K^2

I was under the impression that other than military missiles, rockets are always destroyed with a command from flight control. If something goes terribly wrong right away off the pad, then situation could only improve if you hesitate to destroy it. And if rocket goes off course at high altitude, there is no harm in waiting to see if some systems kick in and manage to correct it. Anything is better than completely losing the payload and the rocket at that point. I don't know if there is such a thing as, "Yup, we just want it to automatically blow up at this point," even with unmanned rockets. It's all situational. ICBMs, on the other hand, are not designed to be easily aborted. In fact Soviets used to not have a system to destroy them from ground at all. United States, but all accounts, did, but that still required quite a bit of back and forward. Which is why these kinds of rockets must come with self-destruct mechanisms. Both to avoid collateral and, in some cases, to avoid giving your enemy pieces they can use to reverse engineer your tech.

Fair. But that merely shifts weight of the amplifiers to the sat. Tech remains exactly the same. The challenge is to take a single photon and turn it into an avalanche of photons while preserving entanglement. A laser already does this, so long as distance you are trying to send the beam to is within the laser's coherence length. Hm. I wonder if this can be leveraged for some sort of point-to-point communication, though. Having a pair producing sat in orbit does allow for some interesting practical uses. I can see why it's getting funding.

It's not as hard as it sounds. There are existing methods to amplify one of the entangled photon pair via lasers/masers for example. At that point, satellite itself can be just a mirror. The trick is then to have it be a very finely tunable mirror that lets you bounce that beam precisely and without significant losses. But that's a mechanical/electrical engineering problem, which you can always solve by throwing enough money at it. The Quantum side is easy for once. Not that it makes it less impressive. Just less amazing.

Technically, an entangled pair is two qbits. And there is actually crossover once you start talking about breaking encryption. An arms race waiting to happen, in fact. But yeah, at this stage, rad hardening isn't an issue, since sat doesn't need to hold on to data for any amount of time, and photons don't age.

Do you understand Higgs Mechanism and why photon is the only massless boson resulting from the SU(2) x U(1) symmetry group?

If the carrier boson is 17MeV, this is going to be something very short-range. In fact, only massless bosons are going to correspond to long-range forces. Of course, existence of a new Higgs-like boson could point to a yet undiscovered massless boson, such as dark photon, as a side effect, but it's a very drawn conjecture at this point, even if we take existence of that new 17MeV particle as a given.

No, entanglement is used for light-speed (or slower) communication. What it lets you do instead is send quantum data over a classical channel. This can be used for teleportation and encryption, as stated in Kryten's post. There is actually a rather infamous No-Communication Theorem in Quantum Mechanics that states that while effect of entanglement is apparently instant, it cannot be used for FTL communication.

Compressor actually does several things. The way in which it improves air flow is by reducing ram pressure in front of the engine. Even if you simply have a pipe that narrows a bit near the back, and start carrying it through fluid/air, because of the restriction in the back, it will start building up pressure in the pipe which will reduce the flow. (Technically, so will completely straight pipe, due to viscosity.) This is similar to problem encountered by Hyperloop train and the reason why Hyperloop is designed with a huge compressor fan in the front. Without compressor, this ram pressure reduces amount of air that can flow through. But the second part is the fact that you actually need a significant pressure increase inside the combustion chamber. That has to do with thermodynamic cycle of the engine. (Lenoir Cycle for jet engines) The higher the pressure change, the more efficient the engine. Of course, at some point, losses in the compressor exceed gains due to pressure increase. This threshold also depends on the air speed and the bypass ratio. Hence the difference between compressors on different jet engine types, starting with turbofans with giant compressors taking up most of the engine, and to the ram/scram jets that forego compressor entirely and use the ram pressure for the heat engine cycle. Feel free to talk to your physics teacher about this, but keep in mind that they aren't necessarily versed in heat engine thermodynamics beyond the very basics of Carnot Cycle. This is the sort of thing that's only very briefly covered in undergraduate courses at university, so they aren't always expected to have learned anything about it to teach physics. If you can track down a university professor, preferably one that deals with thermodynamics, they will be able to explain it much better. Alternatively, a savvy engineer should do just fine.

Majority of rocket packs have legs to help support them while landed/docked. So I don't think it's a distinguishing characteristic of a rocket pack. I would call anything with pilot enclosure a lander, and anything without either a rocket pack or a rocket stand, depending on how the pilot is attached.

Real mobility units have nowhere near enough thrust, because they simply don't need it, but you can certainly build one if you wanted to. Real jet packs using hydrogen peroxide as monoprop can lift a person on Earth and have about 300m/s of delta-V. That's not dramatically worse than KSP equivalent. And if you are happy using more caustic monoprops, similar to these used by space ships, you can almost certainly match the thrust and delta-V of KSP counterpart.

The family of equations this leads to cannot be solved analytically in general form. It's a significant limitation of orbital mechanics and central potentials in general. This has to be solved numerically. If you know anything about programming, it's relatively easy to learn methods that will let you solve simple cases, like orbit-to-orbit transfers. If you don't, and you still want to be able to do it, you'll have to learn that first.

So that it can dock for servicing.

Coal is fundamentally expensive. If demand drops, digging it out will be even more expensive. Yes, if we suddenly stop needing it for power plants, the reserves will be a source of cheap carbon for a while. But I don't see it working out long term.

Nah. They only get payed for ads. If you have Add Blocker, it's perfectly safe to click these links.

Lets start with the fact that photosynthesis is less than 10% efficient, whereas optical rectenas start at about 40%. This is a death sentence for biofuels already, since land availability is the biggest bottleneck in civilized world. But then you have to add farming costs in machinery, labor, and energy consumption. Corn ethanol is not viable in US and Europe by a huge margin. It is not viable everywhere else by a much narrower margin, but then you add transportation costs on top of an already expensive fuel. So lets say with cellulose in the mix you can pass the break-even point. We are talking about net efficiency of less than 1% at this point. Even with free electricity, if you can make this actually cheaper than Jet-A from oil, I'll be impressed. Yeah, solar power works only during the day. Which means you need to store it during the day. Got any idea how to store the massive amounts of energy we consume during a typical night without increasing a cost dramatically? I'll give you a hint. Power companies already have gas turbines. Yeah, you'd be taking a loss of over 50%, but given that infrastructure is already there and energy itself is almost free, it's stupid not to do it. Each modern power plant is going to become a giant battery using H2 generated during the day to power the place during the night. The surplus H2 isn't going to be there because of power usage fluctuations. It's going to be there because electric companies will already need to make huge quantities of it, meaning they'll be able to sell it cheap as well, thanks to economy of scale. So the options for airline companies is going to be LH2 at $0.05/gallon or Jet-A (bio or fossil) at $5/gallon. Long range variants of 777 take nearly 50,000 gallons of fuel and its longest flights use up almost all of it. So even with the fact in mind that you need about 4x the quantity of LH2 by volume, your options are paying about $200,000 to put 40k gallons for a flight or about $8,000 worth of LH2. You'll want to do at least one flight per day minus maintenance, so lets say 3,500 flights in 10 years, and you are looking at savings of over half a billion dollars. For comparison, the plane we are talking about costs about $300 million. If we throw in maintenance and man power, we are looking at saving about half of the airplane's ten year cost. Half. Multiply this by the size of the long-range fleet and you have enough money to build new airports, refueling infrastructure, and roll out new planes leaving just enough for each CEO to cut themselves a huge bonus check. There are other considerations, of course, like that pesky safety factor. But it's going to be cheaper for airline companies to just get lobbying groups to talk about how much greener this is for the environment, and everyone will forget about the few unfortunate accidents caused by poorly trained technicians and really dangerous flammable gas. If you think little things like human lives are going to stop corps from pushing this through, given the insane amounts of money at stake, then you don't know anything about modern corporate politics.

Many times. At least once in this thread. But there have not been any significant breakthroughs since DARPA's TRIP, just some incremental improvements. Enough to where we might be able to replace radiothermal isotope generators at some point in observable future, but nowhere near enough to make them viable for energy storage in commercial vehicles. Of course, there are other metastable isomers and probably quite a few we haven't discovered yet. Or maybe we have, and it's just classified. After all, a lot of Hafnium research went dark very suddenly right after the first paper claiming stimulated emission got published. The capacity is definitely there. Again, using Hafnium 178 as an example, its m2 isomer stores 2.5MeV of energy (1.36 GJ/g, or about 28,000 more energy per weight than gasoline). At the same time, it has half-life of 31 years, emits only gamma radiation, and decays to ordinary 178Hf, which can then be "recharged" to its m2 form. Fact that the only way we know to recharge it is with a particle accelerator and the costs are astronomical, as well as limited quantities of this isotope being available in the first place, are what makes this non-viable as a consumer battery. As indicated, even military was so convinced they can't afford to make any practical use of it that they unclassified all experiments. But if we were to find something with, say, tens of keV energy range and similar half-life? Well, then you could recharge it with an equivalent of a dentist x-ray and radiation from it would be completely safe with minimal shielding. And it would still be about hundred times better than gasoline. This is currently the golden grail of nuclear isomer energy. If we find it, all our problems might get solved just like that. Unfortunately, unlike chemical energies where you can come up with new properties by just bringing a few atoms together, and we can come up with all kinds of "just right" configurations for all sorts of interesting optical phenomena, with nuclear energy we are limited to what's already there. Which is less than a hundred of stable elements with at most a few stable isotopes each. The good news is that it will only take so long to try all of them in all sensible energy ranges. The bad news is that we might just be out of luck on the right isomer existing. So best possible scenario, we'll figure out high energy density nuclear isomer batteries and we'll have minivans capable of making orbit. Worst case, we'll have to figure out controlled fusion or be stuck with chemical energy.

Doesn't matter. With current farming techniques, plant matter takes up more fuel than you could possibly make carbon-for-carbon. Even if you convert cellulose in addition to all the sugars, you're still in the deficit. And we don't produce enough waste cellulose as byproduct to account for our fuel use. Again, we presumably want to convert farming to consume electricity only, but this gives you the idea of the scale of effort required to make synthetic fuel. There is absolutely no way to make any carbon-based fuel remotely as cheap per calorie stored as LH2, provided that you have a source of next-to-free electric power, which is what we're talking about. Synthetic fuels might be a stopgap during transition, and I'm sure there are applications where we'll keep using them, but at the levels of global energy consumption, it's not long-term viable. Primary storage will be hydrogen until something better comes along.

With few exceptions, where spectral lines make a large difference, this fact doesn't actually change the chroma. Yes, H2 plume of the NTR is going to be very, very faint for the reasons you describe, but the color of what little light is going to be emitted is going to be red to deep orange as governed by the black body radiation.

Talk about teseract is not complete without discussing its rotation. There are 6 axes of rotation in 4D space. When projected to 3D, three of them look like normal 3D rotations, and the other 3 look like teseract turning inside out in one of three directions. Here is an animation combining both types of rotation. But integer dimensional spaces aren't so bad. It's fractional dimensions that will drive you bonkers.

Currently, our means of producing biomass consume more fuel than it provides, because we use so much of it in agriculture. Only exceptions are third world countries which can't possibly produce enough to export without switching to first world agricultural methods. Granted, it's easy enough to switch most of agricultural machinery to electric, but it still means that any bio-fuel is going to be many times more expensive than electrolytic H2. As for coal, it's already expensive. Sure, it's much cheaper than oil, but coal-burning power plants are already on a comparable price point to solar. With environmental taxes, coal is more expensive than solar in some parts of the world. (California, much of Europe.) Optical rectenas are going to bring down price of solar by nearly two orders of magnitude. Stop and think about that figure. Nearly 100 times cheaper electric production. Price of electricity will be due to infrastructure only. Nothing we have can compete with this. The only method we know of storing this energy without increasing its cost ten-fold is electrolytic H2. We might come up with something, given that it's going to be an important limitation, but we don't have anything like it yet. And yeah, we'd need new infrastructure for these flying monsters. Just like 747 did. Just like many planes before it. This is not a new problem. Since we are talking about replacing only intercontinental - or equivalent range - flights only, this isn't a problem. They are already tending towards monstrous because they are trying to save on fuel costs. This is exactly the same motivation. Nothing new. We are talking a handful of airports around the world. From there, local flights will connect with either conventional jets or something else, like the aforementioned electric replacements for regional turboprops. This is a projection going entirely off technology we have in experimental stages in the lab. We are going to start producing massive quantities of cheap solar power. We will have hard time storing it. While batteries are going to improve by about a factor of 3 in the near future, most promising being graphene batteries, this is nowhere near enough. Next best thing is hydrogen. We are likely going to see power companies building major LH2 storage facilities to balance the grid. Hopefully, this will allow recycling much of the existing infrastructure. This will mean that large quantities of LH2 will be available really cheap for anyone who wants to purchase it for fuel. Aircraft manufacturers are unlikely to just watch this untapped energy source sit in storage tanks. But like with any projection, any significant change could throw it all off. Maybe we'll figure out how to tap into nuclear isomer energy in the next decade. Maybe we'll have 178m2Hf batteries to store these massive quantities of energy. Seems unlikely, given how much research went into it with limited success, but it's just one of hundreds of parameters that can change. But if things go the way they are going now, little details like requirements for larger airfields, completely new hangars, new safety standards, and new equipment, aren't going to stand in the way of massive capital gains on paying next to nothing for fuel.

If LH2 drops to 1/5th the cost of Jet-A by weight, which is where things are heading with rectennas, it will be economical to build jumbo planes with humongous LH2 tanks to fly long range. Such an airplane will fly at a significantly higher cruise altitude offsetting much of the drag losses. It will still be energetically disadvantageous, but economically advantageous even with higher construction and maintenance costs, simply because how much of plane's operation is fuel costs. In contrast, short hop regional planes might start getting replaced with electrics. We're looking at flights that are currently serviced by turboprops first and foremost, but small regional jets are likely to start being replaced as well. Where Jet-A is likely to remain dominant fuel the longest is mid-range flights. I don't see planes in A320, B737, B757 range being replaced with alternative fuel planes with foreseeable technology. On the other hand, if Hyperloop takes off, we might not need to.

Science is solid. It's honestly a question of how long it will take them to get this to visible light wavelengths and into production and whether something better will come along before that happens. But in either case, this spells doom to fossil fuels. Between advances in photovoltaics and batteries, about the only market for fossil fuels that won't be rapidly collapsing in the next decade is Jet-A. And even airliners might start to transition to LH2 if energy prices drop as much as rectennas can bring it down.

40 years ago, paper on Hawking Radiation was just recently published. Concept of black hole evaporation was not known to many people. Today we know that any black hole we can artificially create in a lab will be losing mass faster than it can accumulate it, therefore, presenting absolutely no danger. Concept of black holes as wormholes to other worlds, likewise, followed from particular mathematical solutions for rotating black holes that have since been proven to be unstable, and therefore, not representing real black holes. So yeah, our understanding of black holes has changed quite a bit.

Look up the profile for Rosetta Mission and do that in reverse. Their first boost was a self-assist from Earth using only a slightly eccentric orbit. That gives you very little delta-E, but significant delta-L, which gives you an orbit with Pe bellow Earth and Ap above, giving you opportunity for boost with Venus or Mars. I don't recall which one the mission actually went with, but both are viable. Running this in reverse in KSP, you could use a gravity assist from Duna to bring you to a highly elliptical orbit that crosses Kerbin's path. You are looking for something with semi-major axis roughly that of Kerbin's own orbit. Use assist at Kerbin to bring you to a nearly circular orbit that intersects with Kerbin again almost exactly a year later. You can bring your dV down to a few hundred m/s. Planning this is not easy, though. I don't know if you can do that with tools that KSP provides you. I'd put simulation of the Kerbin system into something a bit more sophisticated, and crunch out the numbers in advance.

Nuclear Pulse Propulsion, sure. See Project Orion. Economic feasibility is a separate issue, but basic tech was there. If you are looking for something more elegant, we don't have the tech even now.