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Posts posted by RCgothic

  1. By my count Raptor is coming up on half as many launch and in flight ignitions as Rocketlab's Rutherford by the way.

    I think Raptor is on 224 counting all of those that started and burned for more than a second from Starhopper through IFT4.

    Rutherford is on about 490 I think?

  2. I don't know who originally started the "Boeing Astronauts Stranded" line, but it's never actually been the case and it seems like a lot of outlets are just copying the lede and running with it.

  3. Europe clearly needs to do something to compete.

    But even if they put forward a design targeting falcon-like cadence and reusability, by the time it's ready it'd already be obsolete. 

    Needs a much larger rethink than just producing an all-liquid ariane variant.

    They need an engine that can be produced at a rate of several per day, with better-than-Merlin levels of reusability, and enough thrust to not need solid boosters for assistance. 

    Hydrogen engines are out on poor thrust and difficulty to refurb (tricky h2 seals).

    Kerolox is out because of coking.

    So they probably need a methalox engine as a starting point 

  4. The header tanks also have helium COPVs for pressurisation. 

    But also it's probably not safe for NASA to sell the ISS. It's a station that's getting gradually more decrepit and can't reasonably be fixed. If a private entity ended up getting someone killed, NASA could be liable.

  5. Sometimes it's acceptable to just accept the remote chance of a fault because covering it off completely would be grossly disproportionate. 

    The chances of a well-designed cable breaking in normal operation are remote. So we're talking fault cases. What sort of faults could be encountered in interplanetary space? Micrometeoroid impact? And the chances of that severing all the strands of a cable are? If the strands are cross-coupled every so often the broken end wouldn't even rebound especially fast.

    Any strike large enough to take out multiple strands would probably be a LOCA in the far higher probability of striking the main spacecraft anyway.

    Any other plausible fault cases? I'm struggling to think of any 

  6. And for all you know a Merlin (most reliable rocket engine in flight hours ever by a long margin) would have exploded in those circumstances as well.

    Pretty much every instance of engine-out so far on Starship/Superheavy appears to be some form of "rocket failed to provide the engine with acceptable/survivable operating conditions".

    A rocket needs to be looked at holistically.

    Is direct exhaust autogenous pressurisation turning out to be harder than expected? Possibly. But heat exchangers are also massive and complicated and need to move enormous quantities of liquid through a phase change, so we may not yet have reached the point where "stick more filters on it" isn't a better solution.

    For context, each of the steam generators on a nuclear reactor are about half the size of the reactor vessel itself, and there are typically 2-4 of them.

  7. Part two of Tim's interview with Musk is up. 

    Notably it was only the front-right flap that really let go, they can tell by the deployment data. That one was fully deploying, the other 3 more nominally.

    Also where the tiles were missing on the skirt, seems 2 layers of backup ablative didn't burn through, one layer did but not clear that the steel also failed, might have survived. 

    They don't even need infra-red cameras for seeing the hotspots internally, they glow in the visible spectrum. 

  8. Although I have many, many criticisms of Musk, as a chartered engineer myself "not being a proper engineer" isn't one of them.

    By all appearances he has as much of a grasp of technical details as top engineers for a nuclear power plant. There are many decisions that get made during the design process of any system, and they're not always good ones. Iteration is part of the process. 

    The only difference with SpaceX is that we see the iterations happen publicly in hardware rather than purely in private sim.

  9. 34 minutes ago, Exoscientist said:
    • If you're going to the moon, you don't need an orbital depot.

     Can you give the context where he said this? The Starship HLS for Artemis plan requires multiple refuelings. Does he mean a Starship HLS in orbit would itself be the depot?

      Bob Clark

    He followed up by saying that there's no great rush to refuel HLS in orbit, it can be done with sequential tanker flights and the boil-off won't be too bad. Propellant transfer is just docking, and docking to other starships is easy - much easier than docking to the ISS which they do regularly.

  10. There's "never done before" and there's "never done before in a rocket engine".

    For whatever reason there's never been a good enough motive for someone to try and integrate cooling of secondary systems (because regenerative cooling of combustion chambers and nozzles have been implemented since forever) before. 

    Maybe a rocket needs to have a particular mass of fire suppression, number of engines, or level of reusability before advanced integration of instrument lines and wiring inside housings and elimination of flanges makes sense. 

    In my own work I'm bringing together a lot of different things that are fairly common elsewhere but nevertheless equal "never done before in a power plant".

    The main reason for us at least seems to be that when production of a thing is at a fairly steady rate, the people building power plants go on to build new power plants the same as they've always done, and train their replacements to do what they've always done. 

    When demand for a thing exceeds the resource pool, people with different experiences need to get brought in from other sectors and the combination of experiences often unlocks doing things differently from then on.

  11. I was in a work meeting and only caught the stream as the camera was getting coated in debris and just before the lens cracked. Saw the landing, came on here and started reading back. 

    A fin melted. Wait. What?!

    Only then went back and rewatched the stream. Can't believe it made it to a successful ocean landing with that!

  12. So the issue with flight 3 boostback and entry burns wasn't anything to do with Raptors, Quelle Surprise.

    Oxygen line filtration issue and roll control thruster clogging.

    1 hour ago, cubinator said:

    Looks to me like the total duration of 'going well' was about 2 frames.

    The video started at the anomaly, later on it goes back and shows the engine firing apparently normally.

  13. For a similar comparison, the first two full flight lunar modules were probably delivered around the end of 1968. LM-1 flew in Jan 68 on Apollo 5, LM-2 became a test article, and LM-3 flew Mar69 on Apollo 9. Earlier LMs that flew were various degrees of boiler plates and test articles (dev).

    From what I can tell, 75% of the total funds allocated to lunar modules were disbursed by the end of 68.

    That would put a 2nd flight dev-inclusive cost for Apollo at $15B in 2020 dollars, or $7.5B per flight.

    That's rather more favourable to SpaceX's starship's $2B. And that's before considering Starship is VASTLY more capable.

    Over 10x as much downmass, over 35x as much downmass per dollar.

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