a dissipative regime extending over five orders of magnitude in energy. Using point sources of sound (Ingenuity rotorcraft, laser-induced sparks), we highlight two distinct values for the speed of sound that are about 10 m s −1 apart below and above 240 Hz, a unique characteristic of low-pressure CO 2 -dominated atmosphere. We also provide the acoustic attenuation with distance above 2 kHz, allowing us to explain the large contribution of the CO 2 vibrational relaxation in the audible range. These results establish a ground truth for the modelling of acoustic processes, which is critical for studies in atmospheres such as those of Mars and Venus.

In April 2021, the Ingenuity Mars Helicopter took off from the surface of Mars as the first heavier-than-air, the first controlled, and the first powered aircraft to fly outside of Earth's atmosphere. As of January 2022, Ingenuity is still operational, having performed another 17 flights and having traversed a distance of 3.8 km, far surpassing the original goals of the mission. This paper focuses on the control of Ingenuity's flights from an operational perspective, including the search and selection of safe areas for takeoff and landing; the challenges of planning and executing flights between these areas; the influence of environmental parameters such as terrain, atmospheric den-sity, and wind; and the gradual expansion of the flight envelope informed by analysis of the helicopter's aerodynamic and flight control performance.

With Ingenuity's successful technology demonstration flights, NASA has unlocked a new dimension of mobility, exploration, and science for Mars. Just as Sojourner lead to Perseverance, so shall Ingenuity lead to larger more capable exploration platforms. This paper will present the latest future Mars rotorcraft concept in its early formulation stages, called Mars Science Helicopter (MSH). The focus of MSH is to deliver scientific payloads in the 2-5kg range to the newly unlocked frontiers of Mars. Such a rotorcraft would need to be significantly scaled up from the current Ingenuity design, growing in size and configuration to a hex-multicopter ∼3m in diameter and weighing ∼30kg. To make this leap in capability, the vehicle aerodynamic control models, downlinked data, and lessons learned from Ingenuity are critical. MSH will build on Ingenuity's success, and serve as an exploration platform capable of 1 1 Copyright 2021 California Institute of Technology. Government sponsorship acknowledged. starting a new paradigm shift in how science is performed on Mars. The vehicle design, capabilities, mission profiles, and various engineering challenges will be analyzed in this paper. The aerodynamic controls problems associated with scaling up to a larger rotorcraft will be discussed, as well as, the systems design challenges in building a lightweight airborne science platform, the energy challenges of a standalone rotorcraft mission, and the exciting new science which is enabled by MSH.

On April 19, 2021, NASA's Ingenuity Mars Helicopter successfully executed humanity's historic first flight on Mars. In the flights that followed, Ingenuity continued to explore the boundaries of what was aerodynamically, energetically, and operationally possible, and took on increasingly daring missions in the process. Over time, Ingenuity's mission has evolved from a “Technology Demonstration” of the first rotorcraft to fly on Mars to an “Operations Demonstration” of scientific aerial exploration scenarios on Mars. Ingenuity's activities to date have yielded a rich first-of-its-kind data set and extensive operational experience. This paper describes the Ingenuity Mars Helicopter's operation and technical performance. It details the approach and considerations involved in remotely operating a rotorcraft on Mars from Earth. It presents the performance of the vehicle in the extremely thin Martian atmosphere compared to predicted design values, based on analysis and testing on Earth. The agreement between predicted and observed performance has been excellent. This paper also discusses scientific impacts that Ingenuity Mars Helicopter has been able to contribute to the Mars 2020 Perseverance mission during Ingenuity's Operations Demonstration phase. The performance of the vehicle, the operational experiences and lessons learned, anomalies encountered and their resolutions presented in this paper critically inform the formulation, design, and development of the next generation of advanced aerial rotorcraft platforms for Mars and other extra-terrestrial bodies. 1 1 Copyright 2021 Jet Propulsion Laboratory, California Institute of Technology. Government sponsorship acknowledged. 2 2 The research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (80NM0018D0004).

Mid-Air Helicopter Delivery (MAHD) is a new Entry, Descent and Landing (EDL) architecture to enable in situ mobility for Mars science at lower cost than previous missions. It uses a jetpack to slow down a Mars Science Helicopter (MSH) after separation from the backshell, and reach aerodynamic conditions suitable for helicopter take-off in mid air. For given aeroshell dimensions, only MAHD's lander-free approach leaves enough room in the aeroshell to accommodate the largest rotor option for MSH. This drastically improves flight performance, notably allowing +150% increased science payload mass. Compared to heritage EDL approaches, the simpler MAHD architecture is also likely to reduce cost, and enables access to more hazardous and higher-elevation terrains on Mars. This paper introduces a design for the MAHD system architecture and operations. We present a mechanical configuration that fits both MSH and the jetpack within the 2.65-m Mars heritage aeroshell, and a jetpack control architecture which fully leverages the available helicopter avionics. We discuss preliminary numerical models of the flow dynamics resulting from the interaction between the jets, the rotors and the side winds. We define a force-torque sensing architecture capable of handling the wind and trimming the rotors to prepare for safe take-off. Finally, we analyze the dynamic environment and closed-loop control simulation results to demonstrate the preliminary feasibility of MAHD.

Abstract The authors have requested that this preprint be removed from Research Square.

As part of the upcoming Mars 2020 rover mission, NASA is planning to include an autonomous helicopter to demonstrate the feasibility and utility of using helicopters for Mars exploration. Helicopter flight on Mars is challenging due to the extremely thin atmosphere, which is only partially offset by a reduction in gravity. This paper focuses on flight dynamics and controllability issues for the Mars Helicopter: in particular, the areas in which the dynamics differs from typical behavior on Earth. The paper discusses insights gained from modeling and simulation, as well as system identification performed with a test vehicle in the relevant atmospheric conditions, which culminated in the first demonstration of controlled helicopter flight in Martian atmospheric conditions in May 2016.

The Mars Helicopter is part of the NASA Mars 2020 rover mission scheduled to launch in July of 2020. Its goal is to demonstrate the viability and potential of heavier-than-air vehicles in the Martian atmosphere. The low density of the Martian atmosphere and the relatively small-scale rotor result in flows with very low Reynolds number, reducing the lifting force and lifting efficiency, respectively. This paper describes the generation of the improved Mars Helicopter aerodynamic rotor model. The goal is to generate a performance model for the Mars Helicopter rotor using a free wake analysis in CAMRADII. The improvements in the analysis are twofold and are expanded on from two prior publications. First, the fidelity of the simulations is increased by performing higher-order time-accurate OVERFLOW simulations allowing for higher-accuracy aerodynamic coefficients and a better understanding of the boundary-layer behavior. Second, a model is generated for the testing conditions in the 25-ft-diam Space Simulator at the Jet Propulsion Laboratory, allowing for better correlation of rotor performance figures. The higher temperatures in the experiment are expected to give conservative performance estimates, as they give rise to an increase in speed of sound and decrease in observed Reynolds numbers.