Mars flybys

Solar Electric Propulsion (SEP) can be used instead of chemical propulsion to reach Jupiter if large solar arrays and multi-kilowatt Hall effect thrusters are available for the spacecraft. These thrusters are more efficient than chemical engines in terms of specific impulse (Isp) by a factor of about 6–7, however they suffer from extremely low thrust levels compared to chemical engines. These low thrust levels exclude conventional JOI maneuvers from SEP missions to Jupiter. Thus, flybys of the Galilean moons are the only feasible method of capture for SEP missions to Jupiter.

While it is possible to use single-satellite-aided capture with SEP missions, usually these missions expend an inordinate amount of SEP propellant, take 7–9 years to get to Jupiter, and involve captures into orbits that have periods of greater than 300 days. For these reasons, chemical propulsion is generally to be preferred over SEP if the capture options are limited to single-satellite-aided capture. In contrast, double- and triple-satellite-aided capture sequences can capture SEP spacecraft much more efficiently. SEP trajectories that arrive at Jupiter 3–5 years after launch can be captured with double- or triple-satellite-aided capture sequences. These trajectories also expend much less propellant than those needed for single-satellite-aided capture.

If SEP double-satellite-aided capture is used, the spacecraft would still be captured into 300+ day orbits. If SEP triple-satellite-aided capture is used, the orbital periods can be as low as 100–150 days. Due to the efficiency of SEP, these trajectories can allow larger and more capable spacecraft to be captured into Jupiter (assuming the same launch vehicle). Another advantage of SEP double- and triple-satellite-aided captures is that their lack of a chemical JOI maneuver reduces their navigational errors and risks compared to chemical double- and triple-satellite-aided capture.

earth mars cgpi sun — Figure 2: An optimized SEP trajectory from Earth to Jupiter capture that includes a Mars flyby.

JPL’s Mystic software was used to find high-fidelity, optimized SEP trajectories from Earth to Jupiter capture. The trajectories included Mars gravity assists, generally had times of flight of about 5 years, and captured into Jupiter orbit using triple-satellite-aided capture sequences. The interplanetary portion of one of these trajectories is shown in Figure 2. Figure 3 zooms in on the Callisto-Ganymede-perijove-Io triple-satellite-aided capture sequence.

earth mars cgpi jupiter — Figure 3: The Callisto-Ganymede-perijove-Io triple-satellite-aided capture sequence that is used to capture the SEP spacecraft into Jupiter orbit with no impulsive JOI maneuver.