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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...
Although this technology is by far a better way to get payloads into space, all the energy used to create sufficient electricity to do so would make this method of launch just as costly as the previous. Mag/Lev is an excellent suggestion, after we make more breakthroughs in superconductivity and emf it will become a spectacular solution.
Of all the Universal Constants, here's one I know: Nice guys finish last
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!
If I remember a while back, I could have sworn I saw some sort of launch system in either a computer animation demonstration or in a game itself.
This idea would be interesting to apply into space as there is very little friction in space to slow things down. Why not make an addon on to the IIS to launch vehicles to Mars or Venus via this launch method? If the track was long enough it could go faster than convention rocketry. And in fact, less fuel would be needed on the vehicle since the mag-lev was the device that launched it.
Except there's that funny problem about space. If you launch a spacecraft off of the ISS with a magnetic launcher, then the ISS itself is moved in the opposite direction (based on the relative mass of the station to the vehicle). That is, the ISS is launched, most likely to a lesser degree though, than the vehicle is. Kind of like (but not really at all like) dropping sandbags from a hot air balloon.
sounds like a good way for the ISS to magnetically propel itself right out of orbit...
I don't care if it's 90,000 hectares. That lake was not my doing.
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"
By using mag-lev for both takeoffs and landings, the Navy could presumably have takeoffs and landings on the same boat very close to each other, without the complexity of the current mechanical system. But, of course, mag-levs are useless for landings from spacee, since spacecraft usually don't have wings - and those that do can just use parachutes for losing speed.
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"
Now, if they can use solar energy to fire that baby... That would be the shiznit!
Ligaguinggligagiggagoogoogwillgo
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.
dominionrd.blogspot.com - Restaurants on
Based on what I've read so far, it really isn't realistic to expect something like the space shuttle to be placed into orbit 100% from an EM rail. However, I'd go back to those other unconventional designs, like a helicopter or a jet being used as a launch vehicle for something designed to go into orbit. Those are being pushed because the benefit is that they clear the lower, dense atmosphere, which is where a lot of fuel is said to be spent.
If you look at am EM rail as something not to completely launch a vehicle into orbit, but to clear the dense portion of the lower atmosphere (and maybe give it enough velocity to save fuel on acceleration), doesn't it make more sense? That is, an EM rail as part of a greater delivery system, and not the whole delivery system?
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.
let's hope that the Navy research gets us a step closer to not burning all that Oxygen and Hydrogen to get to space...
...We wouldn't want all the resulting water vapor polluting our atmosphere, and our poor mother earth.
"Alcohol, Tobacco, Firearms, and Explosives" should be a convenience store, not a government agency.
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).
This sig made only from recycled ASCII
a payload the size of most smaller sattelites or even a resupply module for the ISS could easily be flung into space with a railgun. The technology is proven, doesnt require special superconductors, and they have plenty of linear space at the cape to build a launch facility. The only thing they would need is a massive amount of electrical energy... like their own power plant.
In fact they were going to build such a launch system back in the 80's... I remember seeing it in a Pop-Sci magazine when I was in highschool.
Do not look at laser with remaining good eye.
They have plenty of foresitgh...
Launching that way makes you only cause large amounts of impact craters. something we are really good at putting on mars. How are you going to decelerate? if you launc, in space, with much more energy than you can overcome with the device it's self you will never stop until impact. Atmospheric breaking works only at slower speeds, the speed you are talking about would probably cause impact damage upon hitting the atmosphere of mars.
Do not look at laser with remaining good eye.
That depends.
In college I was able to drive a 1" steel ball through a 12" brick wall with a 3 foot railgun. (Teflon tube with large coils spaced at a semi-logarythmic scale along the length with a simple computer control.) I am sure the steel ball was travelling at mach 1 or more. firing tests over lake michigan would result in a projectile that could not be tracked visually after firing and would not register on a bullet speed detector sold for testing reloads of standard rifle rounds.
if you dont put people in it, I am sure you could get way over mach 3.
I only recieved a C on the project as the instructor could not see any real use for the device or design... typical...
Do not look at laser with remaining good eye.
Magnets schmagnets, lets just tie a long rope to the space station and we can climb up, like in gym class.
Give the spacecraft a push, so you can wait until a certain hight before you turn on the rockets.
This is great if the rockets then actually ignite. Otherwise you would look kind of silly just throwing a spacecraft high into the air and then just watching as it drops :-)
By the way - to all those posts discussing geo-stationary orbit and earth escape velocity. You dont need to go all that way :-)
The space station is orbiting in approximately 400
km, and it is much cheaper to go there.
Kristian
He, who dies with the most toys, wins
I'm glad that maglev technology is finally being applied to something worthwhile. I'm getting really tired of seeing all the maglev rail transportation projects that never go anywhere (figuratively and literally)... :
Kim Stanley Robinson wrote the RGB Mars book series, in which a space elevator was built on Mars. If I remember correctly (it's been a while since I read it), they modified the orbit of Deimos (or Phobos, I forget which) to geosynchronous, grabbed an asteroid or two from the asteroid belt, and had self-replicating robots build a factory there and start "spinning" diamond-filament threads.
By the time the asteroid got to Mars, most of the cable was already built, at which point it was anchored at a massive hold on the surface, and elevator cars were constructed to go up and down the elevator, using counterweights.
I believe that the problem of balancing it if you tried to "launch" something off the top of the platform was to simply give it a little push away, let it float off on it's own, and then use it's own engines to propel it.
Although it may seem a bit farfetched, I think that within the next decade, technology will allow us to realistically dream of doing this, although since we don't have nice-sized moons like Deimos or Phobos, we'd need to bring a bunch of asteroids in, which would make plenty of people on Earth rather anxious.
Still, it's a great theory, and perhaps some day we can get space elevators for cheap transportation into space.
Gawyn
Freedom of Speech?
Pardon my naivety but if a speed of over 7000 metres/sec is needed to achieve orbit, wouldn't the craft burn up?
And wouldn't it have to be going much faster than that off the launch track in order to be at 7000 m/s as it leaves the atmosphere?
It would be better to use the maglev to achieve the velocity necessary to cause a ramjet (or is it scram?) to ignite so as not to require the assistance of conventional jets, rockets and B52s to launch them.
Dry volume? How about cubic metres? That makes sense to me, but if you want hectolitres, knock yourself out at the many conversion websites.
Seriously, though. Your complaint about metric measurements assumes an American audience.
I'm either 5'11" (say, roughly 6') tall or 180.34cm. Now, which of those gives you a better mental picture of how tall I am? For scientific things, yes, powers of 10 work out real nice and all, but for everyday things, who the heck cares if you have to remember there's 12 inches in a foot... not that hard! The English units make a LOT more sense in everyday sorts of things.
I'm convinced that the ONLY reason "English" units make sense to you is because of your environment. I was always told my height in feet and weight in pounds, but my brother started through the Canadian school system 8 years after me, now that metric has become more pervasive. To him, measuring common distances in metres makes sense.
The only way to make a standard system of weights and measures intuitive to the common person is to make it ubiquitous. Scientific agencies like NASA should be leading the way. So, yes, it really should be dollars per kilogram.
And why the HECK have Star Trek producers ALWAYS used the incorrect pronunciation of kilometre?!? The same as any metric prefix like KILO-gram: it's KILO-metre, NOT kuh-LOM-etre!!! ARGH! That's one of my biggest pet peeves. Imagine saying kuh-LO-gram or cen-TIMI-tre!
Mozilla
Indeed, since O2 + 2H2 -> 2H2O an oxy-hydrogen motor doesn't look like harming the environment at all, unless it's the size of Madagascar. The winnage is in leaving the motor and its fuel supply Earthbound.
OTOH since launches don't happen continuously 24x7 the launcher could use solar/wind/tidal input and store it in superconducting accumulators for the next launch. These variable inputs are much more practical for powering rare events than for things like home heating or lighting. Win again.
I'm sure this was one of the technologies that you get in Sid Meyer's Alpha Centauri - so it must be workable!
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
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.
whoa there...
:)
;) (o-DOM-eter, not O-DO-meter) Actually, since ki-LOM-eters come from France, and many accents in French are on the second syllable, I guess is makes sense! Parle vous FranCAISE? (sorry for the missing accent marks, and stuff...)
you're probably right that it's what you're used to, but my point is that the arbitrary English units are plenty fine, thank you. The primary benefit of metric is that everything converts nicely. Granted. I don't have a need to go converting inches to furlongs everyday, and if I do, I'm sure I can find the conversion rate somewhere.
I guess it's just an American independence thing then... we don't want the French telling us what system of measurement to use.
As far as KILO-meter (or metre, for you French) vs ki-LOM-eter, I guess it just sounds better. Probably related to spe-DOM-eter rather than SPEED-O-meter.
Have a great day! And, hey, we're just having fun here, right?
My other Slashdot ID is much lower.
There are more people looking at this for space launch than just a handful of guys in Huntsville launching model airplanes. And a lot more than $30,000 is being spent on it. These guys just did a little better PR (perhaps the fact that Huntsville is a short drive from CNN's facilities in Atlanta helped). Surely you don't expect CNN to have the latest (or even accurate) aerospace news, do you? Do they do an accurate job reporting about software? Go spend the money on (or find a library that has) a subscription to Aviation Leak and Space Technology, Janes, or better yet Journal of Spacecraft and Rockets if you really want to know what is happening.
U. of Washington EM Propulsion google cache (the original is either down or has been pulled for security reasons)
Gun Launched Satellites JH-APL (.pdf file)
Pounds (of force and mass) are great units for working with rocket equations because you can "cheat" on your units and use specific impulse (measured in seconds... sort of) instead of using exhaust velocity. I also find it makes it easier to use gees as your unit of accel. than using m/s^2 with kg of mass and newtons of force.
Metric is great fun for calculating electrical problems (IMHO), but English is better for rocketry. In adv. physics, just pick whatever strange units (like measuring velocity in %c) make the equations come out easy then convert back when you are done. Units of measure are just a tool, no need to be a zealot about them.
Those are interesting calculations. Now try this. If you just want to replace the first stage, then how long does the track need to be? Assume that the launch starts off horizontal, and then bends through an arc to over 45% toward vertical. And that you are replacing only the first stage. How long does the track need to be? How high should you try to go? Would Pikes Peak be a good launch site?
I think we've pushed this "anyone can grow up to be president" thing too far.
To compensate for drag in the atmosphere you need a muzzle exit velocity aroun 10-11 km/s. You'll still need a rocket on board to circularize your orbit less you come back down into the atmospher on the same parabola that you left. You can use this rocket to help you escape though and leave the the
:)
muzzle at a lower velocity. A 30 km launcher could accelerate cargo to 11 km/sec at 4000 gees, and could accelerate a rocket with people to 1.5 km/sec at 8 gees and save a lot of fuel for the rocket.
Of course, an even better solution is to build your mag lev accelerator into a loop like a particle accelerator... then you can accelerate at whatever rate you want
There are 10 types of people in this world, those who can count in binary and those who can't.
What all this boils down to, of course, is that the most expensive part of lift is the lower stages. As you get higher, it gets easier - thus the various investigations into high-altitude burns after being lifted there by jet, balloon, dirigible, and now maglev.
Yes, the previous numbers were off, but it is asymptotic. Certainly a 2 km or even 100 km rail isn't going to get you orbital speed. Not on this planet. But it is going to reduce the amount of expendables you have to burn (which, in turn, lowers your weight and further reduces how much you have to burn, yadda yadda yadda).
It remains to be seen that it's: 1) significantly less expensive, 2) as reliable (hah), and 3) as flexible (one of the key dearths of jet/balloon high altitude release) as current rocket launch systems. If it doesn't meet all three it'll die. If it does meet all three it may still die simply because there are people in charge that refuse to look at alternatives to big rockets.
Magic Mountain, in Valencia, California. I believe it is the Superman ride. It launches a pretty massive set of roller coaster cars from 0 to 100mph at about 2 Gs. I'm not sure why the designers chose this method, but it is a great proof of concept.
To me, the best use of this kind of launcher would be to get an orbiter up to ramjet speeds, say 500 mph, then let it fly on ramjet power up to a tanker. I'd have the ship fully fueled with LOX, but with almost empty fuel tanks, so that it could be lighter and easier to get off the ground. Once fully fueled, use the ramjet to get to 100,000 ft and Mach 3 or so. From that altitude and speed, single-stage-to-orbit is remarkably easier than it is from the ground. You can use full-expansion engine bells to get good specific impulse, and going from Mach 3 to Mach 25 is significantly delta-V than 0 to Mach 25.
thad
I love Mondays. On a Monday, anything is possible.
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)
I stole this sig from someone cleverer than me.
Yes, NASA is always chronically underfunded for it's intended missions, but fortunately they aren't the only ones working on it. The military invests a lot of money in R&D, including pretty far-out projects (thanks to DARPA), and there's a long, long list of technology transfers. So if the Navy develops this one for carriers, it won't be long before someone applies it to space.
---If you can't trust a nerd, who can you trust?
You're confused -- you want that extra launch velocity from the Earth's rotation for everything except polar orbits.
I hold it, that a little rebellion, now and then, is a good thing. -- Thomas Jefferson
Consider a gas-exhaust rocket. Say that the rocket has a mass of 1000 kg and the fuel has a total mass of 100 kg (don't know if it's realistic, just an example). The efficiency of this process (neglecting heat losses) is 100 / (1000 + 100) = 0.091 = 9.1%. Now, consider the earth/launcher system, with enormous mass compared to the spacecraft. The efficiency of this process is M2 / (M1 + M2) where M2 is a huge number compared to M1. This efficiency is close to 1, or 100%!
What this means is that the vast majority of the energy you put in ends up accelerating the craft. This is opposed to the gas-exhaust system where only 9% of the energy goes into the spacecraft -- the remainder is carried away in the exhaust kinetic energy.
If we ever hope to build large space stations, then cutting the cost of earth launch to $1,000 per pound won't cut it. On the other hand, this technology on the Moon, perhaps with solar cells providing the electrical power, would allow for very cheap transfer of lunar material, refined or not, to points earthward. That could be Earth orbit or L4 or L5.
So long and thanks for all the fish . . . !!!
How come selecting a unit of measure is somehow a government problem? This is a free country. There is nothing to stop you from doing all your measuring and calculating in metric units, if you like them so much. Gov't agenicies, like NASA, generally want all their units to at least end up in metric if you do any contracting for them (how you get them there is usually your own problem). What more would you want? Should we throw engineers in jail who don't "get with the program" and think in metric? Mandate that any manufactured product that is not evenly divisible in millimeters be confiscated and destroyed? If I want to measure all my stuff relative to some long dead monarch's body parts (or even my own body parts, for that matter) then that is my own #@&^ business. Units of measure are a tool, not a religion. There is no reason we HAVE to limit ourselves to just one system. Often using "strange" units can make your equations much easier (eg. measuring accel. in gees instead of m/s^2).
BTW, the "metric to english conversion error" that cost us the mars probe was just one small symptom of a sick management program. Unit conversion alone (either within or between systems) should not pose that big of a technical hurdle for a group like JPL. #@!!, it shouldn't even pose that big a problem to freshman engineering students.
As for metric being easier, now that I own one of these new, cool pocket-sized calculating engines that Messrs. Hewlett and Packard make I can just as easily convert between feet and miles as between centimeters and kilometers. Pick one up yourself, they are a great invention.
"My results seem to be off from what I expected by about a factor of 10. I must have a metric conversion error in... well... somewhere."
Getting something into orbit isn't about altitude it's about velicoity, specifically overcoming the Earth's escape velocity. You need to be able to shoot something from a point inside the atmosphere up so fast that the pull of the Earth is always less than the current velocity of the craft. At sea level this is about 7 miles per second or 25k miles per hour. A aircraft flying around 20k feet above sea level is only a little bit above sea level compared to the altitude of say the ISS which is about 175 miles or so above sea level right now. So shooting it from a conventional airplane doesn't give you much of a boost since launching it from the ground gives it more time to accelerate.
Launching a rocket horizontally is actually less efficient than launching it vertically because when launched horizontally and having aerofoils to create lift the rocket has to expend some of its burn time building lift to get the craft off the ground. Launching a rocket vertically means it doesn't have to waste precious burn time creating aerodynamic lift.
I'm a loner Dottie, a Rebel.
As an exercise for the poster figure out how much heat would be generated by a craft followed by a ball of air shooting down 32km of pipe accelerating to 2260m/s. Friction is a bitch and would tear the fuck out of anything launched from a big gun like that. One of the caveats of using a railgun to launch stuff is there's only air friction to deal with, not a bunch of mechanical friction which builds up and overwealms your propulsive force. You've also got the explosive force of the air when exiting the tube affecting the trajectory of the craft you just fired. See musket.
I'm a loner Dottie, a Rebel.
My father is the John Cole quoted in the CNN article and it's his office that is managing the maglev (among a lot of much more interesting projects), so I am familiar with this particular project. No one at NASA want's to use maglev as the only method for putting anything into orbit, but rather as a launch assist for chemical rockets. You would be amazed at the weight savings just by accelerating a rocket to 500MPH before using onboard fuel. Also, another point missed by most is that while maglev has been around a while, one of the main problems has been power availablity. For an operational system, you will need 3-6 Megawatt's in 6 seconds. To solve that problem (they don't think they could get a large nuclear power plant just for this thing) they are thinking about using VERY large flywheels to slowly spin up and store the energy until launch. And funding is next to nill. The army was kind enough to donate a few model airplains for the test rig. I used to have some MPEG's of this, if I find the URL, I'll post them. For further perusing and some nice pics, try http://std.msfc.nasa.gov/ast/abstracts/0B_Cole.htm l
and http://std.msfc.nasa.gov/ast/index.html
John Cole Jr.
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.
Any sufficiently simple magic can be passed off as mere advanced technology.
Tom Swiss | the infamous tms | my blog
You cannot wash away blood with blood
I did not ask if DEFINING a unit of measure was a gov't problem (which it admittedly is), I asked if SELECTING one was.
I wasn't suggesting that we could all run around with different definitions of a kilogram or troy ounces, but I was suggesting that it is not the gov'ts business to tell me when to use one or the other in my own calculations or private transactions. Of course, the gov't can and does specify units (usually metric) when you do business with them, but that is perfectly understandable.
The previous poster seemed to think that the President Reagan should have some how shoved the use of metric units down the public's throat under penalty of death or imprisonment (isn't all law ultimately based on one of those threats?). I agree that misrepresenting a unit of measure should be a crime, but I really don't think that using a "non government approved unit of measure" should be one. That seems just a little to draconian for me. If I want to think in feet and pounds then that is my decision. If I want to buy 10 fathoms of rope (and can find a rope-seller that knows what a fathom is), then why can't I?
If I have equipment that makes ¼-20 bolts, and my customers want to buy them then what business is it of the President's? Sure, because they aren't metric bolts I may have problems selling them overseas, but if I don't want to export my bolts then I don't care. If the metric bolt market is profitable enough for me to justify the capital expense of new metric based equipment, then I'll buy one and start making metric bolts. But often the capital cost to retool my business to a new unit of measure cannot be justified (see story below). The gov't could put a gun to my head and make me do it. But telling me that it is "for the good of the country" because some pointy-headed academics think it would be cool if we all used the metric system will not magically change the economics of the situation. If it is profitable then the businessmen will do it without coercion... or they will be put out of business by people who will. There is no reason for the gov't to spend billions of dollars brainwashing the entire population into believing that there is only one true system of measurement (and causing huge economic and technical losses as a result) just so a few anal retentive people can feel comforted by the fact that there are now more "nice round numbers" in the world. They would be horrified by a physicist friend of mine who regularly invents his own units so that he could make parts of his equations cancel out or go to zero (and he would then convert back into "regular" units at the end of the calculation).
A brief little aside: All Air Force transports are built with a certain minimum height for the cargo bay area. That minimum height is the height of a knight on horseback, including his helmet. Of course that is not how it is written in the RFP; it is no doubt given in meters or centimeters (because the gov't is trying to encourage metric use)... but fundamentally the unit is "one mounted knight, including helmet." Just like when I see a blueprint in metric units that calls for a measurement of 25.4mm, I know that the real unit that the part was designed to was 1 inch and it was then converted to metric (probably because the customer wanted it that way). Why use such an archaic standard for aircraft cargo areas? Because the cargo areas have to carry U.S. Army vehicles, and those vehicles are usually designed to be shorter than a mounted knight. They are designed that way because they have to be able to pass under bridges in Europe, some of which date back to the Middle Ages. (I'm sure you can see where this is going) The monarchs ruling Europe back then didn't want to have their knights to have to take off their helmet when they went under bridges (because they would be more vulnerable to attack then) so they decreed that all bridges would be built tall enough to permit a fully armored knight to be able to ride underneath it without having to remove their helmets (I'm sure they used some primitive form of a 95th percentile knight, which probably means that there were one or two tall fellows who occasionally hit their head or had to lean over really far). So, modern aircraft are built to an ancient standard because it is cheaper to design the aircraft and tanks to the old standard than to get all the nations of Europe to rebuild their bridges to some nice round metric height like 10 meters. And that is the right decision... even if it screws horribly with the "nice round number utopia" that some people like to fantasize about.
Millihelen: The amount of beauty capable of launching one ship.
What the previous poster meant was, that
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 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)
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)
It has become appallingly obvious that our technology has exceeded our humanity. --- Albert Einstein
simply calculating back from orbit means you can never have enough fuel to lift the fuel you just added, ad infinitum
You have to factor in the fact that your craft gets lighter as you ascend - because it is shedding fuel when it burns it.
"Win treats sysadmins better than users. Mac treats users better than sysadmins. Linux treats everyone like sysadmins."
That only works as far as the string is in atmosphere, a very small percentage of the total length. Buoyancy depends on heavier material surrounding the buoyant object. That's why ocean liners don't fall to the bottom of the ocean, but then again, neither do they hover in the air. Once you're in space, all you've got it gravity.
Jherico
What can the average user can do to ensure his security? "Nothing, you're screwed"
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.
1. it does NOT have to be vertical(watch what the shuttle does soon after launch), so the acceleration can be done over longer distance, so less G's. think rail's in hundreds of miles. Expensive, yes, but less than 100 million per launch of shuttle.
I've done the calculations. Have you?
At 0.5 km/sec, and a maximum radial acceleration of (say) 10 gravities, your minimum turning radius is 2.5km - bigger than the 1km gun!
If you're building a horizontal gun and making the end turn up, turning radius gets _worse_, because of the higher muzzle velocity. It goes up as the _square_ of the velocity! You need a tower high enough that you might as well make the whole gun a tower.
Mount Everest is 4.4 km high. If you carve a giant channel in it, so that your gun gracefully curves, you get a maximum muzzle velocity of around 0.66 km/sec. Still very, very low.
If you just run a straight gun up the side of a mountain the size of Mt. Everest, you get a straight gun around 6 km long. At 10 gravities maximum acceleration (as per previous post), this gives you 6e5 J, or a velocity of 0.77 km/sec.
Still not enough to make a worthwhile difference.
Bear in mind also that tilting the gun at an angle, like you would going up the side of a mountain, gives you much more atmosphere to go through on the way up. If you try to turn the craft in the atmosphere, you're still forced to turn slowly, and your acceleration limit will be much lower than for a turning gun barrel, making the turning radius much larger (turning radius is inversely proportional to radial force).
2. even if it did, you could just build it up the side of a tall mountain, and have it curve gently up, which is kinda the most likly solution anyway, as it put you higher in the air, so less air resistance, closer to orbit, that type of thing.
Air resistance effects are negligable if your rocket's cross-sectional mass is much greater than the cross-sectional mass of the atmosphere it'll be plowing through (15 tonnes per square metre), or if it does most of its acceleration outside most of the atmosphere.
For a conventional heavy-payload rocket, both of these conditions are true, and atmosphere resistance doesn't matter.
A. Safer - all equipment on ground easy to maintain and in case of a failed launch or problem the rail would still result in a partial launch - meaning the pilot could presumably guide the plane/wahtever to a landing.
Maybe, maybe not. What if it tosses it fast enough to come off the rail, but not fast enough to maintain (gliding) flight? No safe landing!
- No need to carry volatile chemicals
Sorry, no. Maglev launched vehicles are going to have to carry significant amounts of fuel to boost themselves into orbit. Otherwise they'll pay an incredible penalty in heat sheilding to overcome the atmospheric heating at launch. (And it will be in different places mostly than that required for reentry, so no saving there.)
B. Cheaper since, once agian, everything is on the ground - no need for throwaway boosters, etc Indeed once you pay for the construction all that is left is electricity and maintence.
Maybe, maybe not. You have to get the launch rate up high enough to amortize the cost.