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sevenperforce

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Everything posted by sevenperforce

  1. Clearly I missed some excitement. So I'm guessing we're looking at a persistently gaseous helium coolant loop? Heat transfer won't be as efficient without a liquid coolant BUT the regenerative heat capacity of helium will probably make up for it. I wonder how much helium it requires, though. Not exactly a renewable resource. I'm also curious as to what kind of local heat sink the generators need. They could be buried underground, I suppose, but a water-based heat sink would be much more efficient. As I understand that was because liquid oxygen and the composite wrapped tanks inside the LOX tank. There was a liquid oxygen incursion into the outer layers of the carbon overwrap. The superchilled helium caused the trapped LOX to freeze into solid oxygen crystals, warping the composite overwrap layers and causing a COPV failure. The energetic failure of the COPV provided ignition energy between the carbon composite and the LOX, and the rest was...toasty.
  2. Crap, I hate how the forum handles those links. Why Are Rockets Complicated? https://vm.tiktok.com/ZM86TyBg5/ Power Cycles Make It Worse https://vm.tiktok.com/ZM86TLYGV/ Those are each 60-second videos with a LOT of information.
  3. Same, not sure how or if it could reenter but it reminds me of the StarTram space plane. https://imgur.com/a/AspxR3B Maybe it wasn't meant to re-enter, but was intended to use aerodynamic passes to change inclination like the X-37B.
  4. Okay now that is just a genuinely excellent idea.
  5. Is that one of the rail mounts for the carriage or is it a linear truck that slides along the chopstick arm?
  6. Carriage being lifted into place on the launch tower.
  7. There was still a fear of what was under the dust - was it all solid rock or a mixture that could support the weight of a lander: https://www.icr.org/article/moon-dust-solar-system/ ICR is known to be a particularly unreliable source. (The reason I happen to be knowledgeable on the moon dust issue is that I used to work with that and related groups, back in my anti-science days, and this was a common bone of contention.)
  8. Minor quibble: by the time of Apollo 11, NASA knew for sure that the moon dust wasn't a foot thick. The unmanned Surveyor landings gave them enough data to establish that the dust was compacted. The larger concern for the landings were the possibility of coming in with a non-negligible horizontal velocity component and the associated tipover.
  9. The ejection seat on the Vostok was absolutely not strong enough to get Gargarin high enough for his chute to open in the case of a pad abort, so they strung a net around the launch site to catch him if they had to abort on the pad. And as we all know, "trapped in a net next to an actively failing launch" is just a wonderful place to be. As for Gemini, I know there's some degree of disagreement over whether the ejection seats would have actually burned the pilots alive or not....
  10. Maybe they can use their excess payload to drop a secondary experimental re-entry vehicle to keep things SPICY.
  11. Because they've found a way to make the flaps better at their job, namely flipping the ship. Keep in mind this is only a fan render; we don’t know whether this is actually what they will look like. We know that they will be slightly smaller and further back but I’m not sure about placement otherwise.
  12. I would argue that they didn’t get successful quickly in the early days. The USSR did, but the USSR concealed its failures. We didn’t get successful by embracing fast failure; we got successful by gratadim ferociter — albeit much more ferociter than Blue. We used a lot of competition to push innovation, which meant we had everything already in place once it was time for Apollo. But that culture of competition engendered a notion that distribution of responsibility enhances safety, which drove costs through the roof. And once the money dried up, so did the innovation.
  13. "Suborbital is a step in the direction . . . of orbit. So . . . it's still good to do something in space." So few words. So much shade. So a payload delay, not an engine delay? Hmmmmm.
  14. I also suspect that having the header tanks place off center will assist Superheavy in performing a more aggressive glide maneuver on its way back, which further reduces propellant consumption during the boostback burn. Falcon 9 depends exclusively on its grid fins to provide the pitch authority for the body lift glide maneuver, but having Superheavy’s center of mass offset that means it will naturally get some body lift even in the passively stable configuration, like a capsule. In addition, superheavy will be using its main tank ullage gas for RCS, which is another reason to keep the header tank separate.
  15. Yep, that’s exactly the impression I got. A better response would have been to say something more like, “Here’s what we’ve done to remedy issues as they were brought to us” rather than “We have all these structures in place so there can’t possibly be any issues.” Indignance smells of indifference; humility would have gone a lot further. If they had slightly changed it to 'we are looking into our leadership practices' rather than 'we as a whole have been maligned' I think it would stink less. Fair as well. The “entire team” line was gratuitous when anyone reading the article could see that the criticism was leveled at the leadership culture, not the workers as a whole.
  16. No, you're absolutely right. This lawsuit is complete nonsense. Like the whole Kraken.
  17. Oh I bet they said she was terminated for cause.
  18. Let’s do the maths, then. Aspirational dry mass of Starship is 85 tonnes. We know the header tanks hold 30 tonnes of propellant. Thus, a notional 100-tonne return payload would increase its total entry mass by a factor of 87%. This means terminal velocity goes up by 87% and the stagnation forces on the flaps go up by 250% during free-fall. However, because speed has gone up, the control authority of the flaps also goes up. So the flaps will be able to handle the control as long as they are structurally able to handle the stagnation forces. And since the vehicle nominally experiences much more than the one gee of free fall during intermediate entry, that’s no problem. As far as the kick-flip is concerned, having additional mass towards the nose actually makes it easier, because the Raptors have a larger moment arm around the center of mass. Starship will need more prop reserves to land, but that’s fine. Starship probably can’t take 100 tonnes to LEO and bring it all back in one go, but no one is expecting that.
  19. Whoops, yes. I meant the Soyuz family. Modern Soyuz is still derived from Vostok and Voshkod. I will note that the F9 booster achieves its 1:1 L/D ratio only in the lower atmosphere. Can’t do that during hypersonic reentry. Try standing on an overturned soda can. Also, a better glide ratio brings back the problems of the Shuttle orbiter’s AoA.
  20. Well, yes. "Fall as a rock" is a feature, not a bug. It can land on three engines if it needs to. Not a problem. If you need to reserve more propellant on ascent to give yourself more propellant reserves on landing, you do so. No big deal.
  21. The only pure ballistic re-entry vehicles (i.e., no lift) that humans have ridden are the Soyuz capsules. And even in a Soyuz, ballistic entry is only a contingency. The Apollo capsule had an L/D ratio of 0.38 at hypersonic speeds, increasing to about 0.68 just below Mach 2. This was somewhat better than the Mercury capsule. In contrast, the Shuttle had a higher L/D ratio during hypersonic flight, but not dramatically higher. The STS orbiter could get an L/D ratio of about 1.5 during the peak-heating, hypersonic phase, increasing to 4.5 at subsonic speeds. This was actually lower that what the orbiter could have attained; wind tunnel testing showed that the orbiter could have achieved an L/D ratio of up to 1.9 in hypersonic flight at the proper AoA (in this case, ~17.5°). However, the orbiter's heat shield couldn't handle entering at that angle; it had to hold an AoA of ~40° during peak heating to avoid burning off the nose and windows. But Starship is not the Shuttle orbiter. It has fewer design constraints since it doesn't have to be able to land horizontally, which means its heat shield can be designed for whatever AoA will provide peak L/D. A flat plate can achieve an L/D ratio of 2.2 at 17.5° or even higher at more shallow AoA (up to 3.5 at 10°). And an ogive cylinder can achieve an L/D ratio of up to 0.85 at hypersonic speeds. Thus, between its flaps and its body lift, it's very possible that Starship can get a hypersonic L/D ratio just as high or higher than the Shuttle orbiter. And since Starship will be much fluffier than the Shuttle, it should have even less loading. Starship's entry profile will be designed to have the highest possible AoA during the initial entry before the air gets thick so that you can slow down as much as possible, then nose farther forward to increase lift to prevent extreme gees, then tilt the nose back again for the terminal descent.
  22. The Buran and STS orbiters had a triangular cross section with flat control surfaces. Triangular-cross-section capsules work. The Buran and STS orbiters worked. Starship has a circular cross section with flat control surfaces. Circular-cross-section capsules work. Starship will work.
  23. The angles of entry would make the scaled tiles problematic. The direction of airflow goes in one way on ascent, another way during peak hearing, another way on terminal descent, and yet another way during the landing burn. The shear forces from the airflow are nonlinear with respect to air density and air speed. I can’t imagine there would be a scale tile orientation that would work for all of those.
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