Posted on 06/25/2004 2:21:35 PM PDT by Junior
Leinster's landing grid.
sorry, I never read any leinster - but I am sure my brother did - he was the sci-fi maven in our family, and he would recommend some really good classics to me on occasion.
Without getting into a you-know-what match (and rehashing most of the thread), I'll merely say that I disagree with your conclusion. (And I only say this lest my silence be mistaken for a concession.)
What was cool about NERVA was its reactor also had no moving parts. The reactor was cooled by the propellant.
If you would like, I could repost my lecture on that very subject.
If it has gravity wells, then post!
Yup. In fact. We can use reaction wheels and torque rods for attitude control without the need for any propellant.
ok. Let me find it :-)
Yeah, I thought that was fairly elegant, although from a pure coolness standpoint, I still rather like Orion. One thing I couldn't figure out on NERVA was contingency operation - if the fuel supply failed while in operation, how would they dump the heat? Or do you just jetison the reactor?
I believe, however, that JIMO was intending to use ion propulsion, with power from the reactor. That means (to silly little me) that moving parts are a high probability - I shudder to imagine the qual tests required for that...
-SV
"Correlation at the far end" doesn't make any sense. Correlation requires both ends. You don't know what that correlation is until you can compare the two sequences, which requires a lightspeed-or-slower transmission.
You're right about that. But that's not the case with anything above or below geosynch. There are quite a few burned out upper stages and retired satelites in an equatorial orbit below geosynch that would not be stationary vs. a tether. The relative velocity might only be several hundred mph, but fast enough to destroy the satelite itself and scatter zillions of parts around to hit other spacecraft. Assuming the tether at geosynch (it's most stressed point) is tough enough to stay together.
But the problem still exists that EVERY spacecraft in orbit below 62k miles WILL be on a tether crossing orbit except the active Clarke spacecraft maintained in place.
The only viable solution would be to have a movable anchor on earth, and predict where to move it to dodge targets.
But how long would it take for movement of the anchor to take effect at altitude? Could you predict the "waves" you would induce in it by moveing the anchor to dodge the target?
No, a space elevator is a neat mathematical and materials excercise. But it's way to impractical to ever build.
1) Use winged vehicles up to mach 7-10 to avoid having to hoist the entire weight of the vehicle with raw thrust (let the wings to the lifting).
2) Use air breathing engines up to that speed, so that oxidizer weight is saved, and the impulse required is less because you're thrusting using mass (the air) you didn't have to lift. You don't need nearly the efficiency as pure rocket.
I think the materials and technologies for this is all in place. It just takes the right aerodynamic artist like Rutan to put everything together.
I don't think such a thing has been built yet because only governments have been truly interested in space flight, and they have huge burocracies to maintain, and worry that any cheap orbital vehicle would merely be cloned by people like Kim Jong Il. Therefore, they kill the good ideas.
In every article I've read the explanation is virtually the same. There's two entangled particles separated at a distance. The position of each particle is known. When the one particle's spin or charge flips the other particle's spin or charge instantly flips.
It's also my understanding that JIMO would carry a nuclear reactor. Insisting on calling an "ion engine" might blunt the political impact and enhance the "cool factor", thereby developing a constituency. I suppose it's a matter of timing; if the mood is right when it's ready to fly, environmentalists will be denied veto power.
I understand the concern about Europan contamination, but I hope the realm of PC doesn't manage to extend itself that far out from Earth.
I suspect that 'nuclear' will be a magnet for all sorts of wackiness, regardless of how it's pitched.
The contamination issue isn't the nuclear materials themselves. Europa is a candidate for non-terrestrial life (one of the reasons for going there) in the water region hypothesized to be beneath the ice shell. If you permit the reactor elements, with their residual heat, to melt through the shell, you have in all probability introduced terrestrial bacteria and such to Europa, where you have water. So, if in 50 years or 500 you return and find life, you now have to sort out whether it was native, or you introduced it (or, more insidiously, the terrestrial stuff wiped out the native stuff leaving little evidence of the previous 'tenants').
As it happens, the RTGs don't generate enough thermal density to melt through the ice (nor do their individual elements), however a reactor typically operates at much warmer temperatures than an RTG and there would, in my opinion, be a substantially greater concern than the reactor would sublime/melt through the ice to the water layer below.
-SV
Elevated placemarker.
Would you have a good example handy?
I don't know whether you misread the articles in question, or whether they actually did say that, but I assure you that that is wrong. It's much more subtle than that. Consequently, it isn't as immediately useful as you paint it...but in some ways, it's actually more philosopically troubling.
I'm in a bit of a quandry here, because if I were to give you an explanation that does the topic justice, I'd be up half the night typing, you'd not want to wade through it, and you'd likely still miss the point, because it really is subtle. So let me try something brief and cryptic, in hopes that it will at least steer you in the right direction. And who knows? Maybe it'll make a sort of sense.
Electrons have spin. Spin has three components: up-down, left-right, and front-back. The problem is that the three components cannot all be defined at the same time. So if you measure the component of the spin in the up-down direction, the left-right spin component, for example, will be undefined. If you then attempt to go and measure the left-right spin component, you'll get a random result.
[Geek alert: You may also have heard that the spin is quantized, in such a way that each component can only have two possible values: +1/2 h-bar, and -1/2 h-bar. These are commonly referred to as "spin up" and "spin down", but don't think that that means an electron can only have two possible spin states. An electron can have an infinitude of different spin states. Unfortunately, you can't measure them: the best you can ever do is to measure one out of the three components.]
It is possible to prepare two electrons such that their spins are correlated. Each electron has an intrinsic angular momentum of 1/2 unit; if you generate electron pairs from states with an angular momentum of zero, the electron spins will be opposite, because angular momentum is conserved.
This is the long-range correlation: if you measure the spin component of one of the electrons in the up-down direction, it will determine the up-down spin component of the other electron. If one is spin-up, the other will be spin-down, and vice-versa. If you instead measure the left-right spin component of the other electron, you will get a random distribution of left and right measurements, regardless of whether the first electron was spin-up or spin-down.
You cannot use this to send a sequence of bits, for several reasons. First and foremost, an entangled pair can only be measured once. With the first measurement, the entanglement is forever broken. Second, the correlation--or lack thereof--is only apparent after you compare the sequences after the fact. No matter how you orient your detector, you see an apparently random result for every measurement. Third, you can't choose what bit you send: the bits are something you measure. If you try to force the electron into any given spin state, the entanglement (and the correlation) are destroyed.
There's much more to it than that. I didn't mention eigenstates or state vector collapse. I didn't really get into non-commuting observables. I haven't even hinted at Bell's Inequality. But I do hope I've answered your question.
Exactly. I have high hopes for this thing but so far the longest nanotubes produced are 20cm long. Not exactly the thousands of miles they need for this project.
Would the wobble and similar lack of circular symmetry in the Earth's spin cause trouble? These do not have local mean zero and thus are not self-cancelling. One would get a small but persistent and non-perodic force acting on the system.
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