Posted on 09/09/2005 5:26:35 AM PDT by nuke rocketeer
We're talking about just a bit more air than that, and hence, "some time after" is going to be quite a bit shorter than with your balloons. After you open your door, there is going to be some point where the pressure at the bottom of the tube is still zero - no air has reached the bottom yet - but is something else, some non-zero pressure, higher up the tube.
Now, if you happen to be standing in the middle of the tube, there is going to be a point where the pressure around you increases from zero to something, and rather rapidly too. The farther away from the mouth of the tube you're standing, the longer you're going to have to wait for that to happen, because the air has to travel down at the tunnel to get to you. But it will happen, because that air is coming, whether you paid attention to Boyle's law or not.
The thing I was proposing was only for interplanetary travel, so no winds to deal with in vacuum. It would be a nuke propulsion unit trailing a tether that would drag the payload capsule along with with it, so no extension cord either. At 0.01 G, the load would not be high, but a unit that could maintain that indefinitely could build up considerable velocity
It's not going to be zero, and that's just about all that matters, innit?
If the pressure behind them isn't as great, as it was at the beginning, a forgone conclusion...
Do you imagine that this is enough to stop the flow to the zero pressure area farther down the tube? After all, whatever the pressure is behind the leading edge, it's not zero, right?
Basically, what you're telling me is that turbulence and M. Bernoulli - and presumably special relativity - are going to conspire to keep the molecules of air from accelerating to c. Well, that's fine, but they're still going to the zero pressure parts of the tube, and they're still going to meet up with your railgun sled somewhere in that tube as they go one way that the sled goes the other.
Well said. We also need a new near miraculous type of power before intending to go beyond where man has never gone before.
NASA needs to get outside the box. Chemical propulsion should be an anachronism. From your great link:
There are still folks trying to figure out how to get through the Van Wyck Expressway alive.
We don't need no stinkin' wings!
You put a nuke under a big steel plate and I guarantee you that sucka will FLY! You just gotta make sure you set off the next one before you fall back down and crash. Two, maybe three "pulses" and you're well out of the atmosphere, assuming you start in the atmosphere.
I think the most rational use of Orion is exo-atmospheric, however. But then you're still left with the problem of getting out of this gravity well before you can really get started.
By the way, I think the best fictional description of Orion I've seen is in Niven and Pournelle's Footfall. That's where the "this sucker will move" line comes from. Pournelle is a long time proponent of the "big dumb booster," including "old bang bang."
We WILL go back to the stars, riding a fire in the sky!
Project bang bang was in Footfall, not Lucifer's Hammer
Those two are Niven and Pournelle's best.
Private enterprise hasn't given us little spaceships to fly around in (like George Jetson).
Some things things are not yet economically viable.
On the other hand, our "communicators" are very advanced.
Well that's not true. Virgin Airlies, or some spin-off, is already placed orders for spacecraft and is selling, or plans to sell, 'space vacations'.
" Entering the atmosphere already above 10,000 (half of the mass of the atmosphere) would decrease structural loading. A high energy laser could also super heat the flight path just before to lesson resistance (like lightning splitting the air). "
Quite early in the discussion, you described an elegant suggestion. I have only two things to recommend to make it even more useful.
First, I would not make it an equatorial mountain. I know the reasoning behind this, to take advantage of Earth's rotation. But I would place the rail gun in Antarctica. The cladding necessary to prevent damage to the ship -- the ablative material which would protect it, would be ice. Maybe even a lot of ice.
The idea about using a laser to heat the air ahead of the vessel is also a good one. That is why I used it in a Science Fiction novel published last year. "...high output laser energy is sent forward to prepare the undisturbed atmosphere in front of the ship to expand and get out of the way, so we can slip through without pushing the air..." (page 189, Chapter Sixteen)
My second reason for locating in Antarctica is a commercial one. Once the ramp is set up to launch "packages" (electro-magnetically) toward the edge of the atmosphere, one could contract with governments or individuals in desert areas of Australia or Northern Africa, or any desert on Earth, to deliver fresh water on a contractual basis for irrigation purposes. This should pay for the overall enterprise, and allow up to five million square miles of desert to become productive agricultural zones.
Better plan on building up the new gravel pad at NO a couple more inches to compensate for the extra rise of sea level.
LOL. Setting aside the fact that an "instant" rise is linear - it's merely a line with an infinite slope - I really don't think you can claim any sort of "cushioning" at all until you figure out just how much air is coming at you and how fast it's going. Basically, you want folks to believe that if you drop a column of air weighing, oh, 2 million pounds or so onto an object traveling the opposite direction at 8 km/s in the opposite direction, it's okay, because the rise in pressure is going to take at least a few milliseconds or so. Gotcha. LOL.
It was never my point that simply opening the end of the tube and letting air rush in was a "great idea"...
Was that really so hard? Really, now.
Mr. Boyle's law certainly states that increasing volume decreases pressure, so I think I've got that one covered.
Still didn't do the math, I see.
However, Bernoulli certainly would NOT support your original posts, which were maintaining a solid flow of air at 1 atmosphere...
They were? You must be thinking of someone else - I don't recall claiming anything specific about the actual pressure of the column, other than that it would be non-zero, and indicating that you could expect an approximate atmospheric pressure of 0.3 atmospheres at 29000 feet. Perhaps before we continue, you'd like to review what I've actually said, instead of responding to what you imagine I've said.
...as the leading edge of the wave would be moving the fastest, with incidentally ever decreasing mass. Why? Because gas molecules bounce around at random.
You can't be serious. Individual water molecules bounce around at random too, but that doesn't obviate the fact that they're all going over the waterfall sooner or later. If you'd like to try calculating the position of each individual molecule, be my guest, but I can save you some trouble by stating that the column of air is headed down the tube. Period.
I don't think anyone considers that significant, insofar as it appears to me that you've simply invented numbers in an attempt to wield them the way villagers wield a cross to ward off Dracula. Any time you feel like putting a little meat on those bones, I'll be around. In the mean time, those of us who've ever felt a blast of air while standing on a subway platform will continue to wonder just what in the hell you're babbling about.
Particles only move when they have more pressure on one side than they do on the other side.
Hello, McFly? Anyone home? Open the window. Observe all that air. All that air creates air pressure outside the tube, whereas there's none inside the tube. Hence, air moves from high to low pressure, into the tube. I don't think I can do this monosyllabically, so please don't make me try.
Thus if air is moving into the tube AND moving down the tube the air mass cannot be of constant density.
As convenient as it is for you to "refute" arguments I haven't made, it's really a touch dishonest. See ya round.
I've decided to outsource your argument. Call your local HVAC people. Ask them how big a blower you need to move air through 50 feet of tube. Then ask them how big a blower you need to move it through a 300 ft tube to keep the same volume of air moving. When they tell you it will require a bigger blower, you may begin your argument, and tell them what morons they are. I'm sure they will be just as impressed with you as I am.
I take it all back - science isn't your problem, literacy is. When you feel like actually reading my posts, do drop me a line, and we'll pick up where we left off.
For those who aren't science fiction fan, the title plays on the classic 1954 short story The Cold Equations by Tom Godwin.
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