# What is the possibility of a railgun assisted orbital launch?

Basic facts: The world's deepest mine is 2.4 miles deep. Railguns can acheive a muzzle velocity of a projectile on the order of 7.5 km/s. The Earth's escape velocity is 11.2 km/s.

It seems to me that a railgun style launch device built into a deep shaft such as an abandoned mine could reasonably launch a vehicle into space. I have not run the calculations and I wouldn't doubt that there might be issues with high G's that limit the potential for astronauts on such a vehicle, but even still it seems like it would be cheaper to build such a launch device and place a powerplant nearby to run it than it is to build and fuel single-use rockets.

So, what is the possibility of a railgun assisted orbital launch?

What am I missing here? Why hasn't this concept received more attention?

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Why suggest a mine? Up is not the big problem in launching stuff. Indeed to get to orbit you need more across than up. Heinlein's rather naive treatment in The Moon is a Harsh Mistress suggested using ridges on mountains that rise toward the east. – dmckee Aug 29 '12 at 15:05
That's also a good idea. Either way, the basic concept of imparting the energy to a spacecraft while it is "on the ground" rather than having it carry fuel with it seems appealing. – AdamRedwine Aug 29 '12 at 15:10
Yes, but the energy required to launch an object from the ground does not depend on whether you impart that energy all at once as in this scenario, or over time as with a rocket. You are only changing from getting that energy through burning rocket fuel to getting it through a power plant. Given that in my scenario you wouldn't have to move the fuel sorce, it seems to me like it should be more efficient even if the initial velocity would have to be very high to compensate for energy loss with increased height and through atmospheric drag. – AdamRedwine Aug 29 '12 at 16:51
I have a friend who has looked into this sort of thing in some detail (and thinks it is feasible). I'll see if he has anything to offer on this question. – David Z Aug 29 '12 at 17:44
@Phill: That exponential formula only applies for rockets that have to hoist the fuel they will use further up. – Mike Dunlavey Aug 29 '12 at 20:04

Ok David asked me to bring the rain. Here we go.

Indeed it is very feesible and very efficient to use an electromagnetic accelerator to launch something into orbit, but first a look at our alternative:

• Space Elevator: we don't have the tech

• Rockets: You spend most of the energy carrying the fuel, and the machinery is complicated, dangerous, and it cannot be reused (no orbital launch vehicle has been 100% reusable. SpaceShipOne is suborbital, more on the distinction in a moment). Look at the SLS that NASA is developing, the specs aren't much better than the Saturn V and that was 50 years ago. The reason is that rocket fuel is the exact same - there is only so much energy you can squeeze out of these reactions. If there is a breakthrough in rocket fuel that is one thing but as there has been none and there is none on the horizon, rockets as an orbital launch vehicle are dead end techs which we have hit the pinnacle of.

• Cannons: Acceleration by a pressure wave is limited to the speed of sound in the medium, so you cannot use any explosive as you will be limited by this (gunpowder is around $2\text{ km/s}$ , this is why battleship cannons have not increased in range over the last 100 years). Using a different medium you can achieve up to 11km/s velocity using hydrogen. This is the regime of 'light gas guns' and a company wants to use this to launch things into orbit. This requires high accelerations ( something ridiculous like thousands of $\mathrm{m/s^2}$) which restricts you to very hardened electronics and material supply such as fuel and water.

• Maglev: Another company is planning on this (http://www.startram.com/) but if you look at their proposal it requires superconducting loops running something like 200MA generating a magnetic field that will destroy all communications in several states, I find this unlikely to be constructed.

• Electromagnetic accelerator (railgun): This is going to be awesome! There is no requirement on high accelerations (A railgun can operate at lower accelerations) and no limit on upper speed. The tech for this exists and there have been papers out on it, here are two of them.

Some quick distinctions, there is suborbital and orbital launch. Suborbital can achieve quite large altitudes which are well into space, sounding rockets can go up to 400miles and space starts at 60miles. The difference is if you have enough tangential velocity to achieve orbit. For $1\text{ kg}$ at $200\text{ km}$ from earth the energy to lift it to that height is $0.5 m g h = 1\text{ MJ}$, but the tangential velocity required to stay in orbit is $m v^2 / r = G m M / r^2$ yielding a $KE = 0.5 m v^2 = 0.5 G m M / r = 30\text{ MJ}$ , so you need a lot more kinetic energy tangentially. To do anything useful you need to be orbital, so you don't want to aim your gun up you want it at some gentle angle going up a mountian or something.

The papers I cited all have the railgun going up a mountian and about a mile long and launching water and cargo. That is because to achieve the $6\text{ km/s}+$ you need for orbital velocity you need to accelerate the object from a standstill over the length of your track. The shorter the track the higher the acceleration. You will need about 100 miles of track to drop the accelerations to within survival tolerances NASA has.

Why would you want to do this? You just need to maintain the power systems and the rails, which are on the ground so you can have crews on it the whole time. The entire thing is reusable, and can be reused many times a day. You can also just have a standard size of object it launches and it opens a massive market of spacecraft producers, small companies that can't pay 20 million for a launch can now afford the 500,000 for a launch. The electric costs of a railgun launch drops to about 3\\$/kg, which means all the money from the launch goes to maintenance and capital costs and once the gun is paid down prices can drop dramatically. It is the only way that humanity has the tech for that can launch large quantities of object and in the end it is all about mass launched.

Noone has considered having a long railgun that is miles long because it sounds crazy right off the bat, so most proposals are for small high-acceleration railguns as in the papers above. The issue is that this limits what they can launch and as soon as you do that noone is very much interested. Why is a long railgun crazy? In reality it isn't, the raw materials (aluminum rails, concrete tube, flywheels, and vacuum pumps) are all known and cheap. If they could make a railroad of iron 2000miles in the 1800s why can't we do 150miles of aluminum in the 2000s? The question is of money and willpower, someone needs to show that this will work and not just write papers about this but get out there and do it if we ever have a hope of getting off this rock as a species and not just as the 600 or so that have gone already. Also the large companies and space agencies now are not going to risk billions into a new project while there is technology which has been perfected and proven for the last 80 years that they could use. There are a lot of engineering challenges, some of which I and others have been working on in our spare time and have solved, some which are still open problems. I and several other scientists who are finishing/have recently finished their PhDs plan on pursuing this course ( jeff ross and josh at solcorporation.com , the website isn't up yet because I finished my PhD 5 days ago but it is coming).

# CONCLUSIONS

Yes it is possible, the tech is here, it is economic and feesible to launch anything from cargo to people. It has not gotten a lot of attention because all the big boys use rockets already, and noone has proposed a railgun that can launch more than cargo. But it has caught the attention of some young scientists who are going to gun for this, so sit back and check the news in a few years.

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This is an excellent answer. – Nathaniel Aug 29 '12 at 19:37
I have to wonder, what is the effect of air friction? It's being shot in the thickest air at what, Mach 25? Seems you need to add a nose cone and some extra speed, just to have enough speed left when you get out of lower atmosphere. – Mike Dunlavey Aug 29 '12 at 19:56
Sweet! I knew I wasn't the only one thinking about this. If you have any open jobs, let me know. ;) Heck, I'll even work for just stock options. – AdamRedwine Aug 29 '12 at 20:23
I'll be sure to let the internet know when this starts up - publicity is going to be quite important. As we'll be doing scale models and slowly testing things the smaller railguns will make for great viral videos :-) Air friction is actually an incredibly difficult topic because it is like hitting a wall if the nosecone is not designed properly. A lot of drag reduction will need to be done in order to survive the launch - and you are right you need to overshoot the target velocity but by how much depends on just how much you can get your air drag down. – Dr. Jeffrey Berger Aug 29 '12 at 22:20
Won't air resistance make achieving high speed in atmosphere impossible? I think even if you reach 11 km/s at railgun exit, you will be quickly slowned down by the atmosphere and severly warmed up. – Anixx Sep 4 '12 at 18:41

There is good research on railguns at the University of Texas at Austin, led by Ian McNab. See, e.g., I.R. McNab. "Progress on Hypervelocity Railgun Research for Launch to Space." IEEE Trans. Mag. 45: 381-388, 2009. There is a list of his publications describing his team's work. The funding comes from the US Army, as there are applications in long-range artillery. There are still research problems, such as a tendency for the rails to vaporize and the problem of the payload overheating in the air at such colossal speeds.

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Nice. Maybe if I decide to go back to school, I can go to UT Austin... not sure how my fellow aggies would feel about that. :) – AdamRedwine Sep 5 '12 at 10:59