Instantaneous Impact Point (IIP) guidance and its applications

Abstract

This thesis proposes a feedback guidance law of a rocket to move an instantaneous impact point (IIP) to a desired impact point. To develop this guidance law, IIP dynamics which describes the motion of the IIP on the surface of the Earth is established in the Earth-Centered Earth-Fixed (ECEF) frame by introducing the time derivatives of the IIP. A near time-optimal feedback guidance law for following the shortest path between the current IIP and desired location is developed by utilizing IIP dynamics. Through the various case studies, this study figures out that the efficiency of the developed IIP guidance law becomes lower as the change in a crossrange direction or backwards direction of downrange increases, while the IIP guidance law performs a near-optimal capability in the downrange direction.

Moreover, for the application on practical missions which require specific purposes (engine cut-off insensitive, fixed burn time and return to launch site), this thesis enhances the developed IIP guidance law and provides an additional function. First, the IIP guidance law is improved to handle the event of an engine cut-off failure of the rocket by developing the IIP hold guidance law which can maintain the IIP at the same location in the presence of the thrust, and the mode switching algorithm which makes the necessary transition between the IIP guidance law and IIP hold guidance law while taking the angular rate limitation of the rocket into account. Secondly, the guidance law for changing the IIP for the rocket with fixed burn time is developed. Lastly, the guidance law that can control the flight path angle of the rocket is developed, in order to improve the performance of the IIP guidance law for IIP change in the negative downrange direction.

The effectiveness of the IIP guidance law and improved guidance laws, in comparison with the optimal solution obtained from GPOPS, is demonstrated through the case studies on the landing guidance of the 1st stage of Falcon 9, developed by Space X.