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Comment by fwefwwfe | Hacker News Reader

How do they know how many times they can re-use the rocket? Do they xray it for cracks every 5 flights?

You measure how much stress is applied to critical components, which uses up some of their finite lives. From experiment and theory, we know how much "damage" is done to a part subjected to a given stress. Similarly we know how much stress on components is generated in each launch. Therefore we can take the total life of each critical part (determined thru experiment and analysis), and divide it by the reduction in life (= damage) for each launch, to get the number of remaining launches. The part with the lowest remaining life determines the life of the system.

I wonder if, once they get a rocket to the max calculated safe launches, which will obviously have some margin built-in, it would be sufficiently worthwhile to keep launching it with low-value payloads (or none at all) and actually test it to failure.

My intuition leans toward no, obviously because launches are very expensive in terms of fuel and other stages, but also because there's no guarantee the test rocket would be representative, so for it to be really meaningful they would have to repeat the experiment several times. Still doesn't seem inconceivable though.

For this rocket, the process for figuring out if they can use it and how was very complex. This rocket was originally flown for the CRS-8 mission on april 8th, 2016. So it took them just shy of a year to ensure that this rocket could be reflown, and that they felt comfortable putting a customers payload on it. They also fired it on the ground many times, and I would imagine checked it for every imaginable component failure.

How ever, for the future, only time will tell how confident they will be able to be in the re-usability of their rockets. Most likely they will retire this rocket, as with the one that was first landed, and put it on display somewhere. After they research it, of course.

Minor correction, Gwynne said that this rocket only took 4 months to inspect. The rest of the delay was due to pushing the launch schedule back after one of their rockets exploded, with payload atop, during testing.

You are correct, they are retiring this rocket. In fact, SpaceX is giving a piece of the rocket to SES to hang in their conference room.

Sometimes I think SpaceX is landing stages so it can put them in museums, parking lots, and conference rooms.

Did they say why they're retiring this stage? A commenter at Ars said they spent a lot of time bringing it up to the latest rev. Seems like a shame not to fly it again.

Because once you have shown it is possible once, it means it can be done again. Why destroy a piece of history when you can destroy number 2 trying to fly it a third time?

They most likely spent the time bringing it up to the latest rev because of the performance improvements and increased reliability of the newer version. They didn't really care about how much time it took to get the second one to fly, as long as they could get it done. This was a really big milestone for their future plans, so it didn't really have a monetary or time limit.

Because its historic. Latter ones will not "suffer" this fate.

They estimate based on data. The biggest constraint at the moment is probably not anything that most people would think of like fuselage strain, it's the engines. The engines burn kerosene and they often run fuel rich, which leads to build up of residues (coking) in the plumbing. This is very difficult to remove and reduces the effective lifetime of the engines.

Once they get this generation of rockets settled into a pattern of high reliability reuse they'll look toward future improvements which will involve switching fuels (from kerosene to methane). LOX/Methane doesn't have the same coking problem so it could enable rockets with much longer lifetimes (a hundred or more flights per stage) and corresponding cost reductions.

Also, at that point the development cycle fundamentally changes because then you can match the airplane cycle where you build a few prototypes or test vehicles and then put them through their paces. Since you expect the vehicles to survive all the time (versus being lost routinely) you can achieve much lower development costs along with much higher reliability.

Or you could chemical wash off the coke if it's economical instead of changing fuel. Depends whether LOX/Methane is strong enough and the hardware still as easy to reuse, fuel and not prone to failure.

If it were that easy they'd be doing it already. It's not that easy.

Ya. I imagine they'll simply swap out the Merlin engines for scaled-down Raptor engines once those are fully ready.

Blue Origins rockets are rated 100 usages. Same as space shuttle.

Blue Origin hasn't flown to orbit yet - they have a sub-orbital rocket, and future plans for more.

Also Shuttle engines were practically rebuilt every launch.

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