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Posts posted by RCgothic

  1. Falcon 9 is now flying heavier payloads reusable than it initially did expendable.

    Maybe it might save a little material cost to build a shorter tank for lighter payloads, but you almost certainly wouldn't save more than half the price of a complete booster, as it appears is possible with reusability. Most of the cost is in the engines and if you cut down on mass too much you get over-engined. Redesigning that octaweb is non-trivial. Also, there are additional tooling and inventory management concerns that would eat into your savings.

    Finally, Falcon 9 went reuseable because Elon Musk wants to go to mars and things like supersonic retropropulsion and reusability are seen as necessary technologies. I'm convinced he'd go for this direction anyway even if it weren't totally financially optimal.

  2. Stage 2 is weird. It provides most of the DV for falcon 9 in order to keep the first stage slow for recovery. But the Space x website advertises the same burn time for F9 and FH second stages, implying no more propellant for S2 on FH. Combined with doubling the payload, that has got to do awful things to S2's DV.

    Either I'm missing something or the core stage 1 is going to have to separate crazy-fast compared to falcon 9. How then do they plan to do core recovery?

  3. Alas poor Jeb. First casualty of this hardcore campaign. Veteran pioneer of the kerbal space program and in particular the first spacewalk and Gemini Rendevous missions. Killed in a tragic launchpad accident when the launch clamps released prematurely. Unphased he initiated the abort procedure but a second oversight meant that at sea level the munar module did not have enough TWR to pull itself clear of the ensuing fireball. He will be missed. As soon as the space program can find two more credits to rub together Valentina will lead on in his stead.

  4. I don't think sci-fi shuttles generally are SSTOs in the conventional sense. When you have enough power to maintain 1g indefinitely you don't have to maintain orbital velocities. Re-entries also don't have to be heat shielded because you don't come in that hot. 

    This also explains why sci-fi ships tend to fall out of orbit when they're damaged/lose power. It's because they were actively maintaining their altitude rather than falling around the planet and missing.

  5. Yup, fizzle at best (worst?).

    If a core is not detonated precisely right, the heat of assymmetric fission will scatter the core, leaving the vast majority unfissioned and all that potential energy unreleased. And that's if any fission at all is achieved. Maybe you get none at all and the implosion charges just scatter uranium all over the place.

    The trick of keeping a mass sub-critical and then making it go prompt super-critical on demand is exceptionally difficult.

  6. I estimate ~300m/s  extra required to get to 1000km and then to a lunar intercept vs starting from 100km and going straight to TMI.

    Perhaps it's not much. For the moon. It is an extra ~500m/s required for every craft trying to get to the space station from earth though, particularly over the multiple supply runs required.

  7. 4 minutes ago, Kryten said:

    Actually the 45 and 13 ton figures are for booster recovery, so it handily beats FH. Expendable LEO payload should be in the region of 70 tons.

    My mistake indeed. It's tricky to keep all these different payload figures straight!

    Guess that puts New Glenn squarely in SLS block 1 territory.

  8. Motokid600 already picked up two of my first thoughts on that vid: grid fins and moving landing platform.

    My other thought was that that is an excessive amount of cowling around those engines.

    As a two stage launcher it doesn't quite compare to falcon heavy to LEO or GTO, yet is much bigger. I guess the difference comes if they can stick a third stage on it'll have greater potential beyond earth orbit (Falcon is pretty much at structural limits).

    Certainly interested in seeing how they do though, and a second launcher in the 45t to LEO range makes it more likely the full payload of falcon heavy will be used, as sat operators like redundant options.

  9. How do they get a crew of four aboard if the space suit hogs the airlock?

    Other than that, the casualness of the whole thing is what struck me. The degree of autonomy of the ship, how easily things are constructed on orbit (and then we install the nuclear reactor!), the aggressive manoeuvres close to other vessels/structures, and the way a repair was made by just piloting a space suit into a jet of venting nitric acid at however many atmospheres and casually plug that right up. And our mars mission is under constriction even as we flyby the moon for the first time. No incorporating lessons learned for us!

    Oh, and the space station was at an altitude of 1000 miles, nicely within the inner Van Allen belt and squandering the oberth effect for moon missions.

  10. The big stuff is just a source for the little stuff, which is the real threat. The big stuff can be tracked and avoided. A cloud of little stuff is lethal. Big stuff spawns little stuff whenever it is struck by anything.

    Enforce an 'everything must be de-orbited at end of life' regulation. That takes away new debris sources. Lasers are the means to get rid of the smaller stuff, but it requires very good tracking and an exceptional power source.

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