AAS 96-121

CRYOGEN THRUST MODELING FOR MSX EPHEMERIS GENERATION

C. von Braun, MIT Lincoln Laboratory

Abstract

In the spring of 1996, the Midcourse Space Experiment (MSX) satellite, sponsored by the Ballistic Missile Defense Organization (BMDO), is scheduled to be launched into an 898-km altitude, near sun-synchronous orbit. A long-wavelength infrared sensor on-board uses a hydrogen cryostat system designed to absorb much of the radiant energy encountered by the sensor. However, waste hydrogen gas from this system is vented to the rear of the spacecraft and out into space, thus creating a small but continuous thrust on the vehicle. Using a viscous, compressible flow model developed to estimate the actual thrust, simulations clearly show that by simply assuming the thrust is constant down the ventline and by simultaneously estimating thrust and drag scale factors with the satellite state vector, cryogen effects can be modeled down to two meters, with low correlation between the two factors. Error sources due to observations, drag and the gravity field were also considered in the study.