Assessment of aerosurface-based hypersonic control of blunt bodies for planetary entry

Engel, Daniel L.

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https://hdl.handle.net/2142/129401 Copy

Description

Title

Assessment of aerosurface-based hypersonic control of blunt bodies for planetary entry

Author(s)

Engel, Daniel L.

Issue Date

2025-04-17

Director of Research (if dissertation) or Advisor (if thesis)

Woollands, Robyn

Doctoral Committee Chair(s)

Woollands, Robyn

Committee Member(s)

• Putnam, Zachary
• Langbort, Cedric
• Allison, James
• Dutta, Soumyo

Department of Study

Aerospace Engineering

Discipline

Aerospace Engineering

Degree Granting Institution

University of Illinois Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Planetary entry
• Entry vehicle
• GNC
• Guidance
• Control
• Entry guidance
• Entry control
• EDL
• Bank-angle steering
• Alpha-beta steering
• Direct force control
• DFC
• Mars entry vehicle
• Mars entry
• Entry, descent and landing
• Angle of attack modulation
• Flight mechanics
• Entry vehicle flaps
• Aerosurface flight control
• Flap-based hypersonic steering
• Hypersonic control
• Hypersonics

Abstract

Recent Mars entry systems, such as the Mars Science Laboratory and Mars 2020 missions, have used hypersonic steering to better target the desired landing site and achieve trajectory objectives during flight. All guided entries of blunt-body entry vehicles at Mars and Earth have utilized bank-angle steering for hypersonic trajectory control. Vehicles using bank-angle steering generate lift through flight at an uncontrolled, nearly fixed, trim angle of attack, determined by the center-of-gravity location. Bank maneuvers are then used to change the direction of the lift vector, providing the vehicle control over its hypersonic trajectory. With only the bank angle available to steer the entry vehicle, control over the longitudinal and lateral motion becomes highly coupled on bank-angle steering vehicles, potentially reducing flight performance. Furthermore, with an uncontrolled angle of attack, vehicles using bank-angle steering do not have the ability to modulate the magnitudes of the lift and drag forces. A proposed alternative hypersonic steering scheme instead modulates a vehicle’s angle of attack (alpha) and sideslip angle (beta). This alpha-beta steering scheme provides a more decoupled control over an entry vehicle’s longitudinal and lateral motion and allows for the magnitudes of the lift, drag, and side force to be modulated on the entry vehicle. Aerodynamic flaps (or aerosurfaces) are a possible implementation of alpha-beta steering, and this dissertation rigorously assesses the flight performance of aerosurface-based implementations of alpha-beta steering and makes comparisons to bank-angle steering, advancing the current state-of-the-art for planetary entry systems through three novel contributions. In the first contribution, optimal control problems are formulated and solved for both steering options to compare theoretical best performance. First, the maximum downrange and maximum crossrange problems are considered for conventional low-lift-to-drag ratio Mars entry vehicles. Results are combined to determine an overall range capability and facilitate comparison to suboptimal constant bank or angle of attack and sideslip angle commands. The resulting optimal controls often differ significantly between bank-angle and alpha-beta steering vehicles, the latter of which can extend range by lowering drag through sideslip angle reversals during entry. While control over the in-plane and out-of-plane motion is found to be more decoupled for alpha-beta steering than bank-angle steering, control over the longitudinal and lateral motion is still not completely decoupled for vehicles using alpha-beta steering. A number of other optimal control problems are then solved for both alpha-beta and bank-angle steering to obtain both quantitative and qualitative deterministic flight performance differences between the two steering options. These problems are solved for entry vehicles corresponding to robotic and human missions and include the maximum altitude, minimum propellant, minimum control effort, minimum error, minimum heat load, as well as the minimum peak heat rate, dynamic pressure, and aerodynamic load problems. While flight performance of alpha-beta and bank-angle steering is similar, alpha-beta steering provides terminal altitudes between 0.5 km to 2.6 km higher than bank-angle steering. Alpha-beta steering is also less sensitive to decreases in maximum vehicle rotational rates and consistently provides improved performance over sweeps of terminal longitude and in a weighted objective function of terminal altitude and peak heat rate. Results also show bank-angle steering leads to values up to 4.4%, 3.3%, and 1.4% higher than alpha-beta steering for the heat load, peak heat rate, and peak dynamic pressure, respectively, indicating improved performance for alpha-beta steering. The second contribution in this dissertation compares guided entry performance of alpha-beta and bank-angle steering on a future Mars entry vehicle for large robotic payloads. Performance is assessed and compared using closed-loop steering commands from both a conventional Apollo-based entry guidance algorithm and optimal control. Monte Carlo simulations using Apollo guidance and a high entry velocity show alpha-beta steering, relative to bank-angle steering, provides an order of magnitude improvement in crossrange error, mean altitudes up to 1 km higher, and half the standard deviation for downrange errors. Results also show alpha-beta steering provides downrange errors with a standard deviation half of that of bank-angle steering. Furthermore, alpha-beta steering is found to provide a lower standard deviation for terminal altitude, Mach number, and dynamic pressure, indicating safer parachute deploy conditions. Much of the poor performance of bank-angle steering is due to errors induced from the open-loop bank reversals characteristic of these systems; with slower entry velocities, these advantages of alpha-beta steering remain but are not as significant. Using optimal control for steering commands eliminates the bank reversals on the bank-angle steering system and is found to provide a much narrower performance gap between the two steering options. Although alpha-beta steering retains crossrange errors on the order of half of that of bank-angle steering, as well as slight altitude advantages, the two steering options perform similarly for the downrange errors. Monte Carlo results even show bank-angle steering can provide improved downrange performance over alpha-beta steering for the utilized onboard models. The final contribution of this dissertation assesses the control performance of a flap/aerosurface-based implementation of alpha-beta steering. Here, a successive-linearization model predictive control algorithm and a linear-quadratic regulator are designed and assessed to track angle of attack and sideslip angle commands during entry. These two control algorithms are assessed in the presence of uncertainty in Monte Carlo simulations for various flap configurations and command profiles. While both control algorithms provide successful command tracking in the presence of uncertainty, the model predictive controller tracking errors are about half the value of those corresponding to the linear-quadratic regulator, indicating improved performance. Large uncertainties sometimes result in the linear-quadratic regulator failing to maintain control of the vehicle, while the model predictive controller remains successful. Comparison of several flap configurations shows the model predictive controller can be applied to various flap configurations successfully with only marginal performance differences between configurations, while the linear-quadratic regulator has a larger performance disparity between configurations and may require additional tuning to avoid controller failures when changing configurations. Managing undesired rolling moments may be a challenge for entry vehicles with flaps, but using thrusters to maintain the bank angle near zero or modifying the angle of attack and sideslip angle commands from the guidance may be effective in mitigating this issue.

Graduation Semester

2025-05

Type of Resource

Thesis

Handle URL

https://hdl.handle.net/2142/129401

Copyright and License Information

Copyright 2025 Daniel L. Engel

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