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RCgothic

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Posts posted by RCgothic

  1. 8 hours ago, mikegarrison said:

    You appear to be confusing design choices with being ahead or behind in the development cycle.

    Almost everything you just listed there are design choices, except "prototypes", "testing", and to some extent "cost". (I'm excluding "development" because that's circular. You can't say they are ahead in development and then give "being ahead in development" as a reason.)

    Cycle, ISP, thrust, TWR, size, and to a great extent cost are all outcomes of decisions made in preliminary design, not evidence one way or another for an engine being "ahead" of another engine.

    (And since both companies are private, and only one of them sells their engine, I wonder how it is that you think you know "cost" anyway?)

    I'm completely willing to say Raptor is at a higher TRL than BE-4, but you should clean up your thinking on what this means and why it is so. Flight test prototypes are a higher TRL than ground test prototypes.

    I take your point, but part of this comes from one of the tweets surrounding the conversation quoted above in which BE-4 was described as "more advanced", ambiguously conflating TRL and sophistication, which is why I went into every metric like I did.

    Also some of Raptor's design aspirations have legitimately moved, such thrust of up to 3.1MN.

    The point stands I think, that I can't think of any metric on which BE-4 is better than Raptor.

  2.  

    18 months ago. BE-4 is a year ahead of Raptor.

     

    18 months later BE-4 is definitely not ahead. In fact I can't think of any metric on which it competes.

    Engine cycle? Raptor's full flow staged combustion is more advanced.

    Development? Raptor is further along.

    Prototypes? Raptor has at least 40.

    Testing? Raptor has flown actual flight articles.

    ISP? Raptor is ahead.

    Thrust? Raptor is already topping BE-4's 2.4MN.

    Cost? Raptor is certainly a lot cheaper.

    TWR? Raptor is on course for better than Merlin.

    Size? Raptor fits all the above in a much smaller package.

     

    It's a little bit amazing how completely you can squander a twelve month lead in 18 months. Blue needs to pick its game up. This is too Gradatim. More Ferociter is needed!

     

  3. Briefly thought it would be cool to see them practice the manoeuvre with old F9s, but on further thought falcon's probably not capable of 1) entering the right attitude, 2) relighting engines in that attitude, and 3) surviving hypersonic sideways flight.

    Also I'm quite attached to the Falcon flight leaders, I don't want to see them lithobrake!

  4. Here's the thing.

    Even if Starship completely fails to survive EDL and they can't fix it. If they never get refuelling in orbit to work. If Superheavy never sticks a single landing.

    Then you can still retool the system as a conventional expendable rocket with ~250t payload to LEO and IDK, a 12m payload fairing, and all 34 engines *combined* will cost about half as much as a single RS25.

    Even if Starship/Superheavy is a complete abject failure, it still renders SLS totally obsolete.

  5. STS could put what, 110t of mass in LEO, 78t of which being orbiter?

    If SLS could put 10m diameter payloads of up to 110t into LEO 3-9 times a year at roughly the same cost as the space shuttle, then that would be a useful capability no matter what it was used for, even in the face of new commercial competition. Sometimes that 110t could be a departure stage for BLEO missions. Useful! I think it would save a lot of money in assurance if crew never had to go up on it, but even so it could still work.

    But I don't understand how you start with shuttle, add an engine, and get less mass to LEO, a quarter of the flight rate, 3x the entire marginal cost of a shuttle flight on SRBs and RS25s alone, and a lunar rocket that can't even put boots on moon properly.

  6. Berger's not wrong. SLS/Orion is stupidly overpriced. If it all worked perfectly for launch tomorrow it still couldn't put boots on regolith. It can't co-manifest a lander with Orion and the lander isn't ready anyway.

    For the price of the SRBs and RS25s alone you can get ten fully expendable Falcon Heavy flights or 20-30 Falcon 9s. You can build a better moon mission around a fraction of that lift capacity with a little in orbit assembly.

    The only reason they haven't is because those boosters came along after Congress made its mind up.

    With even greater commercial heavy lift coming along there's no reason for SLS to continue to operate.

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