While the vertical landing of rockets by SpaceX is certainly a significant achievement, there seem to be many who say that reusability is not actually financially viable. Apparently, it is far too expensive to reuse a rocket and it's generally cheaper to throw it away after one use.

Moreover, reusable rockets generally seem to have far less payload capacities so it seems more prudent to use a lighter, disposable rocket than a heavier, reusable rocket.

I've also read that reusable rockets become viable only at scale, i.e. with enough clients and rocket launches. Apparently the rocket market is going into a significant lull in the coming years, further reducing the possibility that viability can be achieved.

Can someone expound on the financial viability of reusable rockets with sources and hard numbers?

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    A resuable rocket will cost more to manufacture than an expendable one, and will be less efficient for launching a single payload. If original manufacture cost + the refurbisment costs speard across all the launches are less than the extra fuel costs due reusability then the reusable will be cheaper overall. The maximum payload is a bit of a red herring. what matters is that you are cheap enough for the mass you can launch. An argument often made in favour of reusables is they will be more reliable - the flight hardware will have been flight tested. – JCRM Jun 3 at 14:15
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    Remember that Falcon 9 can still fly expendable if the payload is large enough to require it. – Russell Borogove Jun 3 at 14:40
  • are expendable block 5 F9s still on the table @RussellBorogove? – JCRM Jun 3 at 16:19
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    "many" [citation requested] – Martin Schröder Jun 3 at 16:57
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    @JCRM If a customer came to them with a payload too large for a recovery trajectory, and they had a block 5 with ten flights on it, I don't see why they wouldn't expend it for the right price. – Russell Borogove Jun 3 at 18:02
up vote 8 down vote accepted

One interesting counterpoint on costs that is often made (But I think is incorrect), is that with a reusable booster, you make less of them. Which means you are less efficient, and you need to design a line for building them slowly, in a cost effective manner.

This is an argument Arianespace has made.

SpaceX may well face this issue. If they can use the booster 10 times, then they really only need 2 boosters a year to fulfill their manifest.

But they have a manufacturing line designed to build 10-15 cores with sufficient engines (100-150) a year. If you run that at 2-3 a year, you will waste a lot of money and the cost of the booster will go up.

But then SpaceX seems to be cleverer than your average bear, and you may have noticed an odd (for booster builders) decision they made, to keep the second stage structure, the same as the first stage.

Often the structures taper/different diameters, or different fuels, or different materials. In the Falcon 9 case, the first stage and second stage use the same fuels, materials, engines (for the most part M1D vac vs M1D are close enough for this argument).

Thus SpaceX can beat this arguement by ramping up second stage production to keep the line active at an efficient rate.

Engine wise, they still have to slow down, since 1 vs 9 engines is a big rate change for the line). But happily the Raptor engine is much the same size, and needs much the same tooling to build, and they are going to need to make crap loads of them. (31 on the BFB, and 7 on the BFS, so each full ship set will need 38 engines!)

So there are many tradeoffs, and clearly SpaceX believes one way, and prior to their proving it can work, everyone else in the industry believed (and had their own numerical models to prove it) the other way.

  • The argument is with reduced prices, launch rate will rise, and with rising launch rates, prices will fall. – JCRM Jun 4 at 5:13
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    I've heard Ariane with that argument, but I feel like it's either dishonest, or spoken from their position of ignorance and denial. SpaceX still needs to churn out second stages to meet their flightrate, and they overlap heavily with the first stage. And SpaceX isn't building rockets for the same cadence as Ariane - SpaceX is building for their imagined cadence, which they need to launch Starlink. 2-3 cores a year doesn't fit with SpaceX business plans, announcements, anything really except how Ariane thinks the industry works. – Saiboogu Jun 4 at 13:07
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    @Saiboogu Lest it not be clear (And I think I will edit the answer to clarify) I think this arguement is bunk. PS: Good point on the second stage for SpaceX> That was one of the very clever things they did. – geoffc Jun 4 at 13:11
  • That's an argument Arianespace made in the 1980s, when they were designing the Ariane 5. They were looking at a flight rate of 12 per year, in a very different market than we have now. – Hobbes Jun 6 at 7:33
  • So will SpaceX have to majorly rely on the Starlink project to make their reusable rockets viable? I've read that the rocket launch market is going into a significant lull in the coming years, so SpaceX can't really rely on outside clients for achieving viability. – Vikram Jun 7 at 3:41

SpaceX is already offering one of the cheaper launch services using boosters that fly one or two times. The costs per kilogram on an F9 are 2,864USD, coming in second place to the Proton M at 2,826USD per kilogram.

Gwynne Shotwell described the first reflown booster as costing "substantially less than half" what it would have cost to build a brand new one.

All the available evidence from SpaceX indicates the Falcon 9 will be an affordable reusable booster. Most critiques are viewing all refurbishment and reuse through their knowledge of the Shuttle program, which had extensive and costly refurbishment. The block five Falcon 9 design is intended to refly several times without refurbishment, through a combination of components and designs intended to hold up through multiple uses and detailed telemetry feeds to identify problems without requiring teardowns and time consuming inspections.

  • How truly relevant is the "cost per kilogram" metric? Depending on the individual satellite requirements (including those other than weight), aren't there other factors that would influence the real world cost? I'm a complete noob on this but distilling the cost of a rocket launch down to "cost per kilogram" seems overly simplistic. – Vikram Jun 7 at 3:31
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    Cost per kg offers a way to compare the launch cost of different rockets. It is a simplified metric, but that doesn't make it useless. – Hobbes Jun 7 at 6:02
  • Another valid metric is the cost to get an average sized comsat to GEO, and F9 is in line with Ariane 5 in that regard, while offering better schedule flexibility compared to a shared A5 ride. – Saiboogu Jun 7 at 20:08

I'd leave it as a comment but it got a big long, so I'm posting as an answer. Take note that others have already mentioned some engineering trade-offs.

Keep in mind that no matter the numbers someone can come up with to tell that reusable rockets are financially viable, there are a few factors that would only come up with trial and error:

Reliability

How reliable is a reusable booster on its first launch? And on its second launch? And on its $n^{th}$ launch?

This strongly affects the mission success/fail probability, and for normal rockets is computed for the overall system. To be "cheaper" than a non-reusable rocket, the price should take into account the insurance cost related to the launch. I'd expect a booster that was reused several times to be much less reliable than a brand new one, but these numbers need to be publicly available for insurance companies to do their math, and preferably based on flight data not engineering predictions.

Up until here, I wrote from the flight customer point of view who only wants the satellite successfully deployed, but from the rocket manufacturer's perspective: How reliably can you say that the booster will be recovered? What if every other time your reusable booster is destroyed on re-entry?

If you need to ensure return on investment on the first flight then you cannot hope to be price competitive. If you need two flights to have a positive return the situation changes, but what happens when you get a streak of bad luck? Say three missed recoveries in a row, would that make you bankrupt?

Of course the reliability of any product increases over time as the concept and technology matures, but someone needs to have long heritage and stability in this business so that this usual trend takes place.

As another side note: Just because there is someone doing it does not mean it's viable. Think about the Concorde and Tupolev aircraft. Wonderful machines, truly marvels of their time, but their niche market was very small and their maintenance costs too high, so today there are no faster-than-sound commercial aircraft flights.

  • There are some ways in which reliability favors reuse. A reused booster may be more prone to fatigue failures, but it will be less prone to manufacturing defects. Recovery allows engineers to analyze hardware that has actually flown which is impossible with expended hardware. This potentially allows the identification of risks that do not show up in tests. – Lex Jun 7 at 7:00

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