Low-thrust enabled highly non-Keplerian orbits in support of future Mars exploration

The technology of high specific impulse propulsion systems with low thrust is improving, opening up numerous possibilities for future missions applying continuous thrust to force a spacecraft out of a natural Keplerian orbit into a displaced non-Keplerian orbit. A systematic analysis is presented as to the applicability of highly non-Keplerian orbits throughout the Solar System. Thereafter, two applications of such orbits in support of future high-value asset exploration of Mars are detailed: a novel concept for an Earth-Mars interplanetary communications relay, on which the paper largely focuses, and a solar storm warning mission. In the former the relay makes use of artificial equilibrium points, allowing a spacecraft to hover above the orbital plane of Mars and thus ensuring communications when the planet is occulted by the Sun with respect to the Earth. The spacecraft’s power requirements and communications band utilized are taken into account to determine the relay architecture. A detailed contingency analysis is considered for recovering the relay after increasing periods of spacecraft propulsion failure, combined with a consideration of how to deploy the relay spacecraft to maximise propellant reserves and mission duration. For such a relay, a combination of solar sail and solar electric propulsion may prove advantageous, but only under specific circumstances of the relay architecture suggested. For highly non-Keplerian orbits the dynamics of the spacecraft is also briefly extended to consider the elliptic restricted three-body problem and the effects of orbit eccentricity.