SENSITIVITY ANALYSIS OF THE TOUCHDOWN FOOTPRINT AT (101955) 1999 RQ_(36)

摘要

This paper describes the analysis of the touchdown footprint of an asteroid sample return mission. The mission bears similarity with NASA's Origins Spectral Interpretation Resource Identification Security Regolith Explorer (OSIRIS-REx) mission. The target asteroid is (101955) 1999 RQ36 and the spacecraft mass and overall dimensions are similar to those of OSIRIS-REx. A shape model of (101955) 1999 RQ_(36) is employed to create three gravitational models of the asteroid and the models are analyzed in order to select the model that gives good accuracy with the least computational effort. A stable, retrograde orbit, in the plane of the terminator, of 1.5 km radius, is designed and shown to be bound for about 25 days. The descent trajectory, also called the touch-and-go profile, starts from the home orbit and takes the spacecraft to asteroid touchdown by employing three maneuvers. The maneuvers are designed with a Lambert's problem solver so that the first transfer arc is on an elliptic orbit with a periapsis altitude of 20 m and the nominal touchdown speed is 0.1 m/s. For this analysis the target touchdown spot is on the equator of the asteroid at 44°E longitude. The size and orientation of the touchdown footprint are determined using a Monte Carlo analysis that assumes that the off-nominal and uncertain parameters for the asteroid and spacecraft are normally distributed. The resulting 3σ ellipse, projected on a mean sphere of 287.5 m radius, has a semimajor axis of 115m and a semiminor axis of 16m.