andrewas

Adrian Bowyer got there first. http://www.newscientist.com/article/dn7165-3d-printer-to-churn-out-copies-of-itself.html#.U1Ecx1d5fyA

The best specific energy I can find for a battery is something under 1MJ/Kg. A Q-thruster producing 9.81N at 300KW/1N would drain that battery in 0.34 seconds. That could be considered the effective ISP of the system. Tell me again how storing energy is in any way helpful for q-thruster performance? And there are no really exciting battery technologies on the horizon. Lithium/sulfur may double the performance if they can get it to work, which they've been trying since the 60s, but doubling a tiny number still gives you a tiny number. We need orders of magnitude improvement to make battery powered Q-thrusters even remotely viable. No, Q-thrusters, if they have any application at all with current energy generation technology, will be used in deep space missions where they can fire continuously. They do better in the inner system where solar power is plentiful, cutting down the mass of solar panels needed to run them. I still don't think they'll work out for any real mission, its better to carry a few hundred KG of propellant for an ion engine than a huge solar panel for a Q-thruster. And the ability to run forever doesn't help as much as you think, nobody wants an engine which forces you to extend an already multi-year mission so the engine can deliver the required dV. And solar panels degrade over time, so even if you have infinite patience the dV from a solar Q-thruster is finite.

Sun shade to moderate incoming sunlight while we adjust the composition of the atmosphere as a more permanent solution. Taken to extremes, such techniques can restore the climate even from a venus-style runaway greenhouse, though if we let it get anywhere near that bad, we will inevitably lose most of the biosphere. In more minor cases, it might be enough to start sequestering CO2 and managing greenhouse gasses to avoid needing a solar shade - as with every repair job, it's much cheaper and less disruptive to fix it early rather than letting things fall apart until we have to take action.

The citadel rotates for gravity outside of the Presidium, which would be in micro-g so it gets artificial gravity.

I think the next step should be a centrifugal habitat in LEO, to perform partial gravity research and test closed loop life support systems in preparation for a mars mission. Among the questions that need answered are - how much gravity do humans need to survive in the long term, and can animals successfully reproduce in partial gravity. That second one is critical long term, if we can't reproduce in martian gravity then we can't colonize it at all.

Photons, according to KASAspace in the now locked thread where this started. He may have changed his tune since, but he was trying to argue that photons must have mass because they carry momentum. In reality, of course, massless particles travel at lightspeed, massive ones travel below light speed, and Einstein's formula still gives you a division by zero if you plug lightspeed in as velocity without also having a mass of zero.

This http://www.orbitsimulator.com/gravity/articles/what.html should do everything you want.

But you can take the speed accurately without taking the position accurately.

Einstein didn't. Einstein, if I remember what you are referring to, discovered a formula which results in division by zero when particles with mass travel at lightspeed.

It will always be trivial, if tedious, to mod all the costs to zero if you want to play career without worrying about financial issues, assuming that sandbox doesn't satisfy you and career isn't configurable enough out of the box.

ℤ2 is not very useful, at least not to my knowledge. Its probably very useful in some areas, but not to the layman. ℤ12, on the other hand, comes in handy any time you deal with a 12 hour clock. ℤ24 when you use a proper clock. ℤ7 when dealing with days of the week. And the concept is very important in cryptography - some operations that are easily reversible in normal arithmetic become almost impossible to reverse in modular arithmetic.

Yeah, but 'ocean' is not a unit.

No. Radioactive material in orbit is not scary. What is scary is radioactive material on an uncontrolled re-entry, or even better, material that was never intended to re-enter and which should be in graveyard orbit. Even then, most of it is safe enough - for instance, the apollo 13 RTG fuel cask, which was supposed to be left on the moon but which re-entered along with the rest of the LEM, coming through re-entry intact and winding up deep in the ocean with, so far as we can tell, no leaks of any kind. Still, there might be something to fear from old soviet hardware.

It is. Changing the relative masses of the components changes the expected position of the CoM, but the same phenomenon apply. A heavy gyro round a light tower is more sensitive than the reverse, thats the only advantage to doing it that way around. I trust Cambridge to accurately report on whether or not their results are the expected ones or if they show the anomaly Laithwaite predicted. But no matter, because you've replicated it yourself. Since you are the one making extraordinary claims here, Im sure you realize how important it is to document that experiment in every detail, so when you share the video you will give us the masses of the components, show how effective your frictionless surface is, demonstrate and mark the CoM of the static structure, show us clearly how that CoM is rotating around the effective CoM as the gyros mass drops in accordance with Laithwaite's predictions.

Except that, before engines went offline, they were stationary with respect to the cloud of debris. I believe you actually see it accelerating WRT that debris when the engines go online, but I can't find the relevant scene on youtube and my DVD is way over there. Also, falling from that altitude should take days, and they arrive in Earth's atmosphere way to slowly for something that fell most of the way from the moon in a couple of minutes.

The relative masses matter because the change the expected position of the axis of rotation. If Laithwaite was correct and spinning gyroscopes were lighter, then a heavy gyro precessing around a light tower should have an axis close to the tower, depending on how strong the effect was and how much non-rotating mass was on the gyro end of the arm, the result might look exactly like the Cambridge video. Of course, Cambridge say that it proves the opposite, but Momentus doesn't seem to trust trust them. Since I've run across a guy named Momentus who was arguing this kind of thing way back in 2005, who I assume is the same person as our Momentus, I doubt there's any point in trying to convince him other than by encouraging him to replicate that experiment. This isn't something like the LHC, where if you don't believe the results you can't do anything about it because no other machine on the planet can replicate the experiment, this is something that anyone who wants to can replicate with very little money.

Perhaps they just used the equipment they had to hand. Since they already know the outcome, I doubt they put too much effort into that replication. However, what would be the point of lying about the outcome of an experiment this easy to replicate? All you need is a gyro, a tower, and a frictionless surface, ice will do if you are careful with it. I'd offer to replicate it myself, but I lack a suitable gyro and if you're willing to accuse Cambridge of lying, you aren't going to believe a random internet guy if I release a video showing a result that doesn't fit into your view of the world. Instead, I encourage you to replicate it - and please, document it properly, make sure it really is a frictionless surface, level is as well as you can, make sure its actually flat, mark the CoM so we can see if it stays still, publish the masses of the tower and the gyro so we can see if your mark is reasonable. And so on.

We wouldn't necessarily know it was a bug or that we were in a simulation. The only way we could be sure we had a bug, is if we found a phenomenon that we could prove could not be included in a consistent theory.

You're committing the single most common mistake in mech vs reality arguments - you give the mech hypothetical future-tech but the opposition aren't allowed it. Guess what, if mechs are ever built and tried in warfare, they are going to go up against technologically equivalent enemies. For the first few battles the enemy won't be equipped or trained to fight mechs, but that will rapidly change. Its important to consider what conventional forces will do to combat the mechs, rather than simply declaring that your mechs are from the future and thus win by default. Also, regarding point 3 - gears let you trade force for speed, they don't get you any more power. If takes X amount of power to move a limb at a given speed, you can't cheat and gear up a smaller engine to do the job, the engine will simply stall. Walking is less efficient than rolling, your mech needs more engine power than a tank does, relative to its mass.

Does anyone know how the weight of the needed shielding varies with the power of the reactor? I believe it works in our favor as the engine scales up, doubling the reactor power means you need to add another halving thickness to the shield, so the TWR goes up.

Both - UV-C splits regular O2, the resulting single oxygens then react with other O2 molecules to form O3, which is more or less opaque to UV-B. Which hints at why the OPs plan couldn't work, ozone is just part of the earth's shielding, you need the rest of the atmosphere and the magnetic shield to keep everything harmful out.

Which is a good thing, because a 'mech needs a heck of a lot more armour than a tank or aircraft for the same level of protection, and even then has weak spots that are much harder to armour.

OK, that works, the body of the craft has now moved from where it started. Now, get from state 3 to state 1 without cancelling that movement.

And I said that doesn't happen. Except that the larger sail has a smaller payload fraction, but that only lets you approach the acceleration an unladen sail would generate, which is still puny with current technology. We need a much lighter material if we want the kind of accelerations you are talking about.

Solar sails don't scale like that. Double the radius and you quadruple both the force generated and the mass of the sail. Payload fraction goes down so performance does go up, but that can only get you so far. What you need to do to get a high performance sail is to make it lighter. There are various proposals for that, including one group who think they can build a sail from carbon nanotube mesh and get 10g acceleration at 1AU from the sun. Alternately, theres always the laser sail. Put a great big laser in orbit and shine it on the sail of departing ships.