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Magnetic Space Launches
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...
I'm wondering how much of the benefits of this is in the acceleration/speed they hope to achieve in a small space, versus the height they want to reach. I'm an idiot on the subject, admittedly (who's an expert, anyhow?), but which is more unrealistic, building an EM rail that reaches near orbit, or trying to accelerate 100s of tons verticaly to reach a high speed? (I'm still going to assume that they'll use rockets to reach orbit, and not 100% rely on the rail for the energy.)
Well, I don't think the *cost* of energy (in terms of dollars) really is the issue here. It is the amount of onboard fuel which displaces the amount of cargo you can take into orbit. And since fuel has weight, the more fuel you add, the more fuel you need to achieve orbit. So, earth-based electricity vs. vehicle based fuel really would be a plus.
let's hope that the Navy research gets us a step closer to not burning all that Oxygen and Hydrogen to get to space...
Yes, we must reduce emissions of deadly Dihydrogen Monoxide! It's already filling our rivers, streams and oceans, and has been found even in the ice of Antarctica! The time to act is now, people! Before our wells are full of this dangerous chemical!
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.
Jherico
What can the average user can do to ensure his security? "Nothing, you're screwed"
Though I guess you'd have a hell of an "electro-magnetic signature".
pr0n - keeping monitor glass spotless since 1981.
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.
Jherico
What can the average user can do to ensure his security? "Nothing, you're screwed"
Whoa there, son. Y'all from the future? Let's use units we all understand: what's that work out to in bushels of cotton per hectare?
Hmmm, I can't help but think that if we ceased habitually using stone age units of measurement, then we might be able to stop pounding Mars with "landers" ;-)
If you were blocking sigs, you wouldn't have to read this.
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.
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They want to reduce the fuel needed. Meaning the launch vehicles will have to do some thrust by themselves, but not nearly as much.
Also, some people have noted that g-forces would be a problem. Not likely, if we angle the vehicle at a 45-degree starting angle we drastically reduce the ammount of g-forces needed.
Another point, the maglev system is frictionless. The LV is at no time during the launch touching the track. You've seen bullet-trains, right? Same consept. This further reduces the work needed to launch a vehicle.
I do see this system working. It will probably be 10 years or so, but it will work.
This makes me feel REALLY old, but the EML technology research has been going on for over 20 years. I recall the 1990 High School CX debate topic very well and spent most of the year debating EML launchers (prototyped on Sandia National Labs railgun). We spent the summer in the library in New Mexico visiting Sandia and UNM to research our cases. They were already launching coffee can-sized payloads at that time.
Some of the EML experiments from the late 80s and early 90s were visited at a 95 IEEE pulsed power conference: here. Of course, it's been a HOT topic since pre-85, when the first IEEE pulsed power conference was held.
We've been at the brink of maglev space launches for the alst 20 decades. Maybe it'll happen tomorrow. Probably not. There's basically no money in this sort of solution for defense contractors, so it generally languishes in congressional committees when it comes time to fund...
Oh well. It would be cheaper, cleaner, safer, and a whole helluva lot more fun at parties... but the same issues applied 20 years ago as today: it doesn't get funded b/c it's a public works-type solution to space. There's no money for Lockheed in something like that.
I didn't think they launched rockets exactly vertically. To get the orbital speed right, they go off at an angle - possibly after goign straight up for the most dense part of the atmosphere. I suppose for geostationary sattelites they don't need quite the rotation (and they need to go further up). Easier to explain with a picture, but no can do here.
This is why they like to launch from near the equator and always orbit in the same direction as the earth - you get a substantial boost (900 miles an hour according to Monty Python).
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You'd be launching the probe on a tangent to the orbit, not on a perpendicular to the orbit. This would cause the ISS to accelerate along the tangent to the orbit, giving it a higher velocity. You achieve higher orbit by going faster, not by going away from the orbited mass.
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.
And I made a mistake too.
OK, here is the correct formular:
a(t) = a(t)
v(t) = v0 + integrate(a(t))
v(t) = v0 + a(t)*t - Integrate (t * a'(t))
So the speed also increases because of decreasing gravity over time
s(t) = s0 + Integrate(v(t))
s(t) = s0 + v0 * t + a(t)* 1/2 * t^2 - Integrate(1/2*a'(t)*t^2) - Integrate ( Integrate (t * a'(t)))
This is more correct. But what it essentially means is that the higher you go with less gravity, the more easier it is to gain distance (=height)
Imagine a cable running from the top of a 50 km tower into geo-stationary Earth orbit. Travelling on the cable is made through electromagnetic propulsion. Nasa is considering a 50 years timeframe for the space elevator to become real.
Maybe I'll go in space after all.
Men are born ignorant, not stupid; they are made stupid by education. Bertrand Russel
Not quite. First you need the energy of electricity to create the seperated hydrogen and Oxygen in the first place. Then you burn the hydrogen and oxygen at take off. With this new thing, you could skip the second step and use electricity at take off. That leaves the initial energy the same but cuts out the launch H and O consumption. I am always for converting things to electricity. That minimizes the technology we have left to improve. In other words we can focus on production technology as opposed to consumption technology.
Few people here seem to understand the crucial issue. A couple do, but their posts haven't been modded up... here's another try.
You don't build a magrail to give your spacecraft orbital velocity. Of course that's silly, for the reasons given above. You use it to give you some small PART of your velocity. This is extremely beneficial.
The crucial insight is that each bit of fuel you use for some stage of the flight needs to be lifted be even more fuel in the previous stage. Think backwards from orbit and it will make sense.
Say you have a 100-kilo satellite you want to accelerate at a constant rate for some period of time. For the last second of your flight, you need to burn, say, 10 kilos of fuel. That means the second before that, you need enough fuel to accelerate 110 kilos, 100 Kg of spacecraft plus the 10 Kg of fuel you'll need in the next second. So you'll need 11 kilos of fuel for the second-to-last second of acceleration. The second before that, you need 12.1 kilos. and before that, about 15 kilos. If you know anything about exponentials, you can then imagine how much fuel you need for the FIRST few seconds of the flight.
(This is not actually quite how spacecraft usually work, but it illustrates the general point nicely)
Over 90% of the fuel you are carrying is used just to lift the rest of the fuel that is burned later on, and a huge fraction of it is burned in just the first few seconds. And of course each kilo of fuel you carry requires a larger spacecraft to hold it, which in turn weighs more, which in turn requires even more fuel. So, if you can use a 10km or 100km rail to get your first few seconds of acceleration, you save a huge amount of fuel. This means a smaller spacecraft, which in turn means even LESS fuel carried.
The power burned by the railgun/mass driver/maglev whatever may actually be more expensive in raw form than rocket fuel (i.e. kerosene, in Russian rockets, which is less expensive per joule than electricity. US rockets use liquid hydrogen, which costs a bundle because you have to use vast amounts of electricity to cool it.), but it doesn't exponentially increase in magnitude as you head down the rail, because it's transmitted through wires rather than carried as mass in the spacecraft. Every second, you only need the same amount of electricity you used the previous second.
The same is true of chemical-powered ram and shock cannons, where fuel filling a cylindrical pipe is combusted behind the accelerating spacecraft travelling through the pipe. (not recommended for human payloads).
Furthermore, if your spacecraft has wings, this may give you yet another benefit. The shuttle has wings, but launches straight up, meaning for the ascent they are just dead weight requiring a huge, exponentially-scaled mass of fuel to lift. But on an almost-horizontal launching system, the wings can provide lift, and thereby actually be useful on the ascent stage. This of course is made easier if the vehicle already has significant velocity before it even lights its engines.
This whole system may not be a panacea; I'm skeptical too. But it probably is worth looking into, because it may help and doesn't require any technologies that don't yet exist. (unlike skyhooks/beanstalks or other strangenesses)
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Definitely doesn't need to be vertical - you're out of half the atmosphere in 7 miles, out of over 99% of the atmosphere by 50 miles high, and by that point the velocity you need to get to orbit needs to be horizontal, not vertical; you still need some vertical thrust to counteract gravity of course, the main point is there's an optimal thrust/weight ratio beyond the atmosphere that is also associated with a specific curved trajectory, far from vertical...
Energy: time to change the picture.