K^2

"It is a big day today on Tau Ceti as humanity greets the interstellar probe launched from Earth almost a thousand years ago..."

Or practicality simply drops with distance faster than inverse R-square. That's certainly the case with conventional propulsion.

If anyone is wondering, the reason the image looks kind of fake-ish is because it uses morphs as means of interpolation between frames.

1. Your assertions are essentially correct. You just need to keep in mind that exhaust starts out having kinetic energy already. So in the extreme case of the ship moving faster than exhaust velocity, the exhaust is slowed down due to engine operation, and it's kinetic energy is reduced. That means the ship's kinetic energy gain can be higher than chemical energy available in burnt fuel. 2. Because kinetic energy is quadratic in velocity, it's easy to convince yourself with the help of Pythagoras' Theorem that Oberth effect for radial and normal burns is zero. Only pro/retrograde component of dV benefits from it.

Which actually makes it a more interesting question of what should be done if you cloned yourself just before committing a crime. Is it a good enough indication that the clone is also dangerous? Or should the clone be given benefit of the doubt being created pre-crime? Could, ultimately, be a question of whether mens rea was present prior to cloning, regardless of whether actus reus took place pre- or post-cloning. Which would be quite a conundrum to prove.

Two universes question is ill-posed. If they are identical they will evolve exactly the same way. Quantum uncertainty applies only to interactions between a system and sub-system. Not to a closed system. In contrast, if you plan to "open them up" to take a look, it all depends on how well isolated they are to begin with. If you managed perfect isolation, all of the above still applies. If not, then it collapses just as fast as two rooms case. Finally, if you really happen upon two absolutely identical universes, you can, in fact, do all of your experiments twice. However, this experiment is inherently non-reproducible. If you want to create a duplicate universe, all of my earlier comments on no cloning apply. At best, you can create two entangled copies, and there is absolutely no difference between having that and just one copy. Well, for purposes of topic discussed.

Duration of alternative service is 1-2 years. Most people who qualify are these who already have some skills. Most will have completed technicums and are readily able to fill entry level positions in the industry. Counting work there as alternative service creates a great insentive for people to fill these positions, and a good number of them are expected to stay at these jobs even after getting their service counted. Furthermore, modernization of Russian military requires gearing it towards reliance on contracted servicemen, rather than drfated ones. But Russia isn't ready to do away with draft completely at this juncture. Alternative service is a great interim compromise. We don't need people who can be doing professional work wasting their time learning how to peel potatoes in the army. This whole thing is a solution to two existing problems. It would be fair to observe that both of these problems might not have existed if it weren't for a whole bunch of other terrible decisions, but these problems exist, and this addresses them both readily. It's not enough, but it's a great start. In contrast, we see construction of space center, which is behind the schedule and over budget because of theft, corruption, and cronyism. It is in dire need of skilled workers to complete it properly. The correct solution is clearly to halt construction until investigations are over, appoint new people and budget, hire the workers and continue. This can potentially cost years. The Soviet solution is to find a source of cheap labor and throw it at the problem. In this case students, who are under-qualified and will not have time to gain qualification. Furthermore, for a lot of them, work there will do nothing in furthering their education. They are going either because they are given certain liberties to help them pass exams, or because they need money due to stipends being rather low. This is not solving problems. It's compounding them, while creating semblance of work. The only reason this is being done is so that Rogozin can report that he's doing all he can to get construction back on schedule. And while this might create a short boost in progress, it will certainly not last, and what's worse, can result in further setbacks down the line because most people being brought onto the site aren't qualified for that work. Brick laying and electrification are not courses taught in modern universities. Again, for this sort of thing, you want technicum graduates. This is a bad idea. It will end badly. And worst of all, pepole implementing it most likely realize it. This is purely a way to temporarily make things look good, allowing people in charge more time to pocket more budget money. Edit: Not to derail this even further, but the same sort of thing is already happening with the bridge. You know the one I'm talking about. I don't really want to start a discussion on it, but just mark these words, and maybe think back to this discussion a couple of years from now when it's clear how that's turning out.

Not at all. If anything, they should do this for civilian sector as well. It could be great for economy. Even if it applies to military industry only, there should be some trickle-down effect beneficial for the industry in general. Plus military export is still an export. For sake of anyone curious, the topic of that article is recent law equating certain qualified work in military industrial to alternative service. Russia is, currently, a "universal" draft state. Not directly relevant to the topic here, but it could actually help Krunichev in the long run.

I can completely understand some students working in places like that to augment their stipends. As I've pointed out, it's not that I consider it a bad alternative. But you can't tell me that increase from a bit over 100 to well over 1,000 is nothing. Even if we are talking month-long shifts, that's still a dramatic increase. Both in relation to what they normaly have and to the overall work force. And yes, I realize that construction works requires a range of qualifications. From things you can learn in a couple of weeks, to things for which you need to train for years. That's precisely what concerns me. A hundred or two students seems like the right number of people for pushing wheel barrows and mixing cement. They propose infusing something like 300-400 in addition in a single shift? What are they going to learn there in a month? And who's going to take the time training them? I'm worried that a lot of work that requires qualification will end up being performed by people who lack them. Hence my thoughts of polar foxes. Of course, if you need people who can finish an impossible task by an impossible deadline, maybe students aren't the worst choice.

Yup, everything in that article is consistent with what I know about Vostochny. If we agree on this, what exactly is the problem with the statement I've made above? They are getting over 1k students, almost 15% increase in the workforce over the summer. It's necessary because there is a shortage of workers, which is aggrevated by payment delays. In what sense are these students not a replacement for the work force? Not all work force, just a fraction, but not an insignificant one. This is all very reminiscent of certain soviet practices. Although, to be perfectly fair, if I had to something like this when I was a student, I'd have way more enthusiasm for working on a construction site for a space center than digging up potatoes in the field.

Yes. Even though you aren't after a measurement, if you were to be able to make an exact Quantum copy, you would be able to make two sets of measurements on the same state, and that's fundamentally forbiden. Amplification is the Quantum compromise to copying. You can have two states that are identical, but they are also entangled. Measuring one collapses both, so you can still only get a single measurement.

They had some workers from neighborign States suplementing the work force. That is, until they stopped paying them. I don't know if it was enough to keep the project anywhere close to schedule. I know it isn't now. I stand by my word choice. Though, I agree that it deserves a foot note.

Rogozin's statement on the matter. And what word other than "replace" would you use, when there is a shortage of work force due to recent incidents with the delayed payments?

It is still, technically, specific impulse. Amount of impulse per unit of mass of propelant, dp/dm = <ve>. It's only when your m is in pounds and p is in pound-seconds that you end up with silly units and a conversion factor. In metric, effective exhaust velocity is the specific impulse. N s/kg = m/s. But I suppose, simply talking about exhaust velocity and not even mentioning specific impulse might be less confusing at introductory level, so you probably have the right idea there.

Of course, we've actually demonstrated macroscopic quantum states since, so it's a hollow argument. So yeah, back to the experiment, you can't have copies. The no-cloning theorem forbids it. What you can have is an amplified state. A perfectly entangled pair under perfectly symmetric Hammiltonian. In that case, yes, it'd be silly to argue which is which if one gets destroyed. Of course, in reality, decoherence will take place almost instantly. It's your "opening the doors" clause. Any interaction whatsoever from the outside will be sufficient to disrupt this synchronization. So the life time of the quantum doubles will be almost infinitely short. And after decoherence, the state collapses to just a pair of classical copies, entirely distinguishable from one another.

We're not hand-waving it away. We're prioritizing based on it. I don't think we can build it this century. But it's definitely an achievable goal given technology that already exists and applications we can reasonably expect. Which means that this century, and even within the upcoming decades, it'd be worth testing it out. Deploying a station and trying to send a manned expe Look around. You're living in one. Life support is a problem of scale. Make it big enough, plant some trees, and it takes care of itself. Mars is absolutely horrible place for a colony. First, you have to build pressurized domes. On Venus, ambient pressure would match pressure in the habitat, so the panels would only have to stand up to wind. If one of these happens to blow out... you just need to go to a different room. If you happened to end up cut off and have to go through area exposed to the atmosphere... you just need to hold your breath. Well, and take the shower ASAP once you get inside. On Mars, ambient pressure will require you to fully exhale, causing oxygen to evaporate out of your blood into your lungs, bringing useful consciousness to bellow 15 seconds. Good luck saving your rear in case your dome becomes depressurized. And these things are much more likely to happen on Mars, since besides significant stress due to pressure differential, your entire structure is sand-blasted on regular basis. And that's just problems with the habitat. Construction materials on Mars are going to be even more scarce. You'd probably opt for ceramics and silicon over carbon there, since atmosphere is so thin. But key component for just about anything is water, which is going to be super scarce on Mars. Yeah, there are decent supplies of it in a few places. Enough to run an outpost. But you try to build a colony there, and they'll have serious shortages within decades if not years. You'll have to run water mines all over the planet just to supply your cities. Finally, the elephant in the room. Gravity. I lean towards Mars gravity being strong enough to prevent lethal side-effects if the personnel follows strict exercise regimen. But life at a little over a third of Earth gravity is not going to be peaches. It will require daily exercise routine for absolutely everyone in the colony just to keep their hearts pumping and the bones from braking. How well the young and elderly will take it? Well, it's hard to tell. Nobody experimented on it sufficiently. But it's very likely that at best, life expectancy on Mars is not going to be what it is on Earth. And then we have Venus. At an altitude of approximately 60 km, ambient temperatures of about 70°F, the pressure is about 0.5bar, requiring a slightly oxygen-rich environment, but not to the point of being a fire hazard.. Gravity is 90% of Earth normal, and so it causes no serious side-effects. The colony is located above the bulk of the clouds, but still bellow significant number of the sulfuric acid clouds. Note that the later present little danger, since concentration is pretty low at these altitudes. The weather is mostly overcast, but could range from foggy to almost clear. Basically, if you grew up in London, you'll feel right at home. The only planet in this star system with better environment for human colony is Earth. That is simply not even a question. That's not to say that Mars should be overlooked. There are some fantastic mining opportunities on Mars. Mars is easy to launch from, so I expect it to be an important industrial location. That would necessitate constant human presence there. People living with their families. But it would come with hardships outlined above, and I don't expect anyone to start a family on Mars nor to retire there. It's a place you move to for a few years to help build your career in industry or mining. And then you move to the off-world offices on some orbital installation. And then you can retire on a ridiculous cloud city on Venus.

I don't think there was even a separation. The third stage just shut down. But yeah, even if Breeze-M separated, it wouldn't have had a chance. Edit: More news about Vostochny. To replace workers, they are going to send in students from various universities to work over the summer in exchange for postponing the session. Fat polar fox.

If we start taking off the table everything that has not yet been demonstrated, we can only speculate that people will keep doing what they are doing now and nothing new. Which is silly. That said, binding CO2 from atmosphere into useful hydrocarbons under sunlight has been demonstrated. And from there on it's standard petrochemical to get any plastics known to man as well as carbon fiber and numerous other materials. So we have construction covered. Likewise, sunlight, CO2, and water is basically all that the plants need in abundance. All of the above also needs a bit of nitrogen, which is also present in atmosphere. Almost everything else is only needed in trace amounts. There are vital minerals that would be almost impossible to replace. But they are needed for life and construction in such small quantities that they can be actually mined for despite horrible conditions and expense of doing so. Of course, it'd probably be way cheaper to get them from off-world. Ideally, I'm picturing such a colony supplemented with Lunar or asteroid mining to deliver small quantities of metals and minerals needed for nutrition supplements and industry. But if it has to be an entirely closed system this can still work.

If you need something beyond carbon dioxide and water vapor to be self-sufficient, you're doing it wrong.

You can live there, be self-sufficient, and expand the colony. What are other requirements for a colony?

They aren't really dying by thousands in civilized countries where things are built properly, but there are still deaths with major earthquakes anywhere on the planet. We cannot avoid it when we build on tectonic plates. And don't even start me about potential "near future" disasters such as The Big One or the Yellow Stone. Living on this planet is incredibly dangerous. If we build a floating colony on Venus, I can absolutely guarantee that it will be safer than most places on Earth are right now, and in the long run, we could make it safer than any place on Earth. We can improve safety on Earth too, of course. Get it to the point where either one is as safe as anyone could ask for. But you know it's not going to happen on Earth. We'll just keep going the way we are. And so if you accept life on this planet as "reasonably safe," complaining about potential Venusian colony is just absurd.

We have people dying by thousands from earthquakes and other tectonic events every year. That's safe? We can seriously do better than that with an artificial colony on Venus.

Sort of. It clarifies things, but I've basically assumed as much with numbers above. Infinite expansion allows total conversion of thermal energy into mechanical, which is where these numbers come from. I would suspect that decomposition is a factor, but that won't explain Argon. That simply has the 3 degrees of freedom and that's that. It can't possilby have exhaust velocity above sqrt(3RT/M), and that gets me specific impulse of 95s at 1400K and no higher. There is absolutely no place for another 15s to come from. Edit: Just making sure. Argon, first ionization energy: 1520.6 kJ/mol. 1400K won't even make a dent in that. So additional thrust from plasma is impossible here as well.

Yet you seem to be comfortable enough floating on a piece of rock over molten magma. With a large enough platform, what's the difference? Up to a point. Then you start just wasting fuel fighting excessive drag. My estimate assumes quadratic drag, which requires TWR in 2-3 range through most of the ascent.

I'm getting ~3.5km/s of dV for atmo/grav losses + 7.4km/s to orbit with no significant benefits to equatorial launch. So a launch from Venus should be achivable with 11km/s rocket against 9km/s for launch from Earth. I'm using an extremely simple model for the aero/grav losses, though. Could easily be off by enough to agree with your estimate.