ADR GNC CONCEPT FOR THE DREAM CHASER~? SPACECRAFT: THE ENVISAT DEORBITING CASE

摘要

A feasibility study has been conducted to assess the possibility of using the Dream Chaser for an Active Debris Removal (ADR) mission. To assess the mission feasibility, ESA's ENVISAT spacecraft was taken as a reference target. ENVISAT's large size and geometrical and mechanical configuration makes this mission particularly complex. Further contributing to this complexity is the lack of data about the current rotational state of ENVISAT. The Dream Chaser is a unique spacecraft for pursuing an ADR mission. While its primary mission is not ADR, the Dream Chaser provides a platform with significant on-orbit capability with multiple launcher options. Due to this manoeuvring potential, the Dream Chaser may be able to target multiple objects, depending on the deorbit method. Its modular outfitting approach enables mission tailoring with minimal redesign required. The use of the robotic arm is preferred as it is more suitable to be reused on successive ADR missions. Finally, by performing an ADR mission with the Dream Chaser, the development costs for an ADR mission can be spread over multiple missions, targeting a variety of low-Earth orbit (LEO) assets. The reusability consideration has the potential to reduce mission costs for all. This paper shows a Guidance, Navigation and Control (GNC) concept for the Rendezvous (RV), capture, and deorbit of ENVISAT using the Dream Chaser. The assessment is built upon previous analysis conducted during the Dream Chaser for European Utilization (DC4EU) program, which culminated in a mission concept for an ENVISAT ADR mission. As with the DC4EU program, this study confirmed the feasibility of using the Dream Chaser to deorbit ENVISAT. For the assessment reviewed in this paper, the Dream Chaser is launched by Ariane-V to a 445km orbit. The Dream Chaser increases its orbital altitude to match ENVISAT's orbit around 760km. Dream Chaser then performs a Rendezvous and Docking (RVD) with the satellite, and inspects its attitude. With sufficient knowledge of attitude and relative position, Dream Chaser continues its approach along the most favourable rotation axis of ENVISAT, until the robotic arm can be deployed to capture ENVISAT. After detumbling, ENVISAT is set on a direct re-entry trajectory and the Dream Chaser separates to return safely to Earth. The mission duration, approximatively one week, the propulsive capabilities, and the impulse budget estimation are shown to be within the capabilities of the Dream Chaser. The RVD phase has also been simulated with many realistic elements, such as sensors and actuators models, orbit and attitude perturbations, GNC in the loop, and the preliminary results have confirmed the feasibility of removing ENVISAT with the Dream Chaser.