LISA Pathfinder: New Methods for Acquisition of Signal after large Apogee Raising Maneuvers

摘要

The Lisa Pathfinder mission of ESA is designed to demonstrate the technologies necessary for future space-based gravitational wave detectors. Its operational orbit is a large-amplitude free insertion libration orbit around the Lagrange point L1 as this point provides a very stable gravitational environment (low gravitational gradient). The spacecraft has been launched by a Vega launcher from Kourou into an elliptic low Earth orbit with a nominal apogee altitude of 1540 km, a perigee altitude of 200 km and an inclination of 5.2 degrees. In order to escape from its near Earth orbit, six apogee raising maneuvers were necessary before the transfer to the Lagrange point L1 could be initiated. The total delta velocity Δv required to transfer the spacecraft from the low-Earth orbit to L1 reaches as much as 3.1 km/s. As the visibility from the supporting ground stations during the apogee raising maneuvers was not always guaranteed, the actual performance of the propulsion module directly impacted the re-acquisition of signal after the maneuver. The difference in the expected spacecraft position during acquisition, between a 0% and a 110% burn performance, exceeded by several orders of magnitude the acquisition range of the ground station antennas. The strategy to re-acquire the downlink signal in X-Band after each burn had to be carefully analyzed in order to successfully re-acquire the S/C after any potential burn interruption or under/over performance. This paper explains the strategies developed, implemented and used to ensure successful signal re-acquisition after each maneuver.