Comment by thehappypm

Rocket engines are very complex machinery that's difficult and expensive to make. Reusing the rocket allows you to reuse the engine.

SpaceX has also managed to show that reused hardware can be more reliable than brand new hardware. You run the hardware through a number of tests before launch, but there is no better test than an actual launch. Satellites still cost a lot more than rockets, so reliability is a big deal

For the booster I think it’s fairly well established that it’s cheaper to reuse it. It’s not that hard on a booster to come down again, and it doesn’t seem like it’s that much work for SpaceX to refurbish their boosters.

For the upper stage it still remains to be seen. Having the upper stage return from orbit is a lot harder, as we’re seeing with the Starship. You need a lot of thermal protection. Maybe flaps depending on the design.

Jeff Bezos mentioned in a recent interview that for the upper stage they’re working on a reusable and a cost reduced version of the upper stage in parallell. They can’t determine yet which will end up being cheaper. That tells you something about how hard it is to do second stage reuse.

Rocket Lab has shown with the Neutron rocket what’s possible if you’re really innovative with optimising for cost on the second stage. Their second stage will probably be cheaper than the satellites they send to orbit

This was the argument a decade ago when SpaceX was the only one seriously talking about reuse. Given SpaceX is now responsible for the vast majoriy of mass to orbit it is hard to argue with the results, and now everyone serious is investing in reuse.

It's true that in principle, you need a stronger rocket (the whole rocket, not just the motor) and a bunch of extra infrastructure to be able to reuse.

However, without being able to recover a rocket, it's actually quite difficult to figure out just how much corners you can cut, while remaining reliable. Since blowing up revenue payload is an awful way to optimize this, I think this means that disposal rockets will be inefficient in a different way - there will be excess safety margin in the wrong areas.

Reliable re-use also changes the operating model of the company. Since each rocket in stock represents many customers over time, you don't need to be nearly as stressed about exactly matching your manufacturing pipeline to predicted demand. This likely also enables generally faster turn around time (as in from cheque signed to launch).

Finally, as it turns out, it's not unreasonable to expect a rocket to be reused like 20+ times. I think you're point would be reasonable if it turned out that reusing a rocket more than ~3-5 times was difficult. But like... it's REALLY hard to do disposal anything better than something that can be reused 20+ times.

By that logic there should be launchers of similar capabilities cheaper than F9... which there aren't.

Reason 2: Enables increased launch cadence.

There is an older (2015) discussion on this at https://forum.nasaspaceflight.com/index.php?topic=37390.0

Rocket engines are very expensive, and the whole rocket is fairly expensive in traditional construction methods. The cost of the rocket engines dominates the others.