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...
TV faster than slashdot? (Score:1)
Used up in the cost to get the electricity, though (Score:2, Interesting)
Re:Used up in the cost to get the electricity, tho (Score:5, Insightful)
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:3, Interesting)
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).
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.
Re:Used up in the cost to get the electricity, tho (Score:3, Informative)
Re:Used up in the cost to get the electricity, tho (Score:2, Interesting)
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.
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, Insightful)
Re:Used up in the cost to get the electricity, tho (Score:2, Insightful)
Now, if they can use solar energy to fire that baby... That would be the shiznit!
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:Not all used up -- it really is more efficient. (Score:2)
In a nutshell for emphasis: Your analysis, and others repeating the same thing, ignore one simple fact: Mag launching is *very inefficient*. It's unclear that there will be any cost savings, LH2 and LOX are fairly cheap, even reducing their costs by 50% won't affect launch costs much. Just because the energy (fuel) required in the vehicle proper is lower does not mean the total energy requirements in the system are lower.
Re:Not all used up -- it really is more efficient. (Score:2)
While that's the way to bet, many technologies run afoul of physical law and simply *can't* improve much further. Nuclear power plants for example. They've gotten bigger, but not all that much more efficient since their introduction. You also have to look at where the gains come from. Auto MPG increases have partly come from technological improvements, partly by vastly decreasing the size and performance of the vehicles. (To the point where even more technology had to be deployed to restore safety.) Also, the high MPG's are in the commuter cars, the rest of the market has not come down near as far, but you don't hear that in the ads.
So, much the same as the horse drawn carriage gave way to the truck
The horse drawn carriage was not replaced by the truck. A wide variety of different kinds of horse drawn vehicles were replaced by a wide variety of internal combustion vehicles.
eventually H2/LOX engines must be replaced with something else,
Why 'must' LH2/LOX engines be replaced? Their clean, cheap (outside of the US) and efficient. The major costs of launch are not the engines or their fuel, it's partially the overall vehicle (but needn't be) and largely the personell costs (but needn't be either). Don't confuse the expensive, difficult way that NASA/the US Goverment does things with the way they could be done. (Vast improvements in cost can be done with few improvements, but they step on political toes, so they are unlikely to happen.)
but it will happen slowly, and may not be a big (if any at all) advantage to start with.
If there is no clear advantage, it won't be replaced. Rockets are launched in the real world, cost real money, and must be considered in the light of real economics. These aren't computers where everyone rushes out to buy the latest thing whether it offers tiny improvements or just more flash. These are expensive assets used to handle expensive assets. Try hanging out on sci.space.policy (Usenet), things don't work like you assume.
Re:Not all used up -- it really is more efficient. (Score:2)
Um, NASA didn't put any money into the space gun IIRC.. At any rate, the 'space gun' in long abandoned. A gun large enough to be useful required unobtanium for the barrel. A gun small enough to be practical required a projectile that was a fairly large rocket in it's own right, the end result almost no gain, while putting the payload in a very hostile launch enviroment.
Sure, they work, but I can't believe that we have hit the pinnicle of launch propulsion technology
No, we haven't, not even for liquid fuel engines. (No serious research and development on booster class motors has been done for nearly forty years.)
However, the basic principal is still valid, more research and the drive to make the better product to sell will ultimatly drive down the price, and increse effeciency.
Your 'basic principle' is *not valid*. Steam powered locomotive engines reached their peak of efficiency around 1910, yet they grew no cheaper per delivered HP. (In fact they grew more expensive over time as larger units were required to handle heavier traffic while remaining economic.) Steam locomotives were replaced with diesel because the life cycle costs were much cheaper. (While other things were made more difficult.) You make the common slashdot mistake of assuming that all technologies behave like computer/electronic technology, they don't, historically speaking electronics are the abberation, not the rule.
So we agree then, old technology was replaced by new technology.
That depends on how slippery you want to get in defining 'technology', I prefer not to use it in the form used today. (Where even minor implementation updates are called 'new technology', even when they aren't.)
NASA/JPL needs to keep trying now things, or we'll never find something better.
First you need to define what you mean by 'better'. Safer? More reliable? cheaper? All these things and more can be done without new technologies! NASA's problems with safety, reliability, and cost are all due to political and historical causes, not because of some intrinsic property of liquid fuel motors.
Going to acceleration or height? (Score:3, Interesting)
Re:Going to acceleration or height? (Score:3, Interesting)
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.
- No need to carry volatile chemicals
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.
C. The plan isn't to accelerate them vertically as the G forces would kill a man to obtain earth orbit you have to have a speed of (I think) 25 Km/Sec which would, in a vertical launch scenario of say a 1000 meter tower, result in way over the 9-10 G's a human can survie. Instead they will be launched off of a gradually ascending slope spanning a couple of kilometers.
However, and this is a big iffy, in all honesty this technology will go nowhere without superconducting materials to use in the rail. Without these existing, or any future, non-superconducting material cannot hope to maintain the power output/magnetic field necassary to propel an object to Earth Orbit or Near Earth Orbit (NEO).
Re:Going to acceleration or height? (Score:5, Insightful)
The same could be said for New York City. The devil is in the details, my friend. Folks thought the Shuttle would open up cheap access to space, since we'd get to reuse the orbiters. Ha ha.
[To avoid dangerously high acceleration, manned flights] will be launched off of a gradually ascending slope spanning a couple of kilometers.
Sorry, but that's still way too short. To achieve a minimum orbital velocity in a 2-kilometer run, you'd have to accelerate at a little more than 1500 gees. Splat.
Even with a 100-kilometer ramp, you'd be dealing with an average acceleration greater than 31 gees. It appears that, as far as space projects go, this will only ever be useful as an initial-stage boost, or for boosting raw materials into space for orbital construction projects.
Of course, it would still make a nice high-tech catapult for lobbing massive conventional weapons hundreds of miles, but of course no one in the Pentagon is thinking of THAT possibility...
Re:Going to acceleration or height? (Score:5, Funny)
Yup. And for a more manageable 10g, you'd need a 315km run to reach geosynchronous velocity. Of course, you'd also burn to a crisp in the atmosphere ;-)
The advantage of railgun / rocket sled launches is in getting you some of the way up to orbital velocity, but there's still a good long way to go. Basically, you can't reach orbital velocity while still inside the atmosphere, so you have to carry a bunch of fuel up with you whichever way you cut it.
Here's some handy dandy info for those who want to have a play with the numbers and have forgotten their Newtonian stuff:
Geosynchronous orbit is at 42,245m, which requires an orbital velocity of 7869m/s. Gravity is 9.81m/s^2
Distance = half of acceleration times time squared (s = 0.5 * a * t^2) and velocity equals acceleration times time, so time equals velocity divided by acceleration (v = a * t, t = v / a)
If you know the speed that you want and the acceleration that you can tolerate, this gives you:
s = 0.5 * v^2 / a (e.g. for 7869m/s and 98.1m/s^2, s = 0.5 * 7869 * 7869 / 98.1 = 315602m = 315km)
Or, if you know the distance you have and speed that you want, and want to know the acceleration you need:
a = 0.5 * v^2 / s (e.g. for 7869m/s and a 2km run, a = 0.5 * 7869 * 7869 / 2000 = 15480 m/s^2 or about 1578g!)
Re:Formulars are flawed (Score:3, Interesting)
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)
Re:Formulars are flawed (Score:2)
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.
Re:Going to acceleration or height? (Score:2)
Hmmmm - I think I'd start to ask questions when I notice my neighbor building a giant maglev rail on a mountain pointing at me. Nothing is so suspicious as somebody constructing a gun that can only point at your head.
Bad assumptions (Score:2)
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.
Re:Bad assumptions (Score:2)
And? 30-40G is 5 to ten times *larger* than current systems. That means heavier boosters and more vehicle and payload weight devoted to structure. Best guess? A net loss compared to current systems.
I would imagine for manned launches they would use the maglev track of about 25km to accelerate the craft to Ramjet/Scramjet speeds greatly reducing the amount of fuel needed to be carried.
Actually, you need *more* fuel as you are adding the weight of the ram/scramjets to the booster. You'll still need rockets to get the last velocity increment (actually over 50% of the velocity) you'll need to get to orbit. The rockets now (under your scheme) have to carry the weight of the ram/scramjets, their supporting structure, and the TPS to protect them. (also do keep in mind that it's very, very unlikely that anyone will allow a pilotless winged vehicle to reenter and land anytime in the near future.
TANSTAAFL
Re:Going to acceleration or height? (Score:3, Insightful)
Maglev might be able to give these devices a good shove before the rockets kick in and might therefore save substantial amounts of fuel (and fuel saved is weight saved, which then saves even more fuel on the way to orbit).
Easy Funding method... (Score:1)
Just turn the thing into a giant "Tower of Terror" to raise funds
-- Dan =)
Maybe MagLev will save us yet! (Score:5, Funny)
Yes, we must reduce emissions of deadly Dihydrogen Monoxide [dhmo.org]! 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!
Re:Maybe MagLev will save us yet! (Score:2, Insightful)
I don't know the exact cost/[pound|kilo] to get something into orbit, however reduced weight means less cost and less energy needed per launch. Seems like a win/win situation to me.
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:Maybe MagLev will save us yet! (Score:2)
Anyone care to do some sums on circumference, centripetel (sp?) force (oooh ooh centrigugal/centripetal flame war please) and other interesting numbers?
Re:Maybe MagLev will save us yet! (Score:2, Funny)
First Stage (Score:2)
Build your accelerator in a loop (Score:2)
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
Re:Build your accelerator in a loop (Score:2)
Water to replenish space stations could easily withstand 4000 gees... as could other raw building materials... say a solid block of steel.
Folks, you're not getting it (Score:5, Insightful)
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)
Re:Folks, you're not getting it (Score:2)
However, there's no real reason ramjets can't be used in space launches now. . .
One BIG point - (Score:2)
You have to factor in the fact that your craft gets lighter as you ascend - because it is shedding fuel when it burns it.
My conclusions are correct. (Score:2)
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.
Re:Maybe MagLev will save us yet! (Score:2)
Plus, at low altitudes, 7814m/sec is going to vaporize your vehicle very quickly - unless you add a heat-shield. Obviously, 3112 G's is going to mean an unmanned launch. Even 15 G's is pretty unrealistic. So you have to add a heat shield for launch, when you don't intend to even have a recovery.
That's not an optimal design.
Even in an unmanned vehicle - 3112 G's is pretty unrealistic. We CAN build a vehicle that could withstand it, but it would probably need so much reinforcement that there'd be less room for cargo - plus, your cargo would now have to be engineered to withstand 3112 Gs.
So really, you have to accellerate magnetically to some speed, probably subsonic, enough to get the vehicle airborne, perhaps a few thousand feet, and THEN ignite rockets. At altitude, air friction won't be as bad an obstacle (nor will the sound barrier).
I've read (on slashdot, years ago, so don't quote me on this) that the majority of rocket thrust is spent lofting more rocket fuel up through the lower and much thicker few miles of the atmosphere. Clear that barrier, and there's a significant savings already. You can't do entirely without rockets, nor would it be wise to try.
Re:Maybe MagLev will save us yet! (Score:2)
>at sea-level would be tremendous indeed!
and suspiciously similar to reentry
hawk
Re:Maybe MagLev will save us yet! (Score:2)
hawk
This idea is not fairly new... (Score:2, Interesting)
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.
Re:This idea is not fairly new... (Score:2, Funny)
thing in place? A shitload of rockets?
Speed up AND slow down (Score:2, Interesting)
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.
New ICBM delivery method? (Score:3, Interesting)
Though I guess you'd have a hell of an "electro-magnetic signature".
Re:New ICBM delivery method? (Score:2)
An American scientist during the 80s (I can't remember his name, but there have been shows about him and his work on Discovery and TLC) thought about creating a massive artillery piece for launching satellites into orbit. The artillery "barrel" would be almost half a mile long, and it would be a large facility. The US wasn't interested in it, and the scientist, very interested in promoting the tech, went to other countries to promote it. Eventually ended up in Iraq selling the tech to Saddam, where it actually started getting built. It was one of the "weapons of mass destruction" destroyed during the gulf war.
I don't think the idea was ever put into actual practice, but if you can lob a several ton shell across countries, you might be able to change the trajectory such that the satellite cuts through the ionisphere (sp?) and can obtain a stable orbit.
Re:New ICBM delivery method? (Score:2, Interesting)
http://world.std.com/~jlr/doom/bull.htm
http://www-istp.gsfc.nasa.gov/stargaze/Smartlet
http://www.fas.org/nuke/guide/iraq/other/superg
Re:New ICBM delivery method? (Score:2)
Re:New ICBM delivery method? (Score:2)
Turns out that the gun required to launch a useful payload required barrels made from unobtanium and quite long. By the time you added boosters to the payload to cut down on gun size, and move it into something buildable, you didn't save any money and created a very payload hostile launch enviroment. (I.E. pointless)
Cost per what? (Score:3, Troll)
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" ;-)
Re:Cost per what? (Score:3, Funny)
As Pounds is a measure of weight rather than mass, the cost goes down as the weight reduces as the payload goes into orbit.
If you used Kilograms then you would be measuring mass which stays fixed, hence no cost savings
(Top Tip - Always buy a 2.2 Pounds of moon rock, never 1 Kilogram - You will get about 6 times as much rock due to the lower gravity on the moon)
Metric isn't always best. (Score:2)
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.
Re: Metric Units (Score:2)
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!
Re: Metric Units (Score:2)
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?
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:Cost per what? (Score:2)
i dunno, but the one in chains is really one I'd rather avoid . . .
:)
hawk
Re:Cost per what? (Score:2, Insightful)
The reality is that the English units make more sense to you and I simply because that's what we've been raised with. They are no more or less sensical than metric units. Yes, I'm more comfortable with arbitrary measurements in the English system - I know my handspan is 10". I know one of my knuckles is roughly 1". I know how far a mile is, how big a gallon is, and how heavy 10 pounds is.
But to say that 1 kilometer, or 1 liter, or 1 kilogram is obviously not as simple to understand just shows how short sighted you are. If you'd been raised in a country that had transitioned to these measurements decades ago then you'd be wondering what the hell is up with these silly english units.
And yes, the only time it really matters is when you start doing conversions. You don't have to do them? That's nice. Not planning on doing much cooking are you? Because scaling recipes would sure as hell be easier to do with metric than English. Or doing reasonable conversions in any kind of construction (length of wood, sq ft->sq yd vs sq meter, etc). And I'm not even going to get into doing scientific calculations.
Oh, and before someone whines that metric doesn't make sense unless you convert to a metric time system, get a clue. The time system already has a fairly consistant base - base 60. There isn't a single English system that has anything even vaguely consistent. Besides which, once you get to seconds everyone starts using them as a metric baseline - milliseconds, nanoseconds, megaseconds, etc.
As a counterpoint, however, I do wish people would stop bringing up inane English units like bushel, league, hectares, etc. These units aren't used in anything but the same specialized fields that they were originally invented for. The only units that are in common usage are inches, feet, yards, miles (length); ounces, pounds, tons (weight); and teaspoons, tablespoons, ounces, cups, pints, quarts, gallons (volume - yes, this is the single most fucked up system of the bunch).
Re:Cost per what? (Score:2)
I know it's X miles from town A to town B. Fine, I have no need to know that in feet, furlongs, nautical miles or ki-LOM-eters
I know that, rounded to the nearest foot, I'm 6' tall. Closer than you'll get rounding to the nearest meter. Again, no need to convert to inches, hands or miles.
I know that my toilet uses (or is supposed to use) 1.2 gallons per flush. No need to convert to teaspoons, pints, quarts (though that's pretty obvious...) or liters (though that's also stated on the label).
I don't know right off the top of my head the mean distance from earth to the sun in miles or kilometers, but I do know that it is 1 AU, which seems to fit the English system of making the units fit the world rather than the other way around. Oh, I just did the conversion of 1AU to miles and km. 9.300e+7 miles or 1.496e+8 km. I have no need to know this in inches, furlongs, nautical miles, or light-years.
Made my point, right? English measurements are size appropriately to the things measured. There is normally no need to convert between said measures, and if needed, it is easily accomplished.
Happy flaming!
Re:Cost per what? (Score:2)
Re: Raygun screwed us (Score: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."
Re: Raygun screwed us (Score:2)
Re: Raygun screwed us (Score:2)
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 about EM rail to pass lower atmosphere? (Score:2, Insightful)
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?
A few points to make... (Score:3, Insightful)
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.
Re:A few points to make... (Score:2)
Yeah... (Score:2)
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.
Re:Yeah... (Score:2)
Little known fact: H20 is a greenhouse gas. It's not nearly as bad as CO2, but it can contribute to warming the planet. Of course, I seriously doubt that shuttle launches contribute materially to any kind of warming. We don't launch them very often, and the atmosphere is big. It's just that the idea of "water-vapor pollution" might not be as far-fetched as you make it out to be.
On the other hand, lots of water vapor should also cause more cloud formation, which raises the albedo and should lower the average temperature. There are days that I think that climate science is even more dismal than economics...
Re:Yeah... (Score:2)
My uncle was a NASA engineer who built devices to study the ozone layer and the greenhouse effect. His team's opinions were a bit different than the doomsayers regarding the greenhouse effect. Mainly, that the Earth cycles through periods of greenhousing followed by glaciation, and that we are on a warming trend anyway.
The amount of greenhouse gases emitted by humans is comparatively low compared to some natural sources like volcanic eruptions.
Interestingly enough, the Mt. Pinnatubo eruption in the early '90s (was 91 or 92,..) spilled more CO2 into the air than people could imagine, but the dust it spilled into the air lowered the average temperature of the northern hemisphere about
It was very noticable, too. We had snow in August, which is normally our hottest month here. (Normally hits near 100 degrees.) There was basically no summer that year.
If lowering the Earth's temperature by
20 year old technology (Score:5, Funny)
Some of the EML experiments from the late 80s and early 90s were visited at a 95 IEEE pulsed power conference: here [navy.mil]. 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.
Re:20 year old technology (Score:2)
What we need now are some nice scifi devices such as Inertial Dampeners, Transporters, and bigass klingon battle cruisers.
Re:20 year old technology (Score:2)
And for pretty much the same reasons as we've been on the brink of fusion power for about the same length of time... Mainly that there are enourmous practical engineering and economic problems between viewgraphs and working hardware. It's not entirely clear that any money will be saved in the near (10-15 yrs) term between the current systems and a maglev system.
The bulk of our current infrastructure has long since been amortized; to replace it with a new system will be tremendously expensive. (Hence the focus of CATS on minimizing infrastructure requirements.) Hardware costs are (mistakenly) believed to dominate launch costs, but the real cost in current generation systems is in payroll. (Again most CATS efforts seek to minimize the costs of preparing the vehicle (ELV) or turn around (RLV).) The trick to reducing space access costs is to reduce life cycle costs, and maglev does just the opposite by introducing a enormous R&D and capital construction costs right at the front end, especially if not accompnied by changes to other parts of the overall system.
Why not a railgun? (Score:2)
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.
space aged tree fort (Score:2, Funny)
I hope the rockets will work (Score:2, Interesting)
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
Re:I hope the rockets will work (Score:2)
An unmanned wingless craft could be permitted to go splash in the ocean.
Re:I hope the rockets will work (Score:2)
silly magnets (Score:2, Interesting)
Initial boost for ramjets? (Score:2, Interesting)
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.
Of course it will work! (Score:2, Funny)
I prefer the space elevator (Score:3, Interesting)
Maybe I'll go in space after all.
Heinlein (Score:2)
Don't believe everything you see on CNN (Score:2)
U. of Washington EM Propulsion google cache [google.com] (the original is either down or has been pulled for security reasons)
Gun Launched Satellites JH-APL [jhuapl.edu] (.pdf file)
Current biggest electromagnetic launcher is at... (Score:2)
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
Military much better at Tech than NASA (Score:2)
And now, the physics (Score:2)
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.
Not just for use on Earth (Score:2)
Research still needs to be done! (Score:2, Interesting)
Re:NASA's lack of foresight... (Score:2)
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: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:NASA's lack of foresight... (Score:2)
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:NASA's lack of foresight... (Score:2, Interesting)
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.
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.
Red/Green/Blue Mars (Score:2, Interesting)
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
Re:Red/Green/Blue Mars (Score:2)
And the moon would be even easier.
And one could almost certainly build a skyhook that reached down to, say, 30 miles above sea level on Earth. (That's at least twenty miles of cable below the center of gravity, and ? above before it reaches your counterweight.
Then you need your railgun to shoot you high enough to reach the bottom of the skyhook at a fast enough speed to catch it.
Yeah. I 'm convinced. But it would be expensive. I'm convinced that there would be impressive returns, but they would take many years to materialize (and it would depend on pricing issues).
OTOH, Boeing and Lockheed, et. al. would make a bundle while it was being built.
.
Re:Perhaps a silly question? (Score:2)
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.
Re:SCRAM jet launcher? (Score:2)
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...
Re:I'm not an expert but... (Score:2)
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.
Re:MagLev is a crock for Earth launch (Score:2)