shynung

Or both. That guy is absurdly rich.

Why is the proportion variable? What problem would using a single mix all-year-round would cause?

1. Equip spacecraft with landing wheels/skids and an anchor-reel combination. 2. Lower orbital periapsis until it is less than 5 meters above a flat surface, preferably a prepared field. 3. Fire anchor backwards and downwards at final approach; let anchor snag on the surface, unreeling anchor/braking line. 4. Apply brakes to reel, slowing the craft down; if reel runs out of cable, release cable, brake the craft using emergency braking rockets. 5. Touch down, apply brakes to landing gear. 6. ??? 7. Profit!

Grandfather's paradox. Say some important guy died. The hero obtains a time machine and uses it to save the guy. After all happened, important guy lives. Then, the hero would have no reason to go back in time to save them. The hero never used the time machine, since he sees no need to. Because of that, the important guy dies. Repeat ad infinitum.

When manned spacecrafts were first designed, it was thought that the entire outer surface of the craft must be covered in heatshield material. For this purpose, a spherical design, which has the least surface area for a given volume, was used to reduce the needed heatshield coverage to a minimum. Later on, conical designs were found to be able to hold a certain stable attitude at reentry, which is blunt end first. Now, the heatshield has to cover only the blunt end instead of the entire outer surface of the spacecraft, saving mass by reducing the required heatshield material.

Also worth mentioning is that GH2 burns without a visible flame. Place thermometers (or IR cameras) around the vicinity of the equipment, else you might not realize there's a fire until it's too late.

Not only that, an ICBM needs as little drag as possible. Any extra drag means the missile spends more time being vulnerable to interceptors.

They'd have to, else the nukes inside would be useless before long. Though, the machines inside can be designed to endure higher heat loads than a typical manned capsule, so that's that.

That's because public opinions are based on the few significant events that goes through their news feed. Whenever they hear about nuclear power plants, it's always Chernobyl or Fukushima that ran through their mind. The fact that hundreds of other nuclear plants around the world keeps running without a hitch never crossed their minds. And here's where I pinpoint the problem: Bad news sells. A newspaper with the headline "Nuclear Power Plant Explodes, 10 Dead" will sell better than "Nuclear Power Plant Celebrates 15 Years of Flawless Operation", or even "New Nuclear Power Plant Built, Electricity Prices Predicted To Drop By 25%". This is mostly because of how the human mind works, and exploited by news agencies to its fullest; they'd rarely report positive events.

From the gravity aspect, very little. Lunar gravity has little direct effects on earth life in general. it creates the tide cycle of the ocean, but that's about it as far as I know. Radiation, almost nothing. The moonlight is vastly dimmer than the sunlight. About the only thing earthlings use it for are celestial navigation reference, and even then they can just use a visible star. Frankly, the lack of surface gravity and radiation shielding will affect them more than the lack of a moon.

Not necessarily in complete isolation; they could have social interactions with each other. Though, that's a good point.

Good point. At that point, it may be cheaper to store the DNA sequences of said embryos' species in a storage/archive system, and use this to clone them when needed using blank ovum cells and synthetic wombs. Though, if we already have that, it's a step away from simply storing a bunch of sequences from different humans, and cloning them at the destination using the same tech used to clone the animals. The problem then comes down to a reliable automated parenting system to raise enough humans for them to continue procreating the old-fashioned way.

@sevenperforce Separate vehicle, yes, but similar technology. A2's SCIMITAR engine is basically SABRE minus the rocket-mode parts. It still has the same precooler tech, and the same fuselage design, probably trading some tank volume for passenger seating areas. Presumably, support infrastructure for it can be shared with Skylon. However, Nibb's probably more on-point about the lack of market for supersonic passenger transports. The last one that went into service did so at a loss, despite high ticket prices. Also, I covered suborbital airliners before.

Rather than 4 of each animal (there's about 8.7 million of them, and that's the ones we already know, there's probably more), it's more useful to carry 100-150 embryos of only the useful species, like livestock(cattle, pigs, chicken), beasts of burden(horses, mules), and companions(cats and dogs). Or, better yet, cut down the species count by striking out livestock species, and grow synthetic meat. That, or have the beasts-of-burden species do double-duty as livestock. Also, you'd need something to keep the population busy while en-route. A bored population is can be very easily incited to do something drastic, like rioting and breaking stuff. This means it might not be in your best interest to automate almost everything inside the ship (no robot workers), so that the population has something to do. In addition, you might want to have some sort of manufacturing capability on board. Everything from simple tools to high-tech machinery breaks down no matter how robust they are built, so it's a good idea to be able to manufacture spare parts from raw materials found en-route (or carried on board; lightly-processed stuff like steel plates are denser than ready-made items like gears). Not just a stash of ready-made spare parts, mind you; different equipments needs different spare parts (you can't fix a mechanical transmission with a processor chip), and there's no sure way of knowing how much of which part will break more. This will also be another way of keeping the populace occupied.

It is viable, but only for very specific payloads. Something that needs to be delivered fast, and be virtually untouchable in transit. Nuclear missiles, in case it wasn't obvious. So the question turns to how much a single Minuteman missile costs. Wikipedia says $7,000,000, which I assume includes the payload.

I agree, this kind of design screams madness from a civil engineering perspective. The question is, is it crazy enough to actually work?

I think I slightly understand the theory behind it, though feel free to correct me if need be. Tall buildings like skyscrapers swing back-and-forth like an inverted pendulum when wind blows. It keeps itself standing by virtue of the materials used being sufficiently flexible to tolerate the oscillating motion, but it needs a way to stop itself from collapsing due to oscillation-induced structural fatigue. Enter the Tuned Mass Damper. Source: The idea is that the object with the larger mass will transfer its momentum to the object with the smaller mass, and then damping the smaller object's oscillation. The effect is shown on the animation above. The idea, I think, is that, rather than damping the tuned mass oscillation and wasting it as heat, it can be harnessed as a source of energy. It happens so that there is a device that can convert oscillatory movements into electricity. Meet the Linear Alternator. This is a possible piston engine design powering a linear alternator. The permanent magnet is fixed to, and moves with, the piston, while the generator coil is fixed to the engine block walls. The piston starts in the far-right position, receiving a fuel-air mix which is promptly ignited. The expanding combustion gases push the piston to the left, compressing an inert gas in the gas spring chamber. When the piston reaches the far-left position, it exposes holes in the cylinder walls leading to the exhaust, venting pressure in the chamber, and enabling the gas spring chamber to push the piston back into the starting position, completing the cycle. While all this happens, the magnet oscillates inside the generator coils, due to the piston's movement. This generates AC electricity, the frequency and voltage of which are directly correlated to the frequency and travel of the piston movements, respectively. So, putting all that together: 1. The structural design depicted in the website is a pillar which is thicker on the top section than on the bottom section. This makes it top heavy, and very prone to oscillating when blown by the wind. 2. The structure may be equipped with a tuned mass damper, which allows it to transfer the oscillation from the structure to a small, manageable moving part, from which it can easily capture the energy contained by the oscillation. 3. The 'damper' part of the tuned mass damper might as well be a linear alternator, which absorbs the oscillating motion of the tuned mass and generates electricity. And that concludes my analysis of the working of this 'bladeless wind turbine' object. It suffices for me to say that the concept is indeed plausible.

Also, Red Mercury.

Why hasn't anyone proposed using water as propellant? Not exactly great Isp, sure, but it cuts down a lot on spacecraft logistics. No need for funky storage systems, temperature requirements identical to the hab module, can be cracked into hydrogen and oxygen for LSS, fuel for chemical propulsion systems, and Anthraquinone'd into hydrogen peroxide for RCS. If ISRU is available, it's quite common in the Solar system inside icy asteroids.

@fredinno, I have to agree on AngelLestat on this one. Yes, hydrogen airships are flammable. Yes, they can be dangerous if built poorly. Yes, Hindenburg will happen again if precautions aren't taken during flight. But hydrogen airships aren't exactly large floating fuel-air-bombs. They're quite durable, for a few reasons: -Inside the airship's envelope, the gas is kept at barely above local atmospheric pressure. When the vessel climbs, the envelope inflate to compensate. This means if there are any leaks (say, some bloke aimed a machine gun at it), leaks would happen slowly and, due to the enormous volume of the envelope (and their pressurized hydrogen stores) , pressure would go down slowly as well. If the leaking gas caught fire, given a fireproof envelope, it would not bring down the ship, since the slight overpressure ensures that outside air do not get into the envelope. It's still an emergency, since the vessel is on fire, but most likely survivable. -The gas inside the balloon is pure hydrogen. This, on it's own, will not burn; it has to be mixed in with outside air to be able to burn. Even if an explosive charge is set off inside the envelope, all it would do is send a pressure wave spike inside the envelope, popping off safety valves and/or overpressure patches (sections of the envelope designed to fail if pressure exceeds a safe limit). Once on the ground, these are easily repaired and patched over, and the airship is good to go. -The airship envelope is a soft material that won't set off on-contact explosives. Explosive ammunition like this won't be set off on impact, simply punching holes in the fabric smoothly and go unmolested all the way to the outer side, unless it hits something solid inside. Even if it does hit something, pure hydrogen gas do not burn. To bring down an airship quickly, one would need a warhead that can cut through large swaths of fabric, like this: This would immediately drop the internal pressure of the airship, while also letting a lot of hydrogen mix with the air. At this state, the hydrogen airship can be blown up with ease.

Expanding @KerbonautInTraining's response. In an area where the force of gravity is magically eliminated, for any two non-thrusting objects, there won't be any relative movement between them. If an astronaut in a space station released a ball while floating in the station, he would observe the ball either perfectly still, or moving at a very constant velocity. In micro-G environments, such as when in low orbit, each individual objects of the previous scenario are instead at slightly different orbits around the celestial body. Due to this difference in orbit, from one object's perspective, the other would move relative to the observing object, producing the effects described in the post above.

I think walking is more efficient. Less muscles to move, and less contact points on the ground (less friction). Not an expert, though, so don't take it as face value. I might be wrong.

How do we estimate a random animal's limb mass (limb defined as any body part that attaches to the abdomen at only one attachment point, and be movable by the animal) with a given physical structure and average density?

Photon drives need 300 MW to generate 1 measly Newton. Solar-power photon drives are laughably weak.

Should've caught on that earlier. Silly me. Though, I think there are more problems than simply putting as much kinetic energy into a projectile. Terminal ballistics matters too. If a high-velocity projectile overpenetrates the target, less than 100% of its kinetic energy is transferred to the target. Unless the projectile's path gets through some vital component, or ruptures a liquid-carrying pipe, it's not going to do much damage. Here, I think, is where rail/coilguns shine. By varying power input, projectile exit velocity (and therefore kinetic energy) can be varied. This means the same railgun, firing identical projectiles, can be set up to impart as much damage as it could without overpenetration, whether the target is heavily or lightly armored, or even soft targets like meaty creatures.