A paper describes algorithms for guidance and control (G&C) of a spacecraft maneuvering near a planet, moon, asteroid, comet, or other small astronomical body. The algorithms were developed following a model- predictive-control approach along with a convexification of the governing dynamical equations, control constraints, and trajectory and state constraints. The open-loop guidance problem is solved in advance or in real time by use of the pseudo-waypoint generation (PWG) method, which is a blend of classical waypoint and state-of-theart, real-time trajectory-generation methods. The PWG method includes satisfaction of required thruster silent times during maneuvers. Feedback control is implemented to track PWG trajectories in a manner that guarantees the resolvability of the open-loop-control problem, enabling updating of G&C in a provably robust, model-predictive manner. Thruster firing times and models of the gravitational field of the body are incorporated into discretized versions of the dynamical equations that are solved as part of an optimal-control problem to minimize consumption of fuel or energy. The optimal- control problem is cast as a linear matrix inequality (specifically a secondorder cone program), then solved through semi-definite-programming techniques in a computationally efficient manner that guarantees convergence and satisfaction of constraints.
This work was done by Ahmet Açikmefle and John M. Carson III of Caltech for NASA’s Jet Propulsion Laboratory. For more information, download the Technical Support Package (free white paper) at www.techbriefs.com/tsp under the Mechanics/Machinery category.
The software used in this innovation is available for commercial licensing. Please contact Karina Edmonds of the California Institute of Technology at (626) 395-2322. Refer to NPO-42753.
This Brief includes a Technical Support Package (TSP).
Pseudo-Waypoint Guidance for Proximity Spacecraft Maneuvers
(reference NPO-42753) is currently available for download from the TSP library.
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Overview
The document titled "Pseudo-Waypoint Guidance for Proximity Spacecraft Maneuvers" (NPO-42753) from NASA's Jet Propulsion Laboratory outlines innovative guidance and control (G&C) algorithms developed for spacecraft operations in proximity to small celestial bodies, such as asteroids and comets. The primary focus of this technology is to enhance the autonomy and real-time decision-making capabilities of spacecraft during critical proximity operations, including descent, ascent, hazard avoidance, and surface contact.
The G&C algorithms employ a Model Predictive Control (MPC) approach, which is particularly effective due to its ability to incorporate state and control constraints directly into the guidance and control framework. This method allows for the generation of pseudo way-points, which serve as reference trajectories for the spacecraft. The open-loop guidance is based on a pseudo way-point generation algorithm that utilizes a discrete linear-time-varying model of the spacecraft's dynamics, taking into account necessary thruster silent times. This leads to a convex formulation of the trajectory generation problem, which is solved using second-order cone programming techniques, ensuring a global optimum is achieved with a deterministic stopping criterion and a specified level of accuracy.
The G&C algorithm is structured with separate feedforward and feedback components. The feedforward component generates the pseudo way-points, while the feedback control is responsible for tracking these trajectories. This dual approach guarantees the resolvability of the open-loop problem, allowing for robust updates to the guidance profile in a model-predictive manner. The effectiveness of this robust G&C algorithm is demonstrated through simulations, particularly in scenarios involving spacecraft landing on small asteroids with significant gravity fields. Incorporating a gravity model into the algorithm significantly enhances controller performance.
The document also references a publication by J. Carson and B. Acikmese, which details the application of this model predictive control technique and its advantages over other G&C schemes. Overall, the technology described in this document represents a significant advancement in the field of spacecraft navigation and control, with potential applications in future missions targeting small celestial bodies. The research is part of NASA's broader efforts to develop technologies with wider technological, scientific, or commercial applications.
