Revolutionizing Orbit Insertion with Drag-Modulated Plasma Aerocapture

Aerocapture is an orbit insertion maneuver that uses drag of a planetary atmosphere on a spacecraft to transfer it from a hyperbolic trajectory to a closed elliptic orbit. This technique can greatly reduce cost or increase delivered payload mass and it is an enabling technology for otherwise infeasible missions to Jupiter, Saturn, and Neptune (Hall et al, 2005). Although several relatively mature aerocapture technologies are under development, the associated risks of performing this maneuver have prevented them from ever being used on a mission. Current aerocapture devices rely on aeroshells, solid structures that deflect atmospheric flow, and are therefore susceptible to the high heat and dynamic pressure inherent to hypersonic reentry. Aeroshells are limited in size due to launch vehicle constraints and must fly deep in the atmosphere to achieve the necessary drag for orbit insertion. Such trajectories are highly sensitive to perturbations and uncertainties in the local environment, which can be significant in the poorly understood atmospheres beyond Mars. Plasma aerocapture leverages an entry technology called a magnetoshell to achieve orbit with lower heating and dynamic pressures than standard aerocapture systems. A magnetoshell consists of a plasma confined by an applied magnetic field which is fixed to the spacecraft. Some plasma is seeded into the field from onboard fuel storage to initially generate the magnetoshell. Rather than deflect the atmospheric flow as an aeroshell does, the plasma absorbs and utilizes the neutral atmosphere during the maneuver. Thus, the magnetoshell requires little thermal protection since the flow energy is deposited in the plasma and not the spacecraft structure. The plasma is sustained entirely from the mass and energy captured from the atmosphere rather than any onboard fuel and power; only power to the magnet is required to keep the magnetoshell operational. Additionally, the area over which flow interacts with the plasma is defined by the strength of the magnetic field, so the area can be made larger than that of a mechanically deployed decelerator. This means aerocapture is achieved at higher altitudes where dynamic pressure and sensitivity to atmospheric perturbations are lower. By controlling the magnetic field strength, the drag can be modulated continuously, enabling robust control over the flight trajectory. This research aims to determine whether plasma aerocapture is a feasible solution for delivering spacecraft to targets with atmospheres. Because of the novel physics of the magnetoshell, feasibility hinges on multiple questions. First, I will develop an analytic model of the plasma interaction with an atmospheric flow representative of the aerocapture environment. This model will reveal the fundamental physics governing the plasma and the scaling of drag with input parameters such as magnetoshell design and atmospheric conditions. Second, I will develop an experiment to validate the physics observed in the analytic model. This experiment will consist of a subscale magnetoshell impacted by a low-energy neutral beam in a novel “wind tunnel” approach simulating aerocapture conditions. The magnetoshell drag will be measured using a thrust stand and plasma diagnostics will analyze crucial parameters governing performance. Finally, with a solid understanding of these physics, I will develop a tool for simulating trajectories of plasma aerocapture in NASA’s Program to Optimize Simulated Trajectories II (POST2). This module will combine the performance scaling found by the analytic model and experiment with spacecraft configuration parameters so that mission designers can develop plasma aerocapture mission architectures. Addressing these three research areas will ultimately determine whether plasma aerocapture can be reasonably implemented aboard a spacecraft, opening the door to future mission development and solar system exploration.

At present, NASA is studying several mature aerocapture technologies, the drawbacks of which often dictate excessive constraints on their intended design architectures. Maturing MAC to a level competitive with current aerocapture options will relax these constraints and open up new pathways to delivering deep space payloads

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