shynung

While this might be true to some respect, I'd say to Hell with the hypergolics. That thing's so nasty on the anatomy, it should've been limited to unmanned ships only. If it ever goes into the cabin, we'd have another ASTP disaster on our hands. Definitely something not desirable to happen on a multi-month trip to Mars. If chemicals are our best bet, methane/LOX is my best bet. Isp close to LH2/LOX, but with none of the disadvantages of the latter; CH4 is dense, and it will stay put in the tank. Still cryogenic, but much less so than LH2. Plus, Mars has plenty of CO2 in the atmosphere, so ISRU is possible.

I've read somewhere in the 'net that there are people who question the chances of a ship fitted with an NSWR drive to survive turning it on. That said, in addition to all that Isp and TWR, a nuclear salt-water rocket is dead simple. No fussy reactors, just a propellant valve. Works just like a hypergolic, at least in theory.

Because they work. Hypergolics with decent Isp, simple and reliable. Exhaust products are nitrogen oxides and water, pretty harmless compared to the kinds of stuff the other fuels spew out the nozzle.

That's one more part that may fail miserably. Remember Apollo 13? There's a reason why folks like J.D. Clark was paid handsomely to find propellants with a reasonable range of temperatures in which it is in liquid form. Otherwise, we would have never had MMH, UDMH, or IRFNA (inhibited red fuming nitric acid, HNO3 with some N2O4 and HF mixed in). It's out of print. You can read it here.

If one were to bolt SABRE's precooler (from the engine that powers the Skylon SSTO concept) onto the intake of a typical turbojet engine, how much improvement can be expected from the engine, assuming constant exhaust temperatures?

I really hope that means maximum graphics settings on every game ever created in the next 10 years or so. Damn, I wish Fallout 4 wasn't choppy on my rig.

Looking from a computer gamer's perspective, what would a rig with quantum-computing hardware inside can do that non-quantum equivalents can't?

Or, if the ship with the engine really needs to land, an auxiliary solid-core thermal thruster as a landing engine.

That's really cool. Something like this would really help in shipping and construction as aerial cranes. I'm guessing it's just a matter of time until we get fully-autonomous personnel transport craft, the kind we operate by merely entering addresses or GPS coordinates.

Actually, yes, that's what I meant. Also, aircraft post-maintenance testing costs are similar to post-production/quality assurance, because they're usually looking for defects rather than testing capability limits, like bending wings or running engines at full power until it breaks. Those kinds of tests are reserved for new prototypes, whose exact limits and capabilites aren't clearly known.

Actually, I know that's the cyclic stick, and I know what it does. But I get your point; a semi-auto helicopter would probably read that as a 'translate forward' command, and compensate any altitude changes through blade AoA (collective).

Why is this the case? Does this apply to fixed-wing aircrafts?

In the aerospace industry, tests are done every time an airframe receives maintenance. This is to ensure that the fixes and repairs done to the craft won't suddenly undo themselves in flight. For old airframes, this goes double, since older airframes typically has higher chances of failure, due to wear and tear. So, no, I don't think launch prices will go down due to the lessened need for testing. It would only go down if refurbishing a recovered rocket stage is cheaper than making a new one. Both types will be tested anyway, so no savings there. Also, SpaceX probably wouldn't sell low-success-probability launches using old stages, even with half prices. Satellite owners typically object to have their expensive craft launched on even a moderately-unreliable vehicle. At least, it would drive up insurance costs, possibly negating the price reduction of the launch vehicle, rendering it moot.

Interesting. Though, I never see something like that advertised as a feature in aircrafts for sale to private owners. Or is it actually pretty common? Common enough to be installed in most aircrafts that has computerized controls? Also, is it possible to design a system safe enough to be flown by a layman? Sure, some hillbilly would eventually try to fly into something, but is it possible to make a system that would prevent that? Say, disabling all controls and fly the craft on computer until it reached a safe pre-defined attitude and altitude, then switch back to semi-auto?

No, not what we usually call 'Autopilot' these days, but pretty close. In the game Metal Gear Rising, a supporting character (a surgeon, presumably without any flight training) flies a heavy-lift helicopter to pick up a load of cargo that the protagonist plans to secure and obtain. The protagonists asks him whether he's fine flying the helicopter himself, which he replies that the common aircraft of that age has a semi-automatic mode, a technology spillover from unmanned aircrafts, that enables him to act as the protagonist's mission control right from the pilot's seat, while flying a heavy-lift helicopter. So, the question is, how far are we from having that kind of aircraft control system? The one that can be piloted safely by an untrained, multitasking individual?

Autogyros need at least 2 blades to work, and those blades need to be symmetrical. If any one blade falls off, the vibrations its absence induces would shake the craft apart. A multi-canopy parachute system typical of space reentry capsules still work acceptably even when one or more canopies collapse and cease functioning. Also, parachutes, by design, are more reliable than rotor blades. All it needs to function are airspeed, and nothing else. Rotor blades need to be rotated in the first place, something tricky to do in the tight confines of a space capsule, and need to be carefully controlled while in operation, lest the blades stall. Parachutes can be left alone after deployment, and it will work perfectly fine.

I'd say do it with a utilitarian approach. Attempt to minimize damage as much as possible to anything or anyone that might be involved in such a crash. Let's postulate an event: An automated car finds its brakes losing effectiveness, while running at highway speeds in a four-lane highway. In front if it are two cars stopped by a traffic jam ahead; one is a minivan carrying 6 people, the other is a city car carrying 2. The automated car's steering system is functional, so the car can control where it's heading. The highway's road shoulders are too tight for the automated car to pass the two cars ahead, so one or both will inevitably be hit. What should the automated car attempt to do? Hit one?(which?) Hit both by clipping their bumper corners? Attempt to avoid both by running into a safety rail or going offroad?

Parachutes are much simpler than rotor blades. They don't need to be rotating at deployment to function properly, in addition to their deployment being pretty much a set-and-forget affairs. Sure, precision landing is rather difficult, but for a backup system, you'd want it to be extremely reliable, something tricky to do with stuff like deployable rotor blades or rocket engines. What I'd propose would be this: the capsules have rotor blades as the primary descent control system, with parachutes as backup. The rotor blades contain a fuel line, connected to a monopropellant or hypergolic propellant tank at the capsule, and a small thruster at the tip. This constitutes a tip jet, a type of rotor propulsion system that doesn't need a tail rotor. The tip jets can be used to spin the propeller just after deployment, let it autorotate until final approach, then do a powered landing on tip jet thrust. Also, F9's self-landing booster has a set of RCS thrusters near the top of the stage, just under the 2nd stage attachment point. At lower speeds, where grid fins have lower effectiveness, these thrusters, along with the stage engine gimbals, does most of the work.

Why would they do that? A Falcon 9 stage have high thrust engines right underneath. Much simpler to pack more fuel for powered landing. the grid fins are there as control surfaces, not lifting surfaces, which is what autorotating rotors are meant to do. Also, rotors for Dragon v3 seems unlikely. They already have a SuperDraco engine on the v2 version, no reason to weigh it further.

There are other things to worry about. Rotor stowage and deployment, for instance. Also, when the flare fails, solid rockets can be used to lessen the landing stresses, a la Soyuz.

That's still a loss. Say a certain trip needs 30 kg of gasoline fuel using an Otto engine. Density of gasoline about 900 kg/cubic meter, or 0.9 kg per liter. That means the fuel tank needs to be able to hold 27 liters of fuel. Suppose we replace the engine with a fuel cell that's 3 times as efficient. Assuming similar energy densities, that means 10 kg of liquid hydrogen. Since density of liquid hydrogen is only 70 kg/cubic meter, or 0.07 kg per liter, the tank now has to hold a whopping 143 liters of liquid hydrogen. Now here's the kicker: while liquid hydrogen indeed have a larger specific energy (that is, energy divided by mass) compared to gasoline, it has a smaller energy density (energy divided by volume) compared to gasoline. In short, a 1 liter tank of gasoline carries more energy than a 1 liter tank of liquid hydrogen. 4 times more, in fact.

That, and the density's far too low to be useful in most circumstances. It takes a huge tank to carry any useful amount of hydrogen, since a cubic meter of it weighs only 70kg. Typical fuel oils are close to 1 ton per m2.

Hmm. I guess mobile CCs for drones would be the way to go.

Even that's not without its flaws. Communications with the drone would have delays, due to finite light speed, that slows down reaction time compared to a manned aircraft. It ranges from a few microseconds to several seconds. That few seconds might be the difference between pulling away on a mispainted target or wasting a missile on a schoolbus or general aviation aircraft. In short, drones are decent fliers, but ruthless fighters.

Yeah, except we need the pilot. Stuff we use to track enemies like IFF, GPS coordinates, IR signatures, and whatnot aren't entirely foolproof. Drones don't check whether the target they're attacking really is an AA installation or just a church. That suspicious unmarked aircraft that popped on the radar might have just been a passing airliner with an inactive transponder. That blob of IR signature might have just been a bulldozer rather than a tank. Given these targets, a drone would have attacked as ordered, while a human pilot would realize that these aren't the targets they're looking for, and fly away.