ESTIMATING THE MASS OF ASTEROID 253-MATHILDE FROM TRACKING DATA DURING THE NEAR FLYBY

The terminal navigation of the Near Earth Asteroid Rendezvous (NEAR) s pacecraft during its close flyby of asteroid 253 Mathilde involved coo rdinated efforts to determine the heliocentric orbits of the spacecraf t and Mathilde and then to determine the relative trajectory of the sp acecraft with respect to Mathilde. The gravitational perturbation of M athilde on the passing spacecraft was apparent in the spacecraft track ing data. As a result of the accurate targeting achieved, these-data c ould be used to determine Mathilde's mass as 1.033 (+/-0.044) x 10(20) grams. Coupled with a volume estimate provided by the NEAR imaging te am, this mass suggests a low bulk density for Mathilde of 1.3 grams pe r cubic centimeter.