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From hyperbolic arrival to a lunar tour of the Inner Large Moons of Saturn
... An example of a Dione LE observation trajectory built with a homoclinic connection is shown around in Fig. 9. For the detailed analysis and calculations of the LE orbits of the ILMs, the reader is referred to [33]. ...
... According to [33], the LE observation orbits around the inner large moons of Saturn do not intersect (see Fig. 10). Therefore, in order to perform tours between moons, the LE orbits should be connected. ...
... For example, the spacecraft can reach an altitude above Dione as low as 200 km (see Fig. 9), and this close encounter can be repeated as many times as required with virtually zero propellant cost. Comparable performance is achieved for LE orbits around Enceladus (see Fig. 8), Tethys and Dione [33]. This close observation capability for extended time periods was not possible during the Cassini mission, which relied on short flybys with the ILMs. ...
All our knowledge about Saturn and its icy ring system comes from the data obtained during the flybys of Pioneer 11, Voyager 1, Voyager 2 and Cassini, as well as from the observations carried out by Hubble Space Telescope. The discovery of water vapor plumes at the poles of Enceladus and other compelling evidence of the existence of subsurface water in the major moons of Saturn has driven scientific interest and revived plans to return to Saturn. In order to gain insight into the features of this planet and its Inner Large Moons (ILMs)--Mimas, Enceladus, Tethys and Dione--an in situ mission is needed. In general, orbit insertion at a giant planet is very demanding in terms of propellant, due to the large impulse required to achieve capture. It is even more challenging to achieve orbits around moons deep inside the planetary gravitational well, like the ILMs. The majority of the proposed solutions to tour the system of icy moons is based on the patched conics technique with impulsive maneuvers (i.e., chemical propulsion). The more efficient approach presented here is the concept of a lunar tour of the ILMs based on low-thrust (LT) propulsion and low-energy transfers in the circular restricted three-body problems (CR3BP) corresponding to Saturn and each moon. The hyperbolic invariant manifolds of planar Lyapunov orbits around the equilibrium points L1 and L2 of each Saturn-moon system are used to loop around the corresponding moon and to provide initial conditions to move between neighboring moons. These moon-to-moon transfers use a LT control law designed to minimize propellant consumption. LT, combined with a gravity assist with Jupiter, is also applied to reduce the hyperbolic excess speed at Saturn. This enables unpowered capture at Saturn by means of a Titan flyby. Results show that this mission concept saves a significant amount of propellant compared to the Cassini mission. Although LT yields longer transfer times than impulsive maneuvers, the spiraling transfers between moons can be exploited to collect data of the inter-moon environment, rings and moonlets
... The main element of originality of the work resides in the unprecedented concept of achieving orbit around the four moons of Saturn, using only low-thrust (LT) propulsion and gravitational assistance. Preliminary, partial versions of this work can be found in [33,34,35]. Here, we present a complete plan including re-designed interplanetary trajectory with global optimization techniques and revised Saturn Orbit Insertion (SOI) and transfer to Dione, the first moon of the tour. ...
... The investigation is novel in all its aspects, and its major strength resides in its comprehensive approach, fundamental ingredient to achieve the unprecedented result of inserting a probe into orbit around a sequence of moons of Saturn. Preliminary, partial versions of this work can be found in [33,34,35]. ...
We present a novel concept for a small mission to the four inner large satellites of Saturn. Leveraging the high efficiency of electric propulsion, the concept enables orbit insertion around each of the moons, for arbitrarily long close observation periods. The mission starts with a EVVES interplanetary segment, where a combination of multiple gravity assist and deep space low thrust enables reduced relative arrival velocity at Saturn. As a result, an unpowered capture via a sequence of resonant flybys with Titan is possible. The transfers between moons use a low-thrust control law that connects unstable and stable branches of the invariant manifolds of planar Lyapunov orbits from the circular restricted three-body problem of each moon and Saturn. The exploration of the moons relies on homoclinic and heteroclinic connections of the Lyapunov orbits around the L and L equilibrium points. These science orbits can be extended for arbitrary lengths of time with negligible propellant usage. The strategy enables a comprehensive scientific exploration of the inner large moons, located deep inside the gravitational well of Saturn, which is unfeasible with conventional impulsive maneuvers due to excessive fuel consumption.
... The main element of originality of the work resides in the unprecedented concept of achieving orbit around the four moons of Saturn, using only low-thrust (LT) propulsion and gravitational assistance. Preliminary, partial versions of this work can be found in [33,34,35]. Here, we present a complete plan including re-designed interplanetary trajectory with global optimization techniques and revised Saturn Orbit Insertion (SOI) and transfer to Dione, the first moon of the tour. ...
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