RADIOMETRIC ORBIT DETERMINATION ACTIVITIES IN SUPPORT OF NAVIGATING DEEP SPACE 1 TO COMET BORRELLY

摘要

Four months after its encounter with the asteroid Braille, Deep Space 1 lost the use of its only star tracker. After several months of planning, development and testing, new software was uploaded that allowed the spacecraft to restore celestial inertial reference and begin thrusting towards an encounter with comet Borrelly. The new mission plan would have to work within the constraints of the new software as well as minimize use of the dwindling supply of hydrazine, the fuel needed to maintain the spacecraft attitude. In the spring and summer of 2001, as it approached comet Borrelly, the spacecraft lost its celestial reference several times. As the mission plan required nearly continuous low-thrust, the resulting attitude drifts caused the spacecraft to push itself off course. Difficulty in restoring attitude information had a further impact on the spacecraft trajectory. Modeling these attitude drifts before and during attitude recovery periods was necessary in order to determine the new orbit. This allowed for the timely redevelopment of upcoming mission burns that put the spacecraft back on course for its encounter. Once back on course, an approach targeting strategy using only IPS TCMs enabled the spacecraft to start the encounter with Borrelly with high expectations of success.