Optimized low-thrust orbit transfer for space tugs

The application of an optimization technique to a reusable electrically propelled Earth-moon 'space tug' transfer vehicle is presented. Both transfer mission and mission time are optimized and the results showed that significant reductions in the round-trip transfer time can be achieved. In addition, either the initial launch mass can be significantly reduced, while keeping the yearly delivered payload nearly constant, or the yearly delivered cargo can be significantly increased by appropriately increasing the available power. A study was conducted in which a method was derived that simultaneously optimizes transfer mass and mission time by maximizing the transfer mass ratio (TR). The study also involves transfer of cargo from a low Earth orbit to a low lunar orbit (LLO) and the return of all reusable transfer vehicle components, which include the solar arrays, thrusters, and power processing units.