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sevenperforce

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  1. sevenperforce
    Yes, precisely. The thought being that if you can combine the higher efficiency of asparagus staging with a single separation event, you can have the closest possible performance to a refuel-and-refly system. Parallel staging has a much higher efficiency than serial staging, high enough that everything can be overengineered for rapid reuse and still have a good enough payload fraction to act as a crew shuttle.
  2. sevenperforce
    Lovely. I figured there was a way to do that. You can, of course, reserve only two engines for landing and allow the other two to burn out at separation. I'm guess the maximum performance would come from carrying the majority of the fuel in the skirt and crossfeeding it to the core engine so the core is fully-fueled at separation, but that might push the limits of what can wrap around the core without a collision at separation.
  3. sevenperforce
    Very nice. I'd be a little concerned about differential yaw between the two boosters in an IRL configuration, but having the right attachment points should help with that. I wonder what kind of size we'd need in this configuration to take a crew of 7 to the ISS and back. Would three Raptor engines (one on the orbiter and one on each booster) be enough? Lack of vacuum optimization is a bit of a problem, but this could be remedied either by giving the central Raptor a longer but deconverging engine bell (like an SSME) and/or adding a small pair of vacuum-optimized OMS engines for orbital insertion assist and circularization. The other problem is whether the Raptor can throttle deeply enough to land the two boosters on their tails. Oh wow, that's beautiful! Very nice. So can the cargo bay be jettisoned as whole without decouplers, then? What kind of performance difference do you get by adding fuel tanks to the cargo bay skirt (either for crossfeed or simply to fuel the quad)? And if you add a probe core, can you successfully land the quad by itself?
  4. sevenperforce
    Good point.
  5. sevenperforce
    How about a Mk3 to Mk2 Adapter or a C7 Brand Adapter (Slanted)? Arrange those radially and you should be set.
  6. sevenperforce
    Yes, this makes it tricky, as sections attached to separate decouplers automatically detach upon staging, no matter how well you strut them together. The solution, I think, would be to use a single radial decoupler and build the skirt in mirror symmetry around it. Then set the decoupler's force to zero and throw some sepratrons on there. To keep it balanced, you can throw another radial decoupler on the opposite side and just strut stuff to it.
  7. sevenperforce
    The new strongback is stronger and more robust, so it can handle the rapid pullaway. It's better, because it cradles the Falcon right up to the moment of launch, reducing the risk of wind shear damage. They're going to use this strongback for FH because it can support three cores at once.
  8. sevenperforce
    The frame would be prohibitive if used IRL, but it's an excellent kerballed solution. What about something like a revisited S-ID approach? The idea was to take a standard Saturn V first stage and place four of the five F-1 engines on a skirt, similar to the one used by the Atlas rockets. All five engines fire on the pad, but once 70% of the propellant has been burned, the four outer engines MECO and the skirt drops away. In theory, the skirt could be chuted and recovered for reuse. In a modern redux, the skirt could contain crossfeeding fuel tanks feeding the central engine. Then, with modern restartable, deep-throttling engines, the skirt could return to a propulsive landing easily. If you really want to mix things up, you can leave an air gap between the skirt and the core body so that the airflow boosts the thrust of the core engine, making it a partial airbreather. Trouble, then, is how you go about recovering the core, if you're expecting to use this as an orbital passenger shuttle. Boosting a large body into orbit isn't such a bad idea, since a larger body gets draggy at a higher altitude (assuming you use a normal attitude rather than a retrograde one) and experiences lower peak heating. Final recovery is the only sticking point. Might play around with some numbers to figure out what kind of mass fractions this would give us. Suppose we use five Raptor engines... Anybody want to try building this?
  9. sevenperforce
    I've toyed with adjusting the thrust limiter of one engine in-flight to produce thrust balancing via differential thrust. It's possible, but very difficult to do. The US Space Shuttle was not particularly aerodynamic; the line between the center of thrust and the center of mass ran through the side of the External Tank, not through the top of the stack. It practically flew sideways. That's why Challenger broke apart; when the SRBs disintegrated and the External Tank came off, the orbiter was so far from a prograde heading that the aerodynamic forces shredded it. Still, if you are going to stick to a single separation event rather than an asparagus approach, it's what you've got to do.
  10. sevenperforce
    Looks fantastic! Thanks for all the pictures. Now I'm wondering if something like this would be possible IRL. It would definitely avoid the off-axis thrust problems that tend to plague parallel-staged orbiter designs.
  11. sevenperforce
    Looks great! Can I see it on the pad?
  12. sevenperforce
    I agree. At a basic, conceptual level, there's no reason to insist on total reuse when you're launching comsats and cargo. It's much cheaper to throw away the engine and tank on the upper stage than to try and bring them back for refurbishment. But if you're talking about shuttling crew/passengers into orbit, then it is assumed you'll be bringing people back down as well. And that's where a totally-reusable system starts to make a lot more sense. Granted, there's no current market for high-capacity, high-frequency passenger service to and from orbit, but that's beside the point; if there was a market for orbital passenger service, that's when we'd need a reusable man-rated shuttle, and I'm thinking that PSTO would outperform SSTO or TSTO in this function. The Shuttle was designed with lots of crossrange capability to permit RTLS on military polar orbit launches, but a high-capacity high-frequency passenger service would be focused on equatorial launches. So wings aren't completely necessary. You do, however, want to be able to land on land, and you want to have safe, reliable landings with relatively rapid egress. So those are the kinds of considerations at play here.
  13. sevenperforce
    Oh, shoot. There weren't any closeup photos of the boost phase so I assumed the radially mounted tanks visible on the pad were engines. This wouldn't count as parallel staging. The upper-stage engine needs to fire on the pad.
  14. sevenperforce
    Brilliant! That's called a "biamese launch" and it's quite promising for a lot of reasons. There's even a more advanced version, known as a "triamese launch", spearheaded by the UK's MUSTARD design: The outside vehicles separate and return to a glide landing while the center vehicle continues to orbit: With aggressive crossfeeding, the mass ratio for these kinds of designs is ridiculously good. But when this design was created, back in the 60s, reliable crossfeed technology wasn't really within reach. I'd be interested to see a biamese concept that can make use of propulsive landing or perhaps even partial airbreathing.
  15. sevenperforce
    Interested to see what you come up with!
  16. sevenperforce
    Looks great! Using radially-mounted engines to keep the orbital stage's engines clear of the booster is quite kerbal. Got photos? Are the drop tanks recoverable?
  17. sevenperforce
    Here's one relatively simple way to achieve a PSTO system. Start with a Shuttle-shaped delta-winged orbiter and put a suitable number of Raptors under it; replace the cargo bay with an internal methalox tank. Strap a pair of Raptor-powered methalox boosters on either side, over the wings, with crossfeed to the internal methalox tank. The boosters separate and RTLS to land on landing legs; the orbiter continues to orbit and then returns for a gliding landing like an X-37B or the Shuttle. LAS is an issue, though with a high enough T/W ratio on the orbiter, it can just push itself clear of a booster RUD and fly back to the landing site under power.
  18. sevenperforce
    What's the configuration like? Does it take off vertically or horizontally? How about landing? How many boosters, and how are they arranged? What is the LAS setup?
  19. sevenperforce
    I'd be interested to see your design even if you aren't able to successfully fly it yet.
  20. sevenperforce
    Skydive from space is easy enough. Skydive from orbit, not so much. There have been proposals, but I would not want to be the test subject. You can use chutes for convenience in KSP so you don't have to manually fly the boosters back, but the configuration should be such that they could conceivably be landed either on the runway (with landing gear) or propulsively (with landing legs, like a Falcon 9 or New Glenn first stage).
  21. sevenperforce
    Yeah, it would have been tough. Atlantis was already gearing up for another mission, so it was available. It would have needed to be pushed through to launch, skipping 90% of preflight checks, and launch and rendezvous. Then they would have had to actively hold the two ships in a bay-to-bay perpendicular orientation (since neither had a Canadarm for grappling) while they did repeated EVA from Atlantis to Columbia and back, one crew member at a time. Doable, but just barely.
  22. sevenperforce
    We laugh, but there's a slim chance that EVA ship transfer could have saved the crew of Columbia if they'd noticed the body damage before re-entry.
  23. sevenperforce
    Look forward to seeing the pics! Vertical or horizontal launch are both fine; the goal is something that would work IRL, though.
  24. sevenperforce
    That's why I specified 0/0 LAS -- a launch abort which is capable of functioning from zero altitude, zero velocity all the way up. The Shuttle had nothing remotely approaching LAS. Challenger survived the SRB RUD; it just broke up from off-axis aerodynamic forces at max-Q, something an orbiter with proper LAS would be designed to handle. Parallel staging wasn't really the problem there. Columbia was a victim of foam insulation shedding, which was a ridiculous problem with the External Tank, but wouldn't be an issue with anything other than hydrolox. I like the idea of a solid pusher ring that remains attached to the top of the booster on nominal launches so that its dry mass doesn't have to be carried into orbit unnecessarily. I had specified parallel staging because I wanted to see what configurations people might be able to come up with. If you have an orbiter with its own launch engines, the booster functions less like a launch vehicle and more like a launch assist booster with integrated drop tank. The orbiter might actually be significantly larger than the booster (which eliminates several parallel staging problems). If you do go serial with a scaled-down MCT, you can conceivably mount the engines perpendicular to the vehicle axis, since they would only fire once out of the atmosphere. Then they can be used for horizontally-oriented propulsive landing, Harrier-style. What about a VTHL near-SSTO that uses a pair of strap-on boosters with integrated drop tanks?
  25. sevenperforce
    Yeah, basically. At the risk of succumbing to rule of cool, this really is a lot better than the alternatives. You eliminate the dead weight of landing gear and you have no risk of tip-over. Egress is feasible as well (something that seems ridiculously difficult for a proposal like ITS). I see three ways of doing this. The first is to have fully rotating engine nacelles like a V22 Osprey or Firefly's ship Serenity. Drawback here is additional dry mass for the rotation mechanism, as well as moving parts that can fail. Another approach is to use an airbreathing engine (turbojet or turborocket) for launch assist and for landing, since turbine exhaust can be easily vectored to 90 degrees or more (think F35B) and rocket exhaust cannot. The drawback here is increased dry mass to orbit; it would be better to use the turbines on the booster than to carry them into orbit every time. The final, and perhaps most interesting approach, is to have altitude-compensated OMS engines for orbital insertion/maneuvering which are aligned perpendicular to the launch thrust axis. These engines wouldn't fire during launch, but once out of the atmosphere, they could circularize or change orbit without aerodynamic drag. During landing, they would be able to lower the orbiter straight down to the tarmac.
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