An Autonomous Onboard Targeting Algorithm Using Finite Thrust Maneuvers

Abstract

I. AbstractIn earlier investigations, the adaptation and implementation of a modified two-level corrections process as the onboard targeting algorithm for the Trans-Earth Injection phase of Orion is presented. The objective of that targeting algorithm is to generate the times of ignition and magnitudes of the required maneuvers such that the desired state at entry interface is achieved. In an actual onboard flight software implementation, these times of ignition and maneuvers are relayed onto Flight Control for command and execution. Although this process works well when the burn durations or burn arcs are small, this might not be the case during a contingency situation when lower thrust engines are employed to perform the maneuvers. Therefore, a new version of the modified two-level corrections process is formulated to handle the case of finite burn arcs. This paper presents the development and formulation of that finite burn modified two-level corrections process which can again be used as an onboard targeting algorithm for the Trans-Earth Injection phase of Orion. Additionally, performance results and a comparison between the two methods are presented. The finite burn two-level corrector formulation presented here ensures the entry constraints at entry interface are still met without violating the available fuel budget, while still accounting for much longer burn times in its design.

High-Accuracy Moon to Earth Escape Trajectory Optimization

“…Weeks et al 2 and Scarritt et al 10 propose an onboard autonomous targeting algorithm for the Moon-Earth transfer, based on a linear twolevel corrections process. In their work, the magnitude of thrust is also assumed constant and the thrust steering rate is constant or zero.…”

Implementation of an Autonomous Multi-Maneuver Targeting Sequence for Lunar Trans-Earth Injection

“…This is bounded by the following equation, developed in the original formulation: In this equation, the integer subscripts specify the orbit number increasing from the parking orbit (0) to the first and second transfer ellipses (1, 2) to the departure hyperbola (3). Originally, the orbit was defined by making this vector the same as the apolune of the first transfer ellipse: Likewise, the second transfer ellipse remains undefined, dependent on the unit vector of the apolune of the second transfer ellipse, which is constrained to be along the same line of apsides as the departure hyperbola perilune, At this point, the assumption of the equivalency of the eccentricities of the orbits can be applied: 1 2 e e = (9) With this assumption there are still three unknowns and only two equations. An additional relation is needed.…”