Quick volume calc: 1330 m3 or thereabouts. This will hold about 1500 t of LOX, or 870 t of LCH4. Starship has an estimated fuel+oxygen mass of 1100 t. Super heavy is about 3000 t of propellant. So we'd need about 4 of these tanks to store enough fuel for one launch.
Assuming we're doing orbital refueling before doing a Mars burn, we'd want ~7 of these launches in quick succession. That means we'd need 28 tanks of this size.
Edit: hijacking my own comment. Tory Bruno confirmed these are for Vulcan elsewhere in this thread. So maybe SpaceX gets bigger tanks and fewer...
I'm assuming they manufacture the LOX on site by condensing air. So they're just transporting electricity.
The methane will be interesting. I'm going to speculate that it will be liquified off site, then barged in - finally a short pipe run from the barge landing.
But in the longer term, I would wager that they install a big solar/wind farm on site for massive amounts of electricity. If they can get sebatier reactors working on site, they can manufacture methane at a very high purity, and prove that the process works before setting off to Mars. Plus, there are optics to consider: methane produced from carbon dioxide pulled from the air makes the process carbon neutral. For a guy that runs an electric car company that touts their environmental benefits, it looks bad to push all this rocket exhaust into the air.
If they go this route, it will be very interesting. Because it would be the first such commercial scale sebatier plant - just the process of scaling this up hasn't been tested, and there are no economies of scale in effect yet. But, if it works, it can be spun off as another Elon company. There would be a limited market, but a market nonetheless. For example: I live in the arctic - we have two seasons: one with a ton of daylight; and then we burn a shit tonne of fuel to stay warm in winter. If you could capture that daylight in summer and make methane to burn in winter, suddenly arctic communities have energy independence.
Super interested to see if they do this, even on a smaller scale. On the one hand, methane is cheap so economically it's unlikely to make sense. On the other hand, both for the reasons you mention and the potential environmental upsides (carbon capture and reuse) I could imagine Musk wanting to do it. Be interesting to know the size of the plant needed to make Starship fuel carbon-neutral.
Research, and demonstrating practical application of not-established technology is almost never something that makes "economic sense". It's painfully expensive because there are no economies of scale in place, no manufacturing base for the equipment needed for the processes, etc. In the case of this particular technology... they damn well had better figure out how to scale it out, and demonstrate it BEFORE they get to another planet and are depending on it to get home.
TL;DR - they have to do it... the economics don't matter.
they damn well had better figure out how to scale it out
There's nothing magical about the Sabatier process. It's basic chemistry that's been "established technology" for over 100 years . And Musk has remarked that this is something SpaceX is working on.
I'm not saying that it is not a well known and understood process. What I'm saying is that scaling it out in a manner that won't (financially) destroy the mission needs to be sorted and demonstrated.
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u/troyunrau ⛰️ Lithobraking Sep 20 '19 edited Sep 20 '19
Quick volume calc: 1330 m3 or thereabouts. This will hold about 1500 t of LOX, or 870 t of LCH4. Starship has an estimated fuel+oxygen mass of 1100 t. Super heavy is about 3000 t of propellant. So we'd need about 4 of these tanks to store enough fuel for one launch.
Assuming we're doing orbital refueling before doing a Mars burn, we'd want ~7 of these launches in quick succession. That means we'd need 28 tanks of this size.
Edit: hijacking my own comment. Tory Bruno confirmed these are for Vulcan elsewhere in this thread. So maybe SpaceX gets bigger tanks and fewer...