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sevenperforce

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Everything posted by sevenperforce

  1. sevenperforce
    That's what I've done on all of my LESes. Either that, or do it the opposite way -- fairing below, tapering up to close around the LES base.
  2. sevenperforce
    Yes, a FH side booster can SSTO with a couple of tonnes of payload. Easy. But no way it's coming back.
  3. sevenperforce
    Right. The tanker variant has enough tankage capacity to just barely make orbit, but it wouldn't have enough prop for deorbit or landing. And it would have TWR issues on takeoff.
  4. sevenperforce
    Not by any math I've ever seen.
  5. sevenperforce
    Not with enough reserves for landing.
  6. sevenperforce
    I don't foresee BFS being used in SSTO format for Commercial Crew. Really, really unlikely. For a lot of reasons.
  7. sevenperforce
    10,000 lbs / 100 lbs / sec means that the Isp is 100 seconds. You absolutely cannot let those units get away from you. In practice, what you'd most likely do is create a surface area regression model, record burn time, and then adjust parameters (using a series of different geometries) until you have a rock-solid burn rate model. Flow rate is a function of burn rate, which is a function of surface area. But the burn rate also depends on chamber pressure, which is why you have to tweak your parameters until they fit the experimentally-derived burn times. Once you have a good mass flow model, then you can take the thrust curve and determine the specific impulse curve.
  8. sevenperforce
    But it's so damn close.
  9. sevenperforce
    I will have to make my lower fairing go all the way up and close, then place the escape tower assembly on top of the upper docking port of the Soyuz forward module and offset it out of the fairing. If you close a fairing in stock KSP onto a central column, you cannot pull that column free and later blow the fairing.
  10. sevenperforce
    Hmmm...so they jettison the escape tower before the Korolev cross, then jettison the launch shroud separately. I may need to rework my model. Third/upper stage fired. Orbital insertion complete. Healthy Soyuz.
  11. sevenperforce
    Final service gantry retracted. Ignition! Clamp release!
  12. sevenperforce
    It's after 1:44:25 Eastern...is there a hold? I don't speak Russian.
  13. sevenperforce
    http://online.roscosmos.ru/
  14. sevenperforce
    The music is exciting. Do the astronauts select the music? They are dancing to it....
  15. sevenperforce
    Manley is great, but this seems like a bit of an offhand comment that wasn't thought through. Getting from the lunar surface back to Earth entry requires about 3 km/s if you're going to do a propulsive landing once you arrive. Dry mass of the Spaceship BFS variant is about 85 tonnes. If we suppose 10 tonnes of payload (which is probably conservative) and we assume 360 seconds of isp on the engines (since you won't be using the vacuum Raptors the whole time), you'd need to have 127 tonnes of propellant onboard at lunar touchdown. Lifting 222 tonnes on the moon with a TWR of 1 requires 360 kN of thrust. Each of the three SL Raptor landing engines on the BFS has a vacuum thrust of 1900 kN. They can also all vector through the CoM independently. So if they can throttle down to around 20%, they can hover. I think 20% is the deep-throttle rating of Raptor.
  16. sevenperforce
    Elon said the moon landings would be set up for direct ascent returns, so they'd have substantial propellant reserves on landing. The BFR should be able to downthrottle its core engines enough to hover, even on the moon.
  17. sevenperforce
    Well, the thing is that the stats are actually swapped. The current Wolfhound is far heavier than the current Skiff. So that alone would suggest using the Skiff for the terminal stage and the Wolfhound for a lower stage. The low atmospheric isp of the Wolfhound won't be a problem unless it is actually used for the launch stage itself, which wasn't the case for the J-2 anyway. They just need to switch the stats of the two engines. They need a "no plate" version for every engine. Full stop.
  18. sevenperforce
    Dream Chaser would have been able to launch on an Atlas V or a Falcon 9 or even an Ariane 5. It had integral launch abort motors which would have also been used for orbital maneuvering. Propulsive dragon landings were canceled. The CST-100 is very similar to the Apollo CM.
  19. sevenperforce
    Nah, the X-37B is an experimental autonomous orbital spaceplane; it is used as a testbed for NatSec experiments. Also, it launches in a fairing, and it has no place for crew. It's been launched by both SpaceX and ULA. You may have been thinking of Sierra Nevada's Dream Chaser, which is a manned spaceplane. NASA didn't end up picking it for Commercial Crew, though. Boeing's CST-100 Starliner is basically Orion Lite -- a smaller version of Orion with a lighter heat shield, less dV, and shorter-term ECLSS. It will launch on the Atlas V N22 (no fairing, 2 SRBs, dual-engine Centaur).
  20. sevenperforce
    Well that sucketh mightily.
  21. sevenperforce
    Of course the proper way to do it is simply measure thrust and propellant mass with respect to time. You end up with two different curves, fT and fM. The slope of the propellant mass curve is your mass flow; your Isp is given by a function fS(t), where fS(t) = fT(t)/fM'(t). EDIT: If you have a small enough solid rocket motor, it's theoretically possible to measure both thrust and propellant mass as a function of time on a big enough test stand. You can have the rocket laying down on its side on a sled, with one forcemeter measuring the horizontal force on the sled and the whole apparatus on a scale to measure mass change.
  22. sevenperforce
    In honor of the upcoming launch:
  23. sevenperforce
    ISS Expedition 56 This should be launching later today, so out ahead....
  24. sevenperforce
    Nor is the ISP constant. Right.
  25. sevenperforce
    Well, it's not that a couple of the engines have the wrong isp; it's that two of the engines have all their stats swapped. Coding error, not design error.
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