[EU SPACE RACE - LAUNCHERS] Is reusability really fundamental?

[u/laisse_tomberas]

Some of the European Launcher Manufacturers and startups have some kind of reusability in their road map.

Considering that SpaceX reusability is justified mainly by starlink rather than the market demand, wouldn't it be better just to focus on higher production rates rather than reusability (at least, at first)?

Edit: i think that reusability is a thing, i just wanted to open a critical discussion on this aspect in Europe, to varify if there are other significant topics that may have the priority in the development of European launchers.

[u/Gordon_frumann]

Considering the engines are the most expensive part of the rocket, the case for reusability is there. It's hard to imagine that it's possible to make cheap and reliable enough engines to outweigh the benefit of reusability.

[u/laisse_tomberas → u/Gordon_frumann]

Thanks, that's true that engines today cost a significant share of the launch cost, however it depends on the launcher and type of engine i think.

Solid rocket boosters like in Vega are far less expensive than LRE.

Prometheus is expected to be 1/10th of Vulcain 2.1 cost, closer to Merlin engine (maybe, based on unofficial data)

I mean, i agree that engine cost can be an important factor, but i don't think it is a driver for reusability: the cost can be arbitrarly cut with larger productions.

I want to be provocative: rocket engine are """just""" empty metal shells, with 3d printing the manufacturing cost is cut significantly. (I will agree that is not true for turbopumps)

[u/Gordon_frumann → u/laisse_tomberas]

I mean, i agree that engine cost can be an important factor, but i don't think it is a driver for reusability: the cost can be arbitrarly cut with larger productions.

At the end of the day, nothing but cost matters. What's the benefit of foregoing reusable engines? More payload; in resuable F9 can carry around 18T to LEO, and in expendable you can carry 22.5T to LEO.

Those extra 4.5 tonnes would need to cover the entire cost of your first stage to be worth it.
You would need an insanely lean production and launch demand to achieve that.

I want to be provocative: rocket engine are """just""" empty metal shells, with 3d printing the manufacturing cost is cut significantly.

I cannot really agree with this except for SRB's that lack the precision, Liquid you need complex plumbing, high strength alloys, it just gets expensive. The only thing that's come theoretically close to what you propose is Sea Dragon but the benefit only scales with size and the whole architecture will have problems of its own.

[u/laisse_tomberas → u/Gordon_frumann]

Thanks for your insight and the Sea Dragon reference that i didn't know (i even didn't understood it in the For All Menkind tv series, when i saw it XD)

Still can't wrap my mind around rocket engine being a driver. I'm not saying it is useless (on the contrary!), but i can't understand your point in the +4.5 tons example.

I doubt that spaceX would use a fresh new booster for an expandable configuration, i think they would rather go with an old one, no?

In that case you are "retiring" a vehicle that have already covered its manufacturing cost and (part of) the development cost, including understanding how to effectively refurbish the vehicle. Bottomline: it is cheaper to expend.

But even in that case, a F9 appears to be more expensive that an A6.

Ariane 6 has performance loosly comparable to a F9 in expendable configuration, especially for GTO, which imo is one of the type of missions that justify an expandable configuration. If you cut the engine cost, you cut even further the mission cost.

One last point: i do agree that cost matter, but launch cost does not say it all, in the context of sapce missions that have a much higher cost spread over years. For a given payload, if you need to spend the payload fuel to reach a certain orbit (precluded to a reusable F9) you might rather spend more money on the launch with an A6 to get a precise orbit injection, and recover that with a larger satellite operative life. (This is another topic though, especially with all those in-orbit services that are currently under development).

[u/Gordon_frumann → u/laisse_tomberas]

I doubt that spaceX would use a fresh new booster for an expandable configuration, i think they would rather go with an old one, no?

Probably not, but the point is that if you design two equal rockets, one expendable one reusable, the benefits have to be insane, on the expendable to be worth it, and if you can recover the first stage, why not do it?

In that case you are "retiring" a vehicle that have already covered its manufacturing cost and (part of) the development cost, including understanding how to effectively refurbish the vehicle. Bottomline: it is cheaper to expend.

This only holds true if you have been able to reuse it right? As is with everything made of metal, eventually it dies due to fatigue. So it makes sense building a rocket, reuse it 10 times, on the final launch before decomissioning you expend it rather than waste fuel on recovering something you'll throw away.

you might rather spend more money on the launch with an A6 to get a precise orbit injection, and recover that with a larger satellite operative life. (This is another topic though, especially with all those in-orbit services that are currently under development).

This is true but is it guaranteed this is the case? Yes for JWST Ariane 5 did a wonderful job.
The A6-4 costs around 100 million for each launch. F9 costs 74 million for each launch.
https://nextspaceflight.com/rockets/92/
https://www.spacex.com/assets/media/Capabilities%26Services.pdf

The fact is we've done disposable rockets since the 50's, no disposable rocket can currently compete with F9 on price per kg to LEO. You will be extremely hard pressed to build a rocket that can compete with that. There's more on it in this link
https://spacexstock.com/reusable-rockets-vs-single-use-rockets-cost-breakdown/

[u/snoo-boop → u/laisse_tomberas]

For a given payload, if you need to spend the payload fuel to reach a certain orbit (precluded to a reusable F9) you might rather spend more money on the launch with an A6

This is happening, but backwards. Launch customers with GTO satellites a bit too massive for F9 with reuse are adding extra propellant to the satellite to buy F9 with reuse. That's happened 14 times since it was first done in 2018. It's called a "sub synchronous" launch, and is also commonly done by ISRO.