4 ms·

Thank you for elaborating on that point. From some of the other comments, it seems that it's maybe a contentious issue. There's a lot of pressure to include ha

Thank you for elaborating on that point. From some of the other comments, it seems that it's maybe a contentious issue. There's a lot of pressure to include hand-wavy references to "heritage hardware" in the risk assessments for various reasons, but it's not well-substantiated where it exists.

lumost 6y ago
I’d imagine it’s partly due to the view of the public that NASA’s launch tech has regressed since the Apollo program. The Saturn V had crew escape, could deliver 110 tons to leo, and was cheaper per launch than the shuttle. The F1 engine is still considered superior to the shuttle main engines. Pitching new tech when you haven’t matched capabilities from 60 years ago is hard. Combine this with incumbents looking to keep new entrants out of the market and heritage, and reuse become the operative words
- OnlyOneCannolo 6y ago
  Shuttle was canceled because its bay wasn't needed, it was overly expensive, and its service record was pretty accurately tracking the projected 1 shuttle loss for every ~50 flights. There wasn't a strong commitment to the missions at the time, so making something completely new was out of the question. But there was a lot politically and strategically riding on Shuttle, so they had to find some way of keeping some lights on. Those points can be elaborated, but the decision really wasn't much more complicated than that. The F1 and SSME are apples and oranges. They have separate uses and achievements for their times. I haven't heard of either being widely considered objectively superior to the other.
  - MichaelMoser123 6y ago
    At what stage was a shuttle loss per 50 flights projected? Can you expand on this, do you have a link? Was that due to the boosters or some other design constraints? Would a smaller shuttle have fared better in terms of reliability?
    - OnlyOneCannolo 6y ago
      They started PRA of Shuttle after Challenger [1]. I got that number from the SLS PRA and Reliability people, and might have read it in a report too, but I don't remember many more details about it. There's a lot that goes into PRA [2]. Shuttle size was dictated by intended cargo and maneuvers, so it's not really possible to say how changing size would affect it since you'd have completely different design constraints and objectives. [1] https://ntrs.nasa.gov/citations/20150002964 https://ntrs.nasa.gov/citations/20150002964 [2] https://www.nasa.gov/pdf/293261main_62868main_1_pmchallenge_stamatelatos.pdf https://www.nasa.gov/pdf/293261main_62868main_1_pmchallenge_...
      - MichaelMoser123 6y ago
        thanks for the links!
- sathorn 6y ago
  The F1 isn't superior to the SSME. It doesn't really excel at anything (other than being very big maybe.) From another article on that website: "The RS-25 is still considered to be about the best engine ever made with a fairly high thrust to weight ratio and unmatched efficiency." [1] [1] https://everydayastronaut.com/raptor-engine/ https://everydayastronaut.com/raptor-engine/
  - m4rtink 6y ago
    IIRC the F1 still holds a few thrust records (thrust per one engine maybe ?) but is certainly much less efficient than modern engines from Spacex/Ble Origin & Russian construction bureaus (much worse ISP & TVR).

lumost 6y ago

I’d imagine it’s partly due to the view of the public that NASA’s launch tech has regressed since the Apollo program. The Saturn V had crew escape, could deliver 110 tons to leo, and was cheaper per launch than the shuttle. The F1 engine is still considered superior to the shuttle main engines. Pitching new tech when you haven’t matched capabilities from 60 years ago is hard. Combine this with incumbents looking to keep new entrants out of the market and heritage, and reuse become the operative words

OnlyOneCannolo 6y ago
Shuttle was canceled because its bay wasn't needed, it was overly expensive, and its service record was pretty accurately tracking the projected 1 shuttle loss for every ~50 flights. There wasn't a strong commitment to the missions at the time, so making something completely new was out of the question. But there was a lot politically and strategically riding on Shuttle, so they had to find some way of keeping some lights on. Those points can be elaborated, but the decision really wasn't much more complicated than that. The F1 and SSME are apples and oranges. They have separate uses and achievements for their times. I haven't heard of either being widely considered objectively superior to the other.
- MichaelMoser123 6y ago
  At what stage was a shuttle loss per 50 flights projected? Can you expand on this, do you have a link? Was that due to the boosters or some other design constraints? Would a smaller shuttle have fared better in terms of reliability?
  - OnlyOneCannolo 6y ago
    They started PRA of Shuttle after Challenger [1]. I got that number from the SLS PRA and Reliability people, and might have read it in a report too, but I don't remember many more details about it. There's a lot that goes into PRA [2]. Shuttle size was dictated by intended cargo and maneuvers, so it's not really possible to say how changing size would affect it since you'd have completely different design constraints and objectives. [1] https://ntrs.nasa.gov/citations/20150002964 https://ntrs.nasa.gov/citations/20150002964 [2] https://www.nasa.gov/pdf/293261main_62868main_1_pmchallenge_stamatelatos.pdf https://www.nasa.gov/pdf/293261main_62868main_1_pmchallenge_...
    - MichaelMoser123 6y ago
      thanks for the links!
sathorn 6y ago
The F1 isn't superior to the SSME. It doesn't really excel at anything (other than being very big maybe.) From another article on that website: "The RS-25 is still considered to be about the best engine ever made with a fairly high thrust to weight ratio and unmatched efficiency." [1] [1] https://everydayastronaut.com/raptor-engine/ https://everydayastronaut.com/raptor-engine/
- m4rtink 6y ago
  IIRC the F1 still holds a few thrust records (thrust per one engine maybe ?) but is certainly much less efficient than modern engines from Spacex/Ble Origin & Russian construction bureaus (much worse ISP & TVR).