A SIMULATION STUDY OF GRAVITY AND EPHEMERIS ESTIMATION OF ASTEROID 1999JU3 USING SPACECRAFT RADIOMETRIC TRACKING, OPTICAL,AND ALTIMETER MEASUREMENTS

摘要

The Japanese asteroid explorer Hayabusa-2 will be launched in the mid-2010s to return samples from C-type near-Earth asteroid 1999JU3. During the rendezvous phase (i.e. proximity operation phase), we will conduct scientific observations to estimate physical parameters (e.g. gravity field, shape, pole direction, spin-rate, ephemeris) of the target body, which are crucial not only for its scientific investigation but also for spacecraft navigation. In particular, the mass is essential to perform a stable touchdown sequence to collect samples from the asteroids surface. We will attempt to estimate the gravity field of the target body using Earth-based radiometric tracking measurements (2-way Doppler and range) and spacecraft-based measurements (information from optical navigation cameras and laser altimeter) using a global parameter estimation technique. As the first step for gravity field estimation, we performed a simulation study on mass estimation under simple configuration and evaluated the relation between the quality and quantity of measurements and the accuracies of the estimation results. Subsequently, the detectability of the low degree and order gravity field coefficients was also studied. We will also present a method for ephemeris improvement of 1999JU3 using spacecraft relative position data and radiometric tracking measurements.