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> The core stage is structurally similar to the Space Shuttle external tank,[24][25] and initial flights will use modified RS-25D engines left over from the Spa

> The core stage is structurally similar to the Space Shuttle external tank,[24][25] and initial flights will use modified RS-25D engines left over from the Space Shuttle program.[26] Later flights will switch to a cheaper version of the engine not intended for reuse.[27] https://en.wikipedia.org/wiki/Space_Launch_System https://en.wikipedia.org/wiki/Space_Launch_System So they reused as much of the space shuttle as possible, down to using left over engines. Developing a new engine from scratch using a new fuel (methane) like SpaceX did would have been a very risky proposition. Like NASA, Blue Origin and ULA both did much more conventional things and have launch costs multiple times those of SpaceX. The relative cost of NASA's more conservative design decisions is more a testament to Space X's remarkable success with the Raptor engine than NASA being somehow incompetent.

7952 6y ago
It is difficult to assess risk without an indepth technical knowledge of the engine. Particularly when the engine could have a profound influence on how the rest of the rocket is designed.
valuearb 6y ago
Each Merlin Engine costs $1M. A Raptor is expected to cost less than $1M each. Blue Origins BE-4 is priced at $8M each. So how did conservative NASA get cheaper RS-25 engines for only $147M each?
- etrabroline 6y ago
  Those numbers are not measuring the same thing. Those are the marginal cost per engine. What did it cost Space X to develop the design, and what did it cost them to build the production facilities? The price NASA is paying is for delivery, not the cost to produces one more after billions have been sunk. Also, how many do they plan to produce? NASA probably only needs a few dozen RS-25s for the life of SLS, so probably not worth the billions Space X spent developing a new engine.
  - valuearb 6y ago
    The Merlin was developed for the Falcon 1, at a total cost of $90M (including the rocket itself; and Kestrel engine for 2nd stage). It was enhanced for Falcon 9, which has a total development cost of $300M for the first versions, including rocket, tanks, second stage, Merlin Vacuum. The RS-25 was developed in the 70s for the Shuttle, and had a quoted cost of $47M at end of Shuttle life. This is literally the cost to make a few more after all design and testing was done. NASA has spent over $15B developing the SLS, why are they paying three times more for these engines?
    - etrabroline 6y ago
      Because they shutdown the production lines capable of making them for $47 million over a decade ago, and it costs a lot of money to recreate them and get the tooling and personnel needed. It's also the single most expensive rocket ever. It was designed to be the best, economics were ignored because they had the budget to do everything optimally. In terms of basic specs, RS-25 is comparable to Raptor with superior specific impulse, and is a highly proven 45 year old design. Reliability is really the most important stat, given the cost of the payload and other parts of the rocket. Obviously Space X spent a lot of time thinking about economics, with great results, but going for the expensive but sure bet option made a ton of sense for SLS. Merlin is much simpler and smaller and not really comparable to the other two. The RS-25 got new life with SLS, I would expect future NASA craft to use Space X engines.

7952 6y ago

It is difficult to assess risk without an indepth technical knowledge of the engine. Particularly when the engine could have a profound influence on how the rest of the rocket is designed.

valuearb 6y ago

Each Merlin Engine costs $1M. A Raptor is expected to cost less than $1M each. Blue Origins BE-4 is priced at $8M each. So how did conservative NASA get cheaper RS-25 engines for only $147M each?

etrabroline 6y ago
Those numbers are not measuring the same thing. Those are the marginal cost per engine. What did it cost Space X to develop the design, and what did it cost them to build the production facilities? The price NASA is paying is for delivery, not the cost to produces one more after billions have been sunk. Also, how many do they plan to produce? NASA probably only needs a few dozen RS-25s for the life of SLS, so probably not worth the billions Space X spent developing a new engine.
- valuearb 6y ago
  The Merlin was developed for the Falcon 1, at a total cost of $90M (including the rocket itself; and Kestrel engine for 2nd stage). It was enhanced for Falcon 9, which has a total development cost of $300M for the first versions, including rocket, tanks, second stage, Merlin Vacuum. The RS-25 was developed in the 70s for the Shuttle, and had a quoted cost of $47M at end of Shuttle life. This is literally the cost to make a few more after all design and testing was done. NASA has spent over $15B developing the SLS, why are they paying three times more for these engines?
  - etrabroline 6y ago
    Because they shutdown the production lines capable of making them for $47 million over a decade ago, and it costs a lot of money to recreate them and get the tooling and personnel needed. It's also the single most expensive rocket ever. It was designed to be the best, economics were ignored because they had the budget to do everything optimally. In terms of basic specs, RS-25 is comparable to Raptor with superior specific impulse, and is a highly proven 45 year old design. Reliability is really the most important stat, given the cost of the payload and other parts of the rocket. Obviously Space X spent a lot of time thinking about economics, with great results, but going for the expensive but sure bet option made a ton of sense for SLS. Merlin is much simpler and smaller and not really comparable to the other two. The RS-25 got new life with SLS, I would expect future NASA craft to use Space X engines.