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SSME vacuum ISP 452 seconds. Beyond the ability of humans to manufacture at design time. This had a predictable impact on construction cost and delivery date.

by VLM 13y ago

SSME vacuum ISP 452 seconds. Beyond the ability of humans to manufacture at design time. This had a predictable impact on construction cost and delivery date. Beyond the ability of humans to make reusable for a decade after deployment. Eventually turned into one hell of a monster legendary engine, a few decades later. Nothing wrong with an engine development program, but the SSME was ridiculous. Merlin family vacuum ISP a sedate 311 seconds. COTS and evolutionary based on existing engineering practice. Designed for low cost and reliability, not utter extremes of high performance. (edited to correct, not COTS. Kept thinking they adapted a RD series design at the start, but I checked and they didn't. Same general story though, lower Isp and lower chamber pressure and very conventional pintle injector design etc its good engineering aka very boring, all their engine design competitors are far more competitive, which is dumb because fuel and tanks are cheap, engine development isn't) Its very much like comparing the long term reliability of a 2024 specs F1 series racing engine none the less manufactured today in 2014 (or at least they did their best), against the engine in my new Toyota that's in it's 10th mfgr year and is pretty much bulletproof.

hga 13y ago
Bingo. I've heard long ago that the SSMEs were cutting edge, "race car" (exactly those words) engines, and that's why they required a complete rebuild after each mission. In another subthread, someone commented on the Space Shuttle being designed for reuse. Well, sort of, especially at the beginning, at the top, but various ambitions that weren't strictly needed (e.g. the SSMEs, single polar orbit missions) and insufficient budget (turning the reusable first stage every one envisioned before into the kludge of the throwaway tank and massively dangerous SRBs) meant by the time it launched it had no hope whatsoever of meeting those goals. Add bogus safety calculations, and it was never going to be a "space truck". Space X, on the other hand, seems to understand what this is all about. And unlike NASA isn't burdened by implicit requirements like employing lots of people at the maximum number of sites, or the explicit mission of boosting the South's technical prowess.
MrMeker 13y ago
It seemed broken that this comment was at the bottom, so I upvoted it.

by VLM 13y ago

hga 13y ago

Bingo. I've heard long ago that the SSMEs were cutting edge, "race car" (exactly those words) engines, and that's why they required a complete rebuild after each mission. In another subthread, someone commented on the Space Shuttle being designed for reuse. Well, sort of, especially at the beginning, at the top, but various ambitions that weren't strictly needed (e.g. the SSMEs, single polar orbit missions) and insufficient budget (turning the reusable first stage every one envisioned before into the kludge of the throwaway tank and massively dangerous SRBs) meant by the time it launched it had no hope whatsoever of meeting those goals. Add bogus safety calculations, and it was never going to be a "space truck". Space X, on the other hand, seems to understand what this is all about. And unlike NASA isn't burdened by implicit requirements like employing lots of people at the maximum number of sites, or the explicit mission of boosting the South's technical prowess.

MrMeker 13y ago

It seemed broken that this comment was at the bottom, so I upvoted it.