La très catastrophique visite du zoo

Joël Dicker

Description

NASA uses aerobraking (AB) to reduce the fuel required to deliver a spacecraft into its desired final orbit around a target planet or moon with a significant atmosphere. Instead of using the propulsion system to decelerate the spacecraft, AB utilizes aerodynamic drag. While flying through the upper atmosphere of the planet or moon multiple times, the spacecraft maintains a periapsis control corridor such that dynamic pressure and thermal loads on the spacecraft remain within designed parameters. AB has been used four times by NASA: once at Venus and three times at Mars. Although AB reduces the propellant required to reach the final orbit, the reduction comes at the expense of time (typically 3-6 months), continuous Deep Space Network (DSN) coverage, and a large ground staff. The DSN and ground staff are required to design the maneuvers that the spacecraft executes during AB to keep the spacecraft safe and provide the desired final orbit. The combination of duration, staff, and continuous DSN coverage results in a high cost AB operational phase. As AB has evolved, the operations have matured to the point where many of the operational decisions being made by the ground staff can now be made autonomously onboard the spacecraft. With the development of autonomous aerobraking (AA), much of the daily ground operations could be minimized thereby reducing the AB phase costs. In addition, by relegating the decision making to the spacecraft, which eliminates the dependence on staff work schedules (e.g., spacecraft can only perform maneuvers during prime shift and must minimize maneuvers during weekends and holidays), AA can reduce risk by allowing the maneuver to be conducted at the optimal apoapsis opportunity and executed even if DSN or other currently required ground elements are unavailable. Another advantage of AA is that it could provide the ability to handle multiple AB assets at the same time that would otherwise not be economically feasible using the traditional ground-based operational approach. Phase 1 of this study investigated the technical capability of transferring the processes of AB maneuver decision making (currently performed on the ground through the DSN and an extensive workforce) to an efficient flight software algorithm onboard the spacecraft.

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