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Spacecraft Launching Maglevs
M1000 pointed us over to a recent Wired article regarding
NASA picking up maglev technology for launching spacecraft. The reasoning is that the weight-cost of propellant when launching shuttles takes up a high amount of the weight and this would cut down the needs for rocket fuel. Rockets would still be needed for the final launch as the current max maglev speed is 600 MPH. More experiment test models are being worked on now.
Back when I was a member of the Chicago Society for Space Settlement (later to be integrated into the larger L5 society), the big thing was Mass Drivers (basically the same technology as Maglev), on the moon, to launch lunar material into space, for construction of space stations, spacecraft, etc.
This can propel things MUCH faster than 600MPH - I think that the difference is that Maglev is focussed more on a magnetic levitation, to eliminate mechanical drag, but getting to 600MPH does not seem to be much of a boon to me - since the launch vehicle is eventually going to have to reach much faster speeds, thousands of miles per hour - how much would the first 600 save?
The Mass Driver would have been on the lunar surface, so air friction would have been almost nonexistant, but the models we saw rode on rails, so there was mechanical friction.
Seems to me they're probably using "Maglev" as a term people who have read Popular Science would be familliar with, but they must be really talking about a Mass Driver.
The other problem is - accelleration. You wouldn't necessarily want to put a manned vehicle up with this thing, otherwise you'd have to build a VERY long track to stretch the accelleration out over a longer distance to reduce the Gs. Longer track = extreme cost (when you're talking about supercooled magnets and very sensitive sensors, and super-straight track).
"The number of suckers born each minute doubles every 18 months."
These are my friends, See how they glisten. See this one shine, how he smiles in the light.
Every time your monitor screen goes tie-dye-t-shirt you know it's a launch time.
The article says the concept was tested in England, so I doubt it's the same technology, but hope springs eternal.
Escape velocity is seven miles per second or 25,200 miles per hour. I ve often wondered if it's possible to use the same construction techniques that were used to build the "Chunnel" across the English Channel to build a LONG undersea tunnel with it s mouth at the surface.
Then, using a combination of magnetic acceleration and pneumatic pressure, accelerate a
payload to escape velocity without ANY rocket fuel.
Of course the thing would be hugely expensive to build. But once built, throwing payloads
into space would be cheap, cheap, cheap.
(A variation of this was used by the lunar revolutionaries in _The_Moon_is_a_Harsh_Mistress_.)
It would seem that the exit velocity of this device is only limited by it's length. (Okay,
length, air resistance, and C.)
trichard
p.s. Someone do the math to see how long this tunnel would have to be to accelerate
an object from rest to 7mps at 1G, 2G and 5G's.
I'm not exactly sure, but isn't 6-G enough to make you black out?
A human being in good health will black out somewhere between 9 and 11 Gs. At least that's what they say about fighter pilots.
The cake is a pie
I did a little math, and I hope the numbers aren't totally off here... The Space Shuttle, accelerating at about 3gs, takes about 50 seconds to reach 600 miles per hour. The SSMEs (Space Shuttle Main Engines) consume over 1,000 lbs of fuel each second, so by getting rid of that first 50 seconds worth of fuel, you can put an extra 50,000lbs of cargo into orbit.
These numbers apply to the Space Shuttle itself, which is only rated to carry 55,000 lbs of cargo in any case, so think about how important that first 600mph is first and imagine what it could do for a spacecraft designed to take advantage of it. In the case of the Space Shuttle, it would theoretically double the cargo weight capacity (if there were only enough volume to take advantage of that).
Using magnetic assist is an excellent idea. I would like to see the day when a launching track goes up the side of Mt. Kilimanjaro and can toss cargo and ships into orbit almost unassisted.
Furthermore, as bad as coal may be, I tend to suspect that rocket fuel is worse on an environmental impact per joule basis. Unless you're dealing with reeeeealy high-sulfur coal...
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Do I look like I speak for my employer?
The article doesn't go into detail about how much of the actual fuel is replaced by this technology. It does mention a 20 percent reduction in the overall mass of the rocket, but what does that translate into?
Most rockets are huge canisters of fuel with a teensy little area to hold people and cargo. Doing multiple stages helps, but you're still talking about a vehicle that's mostly fuel. So it's probably a 20% (or some number remarkably close) reduction in fuel with a corresponding 20% reduction in bits of rocket to hold fuel. Or maybe it's a 21% reduction in fuel and a 15% reduction of the rest of the rocket. Either way, the fuel reduction and the overall mass reduction won't be too far apart.
How it works
- Take a long tube, a gun barrel, around 100 or more meters long.
- put a rocket in the gun.
- Fire the rocket, and as it passes along the barrell detonate additional charges behind it keeping the pressure in the barrell approximately what it was when the main charges were fired.
- result: hypervelocity projectiles from a relatively low-tech gun
- Fast enough to get things into orbit for under $1 per pound, around 1/10000th of current launch prices.
- Successful prototypes were built, but never orbital ones.
His personal storyWhat got built
- In tests, a 36m gun reached 1/3 of escape velocity
- The Iraqi "Supergun" was built by Bull and had a 1500 mile range if used for ground-to-ground, but only in one direction
- It was actually intended as a prototype of a satalite launch system.
- AARC most of the parts were made by companies who usually make oil well drilling equipment. It's low tech.
Thoughts on the technology- Fuel-air or conventional propellents are much more efficient for vehicle launch than electicity, and don't let anybody tell you different without hard numbers to back them up.
- For a space station, 90% of the mass you need could be thrown up into orbit out of a cannon and nobody would care. The peaches might bruised but that's about it.
- It's not about manned space flight or astronomy, it's about engineering, so why would NASA care?
If I was in the position of backing a launch technology for unmanned cargo launch, this would be it. Everything else is a poor second best, IMHO.Has anyone bothered to do the required math for this before posting about how you couldn't launch people with this thing without turning them into raspberry jam? A little bit of calculation shows that a 1km long track, accelerating the payload at 4g for a little over six and a half seconds will get the payload up to the maximum stated velocity at the end of the track (actually about 100 meters short of the end, but what's a hundred meters between friends?) A human can easily withstand a force of 4g for six or seven seconds.
The track could run essentially parallel to the surface of the earth for most of its length, since it doesn't matter too much what direction your velocity is in, so long as your path doesn't intersect the ground or a mountain or somesuch.
As for how much this would help you: you would be getting about 5% of your required velocity for low earth orbit without the need for onboard reaction mass. The amount of reaction mass you consume during takeoff is something like inverse exponentail (or maybe inverse log. In either case, there are a bunch of constant factors thrown in) so that most of the fuel is used early on. A 5% savings in reaction mass during the first part of takeoff may be worth a lot more (like 20%) in the total amount of fuel needed.
What I'd like to know is where this maximum velocity comes from. I assume that it has to do with wind resistance at sea level, or somesuch, but I'd like to know for certain.
- Jeff Dutky
The problem with air resistance is not that it would merely slow your launch vehicle down. The problem is that your spacecraft would be doing a killer impression of the Stay-Puft Marshmallow Man long before it got into orbit.
Shielding works OK for re-entry vehicles when you've got a nice, thin upper atmosphere to slow you down before you get to the thick stuff. Something tells me that surviving orbital velocities near sea-level is going to require something more substantial than ceramic tiles.
I think it might launch off like Superman: The Escape over at Six Flags Magic Mountain. It uses magnets to rocket off to 100 MPH (world's fastest "coaster") and curves up so you go up to 450 some odd feet. Here's some pictures. Except in the space shuttle's case, it wouldn't stop. Once it reached it's top speed, it would fire it's rockets and go on up. And if the rockets failed, it would just follow the track back down. BTW, that ride is a lot of fun : )
Lacking <sarcasm> tags,
Ah, but those 55,000lb of fuel are partly used to put the 55,000lb of fuel in the air as it is. It is also burnt up before the space shuttle exits the atmosphere. If that 55,000lb of fuel was cargo then the shuttle would be carrying 55,000lb extra for the entirity of its journey, not just the first 60 seconds, so the actual amount extra that the Space Shuttle could carry would be considerably lower.
These numbers apply to the Space Shuttle itself, which is only rated to carry 55,000 lbs of cargo in any case, so think about how important that first 600mph is first and imagine what it could do for a spacecraft designed to take advantage of it. In the case of the Space Shuttle, it would theoretically double the cargo weight capacity (if there were only enough volume to take advantage of that).
Using magnetic assist is an excellent idea. I would like to see the day when a launching track goes up the side of Mt. Kilimanjaro and can toss cargo and ships into orbit almost unassisted.
I wonder how the Tanzanians would react to this :), why not somewhere in te alps of the rockies instead ;-)
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My sometimes helpful blog
what about the computers inside the shuttle? How are they going to shield those from the shear strength of the magnetic field that would be needed to bounce that thing into space?
- This concept is very old. It goes back beyond the British HOTOL aerospaceplane and all the way back to the Antipodal Bomber concept of Werner Von Braun in the 40's. Attributing it to NASA today just shows how backwards NASA is, and how clueless journalists are.
- Sewing machines and electric drills do not use induction motors. They use universal motors. Completely different technology. Again, clueless journalists.
I could go on, but it's late, I'm tired...--
Deja Moo: The feeling that
Time is Nature's way of keeping everything from happening at once... the bitch.
This wouldn't be useful on something like the Space Scuttle (pun intended) because the stack cannot handle 6 G's. Something like a re-designed X-33 (Venture Star) could do it. And I suspect that NASA is suggesting it now because the X-33's design compromises have added so much weight that it can't carry a payload to orbit without several hundred MPH of head start.
Somebody, Congress, please boot the idiot NASA managers who selected the X-33 proposal and hire the guys who designed the DC-X; if we'd just continued with the DC-Y we'd have an orbital test vehicle by now! Oh, I forgot, the program was too cheap and didn't have enough slush to generate your campaign donations! Silly me!
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Deja Moo: The feeling that
Time is Nature's way of keeping everything from happening at once... the bitch.
There is one problem though, that is, there might be a speed limit associated with it. As the craft accelerates, a larger magnetic field needs to be generated to continue the acceleration, this means more current through the coils of wire. Eventually the wire will overheat and short out or simply melt. Previously a speed limit of 600 mph was mentioned, this seems plausible, but id need more data. Also, if the speed can max out at around say mach 10 (about 6000 mph) then scramjets can be used in place of rockets. Scramjets are much more eifficient than rockets since they burn oxygen in the air, resulting in a further reduction in weight of fuel and a commensurate increase in payload capacity.
Sorry, I thought you might be getting a couple concepts mixed. As for commercial aircraft, you're right:many of them already require more space to land than to take off so it's doubtful that saving them 35 seconds or so of acceleration would be worth the cost of adding catapult gear to either the airports or airplanes.
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Deja Moo: The feeling that
Time is Nature's way of keeping everything from happening at once... the bitch.
Since it's on a track, it's reasonably close to the ground, and I guess they don't want to go supersonic that close. Probably the energy required rises steeply there, not to mention strutural strengthening. I imagine sonic booms reflecting off the ground can make for some nasty buffeting.
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Infuriate left and right
Escape velocity may be 7 miles/sec (25,200 mph), but the shuttle doesn't completely escape Earth's gravity - it goes into orbit. The shuttle's orbital velocity is 17,000 mph.
Without creating a gun that could reach close to escape velocity, you could only achieve orbit by performing an OMS burn at the apogee, in other words, circularize the orbit so the probe doesn't just crash down ala Newton.
The problem here is thaqt the size of the OMS burn needed is directly proportional to how vertical the launch was. If you shoot straight up, you need a strong enough burn to accellerate the craft to orbital speeds (17Kmph) which is a lot of fuel and kind of wrecks the point. Also, the lower the metal-nonmetal ratio, the less acceleration there will be on the craft.
So you have to launch at an angle, slicing through a serious cut of atmosphere to make for a projectile moving closer to paralelling the orbit it's trying to get into. This would of course mean a huge slowdown from drag.
So either way, you're toast, unless you're building a gun powerful enough to launch something so fast that even after the parachute that is Earth's atmosphere, it's still going 7 miles per second (and I'd LOVE to see one of these going up. The plasma trail would be quite a sight!) or you've got a gun that's really good at throwing rocks at other people. Metal rocks, mind you. I wouldn't even want to think of the implications of trying to construct a nuclear (or even worse, a biological) weapon that could survive those g-forces and remain intact and functioning.
Makes Pegasus and moon bases seem simple...
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Kevin Fox
As an aside, max-Q changes with the altitude of your launch. Depending upon far more factors than I am competent to analyze it might make sense to move launch sites from Florida (good equatorial boost) to Colorado (smaller boost, but launch track at 8000'-10000') except for the small problem of dropping empty tanks on Kansas.
But if we did that, Washington might not hear about it for a month.
(That's my obJamesBond reference, from _Diamonds are Forever_. Nobody should talk about this stuff without references to diamond encrusted laser spacecraft and bikini-clad starlets.)
But back to the serious stuff, I know that I only have about 85% of the air density from sea level at just over 5000'. I definitely feel it when I'm down in that thick soup at sea level! At 10000' the air density drops to 70% of sea level.
From a launch perspective, a rail in Mexico looks *very* good. (15,000' altoplane?, perhaps 60% of sea level?) It would also give you a good equatorial boost. Unfortunately there's the problems of politics, power (Colorado launch sites could tap into the Western US power grid), and launch techs ill from altitude sickness. Still, with NAFTA it's something to consider if it significantly cuts the cost-to-orbit.
Finally, a quick sanity check is the shuttle's SRBs. I don't recall the exact numbers but I thought they were dropped at something like 6 miles altitude/mach 3. In terms of the total trip to LEO it's fairly modest, but it's crucial because of the high cost of lifting fuel for the later stages. A maglev track in the mountains may be enough to get you 30-40% of the way to where the SRBs are dropped, when using the current shuttle stack!
For every complex problem there is an answer that is clear, simple, and wrong. -- H L Mencken
The last time I watched a shuttle launch, I remember the velocity indicator reading something like 25K mph. It doesn't seem like maglev speeds of 600 mph would accomplish much
Well, imagine for a moment that the ship is 1/10th or less of its current weight. It takes a WHOLE LOT less force to 50 tons into orbit than to put 500 tons... I think with the correpsonding reduction in spacecraft size this is a feasible propulsion method. Most likely a 5 mile track with 3 miles straight to build up speed, and then a ramp that shot it straight up... Probably wouldn't want to use it for manned flight just yet, but it would rock for launching space station parts, and satellites, and anything else that could handle the pressure.
Kintanon
Check out JoshJitsu.info for Brazilian Ji
> Distance = 1/2 acceleration * time^2 = 1/2 * 186 * 4.7^2 = 2000 feet!
> Well thats a little extreme for something that wants to point up in the air.
well maybe not - just build it up the side a mountain somewhere - higher is better! (less air resistance) so is close to the equator - Kilamanjaro (sp?) would probably make a cool space port
Ummm, 2000 feet is only a conventional 20 story building. We have those all over the place. I'm sure NASA can build one that won't fall over when they shoot a 1000ton rocket up the side of it.
Kintanon
Check out JoshJitsu.info for Brazilian Ji
Oops, Someone shoot me. 2000 feet = 200 story building, ok that is a little tall.>:)
Kintanon
Check out JoshJitsu.info for Brazilian Ji
- It did not have to glide to a landing. This allows considerably more flexibility in the aerodynamics.
- It did not have to land horizontally. This is advantageous in two ways:
- There is no requirement to transition from powered flight to gliding flight in order to land; the spacecraft always lands under power, so it can make an emergency landing as soon as it gets rid of enough fuel to avoid collapsing the gear.
- Any flat patch of ground will do for an emergency landing site; no runway is required.
About the only thing the X-33 has going for it is that it behaves more like the Space Scuttle. Unfortunately, this similarity also appears to include development cost and schedule. Our current engines appear to be sufficient to build a much cheaper replacement for the Scuttle, and on a much faster schedule than X-33. In the mean time we are stuck with a vehicle designed in the 70's whose performance is a fraction of what was promised (65,000 lbs to orbit is only a dream) and requires a standing army of over 10,000 maintenance personnel to keep it flying. Worse, we cannot build any more and if we lose even one vehicle it will force other programs (like ISS) to be radically scaled back or even scrapped. Last, the engine technology of X-33 could be applied to a VTVL with little difficulty; however, with a going DC-1 program it would be forced to prove its worth instead of being locked in as part of "the only game in town". You can't escape the conclusion that the X-33 program is more about generating lots of money for contractors than making a cost-effective launch vehicle.--
Deja Moo: The feeling that
Time is Nature's way of keeping everything from happening at once... the bitch.