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.

Comments

Should make life interesting in Florida..

[Apuleius]

Every time your monitor screen goes tie-dye-t-shirt you know it's a launch time.

Is this Livermore's Inductrack?

[Daffy Duck]

The article doesn't mention it, but last year Lawrence Livermore National Labs wrote about a maglev system with a passive track, saying there were plans to test it for use in rocket launches. I'm a huge fan of this "Inductrack" system, but I haven't seen any mention of it in months. Does anyone know if this is the system they're using?

The article says the concept was tested in England, so I doubt it's the same technology, but hope springs eternal.

Dr. Gerland Bull (yes he did get killed).

[Anonymous Coward]

You can read about Dr. Gerland Bull here .

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 story

• He designed large guns in Canada.
• They cut his funding and he went independent
• People didn't take his stuff seriously.
• He freelanced for unpopular nations (China, Iraq)
• He did some work on scud missiles and somebody, probably mossad, killed him.

What 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.

it would be big, but nobody would get smushed

[dutky]

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

You'd end up with spacecraft s'mores!

[RebornData]

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.

Inductrack et al

[cybercuzco]

The official nasa press release for this mag-lev system can be found here This system does use the Inductrack system mentiones earlier, which has several advantages over other forms of mas driver, which this essentially is. The inductrack system is bacically coils of ordinary wire surrounding some sort of ferrous core. The article above mentions that each section of track weighs over 500lbs wich is due laregly to the huge chunk of iron in the center of the coil of wire. This reduces cost and complexety many times. You dont need any cooling apparatus, you dont need any expensive magnets, and its very scalable. To make the track longer just ad a section of track. This is a very promising technology, it could really pave the way for cheap access to space. Heres hoping that nasa will continue to develop it.

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.

Shuttle doesn't escape

[SpinyNorman]

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.

This doesn't really help achieving stable orbit.

[KFury]

So say you somehow got past all the other problems of melting while exiting the atmosphere or creating an all-metal probe so the killer g-forces wouldn't be a problem, all you've done is make something that could launch a projectile.

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...

www.fury.com

Max-Q and mountain launches

[coyote-san]

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!