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sevenperforce

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  1. sevenperforce
    Elon said they should be able to recover the side boosters for the Mars landing.
  2. sevenperforce
    Got to watch this live. Can't wait to see the full video from OCISLY once they pull it from the cams.
  3. sevenperforce
    Thanks! I wanted them to look badass (a small part of why I am so set on a vertical landing in horizontal attitude) but still be functional. The dry mass for the fuselage is higher than for a comparable "simple" liquid rocket (e.g. the Falcon 9 second stage) but I'm not sure if the margin is high enough. I'd need to look at the mass/volume characteristics of wet wings w/o control surfaces in order to get a better general estimate. I really wish there was a way to have biaxial takeoff as well as biaxial landing, for sheer rule of cool as well as enhanced ease of operations, but that's a struggle. Kind of need a supercharger there, unless we can come up with a way to entrain air more aggressively with dynamic compression.
  4. sevenperforce
    On that note, what are some of the advantages and disadvantages of different arrangements of engine clusters? For a nine-engine cluster, you can do the 3x3 of the Falcon v1.0, or the 1+8 octaweb of the v1.1, or you could even do a 3+6 assessment with three triangles. For a four-engine cluster you can do 2x2 or 1+3. I suppose that having a central engine and multiple planes of symmetry is nice, generally.
  5. sevenperforce
    Funky orbital mechanics and the Oberth effect. If you take a Hohmann transfer straight to the moon, you end up having to add the moon's orbital speed to whatever speed you enter the lunar SOI with, which means you need a lot of dV. Getting to EML-1 or EML-2, on the other hand, preloads almost all your energy during your translunar injection burn in LEO, so you only need a few m/s to slide over into an elliptical lunar orbit and then a small burn to circularize. EML-2 is better for this because it is closer to the moon than EML-1, but it costs more to reach. However, if you use the moon's own gravity for an assist, you can reach EML-2 even cheaper than EML-1, which makes it the best option. Longer transfer time though. Elon definitely wants to go direct to Mars when he goes to Mars, but he has talked about going to the moon as practice.
  6. sevenperforce
    I think we are talking about an equivocation of falsifiability and usability. Something which is not scientific can still be very useful, and something which is not very useful can still be scientific. A lack of falsifiability does not mean a lack of validity.
  7. sevenperforce
    I don't think anyone suggested that the requirement of falsifiability is a scientific criterion of scientificity...or, if they did, they shouldn't have because they would be wrong. Mathematical axioms are falsifiable but ideas which are true by definition need not be falsifiable. Not necessarily. Consider two simulated universes with identical physical laws, one of which is programmed to discourage scientific inquiry and one which is not. The former universe will see the "science is useful" hypothesis falsified, but the definition of science will not be in any way changed. Another example would be a universe with extremely complicated laws which came with a Truth Book providing freely accessible answers for all basic questions. Here, again, the definition of science would be the same but the usefulness hypothesis would be false; thus the usefulness hypothesis is falsifiable. More broadly, the hypothesis of the usefulness of science is falsifiable because if the hypothesis were not true, science would not work nearly so well as it does.
  8. sevenperforce
    Your first declaration that a dropped apple will either fall or not fall is not falsifiable and thus cannot be the basis of a scientific theory, but it is logically valid and true by definition. Similarly, the idea that a theory must be falsifiable in order to be scientific is not falsifiable but is still logically valid and true by definition. It is true by definition precisely because we define science based on falsifiability. There is no contradiction in having the definition of science rest upon an axiom which is not scientific in and of itself. There is a suggestion of this because "not scientific" can easily be mistaken for "unscientific", which in turn carries connotations of pseudoscience and false belief, but this is equivocation. The practice of the scientific method is science; the scientific method itself is epistemology. On a related note, it is of course possible to create a scientific theory which deals with the use and usefulness of the scientific method. For example, one could hypothesize that the rigorous use of the scientific method yields more accurate information in the long run than an epistemology which does not depend on the scientific method. This is a scientific hypothesis because it is, in fact, falsifiable. For example, beings inside a simulation could be faced with a world where scientific analysis was discouraged by anomalous interference from the Program.
  9. sevenperforce
    By the time you get to cislunar space the difference between starting with supercooled propellants and non-supercooled propellants is negligible. A modified Dragon V2 I call the White Dragon. White for the moon (even though I know full well the moon is basically the color of asphalt). Radiatively-cooled nozzle extensions for the SuperDracos, no heat shield, larger propellant load, larger internal batteries, stripped-down trunk, and compressed air tank for repeated repressurization to allow multiple EVAs. Might need to launch inside a fairing.
  10. sevenperforce
    The longest (read: most fuel-efficient) route to low lunar orbit is a lunar swingby through EML-2, which takes 6 days. LOX boil-off is 0.2% per day, so you lose 1.2% of your LOX on that six-day transfer. Shouldn't have any trouble reserving enough dV for the crasher-stage landing. However, different trajectories do require a different number of restarts, so depending on the fuel cost of each restart it might be more fuel-conservative to use a faster, more expensive trajectory that requires only one restart for correction/injection. I'm working on a pet project to find a viable route for a manned lunar landing using two FHE, a single unmodified DV2, and a moderately modified White Dragon for the lunar landing and ascent vehicle. I think I can get a crew of 3...maybe 4 if the math ends up being agreeable enough.
  11. sevenperforce
    All measurements involve a margin of uncertainty. Uncertainty in measurement does not an estimation make.
  12. sevenperforce
    Math. Knowing the properties of the electomagnetic fields in the test chamber, you can derive particle masses by studying the paths those particles are observed to follow. Sort of like how if you can obseve the orbits of a planet and its moon, you can determine both their masses. And not faster than the speed of light. Close to it, though. But making it work is a serious engineering challenge. I would point out that if some of the particles did exceed lightspeed, the LHC detectors would absolutely be able to detect it.
  13. sevenperforce
    But he was not wrong in ways that significantly affected the predictive power of his theories on scales that could be measured during his era.
  14. sevenperforce
    Crasher stage. Falcon Heavy boosts across EML-1 or EML-2 onto a collision course with the moon, then restarts and burns retrograde to kill 98% of velocity. The Dragon separates, loses the trunk, and finishes the retrograde burn with a hover landing.
  15. sevenperforce
    Anywhere from 380 m/s fully loaded up to 540 m/s empty. That's at SL, though; vacuum thrust and specific impulse will be a bit higher.
  16. sevenperforce
    I don't have the link in front of me but I am 90% sure I remember Elon saying, "We will be able to go to the moon, so why not? It's on the way to Mars, after all, so it wouldn't make sense not to go there too." Obviously the Word of Elon is not always directly representative of legitimate plans, but it means they are at least talking about it. And like I said, the uprated Falcon Heavy has enough dV to drop an unmodified Dragon V2 on the lunar surface. No big deal.
  17. sevenperforce
    LOX is denser than kerosene.
  18. sevenperforce
    Here's another version, with the ducts on the side and SuperDracos inside the augmentation duct for launch augmentation and supersonic flow control. They fold down with the landing "legs" during landing for biaxial propulsion. Haven't done the math yet though. Crew variant shown.
  19. sevenperforce
    Too many sig figs, I know.
  20. sevenperforce
    I'm endlessly frustrated by depictions of the moon that show the curve while you're standing on it. Or show it only a few 1000 km from Earth.
  21. sevenperforce
    Right, I know about the LFBB design; I'm just trying to figure out your implementation. Yeah, powered descent, but powered by the lift fan.
  22. sevenperforce
    Yeah, belly-to-belly is biamese. I guess I'm not sure what you're trying to get at with a flyback booster. No wheels in the single-engine second render; it lands on the lift fans.
  23. sevenperforce
    Well, it's not actually a lot bigger than a Dragon capsule. Smaller cross-section, actually. This design was essentially a thought experiment to see how small an SSTO could be. The Falcon 9 upper stage is about the same size but is significantly lower in dry mass. Symmetry would demand a biamese launch. The ship is smaller on the belly than on the back so it can act as a lifting body; mating belly-to-belly is really the only way to go.
  24. sevenperforce
    Why not just two?
  25. sevenperforce
    3,790 kg to orbit. You can scale it up for a bit pretty easily -- double with two Merlin 1Ds, triple with three, and so forth -- and gain a little bit in payload fraction due to the square-cube law making the dry mass lower, but your AAR gains will start to suffer as you pack more engines in. You'll also run into more structural issues; this is a low-drag design but the aerodynamic stresses are still pretty high, so a larger version will have to deal with higher moments of torque in flight. My goal was really to design the smallest possible SSTO rather than a large one. Obviously a larger SSTO will have a better mass fraction, but a larger SSTO will also have greater turnaround time and higher reuse costs. Toying with the idea of SuperDraco-assisted takeoff and landing to replace the lift fan...depends on whether I can get the duct geometry to work.
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