cantab

Yeah, getting a plane with a nice slow landing speed is tough in FAR, a problem compounded by the desire to land in the bush and the additional difficulty of wheels now. But I think this brings up what I see as the difference in philosophy between stock aero and FAR. Stock aero is happy to fiddle things to get a desired 'feel'. Landing speeds too high? Just tweak the lift behaviour to bring them down! FAR strives for objectively realistic behaviour. Landing speeds too high? Not FAR's problem provided the aerodynamics is correct for the craft you built. Rather look for ways that craft is unlike real aircraft, and like Flashblade said it's probably down to weight, an entire Cessna 172 with fuel weighs about as much as a Mk1 cockpit alone.

With a moment's thought, it would do neither. It can only explode if a small to medium sized breach would grow rapidly, and I feel confident speculating the hab would be designed to not do that. You can do a simple experiment. Stab a balloon with a pin, and you know it pops. But stick some sellotape on the balloon and stab the pin through where the tape is, and the balloon will be pierced but it won't explode. So it's not hard to make an inflatable structure that doesn't pop. And it wouldn't exactly implode either. If breached the hab would just deflate and collapse under its own weight. The aftermath would kind of look like it had "imploded" but the process would have been slower.

"Both designs utilized a Boeing 747-400F as the carrier aircraft...All concepts, when fully loaded, exceeded the allowable Gross Takeoff Weight (GTOW) of the aircraft platform." That's not very encouraging. You're taking one of the largest and highest-capacity aircraft available, and it's still not enough. As I see it the big advantage of subsonic air launch is operational and infrastructure simplicity. No big specialist launchpad, just any decent airport. No worries about weather at the rocket launch location (though obviously bad weather could ground the plane). Operate out of the temperature latitudes but actually launch the rocket much closer to the equator. But if you're proposing to use cryogenic fuels and aerial refuelling, that's adding a ton of complexity, hazards, and consequent cost. There are good reasons aerial refuelling isn't used in civil aviation, and that's even before we consider the extra problems of handling cryogenics. Pegasus is well-established, and actually one of the most-launched orbital rockets. 23 ton rocket putting around 500 kilos into LEO. Pegasus II was much more ambitious, but so much so that it was to require a brand new aircraft. That's a major extra development cost. Let's say we instead use the highest-payload "off the shelf" aircraft we can have, a 747-8F with a maximum payload of around 140 tons, then scaling up the Pegasus design we're looking at a 2-3 tons to LEO payload. Meanwhile in that same original paper, the "PD-2" design without using aerial refuelling but using RP-1 and LOX rather than solids gets about 6 tons to LEO. That I think is about as big as is worth going with air-launch.

Probably. Intel Management Engine demonstrates the kind of thing that is possible, and a similar feature that isn't disclosed would be very hard to detect. Examining the physical chip with an electron microscope might spot it, especially if the chip is supposed to be to a standard design. I think the hardest aspect would be knowing what chips to backdoor and making sure they'll work properly in the full system, at least if you don't know said full system.

Or indeed make it be something else. On a minute's thought, I'd be rather surprised if the NRO or another relevant US agency doesn't have arrangements to quickly get the images from commercial and research satellites that would be useful to them.

Doesn't the "jam the sensors" approach just make it even more obvious you're doing something dodgy? You might be able to hide the launch timing and trajectory, but if the enemy operating the satellites specifically designed to detect launches sees those satellites are being interfered with, they're going to assume you're launching. And they're quite possibly going to further assume you're launching nuclear missiles and respond accordingly.

Yeah, whatever the technology, disguising the payload as something else works. But let's say you want to conceal even the fact that you've launched *anything*. Rockets are out, they're not only obvious but they look like ICBMs and so are very well watched for. SSTOs may be possible. It would have to fly stealthed or under-the-radar out into a part of the ocean beyond radar coverage, before climbing. My chief query is that stealthing a jet is established, but what about when the rockets kick in? Even outside radar range, could the infrared signature be made low enough to be undetected? Air-launched rockets are the same deal as SSTOs. With a mass driver, as soon as the projectile hits the air it's gonna make a load of shock heating, like a re-entry only even worse. I suspect that might be spotted. With a space elevator, I suppose one could be constructed to have the car movements invisible, then you also maintain operational secrecy and no-one knows what you're doing with it. The problem is that for your enemies it's a known unknown - they don't know what's going up and down and when, but they do know that you *can* move stuff on the space elevator any time you like. A stealth spaceplane, or even a mass driver buried in a mountain, could be a top-secret black project, but a space elevator just can't be hidden.

Does quantum field theory resolve the measurement problem then? And if so how?

More to the point, running OSX on non-Apple hardware is both technically and legally problematic. It's *possible*, sure, but I think most people with a need/want to run OSX are better off just getting a Mac. I mean, if someone told me that I could get a great deal on some hardware but installing Linux (my chosen main OS for close to 15 years now) on it would be both unduly difficult and possibly unlawful, I'd probably walk away.

Intel have acted no worse than 99% of businesses would if they could. Anything to make money.

Be a prime case for something with high efficiency and moderate thrust. The thrust can't be too low because we want to be able to do the transfers in a reasonable time. An arcjet might be suitable, with specific impulses in the 500-1500 s range reasonable, and thrusts rather better than the kind of ion engine the Dawn spacecraft used.

Well actually the Arabic spelling is رجل

An RTG might meet the "fission" part (depending on the isotope used) but it doesn't meet the "reactor" part. In nuclear physics the term "reaction" is restricted to processes where two or more particles interact; radioactive decay or spontaneous fission where one particle decays into several do not count. (This contrasts to the use of the term "reaction" in chemistry, which includes one reagent turning into multiple products).

Wheeee IAU, now they've gone and made it nice and confusing! Specifically, by taking the traditional names that referred to multiple star systems that appear as one star to the naked eye, and arbitrarily deciding those names are appropriate for a single star in that multiple system. The name Alpha Centauri always means at least the pair (OK, sometimes Proxima too), the name Alpha Centauri A always means the single star, but now the name Rigil Kentaurus could mean either depending on when the work was written! And there are several others with the same problem.

OK, let's say that the Star Federation has ignored that bit. The reactor's been designed for maximum power, minimum mass, high operating temperatures*, and whatever other aspects of performance, and safety has been completely thrown out. The reactors on a starship aren't designed to be bombs, but they're not designed to not become bombs either. Basically if the reactor designers and operators are very foolish, what kind of boom might be possible? (*The hotter the reactor core, the hotter its cooling radiators, and since black body radiation scales with temperature^4 that's a big advantage.)

On the topic of exploding reactors, the SL-1 accident is an example. The reactor, designed for a few megawatts, went prompt-critical and its thermal output hit 20 thousand megawatts in four milliseconds, creating a steam explosion and propelling a piece of the reactor fast enough to nail a man to the ceiling. https://en.wikipedia.org/wiki/SL-1 That's probably about as bomb-like as a fission reactor is going to get. I suppose in some reactor types it's possible that the fuel itself, rather than a moderating coolant, would vaporise and drive the explosion, but the general principle will be the same.

It's a common conception, but CoaDE casts doubt on it. I've had ships with only a few cm of armour stand up to impressive amounts of railgun fire, and in order to disable the target rounds need to both penetrate the armour and have the luck to hit a critical component. There's also the factor that you tend to open up at a range where you'll still be missing a lot, so again the 'lucky hit' factor comes in. Lasers for their part take time to ablate through a target. And then there's the need to even get to firing range in the first place - if the enemy has more delta-V than you and really doesn't want to fight, they can probably avoid it. I know CoaDE isn't the be-all and end-all of hard sci-fi, but I feel it's insightful.

Yes and no, I think. If a reactor goes prompt-critical the activity will rise sharply and some sort of nuclear explosion may be possible. However, at most it will be equivalent to a 'fizzle' in nuclear bombs, where the explosion of a small fraction of the nuclear fuel blows the bomb/reactor apart preventing further reaction. The other likely outcome is that the extreme heat changes the reactor so the nuclear reactions are no longer prompt-critical and activity stabilises, which I believe is more-or-less what happens in a meltdown.

IIRC is that after its initial launch and departure, the Hermes stays on a cycler trajectory, which means it flies by Earth and Mars alternately never entering a closed orbit around either. That means that to catch it, the crew ship needs to escape Earth itself and in fact spend as much if not more delta-V as if it transferred to Mars directly. In fact the Delta IV Heavy is not enough to push the Orion capsule that far, but we could assume The Martian has a more efficient DIVH, a lightened capsule, or/and an extra upper stage. In any case, I think it's a bit mean to bash the filmmakers for this. They could have just done what every other sci-fi movie would do and use CGI, and then throw realistic rockets out the window and do whatever they think looks cool. But instead they used actual, honest-to-goodness footage of a real rocket. And for their trouble they get the continuity nitpickers complaining.

There are but they're all paper concepts. Using the reaction to create heat and converting that heat into electricity is the only proven way.

Realistically, fission reactors can be made pretty small. The minimum requirement is that you need a critical mass, but that can be as low as about 10 or 20 kilos. There are certainly reactors you could fit in your fridge, such as the https://en.wikipedia.org/wiki/SNAP-10A that actually flew in space.

The 0.18.3 demo gave me a great first impression of the game, its tutorials got me started and then I went on the internet to learn a bit more. But the 1.0 demo suffers from a poor choice of parts. From memory: 0.18.3 : Large fuel tanks for decent sized, reasonably rigid (by pre-ARM standards at least), low part count rockets. 1.0: Small fuel tanks mean wobbly rockets and a part count spike. 0.18.3: Has gimballing engines, adjustable fins, RCS thrusters, and 1.25m reaction wheels to control your rocket. 1.0: Only offers RCS and small reaction wheels that don't fit in the stack. Controlling your rocket is made unnecessarily harder than in the full game. 0.18.3: Has the 909 which makes a good upper stage engine, which demonstrates the whole point of staging and helps players get beyond low orbit. Good lander engine too. 1.0: Lacks a good upper stage or lander engine. All these part issues come from one source: The tech tree of the full game was allowed to dictate the parts available in the demo, rather than giving the demo the parts to show KSP in its best light. As for the new demo's tutorials, I've never looked. I can't really judge them in the same way a novice would anyway. Regarding PC performance, it's possible that on a PC with very limited RAM KSP will only load if the settings are turned down, which of course is a bit hard to do if the game won't load and show the settings screen! (You can do it by editing the file but that's not obvious to a newbie.) The demo would be less likely to suffer this issue.

Oh joy, I've set off the most eternal debate in sci-fi again. Oops. Monitoring the whole solar system (except for small regions directly blocked by celestial bodies) 24/7 isn't all that hard, not in a future where humanity spans that system. About 400 space telescopes like Kepler would cover the whole sky, duplicate that setup in a few locations for triangulation. Basically anything useful needs to emit heat. More critically if a spacecraft makes an engine burn it immediately gives away its position, and if the burn is long enough relative to the resolution of the sensors the spacecraft also gives away its mass and trajectory. Such a relationship, that doesn't apply to terrestrial vehicles, allows an observer to infer quite a bit about the spacecraft even if it's only a single pixel on the telescope. Maybe there are drives that can get round this, but they're likely to suffer from other issues. There are things that can be done. A silo buried in a low-gravity world, its thermal emissions masked by those of that world's cities, makes a nice hiding place for defensive warships which can launch and surprise an attacking enemy. And ruses, false flags, Q-ships, and so on should all work, although needing to match the performance of a civilian ship limits what can be done.

Even in the prequel era before the Jedi purge, lightsabers were extremely rare. Wookiepedia states there were around ten thousand Jedi, which sounds like a lot but in a galactic population of quadrillions it's a drop in the ocean. Trying to land on the surface of an enemy starship would be plain crazy, risking the lives of your elite peacekeepers doubly so, and not something starship designers are likely to worry about. In any case Star Wars has specific anti-lightsaber materials, but they're rare. The most important doors (ie whichever ones the heroes need to get through!) might use them, and some lightsaber hilts themselves are made of them for obvious reasons.

https://en.wikipedia.org/wiki/Lift-to-drag_ratio#Supersonic.2Fhypersonic_lift_to_drag_ratios So as you go faster, your attainable lift-to-drag ratio approaches about 4. It's about 5 at orbital speed. That means you'd need a TWR of at least 0.2 just to maintain straight and level flight. Which seems surprisingly low actually. I think in practice you'd want higher, but I reckon 0.5 would do it.