K^2

In LEO, you can pick up pretty decent supply of matter to use as reaction mass in that manner. Even in interplanetary space, solar wind has enough intensity for this to outperform a solar sail, which relies on light pressure almost exclusively. Mind, the thrust obtained in this manner is still minuscule. This won't compete even with current generation of ion thrusters. But if you are limited purely by reaction mass, and your only other option is a light sail, this can do way, way better in theory. Whether it ever becomes practical is another question.

\thread. They seriously aren't designed for the same thing. It's like asking if a sedan is better than a minivan.

It looks steeper than it really is, because of the zoom lens, but yeah, it needs to be pretty steep. As Sarge said, it's a brick. It simply cannot match the glide slope of a typical airliner landing. To compensate, it uses its ludicrous approach speed to execute that final flare and kill all of the vertical speed just before it hits the ground. In short, if at first you don't succeed, landing Space Shuttles is not for you.

Of course not. They work for them. Latest example, daughter of izberkom official committing vehicular manslaughter, getting suspended sentence, and then an amnesty for the 70 year anniversary of the V-Day. Hasn't spent a day in jail. Why? Because her mother is responsible for counting the votes of the politicians who have the power to appoint the judges who make the decision in the case. Corruption in Russian politics is so far gone, that you can't even compare it on the same merits. Bribery is just for the common folk now. Paying to avoid a fire/medical/tax inspection, paying to get out of a ticket, paying to get ahead of the line in the clinic. That sort of thing. Politicians don't need to bribe anyone. They wire money directly from budget to their accounts and they appoint judges. Why would they ever need to bribe anyone. But that's still corruption. And it's corruption that's unheard of in the Western world. And so long as people like you keep covering for them, it'll keep getting worse. Rockets will keep falling. Clinics will keep closing. And city officials will keep getting away with manslaughter on the regular basis. There are ultimately just two problems, as you are well aware, and you're demonstrating that you're part of the one that can't be fixed with a bit of asphalt. But hey, at least you're in the majority.

Next Soyuz flight was supposed to take some celebrity along, but that got pushed back. So, you know, we're at least getting a little bit of that. People just aren't hyped up about space enough lately.

Just to try and clarify a little, forcing gyro to precess faster is like applying a torque to a regular rigid object. It can use that torque to lift itself on a support (pivot), but it's the reaction force from the pivot that's doing the lifting.

A bit, but not too complicated. It's a standard cubic spline, keyed from values and slopes. The slopes are computed by taking average from the two neighbors. Just in case anyone is curious.

That's problematic. I could see binding oxygen into a matrix that would keep it at higher pressure, potentially sufficient to maintain metastability, but I'm having trouble picturing this even as an SRB. If you make matrix out of your fuel, under these conditions, it's going to instantly react. If you use a buffer, it's hard to make it not to eat up too much of your ISP.

What makes you think that red oxygen is metastable? Seems to me, if it was metastable under standard conditions, we'd be using it for something. It's not impossible to produce, even if production in large quantities is prohibitively expensive right now.

You are thinking of Universal Constructor (UC) teleportation. The UC disassembles you at source and reassembles you at destination. StarTrek employs UC teleportation, which is heavily exploited throughout the series. This is definitely one of these, "I'd rather walk," scenarios. Quantum Teleportation involves actually transporting matter state. It fundamentally precludes existence of copies. Your state is transferred whole from source matter to destination matter. By every sensible definition of teleportation, including these involving locality limits, QT is actually non-lethal. Unfortunately, QT has some very severe limitations which mean that we almost certainly never will have practical QT for macroscopic objects. The list of problems is lengthy and technical, so I won't get into details unless someone challenges this, but serious, QT isn't happening. That's not to say that it's useless, because there are a whole bunch of quantum information applications for QT. The only type of teleport system that's both feasible in some distant future and that I'd consider a "safe way to travel," in that you actually travel rather than being killed and cloned, is similar to what's used in Stargate franchise. They have a lot of technobabble around it, but the ghist of it is that rather than being disassembled whole, you step through an surface where you are converted into a digital form. The digital space is fully simulated until you are fully within. In the series, they refer to it as the buffer. What that means is that if you are standing half way through the portal, half of you keeps existing in the physical form, and half of you is simulated within the buffer, still allowing connection between neurons, blood flow, etc. So in effect, there is never a point where you are copied whole, but rather there is a gradual transition preserving continuity. That is, until you are fully within the buffer. At that point, your simulation is paused, and data is copied from source gate to destination gate. At the destination end, the reverse process takes place. There is an additional bit within the canon about both matter and data for reconstruction being sent along a wormhole formed between two gates, but that's not particularly relevant. The above scheme is the only practical UC-type teleportation that I'd find acceptable. In addition, the fact that the interface between physical world and the buffer is 2D, it actually makes the conversion process feasible without having to resort to something like freezing the subject. All in all, the only practical teleporter I am aware of that doesn't kill the subject.

I wouldn't classify it as the "only problem," but it's the biggest one, yeah. But as I've indicated, for "very short" interstellar hauls, it's still within capability of existing materials.

Theoretically, based on some estimates I've seen for a magnetic nozzle. I have not looked at these numbers too closely, but there is nothing fantastic about it, other than field strength and fuel itself. The 0.25 c/g I've mentioned earlier, or about 7.5Ms, you can get without doing anything fancy.

ISP in US Engineering convention is defined as mean exhaust over g, hence being related to c/g for photon drives. And units work out. (m/s) / (m/s²) = s. You can think of ee' and μμ' production as consequence of intense gamma radation. (It's a bit more complicated than that.) Which is why you can get the aforementioned 0.6 c/g rather than just 0.5 c/g. I've heard claims of going even higher, but at this point we're firmly in sci-fi territory.

"Fantasize" is a better action noun here. Nope. Never. Not under any circumstance. Do you understand what you just said? How about you write down an equation for it. No? That's because you're putting together words you don't understand into a sentence you think has meaning. It doesn't. Again, "guessing" is a better word here. You have absolutely no basis for that claim, because in order to see that there is a problem in physics, you first need to understand a little bit of it. Putting together meaningless sentences with words you've heard somewhere is not the same thing.

Any actual scientist will tell you that what you need is a good solvent for the given temperature range. At 300K of typical Earth life, you need pretty strong bonds in things like DNA and complex proteins to hold them together against thermal excitations. And to break these apart, you need a strong, polar solvent. Water is by far the best option, and the only available one that's naturally abundant. So at terrestrial temperature ranges, life means water. In contrast, if you are at less than 100K, such as on Titan, hydrogen bonds are frozen solid. Your complex molecules will be held together by van der Waals forces. A polar solvent would ript that stuff to shreds, and no life would be possible. Fortunately, there are non-polar solvents, such as liquid methane. So if we are talking cryogenic life, life means liquid methane. And that makes Titan a perfect place to look for cryogenic life. Granted, life at high temperatures has huge number of advantages. There are more potential energy sources, all of the processes are faster, and you can dump excess entropy way easier. Which means life will be more complex and far further evolved on Earth than it could ever be on Titan. I would not expect anything past simplest bacteria there. Something similar to Earth's Archaea. So finding life on Titan would tell us two things. First, that our definition of "habitable" is a bit too narrow. Second, that two planets within a single star system have developed completely different life independently. And while former has very limited impact, because planets/moons like Titan are unlikely to ever produce complex life, that second statement is extremely powerful. We live on Earth. Which means odds of us finding life on Earth are 100% ab initio. There is no way any species could ever find itself in a barren star system. Which means that us knowing that there is a habitable planet here is absolutely useless. Even if there is just one in all of the universe, we'd be on it. But two planets? Odds there being very few habitable planets out there, yet there being two, so vastly different, in our star system are minimal. If we find life on Mars or Europa, we'd still have to figure out if it had the same origin as life on Earth. For all we know, it did. Panspermia isn't very appealing on global scale, but within confines of a single star system, it's quite plausible. But if we find life on Titan, we know it didn't come from Earth. We know it's not contamination from one of the probes. Life on Titan cannot exist in water, and life from Earth cannot exist on Titan. Simple as. If we find life on Titan, that's two data points from which we extrapolate a very simple fact. When you look up into the sky and look at the stars, more of the stars you see probably have life than don't. There is nothing we can find on Mars or Europa that would be anywhere close to this impact.

Well, that was uncalled for. So is <insert pretty much anything in the Solar system.> The only reason Europa is getting funding is because of the possible life hype. Which is overblown. A lander designed to check for life on Titan can be made on the same budget.

Ugh. Why? What'd we forget on Europa? So we can send a lander there. So we can have it scrape some ice off the surface. There isn't anything close to living anywhere close to the surface. Even if something lives deep inside, which is a pretty big if, and if it occasionally gets ejected with a geyser, and even if we get a lander near one of these geysers, and if we manage to scrape off some ice that came from that geyser, we'd still just find some organic sludge at best, which we wouldn't be able to confirm as life. Waste. Of. Time. Especially, when we can be planning a Titan mission. That is the only body in Solar system where we might find some life on the surface. Life that's radically different from our own, I might add. If we find nothing on Titan, there's really nothing there. That's actual data. Plus, we can look for whatever manages to catalyze acetylene at these rates. But if the acetylene is being eaten by a life form, we will find it. And it will be entirely different from life on Earth, requiring us to drastically expand what we believe to be habitable zone. Even if we find life on Mars or even Europa, it'd likely be life similar to our own. We wouldn't even be able to tell right away if it shares origin with our own. But look at how long we've been looking at Mars, and we still have no confirmation one way or another. Best we've got is, "There was probably life there at some point." With Europa, we won't have even that. In contrast, on Titan, we'll either find something or not. A single mission could either be a very important piece of data, or the most important discovery in history of science. Sending a lander to Europa rather than Titan is just stupid. The hype that Europa is getting is absolutely unwarranted.

Do you know any programming?

Yeah, essentially. Given some thrust profile T(t) and specific impulse I(t), the mass flow rate is given by m'(t) = -T(t)/I(t), while dV is accumulated at the rate V'(t) = T(t)/m(t). So if you know thrust and ISP as a function of time, you can simply take an integral from liftoff to orbit and obtain the dV budget. Of course, by this point, you've solved the problem for which you're trying to get dV in the first place. You essentially need to know the entire trajectory and how much fuel you're burning at every moment of time. In other words, what you really need to do is solve for ascent profile. And that's an even more complicated task, which typically involves considerable numerical skills. For a planet without the atmosphere, good ascent profiles are pretty well known. They involve constant-altitude burn until you attain orbital speed, proceeding to prograde burn until you attain transfer speed to desired orbit. From there, it's identical to Hohmann. The actual dV budget still depends a LOT on TWR, but at least, it's a simple enough thing to compute for a given TWR. Once you throw in atmosphere, this becomes an almost impossibly complex problem to get a perfect answer for. You can get a good ascent profile, though, which is typically all you care about. Only for rough approximations. This isn't something you can put into a formula.

You come up with an ascent profile and integrate thrust over it. There is no simple shortcut here. There are some ways to get rough estimates, but no such thing as a formula for it.

Yeah, when somebody accuses you of making up numbers, stand strong, and keep making up numbers as a rebuttal. What can possibly go wrong when you're ignorantly arguing about matter-antimatter rocket with a particle physicist? Even taking into consideration the lepton production, with bulk of losses caused by μμ' production, you can still get almost 99% of the impulse. In other words, ISP is still closer to .25 c/g than .24 c/g. ee' and μμ' production is also the reason that you really can get up to 0.6 c/g using superconductor magnets. This isn't fiction. It's simple, high school physics. Now, TWR in that scheme is going to absolutely suck given current technology, so what we have isn't practical for interstellar. But this is why I'm pointing out that we can probably get higher thrust in the future. But going back to simply having a led damper and a plasma injector, which is not just something we can build, but something we have built, the TWR is limited by your ability to absorb and radiate heat. Since we're looking at over 2 decades in transit anyhow, acceleration of 0.1m/s² is more than sufficient. That means we need to dissipate 30MW of power per 1kg of mass. At 3,000K, this is trivially accomplished by about 7m² of radiator surface. Tungsten wire with sufficient surface area will take up a tiny fraction of the mass. Similarly, led damper (in thin tungsten shell - molten led is just as good at absorbing radiation) has constant thickness regardless of thrust, so it does not really add to the payload. The only part of ship's construction that's going to eat into your useful payload is the anti-matter storage tanks. And that becomes less and less significant for larger ships. Long story short, there is absolutely nothing to prevent us from building an interstellar matter-antimatter powered ship with effective ISP very close to 0.25 c/g other than antimatter supply problem. But hey, I'm sure that won't stop you from making up more numbers to convince yourself that you're still right.

Not even reflecting. That .25 factor corresponds to just combining matter and antimatter next to a led damper plate. Exactly 1/4 of available impulse will be absorbed. You literally cannot do worse. There are a bunch of ways to do better. Edit: I lied. You can do slightly worse with a dumb pp' burner due to meson/lepton production. The ee' reaction is pure gamma, but bare positrons are hard to store. If you could keep positronium stable, that would be ultimate photon drive fuel. But wishing won't make it so. For existing tech, I'll do a proper check on worst case for anti-Hydrogen tomorrow. The fraction for heavy stuff won't be large, so it should not be a big deviation, but I feel like I owe you guys a number now.

PB666, where are you getting these numbers from? For a matter-antimatter drive, effective Isp is 0.25 c/g in the worst efficiency case. That is 4:1 fuel to payload to get to .2c and back. So 2kg of antimatter to 1kg payload. This is the worst it could be. That factor 10 sounds entirely made up. Which brings to question your ability to gauge other factors as well. For the record, realistically, we can get up to .5 c/g if we can get it to lase, perhaps higher with other trickery, and there are free braking alternatives, such as Bussard Ramjet. That brings fuel fraction down to 50%. And that is just tech we already have.

It's not so much an "outside perspective," as you need an inertial reference frame to consider energy changes. That's why Oberth effect is relevant when you take a massive body as the origin of your coordinate system, rather than the ship that orbits it. From perspective of another orbiting body, energy need not be conserved, as it is an accelerated frame of reference.

I still have fingers crossed for sub-light warp within a century. If we find a gravitomagnetic analog of superconductivity, it should be manageable. Totally useless for manned interstellar flight, but it'd get us buzzing about the Sol system, and probes could reach near destination stars in decades.