A set of tools has been developed to enable assessment of the feasibility of ultra-low thrust transfers in regions of multi-body gravity field influence. Aspects include:

• Trajectory design/optimisation
• Error analysis and stochastic manoeuvre budgets

Navigation analyses have been performed to understand the solution sensitivity to key input assumptions. A case study was performed to understand the performance that could be achieved. The case study focused on the Lisa Pathfinder mission potentially extended from its initial LPO to achieve multiple Sadle Point crossings.

Key issues to be addressed were:

• Developing transfers with low deterministic DeltaV
• Developing transfers with low stochastic DeltaV
• Establishing the feasibility of performing corrections when flybys and/or lower pericentres are present.
• Obtaining sufficient accuracy in the critical mission pahses: Saddle Point crossings for LPF