Robust conventional based midcourse guidance for spacecraft intercepts

The performance robustness of a modified zero effort miss guidance law used during the midcourse phase of spacecraft intercepts, with propulsion system modeling uncertainties present, is addressed. For comparison purposes, a Lambert-energy management guidance law (no thrust termination capability) is also considered. Fundamental differences between the two guidance laws are noted and include: 1) thrust vector pointing philosophies, and 2) dependency upon the nominal propulsion system model. These differences imply the conventionally based intercept scheme is a more forgiving guidance law under the indicated uncertainties. A numerical engagement simulation, exercising both guidance techniques, is undertaken to verify and quantify the performance robustness advantage. In contrast, the two guidance laws are shown to be one and the same as the targeting distance reduces to a level that is synonymous with the terminal phase of the intercept. This equivalence also suggests a specific function for the zero effort miss guidance gain.