/sci/ - Science & Math

Did some math. NOTE: I am not talking about HLS Starship! That doesn’t have a heatshield! I’m assuming SpaceX uses a vanilla Starship for Lunar sorties, like they’ve planned before Artemis.

Starship with 50 tons of payload and 30 tons of bellyflop propellant has a delta V of 7.1 km/s with a full tank (1200 tons) and an isp of 375 seconds (RVacs only).
As seen in this map, LEO to the Lunar Surface and back is 8.1 km/s. Remember, aerobraking let’s us stop into LEO, and eventually land, without spending any prop.
This means Starship needs a 1 km/s boost. Our 1400 ton ship (120 Dry; 50 payload; 30 bellyflop prop; 1200 main prop) would spend 350 tons of propellant boosting itself by 1 km/s, and entering an elliptical earth orbit.

To fully tank up, we can launch a tanker. Once the tanker is filled with 350 tons of propellant, it still needs to be boosted by 1 km/s to meet our ship. This takes 150 tons of propellant. So in total, our tanker masses 650 tons (120 dry; 350 payload; 30 bellyflop prop; 150 main prop).
These 350 tons of prop are enough to fully top off our main ship in order to let in land on the moon and return to the Earth’s surface.

Anyways, assuming Tankers can put 150 tons into LEO, we’d have 9 launches for the main mission (1 Starship + 8 tankers), and 4 for the “top-off” mission. Thus, 13 Starship launches are needed for a Starship semi-direct lunar exploration mission with 50 tons of cargo there and back.