Guidance and Control for a Mars Helicopter

Abstract

As part of a future mission to Mars, NASA is considering including a small helicopter capable of operating independently in the Martian environment. The Martian atmosphere is extremely thin, with a density of only 1-2% of Earth's atmospheric density at sea level; this significantly alters the flight dynamics of the vehicle and has implications for vehicle design and control. In this paper we focus on guidance and control for a Mars Helicopter, and in particular on the challenges that are unique to operating in the Mars environment. In 2016, the first-ever controlled flight of a helicopter in Martian atmospheric conditions was performed in the 25-ft Space Simulator at NASA's Jet Propulsion Laboratory. We provide details of the effort leading to this flight demonstration, including

Flight Control System for NASA's Mars Helicopter

“…• a harsher radiation environment than on Earth, which can leave computing elements susceptible to upsets In previous papers the authors have presented aspects of the flight dynamics [1] and the guidance and control design [2] for a preliminary Mars Helicopter concept, including a test campaign that culminated in the first helicopter flight in Martian atmospheric conditions. Since then, the concept has matured into a complete flight design, and fully functional engineering development models have been built and undergone both environmental and flight dynamics testing.…”

“…This effort involved the design and construction of a demonstration vehicle with a full-scale rotor. Grip et al [1] describes the modeling and identification of the flight dynamics for this vehicle, while Grip et al [2] describes the guidance and control design.…”

“…The swashplate mechanism allows for two types of blade pitch control: collective control changes the average pitch over a rotation, and cyclic control allows for periodic modulation of the blade pitch at a frequency of once per revolution, with a specified phase and magnitude. Compared to the demonstration vehicle presented in [2], the actuation differs in two significant ways. First, the demonstration vehicle featured cyclic control only on the lower rotor.…”

“…The demonstration vehicle presented in [2] made use of a Vicon tracking system, consisting of a set of external cameras used to track features on the vehicle. For Mars flight, navigation is performed using the following onboard sensors:…”

“…Because of this, closed-loop control is required at all times during flight, and ensuring uninterrupted operation of the Control subsystem is a strict requirement. The small scale of the vehicle naturally drives the dynamics to a fast time scale, with an inner-loop crossover frequency of 2.5-3.0 Hz [2]. Thus, keeping latencies in the loop at a minimum level is essential to guaranteeing robust stability across the operating envelope.…”