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sevenperforce

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Everything posted by sevenperforce

  1. It is grounded in stuff we can actually do, with a single exception, which is all of it. Your latest fixation seems to have drifted to "fusion pulse with large and thick bodied nozzle with uber magnetic fields". None of those things make sense in connection with each other. If you have the capacity to control nuclear fusion then just heat your propellant using nuclear fusion and use regenerative cooling on your nozzle; no need for magnetic fields or a "thick bodied nozzle" (whatever that is supposed to mean). I'm not sure why you would imagine that a fusion rocket engine delivering over 8,000 tonnes of thrust would have problems with air ENTERING the chamber. If your wingless vehicle can accelerate into orbit after yeeting off the end of a ramp, then its TWR was already greater than 1 to begin with, so the ramp and wheels were all unnecessary to begin with. No part of this makes sense. If it has no wings then it will fall vertically into the ground.
  2. If it's expendable, why would it need grid fins at all? That's why this whole notion just seems so silly -- it's like you're not thinking about the vehicle as an actual vehicle with actual meaningful parts. You're still going to need a fairing for whatever payload you're payloading. Even if the fairing is no longer than the one on Falcon 9 and only as wide as the rest of the vehicle, it's still going to have a mass of at least 5.7 tonnes. You're going to need a mechanism to open and close that fairing, but let's ignore that. You claim that the weight of the grid fins can be reduced by over 80% "using ceramics" but you give absolutely no explanation or citation for these magical featherweight ceramics; aerospace/industrial ceramic parts are typically closer to half the weight of equivalent metal parts. In the video @tater linked, Elon notes 58 tonnes worth of engines, 80 tonnes tank and structural mass, 20 tonnes for the interstage and grid fins and avionics, and roughly 20 tonnes of residuals after landing. So that would be 178 tonnes right there. Of course we're going up to 33 engines instead of 29 so that brings us up to 186 tonnes. Let's just hypothesize that they can use "ceramics" and other savings to shave 10 tonnes off the interstage and grid fins and avionics. You talked about going to 3mm steel instead of 4mm steel but that's only going to be for the tank walls themselves, not for structural mass. Let's say they can cut 10 tonnes off of tank mass. Add in the weight of the fairing and you're looking at 172 tonnes landed mass. You claim landing gear is 3%, which would be 5.2 tonnes, but I don't know how you're going to manage that; Falcon 9's four landing legs have a total mass of 2.4 tonnes for a vehicle with a dry mass of around 25 tonnes. So 10% would be closer to the right number. Let's be generous and put it at 6% (closer to your 3% number than to F9's 10% number) and peg the landing gear at 10.3 tonnes which takes us up to 182 tonnes. Let's pretend, somehow, that you could put TPS on the butt end and somehow prevent the engines from burning to slag. Then it can enter rear-first. It's absolutely not possible, but let's wave our hands and pretend it is. If Apollo was 15% let's give Superheavy a 10% landed mass margin. So that's 18.2 tonnes of TPS, bringing our landed mass up to 200 tonnes. I'll ignore the mass growth requirements on the landing gear, etc. So what, then, does the landing burn look like? We can assume that like Falcon 9, Superheavy will need to initiate its burn in the transonic regime, at around 310 m/s vertical speed. It needs to limit its hoverslam to around 3 gees to avoid damage; the landing burn will thus take at least 11 seconds (probably longer but we're being generous to your SSTO idea). That 11 seconds will be 108 m/s of gravity drag, so the total burn needs to be 418 m/s. At the sea level specific impulse of 330 seconds, that's 27.8 tonnes of landing propellant, bringing our re-entry mass to 228 tonnes. We will again ignore mass growth, here related to TPS. In space, you'll need roughly 100 m/s of dV to deorbit. We'll ignore ullage and maneuvering RCS and everything else like that. You'll benefit from the higher vacuum specific impulse, so that's nice; it'll cost you a little over 6 tonnes of propellant, bringing our effective dry mass up to 234 tonnes. So let's plug all this into Silverbird and see what it tells us now. This *is* a restartable stage so I checked yes for that box (starting engines uses extra props). I set residuals at 0% because we are already factoring them into dry mass, and I reduced propellant by the amount of propellant needed for deorbit, landing burn, and residuals. So yes. If you can find a way to magically keep the grid fins and butt end of Superheavy from melting to slag on re-entry with 18.2 tonnes of TPS, then you could convert it into a reusable SSTO that delivers ~97 tonnes of payload to LEO. How you plan to do that, or what 97-tonne payload you plan to launch in a 13x9 meter fairing, is anybody's guess.
  3. Probably not better in the sense of absolute resolution. Voyager 2 came within 4950 km of Neptune during its flyby, close enough for its Imagine Science System cameras to achieve 500 meter resolution. We are 19 AU away from Neptune; you would need a primary mirror 35% larger than the dwarf planet Ceres to match that resolution from Earth's location. Voyager 2 only came within 84,000 km of Uranus, so the resolution during that flyby was not as high as the Neptune flyby. Even so it's not much better; you would need a primary mirror just slightly smaller than Ceres to match that resolution from Earth's location. However, JWST can take more pictures of Uranus and Neptune, and it can take them over a longer period of time, and it can take them in a broader spectrum, allowing us to see deeper. We can monitor weather and identify cloud layers and all kinds of cool things.
  4. We will! JWST cannot image Earth, Venus, or Mercury because it needs to keep its mirror pointed away from the sun. But it will be able to image Mars and objects in the asteroid belt and all of the dwarf planets and all of the giant planets. It won't produce the highest-resolution photos of all time, mind you. Despite its sensitivity, its photos of Saturn won't be as good as the ones taken by Cassini and its photos of Jupiter won't be as good as the ones taken by Juno. But it will be able to probe into infrared which will tell us a lot more new things. This is the resolution with which Hubble sees Saturn: JWST can gather six times as much light.
  5. So you smear Apollo-era TPS all over it, add "landing gear", and...what? Watch it burn to slag as it plummets uncontrollably, tail-first into the atmosphere?
  6. I made this to show just how much detail we are seeing for the first time:
  7. Welllllll never mind about that "no visible shockwave" bit. So it does look like there was definitely a detonation wave. That being said, the massive gout of fire that followed suggests only a very minimal amount of fuel actually was involved in the detwave so hopefully that's a good sign.
  8. If there was a fuel-air detonation, it was a very small one. There was no visible shockwave, which is what you would expect to see from a proper stoichometric fuel-air detonation. My guess is a small fuel-air detonation near the vehicle followed by conflagration of fuel-rich preburner exhaust. If there was damage to the vehicle it would have been from the initial small detonation; the conflagration should be less of an issue. Delta IV Heavy lights itself on fire at launch, after all; I can't imagine a little gout of fire is any more dangerous of a regime to the booster than the expected re-entry conditions. The fire probably damaged GSE, though. My guess is that they'll need to replace a half-dozen engines and a few dozen GSE parts. I don't know why they would be running the fuel preburners without an overpressure notice. That seems dumb.
  9. How fast can you get a car moving on the runway? Here's the twist: you can't use powered wheels or reaction engines. You must build your drive wheels from structural parts and drive them with rotors. DLC will obviously be required. How fast can your vehicle go?
  10. Garbage in, garbage out. The "10% of dry mass estimate" is a garbage number so you get meaningless results. Absolutely meaningless. No, there isn't enough space on the back end to fit bigger engines. 33 is crowding it quite a bit already. Silverbird isn't going to factor in additional Isp losses from a poorly-optimized sea level nozzle.
  11. Mainly because of professional drivers I think. It might be because the graphic is showing fatalities per billion passenger-miles, not fatalities per billion miles. If a crowded bus has between 30 and 50 people on board then its passenger-miles number is multiplied dramatically in comparison to a passenger car that may only carry one or two people. Add to this the fact that most buses operate at relatively low speeds. Accidents may be every bit as common but actual fatalities are going to be extremely rare because you're just not traveling fast enough to have serious injuries. That's probably why the number is higher for trains; train accidents are more likely to kill you. Of course, so are plane accidents. But planes go much faster much faster than trains so the passenger-mile number will be skewed in their favor.
  12. Yeah, once the SRBs light up there is nothing you can do to stop them However, SLS does have a solid-fueled launch abort system which can pull the crew to safety if the launch fails. The Shuttle did not have this, and so any abort prior to SRB separation was LOCV.
  13. But not towards the nearby planet. Directly towards the nearby planet. The whole battle is taking place directly above the curve of a planet and all the ships have their "down" oriented planetward.
  14. I once used this approach to drop cluster bombs that floated down on chutes and launched fireworks at touchdown. That was cool. With the ability of the KAL-1000 to toggle same vehicle interaction on parts, I wonder if there is a way to use same vehicle interaction nondestructively, perhaps with a docking port on a hinge or something, to turn outside stimuli into KAL input. Can a docking port with same vehicle interaction enabled dock with a port on the same craft?
  15. One thing you can do with a KAL-1000 currently, which is pretty cool, is to use it to mimic the landing probes used by the LMs in the Apollo program. Put one KAL-1000 on the LM, loop it, and program it to set the landing engine thrust limiter to zero. Attach a piece with very low impact resistance, offset it so that it hits the ground before the landing legs, and then attach a second KAL to that piece. The second KAL is also looped but has higher priority and sets the landing engine thrust limiter to 100%. Have them both activate at staging. At touchdown, that piece will break, severing the connection with the second KAL and allowing the first KAL to take over and shut down the engine.
  16. The logic gates and the meta game are AMAZING. It's a shame the KAL can't accept inputs other than from the user, though. That would really make things exciting.
  17. A while back I used pistons, fireworks, and rotation servos with a KAL-1000 to make a fully automatic multi-burst-mode recoil-compensating rotating GAU-8 Avenger which I then mounted on an A-10 Warthog. Ammo is low unless you turn on infinite fuel. And while I was using KAL abuse to increase the projectile speed of the firework launcher for visual effect (and to actually be able to destroy buildings), that's not necessary to the design. I could have made the rear part of the fuselage shorter and put the Wheezleys inside of 1.875-m fairings to make it look more realistic. EDIT: Just like on the real A-10, the rotation ensures that the barrel which activates is always exactly centerline of the aircraft, which prevents the recoil from producing any yaw on the vehicle. It has 7 barrels just like the real GAU-8.
  18. UPDATE: I tried using RAPIERs but apparently they have a wildly offset center of mass and as a result it is impossible to put them in anything remotely resembling a stable flight configuration for a horizontal takeoff unless it's substantially longer. As ugly as it might be, there's actually no clipping, other than the clipping into the wing. All of the pieces are node-attached. The longest span is the air intakes and the small sized nosecones. This "plane" with the RAPIERs can of course be launched vertically to terrific effect but then it becomes more of a rocket, even with the RAPIERs in airbreathing mode. I've experimented with a few different launch profiles and the best speed I've gotten is 1562 m/s which at 2 meters in length gives a score of 781 body-lengths per second. Better than the Junos but not by as much as I expected. The trick with the RAPIERs is getting high enough to find reduced drag and not burn up but not so high that you run out of air before you've gotten to your top possible speed. I used infinite fuel for this run because I wanted to get a feel for what was possible. I could of course replicate readily enough without infinite fuel by using drop tanks.
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