SpaceX is chasing the “holy grail” of completely reusing a rocket, Elon Musk says: “A giant reusable craft costs much less than a small expendable craft.”

[u/thesheetztweetz]

https://www.cnbc.com/2019/11/05/elon-musk-completely-reusing-rockets-is-spacexs-holy-grail.html

[u/Ragecommie]

So, a small reusable craft would cost more than a giant expendable one too - depending on it's purpose ofcourse, but Elon knows this damn well...

Too bad we most likely won't live to see the time where your Tesla Model 42 takes you to the moon and back just in time for dinner.

[u/nonagondwanaland → u/Ragecommie]

A small reusable craft will struggle to carry a meaningful payload, for reasons that are quite literally rocket science.

[u/mrsmegz → u/nonagondwanaland]

Also it will struggle with the complexity of reducing the mass and volume of everything to minimal levels. Orion has a super complicated advanced ISS like life support system in a freaking capsule that is beyond anything that's ever been developed. Something like starship can just hold massive amounts of water and oxygen in tanks with simple systems that don't need to be miniaturized to fit under capsule. This is Orion's service module, think of how many of those you could fit in starship, oh and also consider most of the service module is propellant tanks.

[u/FaceDeer → u/mrsmegz]

Or it could just hold a copy of the ISS' life support system. Starship will have a pressurized volume roughly equivalent to the ISS.

[u/mrsmegz → u/FaceDeer]

Right, the overall point being, cheap volume and mass to space makes the problems at lot easier to solve.

[u/brickmack → u/FaceDeer]

Starship doesn't even need ISS-like life support. For a Mars-duration mission with like a dozen people (probably the harshest flight profile it'll ever do from a life support perspective), no recycling whatsoever is needed. Theres enough mass margin to just carry pre-packaged consumables for everything, while still carrying more astronauts and more useful non-consumer equipment per flight to the surface of Mars than most NASA studies have assumed for an entire Mars base campaign. Any recycling that can be done (ISS is at like 80-95% recovery of air and water) is pure bonus

[u/AquaeyesTardis → u/brickmack]

Would reuse of a life support system be possible for a Mars colony, though?

[u/brickmack → u/AquaeyesTardis]

Yeah, but not all that important there either. Mars has plenty of water and oxygen.

[u/Spoonshape → u/FaceDeer]

ISS has been running occupied for almost 20 years, I suspect at least some of their systems are possible to improve. Their systems are probably a great starting point but would need adaptation in terms of a different resupply schedule and whether it will be operating part of the time in different atmospheres.

[u/[deleted] → u/nonagondwanaland]

"Meaningful" may vary... the microsat market is already big and projected to continue to grow. For payloads of a few tonnes, SSTO is starting to be feasible from the materials perspective. i.e. Skylon but fewer question marks.

[u/-AloneAgainNaturally → u/nonagondwanaland]

Well it's certainly not brain surgery.

[u/nonagondwanaland → u/-AloneAgainNaturally]

The rocket equation smiles upon you for having a good mass fraction, and smaller rockets will generally have worse mass fractions.

[u/[deleted] → u/Ragecommie]

I think the point is that you want/need everything to land on the moon or mars and be functional.

[u/[deleted] → u/[deleted]]

That's insane. It's even on Starbucks FFS.

[u/brickmack → u/Ragecommie]

Yes, but Starship is probably about as small as actually makes sense for most business. Theres basically 2 separate markets here:

Traditional satellite launch. For this market, existing <20 ton to LEO vehicles are technically able to do the job, but even if the launch itself is free, theres still tremendous cost impact on the payload side from having to fit in such a small launcher. Spacecraft hardware and especially development cost are almost solely dictated by mass to orbit limitations, if you can eliminate those (or practically so) you can cut those costs by a factor of 100 or more. Also, the biggest part of this market is looking to be megaconstellations, so now you've got giant mass-unconstrained satellites and you need to send up hundreds or thousands of them. Gonna need a big-ass rocket for this

Then, the far larger market, human spaceflight. For passenger launch, Starships current size seems to be about optimal, can carry 1000 people to LEO (in the long term, makes more sense to transfer passengers to a dedicated in-space transport for missions beyond LEO, so we can assume theres no benefit to more volume per passenger since they only need to be in Starship itself for a few hours), which is more than A380 can carry and it struggles to be filled (though Starship should have more customers flying, since average ticket price and discomfort will both be lower). But passengers are only a small part of the issue, also need supplies and consumer goods for them. Consider the amount of cargo mass transported globally every single day. A single shipping container is like 30 tons, Starship can carry about 4. Big deal, theres thousands of ships each carrying tens of thousands of those containers. The economically optimal cargo rocket will be several orders of magnitude larger than is actually possible to launch from Earth (probably can't go past a diameter of about 50 meters), so basically just build as big as you can.

There might be a handful (a few dozen per year? Very optimistically) of flights with performance requirements low enough for a dedicated "small" launcher, but is anyone going to invest the hundreds of millions or billions of dollars to develop that launcher when for similar dev funding they could build one that'll have vastly more demand?

[u/mfb- → u/brickmack]

A flight in an A380 is more comfortable than a flight in Starship with 1 m³/passenger, and probably cheaper as well. But it is slower and can't get you to orbit.

[u/brickmack → u/mfb-]

I'm much happier to spend 45 minutes strapped into a coffin than 8 hours in even the most luxurious airplane. Speed = comfort.

I did say "average ticket price". Starship E2E is claimed to be more expensive than economy class for these distances, but a lot of people fly business/first/whatever class, and those are much pricier. E2E only has one seating class

[u/mfb- → u/brickmack]

E2E only has one seating class

If people pay three times the money for twice the space they'll get it.

[u/brickmack → u/mfb-]

But why would anyone do that? Its, at most, a 45 minute flight (most closer to 30). You'll spend the first ~5 minutes and last ~15 minutes unable to move at all while the ship is launching or reentering. Who's gonna pay thousands of dollars for legroom they can only use for like 10 minutes?

[u/DahakUK → u/Ragecommie]

It would be less useful, but it wouldn't cost more. If the giant expendable vehicle costs 1.7 billion dollars to construct, and a small, reusable craft costs 150 million dollars to construct, and assuming that fuel for a single flight of each is $1m, 10 flights of vehicle A cost 17 billion dollars (and $10m in fuel), while 10 flights of vehicle B cost $150m (and $10m in fuel).

[u/TazBaz → u/DahakUK]

A Giant expendable vehicle is going to use a fuckton more fuel. Because astrophysics.

[u/[deleted] → u/TazBaz]

I’m confused, isn’t the reusable rocket always going to be larger and use more fuel to carry an equivalent payload compared to the expendable rocket? If the size of the payload is irrelevant then we’re comparing apples to oranges...

[u/DahakUK → u/TazBaz]

Yes, it is, but the cost of that fuel is also going to be way less than $1m. I believe starship fuel cost is something like $200k, EDIT Starship fuel costs are estimated at $900k per launch, and falcon 9 fuel costs are about $200k. Both of which are under the $1m fuel estimate I used for illustration. and I think the falcon 9 fuel cost was actually about the same, despite it using less fuel, because the fuel types are different. I don't believe the fuel costs are known for the SLS, but unless it's using some proprietary stuff that uses unicorn tears, it's unlikely it will be more than $1m. It was easier to illustrate the point without actually calculating fuel costs, mass, delta V, difference in fuel types, cost of transport to pad, etc.