C. E. Helfrich

Navigation for low-cost missions to small solar-system bodies

Abstract A variety of low-cost space missions planned by NASA for flight in the late 1990s and early 2000s will involve rendezvous with, and orbits about, small solar-system bodies such as asteroids and comets. Rendezvous missions of this nature have never been performed, all previous small-body encounters having been flybys. Thus in navigating these missions there are a number of issues and challenges which are new. This paper will identify the different mission phases for small body encounters and the navigation requirements, objectives and goals involved with each phase. In addition, certain practical limitations with respect to mission design will be identified and the scientific information obtained by navigation during the mission discussed. The phases and issues addressed in the paper are: preencounter characterization, encounter and rendezvous with the body, post-encounter characterization, initial orbit strategy and the mission phase itself. Each of these phases have integral importance and are critical to the success of the entire mission. Inherent in each of these phases are all the traditional navigation concerns, such as a priori knowledge, maneuver design and execution, data acquisition, orbit determination, orbit reconstruction and control. The paper explains how these traditional roles will be implemented for future small-body missions, including the use of autonomous navigation where practical. Navigation of spacecraft to and about small solar-system bodies is challenging and raises many issues of fundamental importance which should be understood by the mission navigators, designers and sponsors. This paper will identify the most important issues and discuss ways in which they may be dealt with. It also provides a methodology with which to approach navigation for small-body missions.