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Everything posted by sevenperforce

  1. Your proposal that gravity could potentially be the result of 4-space acceleration has a chance of being not only useful for understanding, but actually true. However, the comparison with the common analogy of metric expansion as the expansion of a 4D hypersphere is limited, because that is only useful for understanding and is not actually representative of reality as we know it. Your conjecture may be correct. Maybe there really is an acceleration in 4-space causing the spacetime curvature we observe in 3-space. But even if that’s correct, that would be a separate acceleration/expansion/etc. than the metric expansion of the universe caused by dark energy.
  2. I am quite certain that the plan has been once-around without an orbit for quite some time now.
  3. This is pessimistic. He is incorrect, incidentally. SLS has abort-to-orbit capability in the event of premature shutdown at almost every envelope of flight. But pessimism is always the best approach, especially as a public figure. If you're wrong, everyone's happy and no one cares. If you're right, you're a prophet.
  4. It's a crewed landing. Artemis I is tonight (we hope). Uncrewed SLS Block 1 all-up test. Artemis II is the first crewed flight of SLS. Lunar free-return. Artemis III is the first crewed lunar landing of the program. Orion and Starship HLS will meet up free-flying in cislunar space for the transfers. Artemis IV is the first crewed visit to Gateway. This announcement adds a crewed landing to Artemis IV and says it will happen via Starship HLS through the Gateway.
  5. You would have been really confused if I had gone with my first draft, which called them “STS” and “SLS”.
  6. As requested: Also I updated the last one:
  7. Oh, shoot, Excel stacked min on top of max rather than showing them on the same scale. My bad. That's corrected.
  8. Here's a comparison for 14 and 33 Raptor 2s at minimum thrust and at full thrust.
  9. Yikes. Source? So, two more static fires, removal from the launch mount to make minor repairs and updates, three more static fires, some on-pad work, another static fire, and then orbital launch attempt.
  10. So much sheer kablooey If those 14 engines are at full throttle, that's about 50% more thrust than Falcon Heavy and almost as much thrust (though not quite) as SLS block 1.
  11. It certainly cannot be an expression of expansion within 3-space, which is why the ongoing and observable metric expansion of the universe is not the source of gravity. I could be wrong, but I don't believe they are in fact functionally distinct. They are the same. Special relativity says that it is 100% impossible to tell the difference between acceleration resulting from an external force and acceleration resulting from a gravitational field. Now, a gravitational field will have tidal effects, which may be detected in some other way, but that raises issue of measuring the distances, which themselves are subject to the gravitational field, so special relativity holds. You're correct that if 3-space was uniformly expanding at a certain rate (it's not uniform, even under metric expansion, until you get to intergalactic distances), then you wouldn't experience any acceleration. However, I don't believe that's quite what the OP is suggesting. What OP is suggesting, as I understand it, is that there is a fourth spatial dimension which is undergoing some sort of acceleration, and it is the acceleration in that fourth spatial dimension which causes the stress-energy-momentum tensor to behave the way that Einstein's field equations say it behaves.
  12. Metric expansion can be conceptualized by imagining 1-space expanding around a 2D circle or 2-space expanding around a 3D sphere or 3-space expanding around a 4D hypersphere, but that doesn't mean the 4D hypersphere is the actual shape of the universe. It's just a concept to understand metric expansion without resorting to infinities. I don't see any reason why gravity couldn't be the result of an acceleration in 4-space, but that acceleration, if it exists, is distinct from the metric expansion of the universe.
  13. You'd have to give an example; I don't think I've seen it. That might be difficult since the recent FH didn't have any views of the upper stage after staging.
  14. The payload was just very heavy. At 6.6 tonnes, first-stage recovery would have necessitated an orbit with an apogee lower than a proper GTO (compare the Galaxy 33/34 mission back in October, where the 7.4-tonne payload could only be lofted to around 20,000 km; the same was true for SXM-7 and SXM-8). Usually, GTO launches have an apogee even higher than the 35,800 km of GEO. A higher apogee allows for a bi-elliptic transfer, which saves propellant on the payload and thus increases the lifetime of the satellite. The customer paid extra to expend the booster. Example? I don't believe they ever would push them beyond design limits. They don't want to risk damage to the engine before the payload has separated.
  15. How? All-moving control surfaces on aircraft are lift surfaces. By moving in their rotational axis, their angle of attack changes, which changes the amount of lift they generate, producing forces about the center of mass to induce pitch, yaw, or roll. The flaps on Starship are not lift surfaces. They are drag surfaces; essentially nothing more than airbrakes. They do not produce lift (other than body lift, which is irrelevant here), and so changing their angle of attack doesn't do anything. The use of airbrakes to control aircraft is not new; flying wings use it for yaw control. The B-2 bomber has split ailerons; if it needs to yaw to the left, it will deploy the ailerons on its left wing in opposite directions, which increases drag on the left wing, which pulls the aircraft to the left. But in that situation, adding another axis of rotation wouldn't do anything, because the ailerons are not producing lift in the yaw plane, only in the pitch/roll planes. What you are suggesting is that changing the angle of attack on the Starship flaps would alter their control authority. It will not, because changing the angle of attack of a control surface does not produce new control forces unless that control surface was already providing aerodynamic lift. Here is a CFD simulation showing that the flaps are not producing any lift: If you do the calculation the amount of propellant used for landing is far less than 30 tons. The 30 tonnes of propellant is used not only for landing, but for the deorbit burn as well. A deorbit burn requires around 100 m/s of Δv. Starship will need roughly 7 tonnes of propellant residuals. So only 23 tonnes can actually be used. An empty Starship has a mass of just over 100 tonnes, approximately, plus the 7 tonnes of residuals. For the tanker variant, 27 tonnes of propellant gives around 630 m/s of Δv, which is certainly more than needed. But Starship needs to be able to return downmass as well. With a notional 50-tonne return payload, that's less than 450m/s. So after the deorbit burn, that's less than 350 m/s to execute the flip and come down to a soft landing while also fighting gravity drag. As you yourself pointed out, the lowest you could expect for that whole process is 250 m/s. Does that settle the controversy?
  16. Really intriguing! I like this kind of conjecture. One correction/caveat. The concept of a 3D expanding balloon is often used to illustrate the idea of metric expansion of 2-space, which can then be used to conceptually understand the metric expansion of 3-space. However, the expansion of 3-space itself is not occurring "in" 4-space. The universe is (as far as we can tell) topologically flat; it should not be supposed that the 3D universe is expanding in a 4-dimensional hypersphere. So with that understanding: yeah, I can't think of any specific reason why the stress-energy momentum tensor that defines spacetime curvature in general relativity could not be the result of 4-dimensional acceleration. Whether true or not, it's certainly a great way to conceptualize it. However, if there is actul physical acceleration in 4 dimensions which causes gravity,, such 4-dimensional acceleration would be independent of the observable accelerating metric expansion of space. And we should be able to know this anyway because the rate of expansion of the universe has changed through its history, but there is no evidence that the degree to which mass curves space has ever changed through the universe's history.
  17. Apart from the extraordinary weight penalty of having flaps and hinges which move in multiple axes rather than just one, adding another axis of control authority to the aft flaps won't help at all if the moment arm from the center of mass isn't long enough. That's just basis physics. Locating the landing propellant in the nose rather than keeping it in the LOX tank pulls the center of mass just far forward enough that the aft flaps have control authority. Without this, the aft flaps would have zero control authority, because the engines are very heavy and so the center of mass would be between the flaps themselves. Giving the aft flaps a new control axis wouldn't help because zero times anything is still zero.
  18. What are the possibilities here? (A) Eric Berger, who we know is quite intelligent, has had a complete mental breakdown and thinks something is possible when it absolutely isn't (B) The Defense Department has a new, secret version of nuclear thermal propulsion with performance rivaling that of Project Orion (C) "around cislunar space" simply means "around cislunar space" and does not mean "from LEO to cislunar space" It absolutely does not.
  19. This might be better placed in the regular Chinese space program spot, but I'm trying to figure out the minimum amount of work China would need to do to make this not happen again. If they simply added propulsive vents to the tanks and some basic star trackers to be able to maintain pointing, surely it would be able to use propulsive vents to point retrograde. Then firing additional propulsive vents should be enough dV to lower perigee, right? If the tanks are pressed to something on the order of 2 bar and the stage has 2% propellant residuals, how much dV would that provide if you just vent it all?
  20. One thing that would be super nice would be if all of the entry points so far -- Cote d'Ivoire, the Maldives, Borneo, and now the Pacific Coast of Central America -- were along the same great arc. That would suggest that China designs the re-entry such that the vehicle is at least expected to come down within a single orbit. Unfortunately, those four points are not at all along the same great arc.
  21. A more-rapidly rotating planet will tend to become progressively more oblate. The increased distance to the center of the Earth and the increased centrifugal force at the equator combine to have progressively lower and lower effective gravity at the equator. That's about the only change. My dude, the atmosphere rotates with the Earth.
  22. Definitely coming down much more rapidly this time, likely thanks to the low perigee. Looks like it will come down over DC (where I am) if it is just 27 minutes later than the current estimated splashdown point. In a 6-hour window. Lovely.
  23. The Epstein Drive in that series is a torch drive that employs Brachistochrone trajectories. An airbreathing gas core MHD engine could get very high specific impulse and reasonably high thrust, yes, but thrust drops off once you're out of the atmosphere. Of course, that's perfectly fine. You don't need high constant acceleration for some specified period of time. I don't know why you keep insisting otherwise. Your total dV is your total dV, whether you dump it in 70 minutes or 20 minutes or fifteen hours. Saying "speed and velocity" is like saying "temperature and hotness" -- one includes the other. If your velocity vector is the same, then it needs to be your velocity vector relative to something. Is it your velocity vector relative to the Sun?
  24. Oh dear, this again. Acceleration is NOT a feature of a "rocket drive" at all. A rocket engine produces thrust. Acceleration is the result of dividing thrust by mass. Let me say it again. Rocket engines DO NOT produce acceleration; they produce thrust. Period. And because the mass of a vehicle changes over time, the acceleration of a vehicle changes over time, assuming constant thrust. Specifically, it goes up. Since you said "3g max acceleration" I'm going to assume (probably wrongly) that you're thinking of something sane. For a vehicle to have a 70-minute burn time with 90 tonnes of propellant and achieve 3 gees at burnout, then (clearly) it must be burning 21.4 kg per second and it must be yeeting those 21.4 kg/s out the back end at a sufficient exhaust velocity that the impulse to the dry mass of the vehicle is 29.43 m/s2. This gives a range of values depending on the dry mass of the vehicle and thus the corresponding mass ratio. Here are some comparisons: Ratio of Fuel to Dry Mass Thrust (kN) Isp (sec) Initial Acceleration (gees) Total Δv (km/s) 24:1 (typical for some chemical upper stages) 110 465 0.12 14.7 6:1 (typical for a laden first stage rocket) 441 2,100 0.43 40.1 3:1 (enough thrust to get off the ground) 1,177 5,606 1.00 76.2 1:1 (typical for aircraft like a 747 or a B-2) 2,649 12,618 1.50 85.8 Having a specific impulse in the range of 2,000-5,000 seconds isn't completely out of the question; that's the theoretical specific impulse range of your typical open-cycle gas-core nuclear rocket. But of course a gas-core nuclear rocket sprays out rather unpleasantly radioactive exhaust, and it's doubtful that you'll be able to get the amount of thrust you need. The NASA studies of gas-core designs found they wouldn't produce enough thrust to even lift half the weight of their pressure vessel alone, and that's before factoring in the weight of a moderator/reflector and radiators. If you want to get up above 12,000 seconds of specific impulse, you're going to need a better energy source. Antimatter could do the trick. If you had perfect conversion of potential energy to kinetic energy, then you'd be accelerating your 21.4 kg/s of propellant to 124 km/s, requiring 164.5 GW of power. That's going to require you to burn about one milligram of antimatter per second, or a total of 4.2 kilograms over your entire journey. Of course, you won't, because the maximum efficiency of any heat engine (the Carnot cycle) is around 70%. That means 30% of your energy is lost to heat, so you're actually going to need 6 kilograms of antimatter. But that means we're going to have to have a way to reject 70.5 GJ of thermal energy per second. There are two ways you can do this. The first is by using an open-cycle cooling loop where you're just dumping part of your propellant overboard. That propellant will of course achieve very high temperature (that's the point) so it will basically be an entirely separate rocket engine similar to a regular NTR, except the heat it's receiving is waste heat from the antimatter rocket rather than from a nuclear reactor. Assuming liquid hydrogen propellant and a coolant exhaust specific impulse on the order of 1000 seconds (but now benefiting from the 70% limit of the Carnot cycle), each kilogram of coolant is carrying away 69 MJ of heat and producing an impulse of 9.8 kN. But at this rate, you'd need to be dumping over 1000 kilograms per second just to deal with the waste heat of the engine, and our propellant budget is only 21.4 kg/s. So we turn to the second approach: a closed-loop cooling cycle where the coolant runs through a series of radiators and is then injected into the reaction chamber as the main source of propellant. That will work, but it will approximately double the weight of your engine. But let's suppose we ignore all of the waste heat issues entirely. Some antimatter engines have T/W ratios on the order of 4:1, and so if we're just gonna handwave and say this is achievable here, we'll end up with an engine that weighs around 67 tonnes. This leaves 23 tonnes for payload, structure, and propellant tanks. If you double the amount of propellant then you cut your acceleration in half. If you double your thrust to accommodate this, you use up your propellant twice as fast, and you're right back where you started. You can't exactly "lighten the ships mass" when your engine and propellant alone are 87% of the ship's laden mass. And if you're trying to accelerate at 3 gees the entire time...that makes no sense. Engines don't produce acceleration; they produce thrust. As your mass goes down, your acceleration will go up. So space is accelerating past you, but you're not gaining kinetic energy? Ok, let's imagine that. If you have this, you don't need 70 minutes of whatever wacky acceleration you're imagining. I'm assuming you can't activate this impulse warp in atmosphere? So you just need about 2 km/s to get out of the atmosphere and point in the desired direction, and then engage impulse warp. At three gees of acceleration, that's going to be a burn time of just about 68 seconds, and you're going to only need a fuel to dry mass ratio of about 1:1. The problem is this: when you drop out of warp, you said you have the "actual velocity and momentum vecotor [sic]" from the beginning. But actual velocity relative to what? Relative to your home planet? Relative to your destination? Earth is moving at 30 km/s around the sun. If I point my vehicle toward Jupiter and warp toward it at 3 gees, then drop out of warp near Jupiter, I'm going to be outpacing Jupiter by a whopping 7 km/s. And that's if Jupiter is perfectly lined up with Earth so that our velocity vectors are pointing in the same direction. If our velocity vectors are pointing in different directions, it gets even worse. Why? Why would multiple nozzles be any different from a single nozzle? In terms of thrust and heat, this makes no sense at all. Increasing the number of engines doesn't make it less efficient. It increases your dry mass but the specific impulse isn't going to change. Please just learn the rocket equation.
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