Mostly Ignorant Ars Centurion
3y
383
Buffy said:
Or the Saturn V.

Seriously, though, one of Starships selling points is that it's cost per launch is low, but if you have launch 22 of them for a single lunar mission, it starts to add up.
I think you raise a fair question, so it got me thinking about it.

SpaceX estimates that a fully reusable Starship will cost between $2-$10M per launch. Let's use the upper bound of that estimate, then add a zero to make sure and call it $100M per launch.

Let's say Musk is hugely incorrect and it'll take 20 launches to fuel up a depot.

We're talking $2B to fuel a depot, plus the cost of the depot vehicle, so let's say it's double a normal Starship and is $200M. That's $2.2B to deliver about 100 metric tons of material to the Lunar surface.

Artemis launch costs are a little over $4B per launch, but we'll round down. $4B to deliver an estimated 27 metric tons to the Lunar surface.

Granted, I'm estimating here, but I used a lot of worst-case thinking with Starship costs and it still comes out to half the cost of the only other viable-ish option. Lots for SpaceX to prove yet technically (so does Artemis for that matter, but I'd argue not as much).

Super3DPC Ars Centurion
8y
360
dmsilev said:
A more serious back-of-the-envelope calculation. A full fuel load for Starship is something like 1500 tons, roughly 3/4s LOX and 1/4 liquid methane. We don't really know what the actual LEO capacity of the current version of the stack is, just that it's at least 26 Mk 3 Starlinks plus the dispenser. Call it 55 tons minimum. Let's assume that there's a fair amount of margin in these test flights, future optimization, etc. and say that in the near future 100 tons of payload per flight is reasonable (with the 200 ton design goal well into the future). If they need to transfer a full fuel load into the lunar Ship, that's ballpark 15 launches even without any boiloff or transfer losses.

So yeah, I believe 22 as an estimate, unless HLS Ship doesn't need a full load of fuel for TLI, Lunar capture, and descent/ascent.
It sound like something completely absurd for flag and footprints mission. But for long term permanently manned outpost on the moon, there really is no other way. At the beginning of establishing a base, before ISRU can start, we need lots of hardware on the moon. Habitation module, rovers, construction vehicle, all have to be delivered pretty much in one peace to the Moon.

Face it: the limit is not SpaceX. The limit is rocket equation. There's no way of landing dozens of tons of hardware on the moon with chemical rockets without refuelling dozens of times in earth orbit.

dmsilev Ars Tribunus Angusticlavius
17y
7,869
Subscriptor
The other thing to consider is that getting from LEO to the lunar surface is something like 5.5 km/sec of delta v (Solar system "subway map" chart). Add in another 1.5 or so km/sec to get off the lunar surface and into LLO, where the crew could transfer to Orion for the ride home. That's 7 km/sec needed, which from searching around seems to be pretty close to the dv budget for a fully fueled Starship. So, for Musk's "6 to 8" estimate to work, each tanker really is going to lift 200 tons of cargo to LEO.

Super3DPC Ars Centurion
8y
360
ISUAero1986 said:
I know a few people inside the program that will privately admit the plan is stupid and NaSA should never gone this route.
What we're seeing is the limit of chemical rocket. I agree that for flag and footprint mission or crew rotation mission, using starship is absurd unless the crew being rotated numbered in high tens. But for establishing moon bases, using chemical rocket, dozens of times of refueling is the only way to go to land dozens of tons of cargo on the moon.

After the base is established and can do fuel ISRU production, we can use lunar cycler to reduce the number of refueling launch from earth (material and crew transfer vehicle from earth to lunar cycler then dedicated lunar orbiter from moon to cycler and back). But without dozens of refueling flight per lunar landing, there's never going to be ISRU on the moon. Not on the scale required for on site lunar orbiter / lander.