The end-of-life disposal of Galileo satellites is needed to avoid collisions with operational spacecraft and to prevent the generation of space debris. Either disposal in stable graveyard orbits or disposal into the atmosphere exploiting eccentricity growth caused by lunisolar resonances are possible. However, there is a concern about the predictability of MEO orbits because of possible chaotic behaviour caused by the overlap of resonances. In this work, we investigate if Galileo disposal orbits are predictable and if safe disposal is possible under initial uncertainties. For this, we employ finite-time Lyapunov exponents (FTLE) and sensitivity analysis and compare these two methods regarding their practicality for analysing the predictability of disposal orbits. The results show that FTLE are not suitable for determining if an orbit behaves chaotically or not on the time scale of interest. Sensitivity analysis, on the other hand, can be used to quantify the effect of uncertainties on the orbital evolution and to determine if safe disposal is possible. In addition, we show that reliable re-entry disposal is feasible with a limited \Delta V budget. However, safe disposal into a graveyard orbit is not always feasible considering uncertainties in the disposal manoeuvre and dynamical model when the available \Delta V for disposal is low.

中文翻译：

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关于伽利略处置轨道的可预测性和鲁棒性

需要对伽利略卫星进行报废处理，以避免与运行中的航天器发生碰撞并防止产生空间碎片。可以在稳定的墓地轨道上进行处置，也可以利用由日月共振引起的偏心率增长将其排放到大气中。然而，由于共振重叠可能导致混沌行为，因此对 MEO 轨道的可预测性存在担忧。在这项工作中，我们调查伽利略处置轨道是否可预测，以及在初始不确定性下是否可以安全处置。为此，我们采用有限时间李雅普诺夫指数 (FTLE) 和灵敏度分析，并比较这两种方法在分析处置轨道可预测性方面的实用性。结果表明 FTLE 不适合确定轨道在感兴趣的时间尺度上是否表现混乱。另一方面，灵敏度分析可用于量化不确定性对轨道演化的影响，并确定是否有可能进行安全处置。此外，我们表明在有限的 \Delta V 预算下可靠的再入处理是可行的。然而，当可用于处置的 ΔV 较低时，考虑到处置机动和动力学模型的不确定性，安全处置到墓地轨道并不总是可行的。我们表明，在有限的 \Delta V 预算下，可靠的再入处置是可行的。然而，当可用于处置的 ΔV 较低时，考虑到处置机动和动力学模型的不确定性，安全处置到墓地轨道并不总是可行的。我们表明，在有限的 \Delta V 预算下，可靠的再入处置是可行的。然而，当可用于处置的 ΔV 较低时，考虑到处置机动和动力学模型的不确定性，安全处置到墓地轨道并不总是可行的。