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Daniel Guggenheim School of Aerospace Engineering
Daniel Guggenheim School of Aerospace Engineering
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ItemModel Predictive Path Integral Control for Spacecraft Rendezvous Proximity Operations on Elliptic Orbits(Georgia Institute of Technology, 2023-08) Sasaki, Tomohiro ; Ho, Koki ; Lightsey, E. GlennThis paper presents a nonlinear control framework for spacecraft rendezvous and proximity operations on elliptic orbits using Model Predictive Path Integral (MPPI) control. Path integral control is a sampling-based nonlinear stochastic optimal control algorithm that can avoid linear and quadratic approximations in both dynamics and cost functions. While this control method has gained popularity in the robotics community due to its algorithmic effectiveness, it remains unexplored in astrodynamics. This paper demonstrates a comprehensive closed-loop simulation of spacecraft rendezvous employing MPPI and evaluates its control performance through these simulations.
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ItemTranslunar Logistics with Low-Energy Transfers(Georgia Institute of Technology, 2023-08) Gollins, Nick ; Shimane, Yuri ; Ho, KokiLow-energy lunar transfers (LETs) utilize three-body mechanics with fourth-body (solar) perturbations to provide an alternative to direct lunar transfers. The offer of reduced lunar orbit insertion cost in exchange for longer time-of-flight and potentially higher transfer insertion cost presents an interesting trade-off when planning the logistics of multi-mission lunar exploration campaigns. This is particularly true for logistics featuring spacecraft with a variety of launch vehicles and propellant types, as the logistics of each spacecraft are impacted by the costs and benefits of LETs differently. This paper presents a translunar logistics model featuring LETs, discusses the trade-offs versus direct transfers through some case studies, and highlights the scenarios in which LETs prove most useful.
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ItemOptimization of Earth-Moon Low-Thrust-Enhanced Low-Energy Transfer(Georgia Institute of Technology, 2023-08) Takubo, Yuji ; Shimane, Yuri ; Ho, KokiThis work proposes an optimization method for the novel class of lunar transfer that leverages both low-thrust acceleration and weak stability boundary effects simultaneously. Such translunar orbits are aimed at filling the gap that exists in conventional transfer options in the trade-off between the time of flight and mass ratio. We first generate the candidates for the initial guess via backward propagation from a cislunar periodic orbit. These trajectories are corrected into feasible solutions, then further optimized based on a multiple-shooting method with a Sims-Flanagan transcription. The obtained transfer time of the solutions is around 45-70 days, which is almost half of the traditional ballistic transfers (90-110 days) with a few percent increase in its propellant mass, showing a huge benefit of performing the low-thrust propulsion in the Earth-Moon low-energy transfer.
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ItemCharacterizing Low-Thrust Transfers from Near-Rectilinear Halo Orbits to Low Lunar Orbits with Q-Law(Georgia Institute of Technology, 2023-08) Shimane, Yuri ; Preston, Dyllon ; Ho, KokiNear rectilinear halo orbits (NRHOs) are an integral orbital regime in humanity's permanent return to cislunar space. Traffic between the NRHO and low-lunar orbit (LLO) is expected to increase dramatically, supporting cislunar activities. Linking NRHOs and LLOs via low-thrust transfers will be a vital piece of transportation infrastructure. This work provides an assessment of low-thrust transfers from NRHOs to LLOs using Q-law, a Lyapyunov feedback controller based on Keplerian elements, treating the Earth as a third-body perturbation. Leveraging the deterministic nature of Q-law, low-thrust transfers between NRHOs and LLOs are characterized for various propulsion systems, spacecraft mass, and departure windows.
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ItemSensitivity Analysis of Separation Time Along Weak Stability Boundary Transfers(Georgia Institute of Technology, 2023-08) Nolton, Isabel ; Tomita, Kento ; Shimane, Yuri ; Lee, Hang Woon ; Ho, KokiThis study analyzes the sensitivity of the dynamics around Weak Stability Boundary Transfers (WSBT) in the elliptical restricted three-body problem. With WSBTs increasing popularity for cislunar transfers, understanding its inherently chaotic dynamics becomes pivotal for guiding and navigating cooperative spacecrafts as well as detecting non-cooperative objects. We introduce the notion of separation time to gauge the deviation of a point near a nominal WSBT from the trajectory's vicinity. Employing the Cauchy-Green tensor to identify stretching directions in position and velocity, the separation time, along with the Finite-Time Lyapunov Exponent are studied within a ball of state uncertainty scaled to typical orbit determination performances.
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ItemLearning Reachability for Hazard Detection Avoidance in Planetary Landing(Georgia Institute of Technology, 2023-08) Tomita, Kento ; Jo, Beyong-Un ; Ho, KokiAutonomous hazard detection and avoidance (HD&A) poses a stochastic perceptionaware guidance problem, where the visible surface depends on the trajectory, and the safest target locations are kept updated. For the concurrent optimization of the target and trajectory, evaluating the reachable surface under guidance constraints in real-time is critical, but it requires solving optimization problems multiple times. To bypass the optimization-based computation of the reachable surface, we propose to learn the parameterized reachable surface by a neural network, which ultimately enables the reachability-aware guidance algorithms. This paper presents the proposed parameterization method and validation results by numerical simulations.
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ItemCislunar Satellite Constellation Design via Integer Linear Programming(Georgia Institute of Technology, 2023-08) Patel, Malav ; Shimane, Yuri ; Ho, KokiCislunar space awareness is of increasing interest to the international community as Earth-Moon traffic is projected to increase. This raises the problem of placing satellites optimally in a constellation to provide satisfactory coverage for said traffic. The Circular Restricted 3 Body Problem (CR3BP) provides promising periodic orbits in the Earth-Moon rotating frame for traffic monitoring. This work converts a spatially and temporally varying traffic coverage requirement into an integer linear programming problem, attempting to minimize the number of satellites required for the requested coverage.
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ItemCostates Feedback Control for Mass-Optimal Low-Thrust Transfers(Georgia Institute of Technology, 2023-08) Shimane, Yuri ; Izzo, Dario ; Ho, KokiDesigning efficient low-thrust trajectories involves solving optimal control problems, which can be computationally intensive. One promising approach to tackle this challenge is to use a neural network (NN) as a scheme for obtaining the control input that guides the spacecraft to its targeted orbit. This work explores the use of a NN for learning the costates from the current and targeted states, which can be used together with Pontryagin's maximum principle and optimal control theory to derive the control to provide a feedback loop for controlling the spacecraft. In effect, this is a policy approximation scheme, even though it does not explicitly have the controls as its output. The proposed method is applied to a set of orbits departing from near-ecliptic near-Earth object targeting the Earth's orbit for a mass optimal orbit transfer.
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ItemTerminal Landing Guidance Law Using Analytic Gravity Turn Trajectory(Georgia Institute of Technology, 2023-01) Han, Seungyeop ; Ho, KokiThis paper introduces the terminal landing guidance law based on the analytic solution of gravity-turn trajectory. Characteristics of the derived solution are investigated, and the solution is used for the generation of a reference two-dimensional vector field that satisfies terminal landing conditions. In addition, the vector field is further expanded to consider ground collision avoidance as well as three-dimensional problem. A nonlinear control law is applied to track the reference vector efficiently within a finite time. The effectiveness of the proposed method is demonstrated through nonlinear numerical simulations, and performances are compared with existing methods.
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ItemConcurrent Optimization of Gravity-Assist Low-Thrust Trajectory with Power Propulsion Subsystem Sizing(Georgia Institute of Technology, 2022-08) Shimane, Yuri ; Preston, Dyllon ; Ho, KokiLow-thrust technology is a key driver in current and upcoming space exploration missions due to their high specific impulse. A challenge when designing low thrust trajectories is due to the inherent coupling of the power and propulsion subsystems with the trajectory, as the spacecraft mass greatly affect the obtainable acceleration by a given propulsion subsystem. To this end, this work proposes an approach for coupling the sizing process of the power and propulsion subsystems to a direct-transcription-based trajectory optimization problem, which enables a concurrent trade-space exploration of both the trajectory and the spacecraft design.