Design Of A Reusable Space Tug

The paper deals with the conceptual design of a space tug to be used in support to Earth satellites transfer manoeuvres. Usually Earth satellites are released in a non-definitive low orbit, depending on the adopted launcher, and they need to be equipped with an adequate propulsion system able to perform the transfer to their final mission orbit. In order to reduce the mass at launch of the satellite system, an element pre-deployed on orbit, i.e. the space tug, can be exploited to perform the transfer manoeuvres; this allows simplifying the propulsion requirements for the satellite, with a consequent decrease of mass and volume, in favour of larger payloads. The space tug here presented is conceived to be used for the transfer of a few satellites from low to high orbits, and vice versa, if needed. To support these manoeuvres, dedicated refuelling operations are envisaged. The paper starts from the mission statement and mission objectives and proceeds with the derivation of the requirements through the application of functional analysis and concept of operations. This approach is applied both at System of Systems and at System level and leads to the identification of the architecture and operations at both levels. Then the paper focuses on the detailed definition of the space tug, from the subsystems' assessment up to the budgets' development, through an iterative and recursive design process. The overall mission scenario has been derived from a set of trade-off analyses that have been performed to choose the mission architecture and operations that better satisfy stakeholder expectations. Eventually, in the last part of the work, main conclusions are drawn on the selected mission scenario and space tug and further utilizations of this innovative system in the frame of future space exploration are discussed. Specifically, an enhanced version of the space tug that has been described in the paper could be used to support on orbit assembly of large spacecraft for distant and long exploration missions. The Space Tug development is an activity carried on in the frame of the SAPERE project (Space Advanced Project Excellence in Research and Enterprise), supported by Italian Ministry of Research and University (MIUR), and specifically in its STRONG sub-project (Systems Technology and Research National Global Operations), and related to the theme of space exploration and access to space