Magnetic Space Launches 301
DiZNoG writes "This CNN article discusses NASA experimenting with the idea of using Mag-Lev technology to launch payloads into space. Mentioned in the article is that the U.S. Navy is working on the technology for it's aircraft carriers to launch fighters. Unfortunately the NASA project is horribly underfunded ($30,000) for research. Cool technology, let's hope that the Navy research gets us a step closer to not burning all that Oxygen and Hydrogen to get to space...
Re:NASA's lack of foresight... (Score:3, Informative)
Lots of reasons. First problem is to keep the ISS from being flung in the opposite direction of the direction of the launch. You could possibly solve that one by making each launch fire the actual launch vehicle and a waste mass in the opposite direction to conserve momentum, but then you double the power requirements and the mass you have to get into orbit.
The next problem is that because of tidal forces any long linear object in orbit will be pulled into an orientation where the long axis of the station is pointed directly at the earth. The center of mass of any object in orbit at orbital speed, but anything closer to the earth is moving slower than orbital speed (because speed to maintain orbit gets faster the closer you get to the center of the earth, but the whole object can only go at a fixed speed) and anything further away from the center of mass of the station is moving faster than orbital velocity.
At any rate, if you've got a long structure in orbit, one end will point at the earth, the other directly away. The amount of energy required to point the launcher anywhere remotely useful would probably be better spent attached to the object you want to launch in the first place.
Re:Perhaps a silly question? (Score:5, Informative)
I'm not positive, but I'm pretty sure that no material has the tensile strength to hold its own weight all the way to the moon. If you held a 5 foot string, it weighs practically nothing. If you dug a 100 mile hold and held a 100 mile string that was dangling down it it would rip your arm off. If you suspended it from something stronger than you, the string would just break under its own weight.
Plus you can't anchor a string to the earth and the moon. The earth rotates much faster than the moon orbits. If you attached it to just the earth it would only line up with the moon once a day, and it would be going so fast as it passed it you would be smashed into the moon. By the same token if you attached it to the moon, it would fly around the earth every 24 hours, meaning it would be blazingly fast, about 350 mph. Bad rope burn if you try to grab it.
However, it might be possible to build a 'string' that is strong enough to simply lead into orbit. Anchor one end to the earth, and the other to a large mass slightly outside geosync orbit, which is still way way closer than the moon. Then you can climb the string all the way to the mass and be flung away from the earth. At any rate we still don't have strong enough string. Yet.
Re:Maybe MagLev will save us yet! (Score:4, Informative)
3112 gees
100 gees
15 gees
8 gees (comfy?)
Think about how long you watch a shuttle launch, and that it's accelerating for that entire time. It takes a long, long track to pull this off. Better to build short, fast ones and use them for launching construction materials into orbit.
Re:Used up in the cost to get the electricity, tho (Score:4, Informative)
The advantage here would be that you dont need to burn fuel to make the fuel move. You dont need to add extra weight to get started. Im not an expert, but i assume that the basic idea would be gather speed (not even necessarily vertically to begin with), and then launch it vertically. It needs to be vertical to escape the drag of the atmosphere as quickly as possible.
Re:Used up in the cost to get the electricity, tho (Score:1, Informative)
Re:NASA's lack of foresight... (Score:2, Informative)
Err... the (instaneous) velocity of the ISS is perpendicular to the radius of orbit (as would be the drag but in the opposite direction)) and so surely you wouldn't be aiming that way!
Simon
Re:Cost per what? (Score:4, Informative)
The one you are more used to of course. That doesn't make it better in any objective sense.
I'm about 190cm (say, a handswidth under 2m), or 0.009 furlongs, or 0.3 rods, or 0.09 chains. Which of those gives a better mental picture?
Incidentally are you really 5'11" to within 1/200th of an inch? If not, the apparent accuracy of the ".34" you quote is completely bogus.
> Does metric even have "dry volume" measurements?
Yes of course. Cubic metres. Same as wet volume, since a volume doesn't actually change depending whether its contents are wet or dry. The dimensions of volume are length^3, so the SI unit for volume is (unit for length)^3.
Re:NASA's lack of foresight... (Score:3, Informative)
Lots of counterintuitive things happen in orbit. For example, if you are chasing a probe and accelerate toward it, it will move farther away - you accelerate, you go into a higher orbit, and your orbital period decreases, so you aren't going around as fast. The probe's orbital period stays the same, so it's now going around faster than you.
Re:Used up in the cost to get the electricity, tho (Score:2, Informative)
You're confused -- you want that extra launch velocity from the Earth's rotation for everything except polar orbits.
Not all used up -- it really is more efficient. (Score:2, Informative)
Well, not exactly. In a traditional launch, the initial thrust has to get the mass of the payload PLUS a whole LOT of fuel moving. But as the fuel burns, each pound (or ounce, or whatever unit you want) of fuel adds more actual acceleration than the last pound did, because it has the same thrust but less mass that it has to push. The efficiency of the energy spent can be calculated by taking the integral of how much thrust is produced as the mass it needs to push decreases. As the launch progresses, each ounce of fuel has more effect (in the goal of accelerating the rest of the fuel and the payload) than the previous one did.
In the mag-lev case, the mass of the object being launched starts out MUCH MUCH smaller than in a traditional case, and the entire object stays at that smaller mass. By the time the object has reached its target velocity, (I'm simplifying the math a little here) the total energy spent has been mass(final) times velocity squared, instead of the of integral of the mass(inital to final) times velocity squared (mass and time being our changing variables). It'd make more sense if I could figure a way to show mathematic equations in html ;), but if you've had some calculus it should make sense. Much less energy is actually used to get a given amount of mass to a given velocity.
Obviously, it still requires energy, but not nearly the amount of energy for a traditional launch. Likely (at this point in the development of the technology) the mag-lev launch would still require some fuel burn at the end, to get the vehicle from the post-mag-lev velocity to an orbital velocity, and to get it up to the right height, but a lot of energy would already have been saved.
In a nutshell, for emphasis: the vast majority of the energy required to launch something into orbit is used at the beginning of the launch, and mag-lev technology would be able to reduce the initial launch sequence's energy dramatically.
Re:Used up in the cost to get the electricity, tho (Score:2, Informative)
1 molocule Hydrogen (H2) + 2 of Oxygen (O2) gives 2 of water (H2O).
If Slashdot accepted PRE, SUPER, and SUB tags, this would be a lot clearer.
You are right, it takes a lot of energy to make Hydrogen, but according to Web Elements [webelements.com] the normal approch to making Hydrogen is stream + ( carbon or methene), electrolsys of sulphuric acid (SO4+ goes through a complex system, and releases Oxygen, but is far more conductive that water) is too expensive, but it might be different if you want an oxygen supply as well. The reactions above produce carbon dioxide, so unless its aneroibic methene, Hydrogen rockets will still produce excess CO2.
Anyway, for space launchs, the rocket must either be self powered, or doing atleast the escape velocity when it leaves the end of the launch-rails, which, for the Earth, is 11km/sec, well above the speed of sound, so unless you lauch from the top of a mountain, there will be too much atmospheric drag for non-self powered lauches.
To determine the escape velocity use this formulae
sqrt(2 * Gc * M / r) (from Astronomy 120 [yale.edu])
Where Gc is 6.6725e-11 kg-1m-1s-4
M is planent's mass 5.9 72e24 kg for Earth
r is distance of launch from planet's centre (6.378e6 m)
Re:Used up in the cost to get the electricity, tho (Score:3, Informative)