Optimal control techniques for multimode propulsion mission design in cislunar space

Multimode spacecraft propulsion is an emerging, enabling, and enhancing technology that combines two or more propulsive modes (e.g., chemical and electric) into one system using a single propellant. The primary benefit of this technology is that it can provide reduced propellant consumption for a given transfer in comparison to an all-chemical approach and reduced transit time in comparison to an all-electric approach. It can also significantly increase the maneuvering capability domain of a spacecraft in comparison to single mode (i.e., all-chemical or all-electric) propulsion systems. Additionally, multimode propulsion provides mission flexibility and adaptability because the propellant may, in principle, be used in any mode at any time. Despite these benefits, there is presently a lack of mature techniques for designing optimal multimode transfers—particularly for chemical-electric multimode systems. In this dissertation, indirect optimal control techniques are developed for solving optimal multimode orbital transfers. Using an indirect approach results in the automatic selection of the burn sequence (i.e., which mode should be used at every instant). This yields more optimal transfers in comparison to the traditional approach in which the burn sequence is manually selected. Two types of optimal control problems are solved: minimum-fuel and propellant-constrained minimum-time (PCMT). The former is the primary focus of this dissertation and examples are shown for interplanetary, geocentric, and cislunar transfers for systems with large performance differences (i.e., thrust and specific impulse) between the modes. Forward single shooting is used to solve the example interplanetary and geocentric transfers in combination with hyperbolic tangent smoothing (HTS) for the throttle. To solve multimode cislunar minimum-fuel problems, a new technique is developed using modified equinoctial elements (MEE), HTS, forward-backward multiple shooting, two reference frames (Earth-centered and Moon-centered), and highly consistent dynamics. The method is demonstrated with multiple two-mode transfers as well as a three-mode transfer. The PCMT problem is particularly relevant for mission recovery efforts (e.g., after a launch injection failure) or spacecraft with hybrid propulsion systems (i.e., systems with two or more modes that are not integrated and do not share propellant) with fixed propellant budgets. To solve this problem, a penalty function approach was combined with HTS to enforce a maximum propellant usage constraint on the highest thrust, lowest specific impulse mode. The method is demonstrated with a three-dimensional transfer from a geostationary transfer orbit (GTO) to geostationary orbit (GEO) that was solved using MEE and forward single shooting. Finally, note that the techniques developed here are agnostic to the propulsion system. As a result, the methods apply equally well for spacecraft with hybrid propulsion systems as to those with multimode propulsion. While multimode propulsion is still a maturing technology, there are many spacecraft currently flying with hybrid propulsion. Accordingly, the methods developed here are applicable not only to future multimode missions, but also to near-term missions with hybrid propulsion.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Aerospace Engineering

Grantor

University of Illinois Urbana-Champaign

Year dc:date

2025

Author dc:creator

• Cline, Bryan Christopher

Contributors dc:contributor

• Woollands, Robyn M
• Rovey, Joshua L
• Allison, James T
• Coverstone, Vicki L

• Optimal Control
• Indirect Optimal Control Techniques
• Space Mission Design
• Space Trajectory Optimization
• Cislunar Space
• Multimode Propulsion

Statement dc:rights

• Copyright 2025 Bryan Christopher Cline

Language dc:language

en

Handle dc:identifier

https://hdl.handle.net/2142/132571

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/132571