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Everything posted by sevenperforce

  1. Now, if you could mount the boosters on either side of the orbiter and send it up in parallel launch style, that could work.
  2. Yeah, and even weirder he conceptualized launching it on a pair of Falcon 9s: Putting in SuperDracos for aux is nice and all but it's not like they're going to be a meaningful contributor during abort. Eight SuperDracos together produce only a quarter the thrust of a single sea level Raptor 2. Could be useful for moon landings though.
  3. That's how most of the flying wings I've built in KSP fly, but in real life you have to be able to have full control in an engine-out scenario, which is where you run into problems. A more workable solution is differential drag via split ailerons. Rather than just having a single aileron control surface at the tip of each wing, you have two overlapping ones, and so you can either deflect them up or down in a pair (to control roll) or you can deflect them in opposite directions to induce drag. By making the tip of one wing more draggy than the other, you turn the plane toward that wing in the yaw axis.
  4. I beg to differ. Flying Wing Starboost88 Beautiful! Of course I mean in real life. But yes. I'm trying to think whether there is any better orientation to come up with in terms of engines than the one in the NASA study. Excited to see what you come up with!
  5. Unrelated to the launch, I'm surprised I never saw this anywhere on this thread. It's a cool concept from a couple of years ago. Full concept art gallery is here.
  6. So not only magic Isp but magic engines. Because either those engines rotate or are duplicated and still don't overdo the mass issues of SSTO. And of course all those SF vehicles somehow don't abuse the landing pad (Kirk landed his Klingon Bird of Prey in a 20th century park, Stormtroopers stood nearby the Millennium Falcon when we first saw it take off) even with a TWR>>1. On the other hand, Arthur C. Clarke was right about the definition of "magic" and such things might well be possible well before the 2200s. Oh yes, magic indeed. Of course, the slower the exhaust is moving, the less dangerous it is to be in the vicinity. And fortunately the ground has a bunch of thick air around it which tends to be useful for such things. I've always wanted to come up with a realizable way that you could have air intakes with extremely high bypass in one direction and progressively lower bypass in the other direction so that you wouldn't need variable geometry for an airbreather. Just rotate the nacelle based on speed and altitude.
  7. Oh, that's very cool! One of the specifics about the bi-directional flying wing idea is that it's supposed to NOT be symmetric in different flight modes. But yeah, very nice job.
  8. Looks like they used an Einstein doll for the zero-g indicator. And nose cone deployment started! All systems go.
  9. Entry burn start. Nice pretty Eye of Sauron. I love seeing that hard-over body lift turn into the wind at the end of the entry burn. SECO -- we have Endurance in orbit! Landing burn, and down! Very shaky coming in, though. And a nice clean separation from the second stage. Endurance is flying free.
  10. Very cool shot -- the camera on the booster picked up the sight of the thrust plume from its own ascent rising off the coast.
  11. Feels so strange to see that shiny white new booster. We haven't had a brand spankin' new booster launch since Starlink 4-15 in May. Vehicle is on internal power. And we've lit that glorious candle! Go Endurance! Through Max-Q and throttling back up. That nice white-and-black booster sure is purty. Separation and second-engine start confirmed! Endurance is well on its way to orbit.
  12. Did a little digging on that, and yes, you're correct. Looks like they use a single shaft and simply use a variable mixture ratio valve to adjust the amount of fuel entering the injectors, accepting the pressure differential. Still, I feel like this may be easier for the RD-180 due to LOX and RP1 having more similar densities in comparison to LOX and CH4.
  13. I'm unsure whether Dragon's trunk can hold something large enough to do that.
  14. Flying wing designs are very good for low-drag applications, but they're pretty slow. The ways of fixing instabilities in flying wing flight result in increased drag at supersonic speeds; no supersonic flying wing has ever been built. However, with Breaking Ground robotics, we could fix that. One of the coolest ideas NASA has played around with is the bi-directional flying wing: a flying wing that takes off along its short axis but then can fly supersonically along its long axis: Here's a rendering from a NASA study that shows it in supersonic flight: Ostensibly, the engines are mounted at or very near the vehicle center of mass and are able to rotate by up to 90 degrees to switch between the two different flight configurations. I'm guessing it also needs control surfaces that can be switched on and off. Your challenge, should you choose to accept it, is to build and fly an aircraft which is able to take off with a prograde cockpit facing one direction, then transition to flying with a prograde cockpit at a 90 degree different direction. Additional challenges: Reuse Me! Not only can your aircraft take off and transition to stable flight at the new orientation, but it can also transition back and land safely in its original configuration. Look Ma, No Wheels! Build an aircraft which doesn't use reaction wheels or RCS and relies solely on aerodynamic control through all modes of flight. Double Trouble! Instead of using rotating engines, try having completely separate engines for forward and sideways flight. To Infinity! Exceed the speed of sound in your "sideways" flight orientation. And Beyond! Make it to low Kerbin orbit.
  15. It's not (particularly) a problem of interaction between the stabilizers and the wing surface, although that can come into play. Rather, it's more an instance of one thing leading to the other. Because vertical stabilizers are so close to the center of mass, they don't have a very good control moment over yaw. Because they don't have a very good control moment, they must be very large in order to effectively damp yaw. Because they are much larger than you would need on a conventional aircraft, they create much more drag (all by themselves) than the vertical stabilizers of a conventional aircraft. You can. But at this point you basically just have an ordinary plane.
  16. Another note -- we like to yammer a lot about SSTOs, but for science fiction purposes the more useful vehicle is the SSFO -- Single Stage From Orbit. You really want a vehicle which can leave low planetary orbit, re-enter and land, perhaps ferry itself between a couple of destinations, and then return to orbit again, taking off and landing vertically each time but remaining in a horizontal attitude throughout.
  17. The coolest spaceplane I know is the Serenity from Firefly. Unfortunately, having two engines on a swivel each opposite the center of mass gives you massive amounts of roll control, but no pitch control (and yaw control only by differential thrust). So that's not as pretty as you might think. The "ultimate" spaceplane (to me) is one that can re-enter, land vertically in a horizontal attitude, take off vertically in a horizontal attitude, deliver cargo or pick up passengers, fly to somewhere else, then land vertically once again. That vertical takeoff means it doesn't need a prepared runway, and the self-ferry capability is what will make that so useful.
  18. As @Beccab said, yes it does. There are twelve "canted" Draco engines which are used to control pitch/roll/yaw as well as perform short-distance translational maneuvers for docking, and then there are four main Draco engines under the nose cone which perform all major burns. The deorbit burn takes about 10 minutes, if I recall correctly, and expends about 100 m/s worth of dV. When I say that the other 12 engines are "canted" I mean that they point at odd angles. This allows them to be used in pulses to rotate the vehicle around its center of mass. But it also means that firing them together is not an efficient way of giving the spacecraft more forward momentum because even though their thrust CAN balance, it ends up losing efficiency.
  19. SuperDraco doesn't **need** to operate in the atmosphere; it operates just fine in a vacuum. It is just wildly overpowered for use in space. For additional reference, a single SuperDraco is three times as powerful as a RocketLab Rutherford engine. It doesn't operate at particularly low pressures, either. The difference in specific impulse is because the SuperDraco has a truncated nozzle to allow deep throttling since it was originally intended to support hovering landings on Earth or Mars. It does not have a turbopump; it is entirely pressure-fed just like the SuperDraco. Because Dragon doesn't need to carry a bunch of dV, it can afford to have very beefy high-pressure tanks. SuperDraco's increased complexity is partly from the fact that it is regeneratively cooled using the hypergolic fuel, allowing sustained firing (which, again, really wasn't as necessary as originally planned). It is 3D-printed, though, which helps make the regenerative cooling a little simpler. The SuperDracos can still be throttled despite using burst discs for startup, and since they can be throttled they can also be shut down. They have to be shut down because the capsule can still use the remaining propellant for maneuvering/pointing via the Dracos. I believe the difference (with respect to the burst disc) is that the SuperDracos receive the full tank pressure rather than the step-down pressure that the Dracos use. **performs brief "of course I was right" dance**. The forward translational thrusters can't be fired with the Dragon nose cone closed. Obviously. I confess I was taken aback by how large Dragon is compared to Hubble. For some reason I had it in my head that Hubble was bigger (e.g., Skylab sized) but I guess if it was carried in the Shuttle docking bay then this makes sense. You are correct. The docking adapter soft capture ring on Hubble is not at all compatible with the standard forward docking adapter on Dragon. They will need to do a telescoping bespoke adapter in the trunk. There would be a pretty nasty limitation on the physical dimensions of any such trunk airlock. There's just not that much room in the trunk. Doing an extending trunk or fairing would require re-rating the whole vehicle due to the OML changes. And they'd still be left unable to perform a boost burn. Here's a better render of what the reboost would look like in real-time, from an NSF member: The soft capture ring on Hubble can't be used directly for the official "grip" because it's, well, soft. Hubble has hard "towel bars" that can be gripped by a bespoke system for hard capture. However, if the adapter is extensible already, then it's possible that they wouldn't need the towel bars at all. They could extend the adapter, execute soft capture, and then retract the adapter, pulling the base of Hubble flush against the trunk. The trunk handles all gee-loading on Dragon during launch compressively, so the trunk will easily be able to transfer the comparatively much lower forces directly into Hubble's structure.
  20. That is the PAF and upper bulkhead of the second stage propellant tank. Note that while this is the cutaway/schematic for the v1 cargo dragon, which had berthing rather than docking, the dimensions are approximately the same for Dragon 2. The Draco engine is a very small bipropellant engine used for RCS and in-space maneuvers. It has a vacuum-expanded nozzle and gets about 300 seconds of specific impulse in short bursts. With each burst you get a short puff at about 90 pounds of thrust, which is enough to rotate or realign the capsule but otherwise isn't particularly significant. The SuperDracos are much, much larger bipropellant engines. They run on the same propellant as the Dracos but they are intended only for abort and they produce an immense amount of thrust for their size: up to eight short tons of thrust per engine. They are significantly more powerful than the Kestrel engine used on Falcon 1's upper stage. With all eight SuperDracos at full throttle, the abort thrust of Crew Dragon is 30% greater than the full thrust of the SLS Block 1B Exploration Upper Stage and more than half as powerful as the J-2 vacuum engine on the Saturn V third stage that propelled the Apollo astronauts to the moon. Although the SuperDracos and the Dracos both draw from the same propellant tanks, the SuperDracos are single-use and are activated with burst disks rather than standard valves. They also have nozzles sized for sea level so their specific impulse is extremely low. They are not at all suitable for use in space.
  21. So, the reason we get the Perseids and the Leonids and so forth is not because we are in any kind of sync with the comets that created them, but because those comets regularly shed portions of their mass each time they go around the sun, which scatters material around the course of their orbit. Such a thing could be possible for the galaxy. However, it would be on a much larger scale. Rather than a comet shedding little pieces of ice and rock, think about a globular cluster getting twisted and stretched into a long orbiting string of stars by tidal forces over billions of years. That’s more likely. Research “stellar streams” if you want to learn more about what can happen to globular clusters.
  22. One other cool possibility: SpaceX could use a Dragon XL spacecraft with an APAS docking adapter on the tail end and a hatch on the side. The XL could perform all the reboosts using its main forward thrusters and it could also allow Polaris II to dock with it and use it as an airlock to test Hubble servicing.
  23. I don't believe so. Modifications to allow them to be restarted would invalidate human-rating. Also they are less efficient than the Dracos, both in terms of vacuum specific impulse and cosine losses. I think the gee-loading could potentially be within limits, although it would be iffy. The SuperDracos are not only canted out but are also canted at an angle to allow roll control by differential throttling, so you'd have to fire a minimum of four. Even at 20% (minimum throttle), that's 58.4 kN, reduced by cosine losses to 56.4 kN. Crew Dragon masses about 12.5 tonnes and Hubble is 11 tonnes and so that's about 0.25 gees which is probably just on the edge of what Hubble and the docking system can handle. I'm sure that adapting the docking software to allow "back-in parking" is a shorter pole than major hardware redesigns.
  24. Keep in mind that everything in the galaxy is orbiting the galaxy (except the pressure wave arms themselves) and so there's no meaningful astronomical alignment that would happen once per orbit.
  25. Someone over on NSF pointed out that these are probably ellipsoidal caps, not spherical caps, so I recalculated. While the lower (assumed CH4) booster tank volume somewhat intuitively remains the same, the upper (assumed LOX) booster tank volume goes up from 238.3 cubic meters to 255.4 cubic meters, bringing the apparent mixture ratio up from 2.99 to to 3.2 which is still surprisingly fuel-rich but not as severely as before. Booster propellant mass goes up, from 363 tonnes to 382 tonnes, and upper stage prop mass goes up from 84 to 90 tonnes. If the 1.27:1 TWR holds then we are looking at a total vehicle dry mass percentage of 11.1% which makes sense.
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