How many tankers are needed for each Mars cargo flight?

[Vultur]

I started doing the math in the BO section "plans" thread - can it really be only 3 or 4 tankers per Marsbound ship?

there's probably no great need to shorten trip time for cargo, so it can probably be close to a basic TMI of 4 km/s or so (varying by synod). Say 5 km/s.. if exhaust velocity = 3600 m/s (since they need SL Raptor for gimballing) then that's a mass ratio of right about 4. If a Mars ship is 120 tons dry mass + 100 tons payload, that's 660 tons propellant - if v4 tankers manage 200 tons, that's only four tankers (so if it's $5M/launch, $25M/out bound ship).

If the delta-V needed is closer to 4 km/s, three tankers (and $20M/out bound ship)..

3 to 1 probably won't work since some extra propellant is needed for the landing burn on Mars.
Still, a 4 to 1 ratio seems exceptionally good.

[meekGee]

I started doing the math in the BO section "plans" thread - can it really be only 3 or 4 tankers per Marsbound ship?

there's probably no great need to shorten trip time for cargo, so it can probably be close to a basic TMI of 4 km/s or so (varying by synod). Say 5 km/s.. if exhaust velocity = 3600 m/s (since they need SL Raptor for gimballing) then that's a mass ratio of right about 4. If a Mars ship is 120 tons dry mass + 100 tons payload, that's 660 tons propellant - if v4 tankers manage 200 tons, that's only four tankers (so if it's $5M/launch, $25M/out bound ship).

If the delta-V needed is closer to 4 km/s, three tankers (and $20M/out bound ship)..

3 to 1 probably won't work since some extra propellant is needed for the landing burn on Mars.
Still, a 4 to 1 ratio seems exceptionally good.

That was the number put forward before fast transits were considered, but it's super-sensitive to mass fraction, and I don't think even SpaceX knows what the number will be, either in 2026 (v3) or much less on 2028 (v4).

[geza]

In his presentation on May 29, this year, Elon provided an estimation to the future transfer capacity to Mars. He assumed 10/day launch frequency with 200+ t to LEO each. It lead to 1,500,000 t to LEO and 250,000 t to Mars per transfer window.

This numbers mean that he assumed 5 tankers for each flights to Mars. Probably, he wanted to say something on the safe side.

[Jimmy Murdok]

This is one of the interesting things about having Jared on NASA. He wants to make this happen even as soon as next year if engineering is sound.
Having the backup from NASA will smooth out lots of criticques and help to handle contamination fears to certain extent.
Numbers don’t lie, is far easier than Moon missions, and to be seen, but the sociological impact of landing massive cargo ships on Mars will change the perception of what’s possible.
I wonder about which one will have more impact before 2030: HLS moon manned landing or a handful of unmanned ships with robots preparing the ground for humans on a planet?
This might be the low hanging fruit that Jared needs to offer to the president before the end of the mandate, although planets are not very aligned to Starship readiness during Q4 2026 and mandate closes when ships would still be on transit Q4 28/Q1 29