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sevenperforce

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Everything posted by sevenperforce

  1. Curious...if they were designing JWST today, what approach would they use for robotic refueling? Something like Progress?
  2. A little something for the holiday…. And this is if it doesn’t load
  3. “The hopes and fears of all the years are met in thee tonight.”
  4. I was paraphrasing from memory. I looked it up and the actual exchange is even funnier.
  5. No, it's not that at all -- it's how you discredit an expert witness, as an attorney. Expert witnesses are annoying because they are able to give opinion testimony based on evidence that wouldn't otherwise be admissible. So if you can discredit an expert by showing that they don't know what they are talking about, you can make the jury (or the judge, in this case) disregard their opinions. In this situation, Behe created his "one chance in 1017" opinion based on completely nonsensical parameters. The attorney cannot just stand there and say "You're wrong and here's why" because attorneys are not allowed to testify; they are only allowed to ask questions. So, as an attorney, you have to lead the witness by the nose, one question at a time, until he discredits himself.
  6. But those extremophiles didn't evolve independently of the rest of Earth's ecosystem. The question is whether Mars ever hosted life that was complex and diverse enough to produce the selection pressure required to create extremophiles. Speaking of extremophiles in rock, I'm reminded with amusement of the moment in one of the ID cases (I think it was Kitzmiller) where Michael Behe gave "expert" testimony about the probability of a particular evolutionary pathway in bacteria happening even once in a billion years being something along the lines of 1:1017. The cross-examining attorney said, "You are aware, aren't you, that there are approximately 4 billion bacteria in a single teaspoon of soil, are you not?" Behe answered, "Yes." The attorney said, "And there are about a million teaspoons in a cubic meter of soil, isn't that correct?" Behe nodded. The attorney said, "Okay, so if my math is correct, you would need about 20 cubic meters of soil to have approximately 1017 bacteria, isn't that right?" Behe said, "Yes, that sounds right." The attorney then asked, "And it is generally accepted that there are more than 20 cubic meters of soil on the planet, isn't that correct?"
  7. A good comparison would be between Skylon as a suborbital first stage and something like RocketLab's new Neutron design. One difference between the SABRE engine and other airbreathing engines, like the SR-71's Pratt & Whitney J58 (a combined-cycle turbojet and afterburning ramjet) and the engines on the X-43, X-51, and HAWB (scramjets) is that SABRE is not an inlet-based jet engine at all. It is, fundamentally, a rocket engine. In airbreathing mode, it uses a separate compressor and precooler to inject supercooled air into the rocket engine chamber at 141 bar. This is very different from a turbojet, where the pressure in the combustion chamber is less than 25 bar for jet fighter engines and no greater than 40 bar for the very highest-performing engines like the J58. Scramjet engines have even lower combustion pressures, since high compression ratios slow down the airflow due to Bernoulli's principle, and scramjet engines need supersonic combustion in order to function. Because combustion pressure (to a first order) scales with T/W ratio, this means the SABRE produces much more thrust for its weight than something like a J58 or an F119, and vastly more thrust than a scramjet engine. It also means that operating in pure rocket mode is straightforward; simply close the inlet, stop injecting supercooled air, and start injecting liquid oxygen instead. However, because it is a rocket engine, it produces a rocket plume. And because it is a rocket engine designed to operate at sea level, it is significantly underexpanded at altitude. This is a problem. A 2015 NASA study found that operating the Skylon design in pure rocket mode would result in what the study termed an "adverse thermal environment" for the back end of the vehicle: As you might imagine, "adverse thermal environment" is a clever euphemism for "barbecue" as it relates to the back end of the plane. So if you were going to compare Skylon to Neutron, you should limit it to its maximum airbreathing velocity of around Mach 5.4. This makes the design a lot simpler, because it doesn't have to carry any liquid oxygen at all. It takes off horizontally, accelerates at a moderate ascent angle, and then pitches up during the final acceleration phase in order to achieve a suborbital trajectory. Let us suppose that once outside of most of the atmosphere, it opens its payload bay and releases the same upper stage that Neutron uses. Thus, the question becomes: what's more cost-efficient? Should we fly that expendable upper stage with Neutron or should we fly it with Skyon? I suspect (although I do not know for sure) that Neutron, if it works as advertised, is going to be substantially more cost-efficient than Skylon would. [T]he precooler’s helium cooling system dumps heat into the hydrogen fuel in air-breathing mode so other fuels wouldn’t really work for that. Hydrogen is also very light and has a higher specific impulse. Don't write methane off completely. Hydrogen has a much better heat capacity than methane, but methane is MUCH more dense. An airbreathing methane-based SABRE engine isn't entirely impossible, especially if the use of hydrogen is unnecessary since you never need that high specific impulse to push into orbit. Plus, liquid methane is more easily stored in wings. If you're going to be getting to any sort of useful suborbital velocities, you will need the full cooling capacity of SABRE.
  8. Please no kablooey. This would be as disappointing as when Starship Mk1 had its oopsie (and far more of a setback).
  9. Ah, yes. The "aliveness test" needs to be completed. Also known as the "poke it and see if it jumps" test.
  10. All of these questions, @Spacescifi, sound a little like asking, “If people could fly like Superman, how high could they fly if they only ate cereal?” There is so much undefined about this question that it is not only impossible to answer, but there is no set of assumptions or other ideas which can be adopted to make the question make sense. The problem is not that the question invokes a fictional character with fictional abilities; that’s fine. The problem is that it attempts to connect physical reality to that fiction in a way that doesn’t make sense. If people could fly like Superman, then they would have the flight powers of Superman; there is nothing in either the fictional DC Comics world or the physical world where a cereal diet has a relationship to maximum altitude. It’s just undefined, like dividing by zero or trying to find the last digit of pi. If you want to write a story with a spaceship, that’s great. But let the plot dictate what your spaceship needs to do, not the other way around.
  11. VASMIR doesn't throttle its thrust so much as it has the ability to shift gears. It can produce high thrust with low specific impulse or low thrust with high specific impulse. VASMIR is not the only engine that can do this. Even the F-1 engine on the Saturn V could adjust its mixture ratio in flight, using more oxidizer at launch for greater thrust and less near the end of the burn for greater specific impulse. That (along with a larger Descent Engine nozzle) is how they were able to add enough dV to send rovers to the moon without adding any fuel. Certain nuclear thermal rocket designs do this as well, pumping liquid oxygen into the nozzle to add thrust but decrease propellant velocity. There isn't one. Not because engines can't "shift gears" but because what you're describing is a physics-breaking monstrosity which cannot exist. Something which cannot exist cannot have properties subject to probing by the laws of physics. Not to be pedantic, but you haven't really designed anything. You've simply stated a series of specifications which cannot all be simultaneously true. What course corrections do you need? No one needs multiple hours of one-gee thrusting for course corrections. If your story needs abrupt course corrections then simply have it carry a little more propellant. No one is going to be adding up how much propellant you have used. What you have described is nothing like a scifi classic SSTO, so I'm not sure why you would apply its properties to SSTOs. No, they would have the same power to mass requirements. Clustering is key.
  12. Well, 99.99% efficiency would be 0.01% waste heat. But there is a thermodynamic limit to the maximum efficiency of a magnetohydrodynamic thruster, somewhere around 87% even with superconductors. So you're not getting rid of that heat. In any event, what you are describing is not a magnetohydrodynamic thruster at all, anymore. You just have a pure fusion rocket, with liquid hydrogen going in one side and disassociated deuterium plasma coming out the other side. Sufficient inertial confinement for proton-proton fusion is something that even a star struggles to accomplish (the mean time for any proton to undergo fusion with another proton in our sun is on the order of 9 billion years). In a vertical-takeoff ascent, the thrust line of the main engines will intersect the surface for somewhere between 90-150 seconds. Let's say 100 seconds. In that time, the plume will dump approximately ten megatons TNT equivalent into the surface of the Earth, and it will do so using relativistic particles. If this occurs over the ocean, it will vaporize 4.7e9 kilograms of water (that's based on enthalpy of vaporization; heat capacity is a rounding error at this point), producing a superheated steam explosion approximately 35 kilometers in diameter. This is not an SSTO. This is a super fusion torchship which can leave Earth, fly to Pluto, land, and come back to Earth on a single tank of fuel. This is not part of any SSTO class of vehicles. With exhaust traveling at 0.3% of the speed of light, I would say you should be at least as far away as the moon before you point your engine toward Earth.
  13. Yes, thrusting for one hour at three gees or for three hours at one gee produce the same total impulse. I was not saying that those were different examples. I was saying that those two (equivalent) examples were completely different, separate, and dissimilar from your first example, where your spaceship burns 10% of its mass as propellant to reach LEO. If you have a vehicle which can thrust for an hour at three gees, then it doesn't need to burn 10% of its mass as propellant to reach LEO. Reaching LEO would burn less than 1% of its mass. Well, here you may be right. An Arleigh Burke-class navy destroyer has a minimum displacement of around 7000 tonnes. In the example you've given, where the main engine delivers three gees of acceleration, you're looking at a thrust of 206 meganewtons. At a specific impulse of 105,100 seconds, the mass flow is approximately 200 kilograms per second. That might not seem like much, but if these 200 kilograms are accelerated to 0.3% the speed of light, that's a power rating of 1.06e11 kW. Not only is this the minimum power requirement of your engine (we'll get to that in a second), but more importantly it's the amount of energy in the engine plume. That is the equivalent of about 7 Hiroshima-sized nuclear bombs exploding every second. At this exhaust speed, the plasma plume doesn't even notice the atmosphere as it effortlessly excavates away the Earth's crust, leaving a time-zone-wide supervolcano at the launch site. Let's talk about the engine energy requirements. VASMIR has a peak efficiency of about 73%, although conceivably a super-advanced model could reach a peak efficiency of around 87%. That should be approximately the physical limit. That means the engine will produce 1.6e10 kW of waste heat. With only 200 kilograms of propellant being expended per second, there's nowhere for that heat to go and no way to regeneratively cool the engine. Let's assume this navy destroyer spaceship has a surface area of around 8,300 square meters, just like the USS Cole. The spaceship will heat up until each square meter is radiating 1,927 kilowatts of heat. Assuming that the exterior surface is a perfect blackbody and ignoring the atmosphere, the average temperature of the spaceship will be 4,124 K or approximately 3850 degrees Celsius. That is significantly higher than the melting point of tungsten as well as the boiling point of steel. And that engine? This "energy source" will need to come up with a way to produce 2.2e11 kW. Envisioning such an energy source will be left as an exercise for the reader. However, note that if pure fusion were used as the energy source, this would require the continuous fusion of approximately 350 kilograms of hydrogen per second. At least we don't have to worry about having enough propellant.
  14. Do you know what "air friction" and "electrodes" and "regenerative cooling" are? Because it doesn't seem like you do. What you are describing has absolutely nothing in common with VASIMR (not "vasmir"). What you are describing is a torchship. First of all, the total weight of your proposed ship is ABSOLUTELY irrelevant. It doesn't matter. If you have a source of energy like the one you're describing, you could launch a spaceship that was 10 tonnes or 100 tonnes or 1,000 tonnes or 10,000 tonnes or 100,000 tonnes. Everything is scaleable. Saying "enough density and speed that it can launch navy destroyer weight" is meaningless, because it doesn't matter how big your payload is. If you want a bigger payload, cluster more engines. Everything scales. In your first example, where your vehicle can reach LEO from Earth's surface in a single stage while expending only 10% of its mass as propellant, you will need an engine with a specific impulse of roughly 9,200 seconds and a T/W ratio that is large enough to get off the ground. Such an engine would have nothing in common with any engine that actually exists or has been proposed. In your second example, where your vehicle is capable of going for 1 hour at 3 gees of acceleration or 3 hours at 1 gee of acceleration, it will have developed a whopping 105,498 m/s of dV. This is not a torchship; this is a blowtorchship. It is as different from your first example as an SR-71 is from a V-1 buzz bomb. Using the same mass ratios you described before, we would be looking at a specific impulse of approximately 105,100 seconds, or roughly 0.3% of the speed of light. You would need continuously evaporating Planck black holes wrapped in small, frangible moons to achieve that kind of thrust and impulse for even five minutes, let alone hours. I feel like I've said this before, but let me say it again, @Spacescifi. If you want to have spaceships that do a thing, say that they do the thing. Don't try to make the science work because it won't. Call it warp drive or slipstream or temporal displacement or whatever else you want to call it, but don't try to make science do something it doesn't want to do.
  15. I have a **very** cheap telescope, but it does have a handful of swap-out lenses, inverters, and the like. I am able to resolve the rings of Saturn and the moons of Jupiter, and I can make out Mars as a fuzzy disc and Venus as a crescent (at least, during its crescent phase). And of course I can resolve practically any lunar crater in shimmering glory. It is my understanding that as telescopes go, there is a fairly substantial jump in price between something like this, and something that can resolve galaxies and nebulae. So I would say, either get a really good cheap telescope, or a really cheap good telescope. Literally everything in your answer is what I was about to say.
  16. I think @sevenperforce meant that the gap in cost between SRB and liquid is much smaller IRL than in KSP. Not that solids are necessarily more expensive. I'm pretty sure it's still cheaper to build a solid booster than a liquid one for the same thrust and total impulse. Yes, that's what I meant -- solids are more expensive comparatively than you would think from KSP, even though they are still a little cheaper than liquids. They're just not massively cheaper as depicted in KSP. Solids also have some unpleasant attributes, like the fact that you have to ship them from manufacture to launch site already filled with their propellant. Even though modern solids are very safe from accidental ignition, that's still a LOT of weight to carry around; liquid-fueled rocket stages are comparatively lightweight and so shipping isn't nearly as costly or challenging.
  17. Well, real-life solid rocket boosters are much more expensive in comparison to liquid alternatives than is suggested in KSP, so that's one big difference. But it all comes down to design choice. For example, the liftoff TWR of the Falcon family of rockets is already quite high, and so adding SRBs would result in increased complexity, higher stresses at MaxQ, and a higher staging velocity. And since the Falcon family prefers a lower staging velocity to allow recovery of the booster, solids don't make sense. For vehicles like Atlas V, Delta IV, or Vulcan, all of which use very high staging velocities and have overbuilt cores, solids are a good addition.
  18. I have a great deal of respect for Ethan, so I trust him, but I have not been able to independently verify the dubiosity (is that a word, or is it dubiousness??) of EPJC. That being said, Dr. White's prior...activities...leads me to treat everything he says with a grain of salt. This paper is at the very limits of my understanding of physics (despite my degree therein), but from what I was able to glean, they were able to establish a stable, non-spherically-symmetric negative energy distribution using the Casimir interaction and associated mechanisms. If that's true, that's awesome. And it would be fairly easy (relatively or relativistically speaking) to confirm superluminal signal transfer using such a system. This is not a "warp bubble" per se but if true, it's enough to say yes, this is something we can work with.
  19. So, I’m a little skeptical. This guy has been working on the Alcubierre metric for a while now, and so I’m not entirely sure this wasn’t what he was already looking for. But regardless, it’s a cool possibility. https://scifi.radio/2021/12/07/darpa-researchers-create-first-genuine-warp-bubble-by-accident/ Working with the Casimir force evidently caused the formation of stable positive and negative vacuum energy distributions, which would literally be a (tiny) warp bubble. I read the source article, which is peer-reviewed and offers a mechanism for testing, which is quite exciting. This isn’t a vanity journal, is it?
  20. Boy, I sure was wrong about the external engines not needing GSE for startup. Although I suppose I was right about the igniter being localized to the engine. The GSE provides press gas for startup but it doesn’t provide ignition.
  21. The V-2 was not a cruise missile; the V-2 was the first ballistic missile. The V-1 was a cruise missile. Cruise missiles are designed to fly on non-ballistic, powered trajectories, usually (but not always) using airbreathing engines. For the V-1, it was a pulsejet engine. It is possible to build an unguided cruise missile, although in practice it isn’t typically done; even the V-1 had a crude guidance system. A “missile” is anything with a physical target. In the era of seige warfare, the projectiles launched by ballistae and catapults were referred to as missiles. Even rocks and bricks thrown by an angry mob used to be referred to as a “hail of missiles” because a missile was anything thrown, launched, or propelled toward a target. A rocket, on the other hand, refers to a vehicle with a particular type of propulsion. Technically, a rocket is a subset of reaction engine, where a reaction engine is any engine which produces thrust by the expansion of a fluid from a high-pressure to a low-pressure region. Rockets usually add thermal energy to their working fluid while it is compressed, though they don’t necessarily need to (e.g., cold gas thrusters and water rockets). The term “rocket” is usually used to refer to a reaction engine which contains its working fluid within itself, as distinguished from reaction engines which compress and release ambient fluid (e.g. turbojet, pulsejet, ramjet, or a hydrojet). So a missile is something with a target; a rocket is something with a particular type of propulsion.
  22. I feel like there are some inefficiencies there, but since they are using only RTLS trajectory they will probably be more lofted generally.
  23. Agreed. One may argue private property is inherently theft, but that's beside the point. There are no guarantees in real estate. What happens if you buy two beachfront vacation properties (like this woman) and then something happens that makes people not want to ever rent in that area? That's the nature of investments: they carry risk. If you invest $100,000 in real estate believing it will be worth $500,000 in 20 years, and then 5 years later there's a flood and the entire property is ruined, insurance doesn't pay you the $500,000 you were hoping for; they reimburse you for the $100,000 you put into it (and probably a little more for 5 years of appreciation). Same with eminent domain condemnation.
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