2016.A.4.1. Astrodynamics of Interplanetary CubeSats
Francesco Topputo (1)
- Politecnico di Milano, Italy
astrodynamics, ballistic capture, dual propulsion
By definition, interplanetary cubesats have limited resources in terms of power generated, propellant stored, and thrust exerted. Compared to the maneuverability of conventional probes, interplanetary cubesats have a much less control authority, and therefore their capability of executing orbital maneuvers is strongly limited. These features set new challenges in astrodynamics, especially in the preliminary trajectory design phase.
This work elaborates on the requirements needed to enable deep space exploration through cubesats, with a focus on preliminary trajectory optimization. These arguments are applied to the case of a cubesat mission to Mars. Such a mission is deemed difficult given the inability of the cubesat to achieve a standard, closed orbit about Mars, the latter being a massive target.
Two solutions are proposed and critically assessed. The first one foresees using ballistic capture at Mars arrival. This is a mechanism that exploits the simultaneous gravitational attractions of both Mars and the Sun upon the cubesats. It can be shown that ballistic capture 1) enables avoiding the impulsive maneuvers at arrival, 2) involves safer, robust orbits with respect to possible propulsion failures, 3) allows widening the launch windows (this is ideal in the case of cubesats, which are likely launched as secondary payload with no control on the launch date), 4) well fits with the micro propulsion available in interplanetary cubesats.
The second option is using a dual propulsion cubesat. In summary, this concept uses chemical propulsion to escape the Earth, and the low-thrust micro propulsion technology in the rest of the mission. In a dual propulsion cubesats 1) the Earth escape is achieved with a chemical burn, and thus the Earth escape duration is short, which in turn significantly decreases the time to go in the deep space, 2) multiple passages in the radiation belts are avoided, and this in turn avoids having tick walls and solar arrays coverglass, with consequent increase of the overall efficiency of the platform, 3) a dual staged cubesats has to be implemented: the masses associated to the chemical propulsion are thrown away after the escape maneuver to allow the subsequent low-thrust propulsion to act on a higher thrust-to-mass ratio.
These two options are stated in astrodynamics terms, and preliminary solutions implementing dual propulsion cubesats that perform ballistic capture at Mars are shown.
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