K^2

We don't have the resources to replace power production with non fossils in foreseeable future. We don't have infrastructure or readily available fuels for nuclear. Solar would require a huge investment. It takes several years for a single panel to generate enough electricity to cover energy used in production. We can't make that investment upfront right now. And other renewables are nowhere sufficient. We can, and should, reduce our dependency on fossils, we should look into ways to reduce CO2 emissions from existing plants, and we should convert our transit to electricity as much as possible, as that is more efficient. But peak CO2 production is still decades away, I'm afraid. And that's just peak production. Peak levels are easily over a century in the future. If CO2 levels are as big of a problem as some research suggests, we are royally screwed. I'm inclined to think that anthropogenic impact is overestimated, but even then, we're in bad state. We will need to figure out how to bind CO2, rather than only trying to reduce production. And not only at power plants. That Sahara place looks like it'd make a nice garden with a bit of work.

There aren't a lot of options. Batteries won't last that long. Solar isn't available. The only power source we have that will work on Venus and isn't technically a heat machine is a fuel cell. But that still has all the same problems. It needs to operate in a certain temperature range and produces considerable waste heat that you have to get rid of.

Gravity is proportional to energy, not mass. So it compensates itself. As I've mentioned above, speed of light isn't really a variable. Just a conversion factor. No. There simply aren't any paths that lead out of the black hole. Going in any direction leads you back into black hole. That's how it traps light.

Standard Model effectively says that even if tachyons exist, they don't interact with normal matter. At which point, does anyone even cares?

Speed of light variations would absorb into metric, which varies already. Since metric is the thing we actually care about, speed of light is effectively constant. It's just a local conversion factor between time-ward and space-ward directions.

If you keep TWR constant during burn, rather than total thrust, optimal takeoff has to be time-mirrored copy of optimal landing. So even in more realistic case, you do expect strategies to be similar, if not the same. But it's kind of hard for me to insist on that without having formal proof of optimal solution here. Constructing such proof looks to be a mess, however. For starters, you are trying to optimize fuel consumption while consuming it at a constant rate. And your destination isn't a point in space, but rather a state. That suggests that what we want to do is find the shortest path in the E x L space, since energy and angular momentum fully determine the desired orbit. However, dE/dt will depend on current velocity and dL/dt will determine on current altitude. That's in addition to thrust direction, which is what we want to optimize. And velocity and altitude on given orbit will depend on mean anomaly. Additionally, we have a restriction that altitude can't drop bellow surface elevation. Zero vertical velocity ascent implies T = t, which means mean anomaly always stays zero. (It jumps to 2 pi past circularization.) That has the right feel to it, but I can't think of a simple way to prove that it's the answer, and I'm afraid to even sit down and write out all of the formulae to do this properly. Edit: Do you have a proof that it's optimal strategy for ascent, Slashy? Again, it seems like it should be, but I'm interested in formal proof. I would be happy with first order optimal condition verified. Edit2: Actually, with above in mind, I definitely can do a check for first order optimal condition on this rigorously. That would prove that it's at least locally optimal, and that'd be a great start. (Except that altitude constraint is going to be a pain. Gah.)

That's just matching velocity at one point on trajectory. Instead, you maintain constant zero radial until you are on Hohmann. That's the same strategy as has been used for landings on many of the maximizing efficiency challenges. It beats suicide burn by a significant margin, even if the later is perfectly executed. And, needless to say, it's much easier to execute and much safer than a suicide burn. Hohmann or bi-elliptical are clearly optimal under infinite TWR limit. But under finite TWR, getting to that initial Hohmann is a non-trivial optimization problem. I'm just wondering if anyone managed to actually solve it.

Has it been proven that zero vertical velocity landing/takeoff are optimal efficiency? I know all empirical tests point that way, but I'm wondering if anyone managed to confirm it with equations.

I'd totally go. I mean, I think I'd prefer to walk on Martian surface, but flying a blimp on Venus? Sign me up!

Very apt description, because it is exactly like pulling yourself up by bootstraps. It's the same reason why you can't put a windmill on an airplane to help power the engines. In principle, you could have a Bussard ramjet in there. That at least doesn't have you going against conservation laws. But these things also tend to generate far more drag than thrust. Your best bet is still avoiding interaction. Cloaking the ship in the blind spot of the bubble is the best option for that. But that would require a very creative warp bubble geometry.

I wouldn't say it's not known. The trajectories in Alcubierre Metric are well studied. We know that under Alcubierre drive, the ship will be in a lot of trouble. There will be gamma radiation due to blue shift. Gamma bursts from various impacts, and there are trajectories for encountered matter through the ship. Nothing can take that sort of beating. What isn't known is whether there can be something done about it. Alcubierre Metric is the simplest, most studied warp metric. But the possibilities are limitless. It might be possible to arrange the gravitational fields in a way that leaves the ship in a "blind spot". That way, neither radiation nor matter are a problem to the ship. The problem with causing radiation damage to whatever's at destination is trickier. Matter can't move faster than light with respect to ship while in the bubble. So fundamentally, anything that gets into the bubble has to be dragged along. That guarantees a shower of gamma radiation from the edges. But there might be ways to minimize the effect and to try and direct it in a predictable way so as to avoid damaging anything. The article talks about Alcubierre Drive. Reading an article, rather than just looking at pictures, usually helps.

Erm... Why not simply set up a custom board, something like Simple Machines Forum, on a free/cheap hosting site?

It, typically, won't let go of that energy all in one go. There are usually several levels with lower energy bellow that one. In that case, instead of emitting one photon with all that energy, it will emit several with less energy. This will keep happening until energy levels are low enough to start exciting molecular or atomic vibrations. At that point, that energy is just heat.

I'm having some technical difficulties with my PC. That's setting me back with some work. I don't think there's any risk of me going completely dark, but I might be a bit useless for a few days.

That SM mass includes over 7T of propellant. It's a touch over 13T total empty. So you could either dump some fuel or use it for a boost. Either way, you can get to TLI on a Heavy.

Lets start with the fact that that guy is saying horribly wrong things. Brick is made up of minerals, most of which are transparent in their crystalline form. In fact, most everything is at least somewhat transparent as a crystal. Or as a liquid. Or as a gas. It takes some effort to make something with homogeneous structure opaque. And the reason for that sort of goes back to your question. If photon has too much energy, it can't be absorbed either. Glass is basically opaque in infrared, for example. You'd think if visible light has not enough energy to excite electrons in glass, IR wouldn't have a chance. But there are levels there that can be excited. Visible light simply has too much energy. So there are really two ways that something can be opaque. Absorption is one of them, but material has to absorb across a broad range. A lot of organic materials with complex molecules do that. Metals also do that, because they have entire bands of energy levels accessible to electrons. But most non-conducting crystals do not. They might have absorption in a specific band of visible light, giving them a color, but they are still mostly transparent. The second way is with refraction and diffraction of light. That's the real reason why bricks are not transparent. It's the reason sand isn't transparent. It's the reason that snow and crushed glass are not transparent. If you have a tiny little crystal of transparent material, instead of simply letting light through, it will be diffusing light. Take a lot of these together, and light simply cannot propagate in a straight line. What little light gets to the other side by random chance has to travel a much, much longer distance to get there, which means there are far more chances to get absorbed by some impurity. As a result, material is opaque.

Really, really, really needs pictures. Even if they are just hand-drawn diagrams.

Falcon Heavy ought to be capable of setting it up for a free-return fly-by, and it will be ready long before SLS, so it seems worth considering.

These are very important factors in aircraft design, but you also have a lot more tools for dealing with them. For starters, these things don't have to align quite as well as they do in KSP. You still want CoM ahead of your wing CoP for stable flight. But the trick is that the airplane's horizontal stabilizers provide negative lift. So as the airplane speeds up, they push the tail down, balancing against airplane's CoM. In addition to that, you have trim tabs, which allows you to adjust how much negative lift you get with neutral input. These things are in KSP, but because aerodynamics is so much simplified, they don't work quite right. Specifically, you have one, fixed CoP. On a real aircraft, CoP shifts dynamically. That means that KSP aircraft have a very narrow envelope. CoM can only be a hair ahead of CoP, and CoT has to be on the same line. For a real airplane, CoM has an envelope of good locations. You do still have to check to make sure that CoM is within the envelope. (weight and balance) But it's far, far more forgiving than KSP.

KSP rocket engines have TWR way bellow that of real world engines. Tank useful weight fraction is also different. So is aerodynamics. You'd need to install a lot of mods before comparison is half reasonable. Simply replacing Kerbin with Earth and running everything else vanilla would make for a far less efficient SSTO than would be in real life.

Eh. Plane launches aren't terribly useful. Not enough starting velocity to really bother with. But if you replace plane with a good rocket stage, then we're cooking with gas. But yeah, either way, that's the idea. But description I was replying to makes it sound like they want to use something like Dragon as final stage, with first and second stages being reusable. And that sounds silly to me.

In order to pass through intact, it has to be neutron matter or denser.

There won't be a gas to liquid transfer. Hydrogen's critical point is 32K. Meaning, above 32K, there is no fluid to gas transition. As you increase pressure, the supercritical hydrogen simply gets denser and denser. Helium's critical point is even lower. I don't recall what the rule for critical point of mixtures is, but either way, Jupiter's atmo seems way supercritical. The first real phase transition you should hit, with a definitive boundary, is hydrogen to metallic hydrogen. Here, things start to get murky. I've seen a lot of contradicting predictions for properties of metallic hydrogen. They range from ordinary fluid, to superfluid, to supersolid, to ordinary solid. All that anyone really agrees on is that metallic hydrogen is wickedly weird. If it is, indeed, a fluid of some kind or a supersolid, the probe will keep sinking. In fact, in superfluid or supersolid it will be almost dropping as it would encounter a very sudden reduction in viscosity. If you keep sinking through metallic hydrogen, eventually you will hit a solid core. The outer layer will most likely be solid helium. Bellow it, there is likely to be a rocky core as well. But that layer of solid helium is likely to be the first definitive "surface" of Jupiter.

They aren't exactly orbiting. Quantum Mechanics, etc. And the angular momentum of the ground state of hydrogen is already zero. So they are already "stopped". Or rather, as still as they are going to be. Good Wikipedia article to start with.

They might have some contamination concerns. It's also not exactly light. But a proof of concept could have been done.