# BFR to Callisto!

[From here]

As mentioned previously, going to the moons of Jupiter doesn’t have the option of braking in a moon’s atmosphere – Jupiter’s major moons don’t have “atmospheres” as such, just surface bounded exospheres. However there is Jupiter’s atmosphere. And Jupiter’s gravity well. Falling from infinity means a minimum entry speed of 59.5 km/s – though if we parallel the equator, Jupiter’s spin at 12.5 km/s means we’d hit the atmosphere at 47 km/s.

Of course to get to Jupiter we’re coming from “infinity” with some additional speed. In the “Easy Elliptical” case we’re talking a re-entry speed of 60.7 km/s, or 48.2 km/s relative to the clouds. To save on fuel, the BFS skims off just enough speed to enter a highly elliptical orbit [at 59.24 km/s], out to ~100 Jupiter radii. Surprisingly, though the difference is just 1.46 km/s, the amount of energy to be dissipated is considerable – 70 megajoules per kilogram of space-vehicle.

To get to Callisto we’re using a Bi-Elliptical Transfer Orbit – first from 1 Jupiter radius to 100, then from 100 to Callisto’s orbit at 26.33 Jupiter radii. Doing so reduces the delta-vee budget considerably, but takes 53 days.

The Bi-Elliptical Orbit puts the BFS into low Callisto orbit for a delta-vee of 3.63 km/s, whereas just aerobraking into an orbit direct to Callisto, plus braking into low orbit, needs 4.77 km/s. Landing needs about 2 km/s, thus touch down will require preparation, with a Tanker on hand. Callisto has water ice and dry ice available on its surface, so In Situ Resource Utilization (ISRU) will be possible with a suitable power supply.

## 3 Replies to “BFR to Callisto!”

1. What do you think about sending along a fleet of BFRs, and having two of the three provide propellant for the third BFR, like in-flight tankers… or glorified drop-tanks.

The third BFR uses all this propellant to perform a braking burn.

The two ‘tanker’ BFRs perform a gravity turn and some propulsive maneuvers to make a perfect return trajectory that places them on a collision course with Earth in a few years.

1. Good idea. Was contemplating that very thing, though not as heroic as my discussion of last year’s ITS.