The precise management of the Right Ascension of the Ascending Node (RAAN) is critical during the Orbit Raising Phase of electric propulsion satellites targeting inclined orbital planes in Medium Earth Orbit (MEO), typically used by GNSS constellations. Failure to align the RAAN with the target orbital plane can degrade or even jeopardize the overall mission performance. This paper explores strategies to mitigate RAAN drift impact, focusing on the introduction of a RAAN offset at injection to improve robustness against operational contingencies during orbit raising, such as thrust underperformance, unplanned interruptions, or delays in the orbit-raising start, all while adhering to strict fuel budgets.

The RAAN offset strategy deliberately adjusts the satellite's injection RAAN ahead of the nominal trajectory, which is optimized for minimal fuel usage. This approach increases tolerance for initial delays during orbit raising, enabling extended compensation periods within a fixed delta-V budget. To minimize the time penalty under nominal conditions, immediate, i.e post-injection, out-of-plane thrust is required to correct RAAN drift early along the transfer. However, through the proposed RAAN offset strategy, all or part of the delta-V spent for RAAN correction at low altitudes can be saved, thus gaining enhanced compensation capacity for longer contingency durations at higher altitudes.

This paper evaluates optimal RAAN offsets as a function of injection altitude and the delta-V budget allocated for contingencies. It derives the delta-V needed to compensate for any unplanned thrust contingency along the transfer, deriving the maximum contingency duration that could be compensated at a given altitude for both immediate and delayed RAAN drift corrections strategies. Notably, simulation results demonstrate that the initial Orbit Raising delay that can be compensated by offsetting the injection RAAN more than doubles with respect to the scenario where this strategy is not employed.

The study concludes that the RAAN offset strategy enhances resilience to contingencies, optimizes fuel usage, and ensures mission timelines are maintained, offering valuable insights for improving the reliability and efficiency of satellite Electric Orbit Raising in complex operational environments.