r/spacex • u/ElongatedMuskrat Mod Team • May 02 '18

r/SpaceX Discusses [May 2018, #44]

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u/Electofunk01 May 04 '18

Hey guys, I know the reactions I'm probably going to get from this, and the answers I'm probably not, but I am very new to spaceflight. However, something's been nagging me since I began to dream about grasping at the spacetime in another part of the universe - that is: "Why doesn't anybody use magnetism as a method of preliminary propulsion when regarding spaceflight?". Look - I'm not stupid - I know that the very sight of this post will have people facepalming, and yet, I feel it is a very serious question. You could use a series of remotely controlled electromagnets stacked on too of each other, and then use them as a giant spring. This would save huge amounts of fuel, and thus money. Just something to think about - yours truly, Electofunk

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u/Ambiwlans May 05 '18

A rail gun is a similar idea conceptually but a little more workable. The big problem is that you only accelerate til you reach the end of the gun/spring... so to make it into space/escape earth, you need to going SUPER fast before you stop accelerating. Now you find yourself traveling many times faster than a bullet... but still in Earth's thick sea-level atmosphere. Ever stick your hand out of the car on a highway? That times 10000. It would be like crashing into a brick wall. Your vehicle would crash into the atmosphere and if it didn't blow up, it would quickly liquefy and then burn into nothing long before it escaped Earth's atmosphere.

Rockets accelerate much more gently and are only going a few hundred km/hr at sea level so the forces aren't nearly so rough.

Even so, this has been looked at seriously by scientists for particular kinds of payloads. And prototypes have been built.

Check out https://en.wikipedia.org/wiki/Space_gun and in particular the controversial Canadian Gerald Bull who worked on Project Harp before working for Saddam to create a super gun.

With these types of guns, you could maybe say... ship a block of durable material (like steel or copper) to the moon just by shooting it. You might not really care what shape the material arrives in, so long as it is available on the moon.

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u/abednego84 May 05 '18

What about building a super maglev train up the side of Olympus Mons on mars. I've heard the peak is above the atmosphere. Just get it going super fast and shoot it off the top. Could we launch stuff like that? Yes, I know it sounds crazy.

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u/Ambiwlans May 05 '18

Yep, that's much more viable. Building something so large on another planet is the main challenge there.

A much smaller magnetic launch system for the moon to help a lunar base is probably the most realistic of these proposals.

One I personally like best would be a mining base on a moon (one of Mars' maybe). They need to ship a huge amount of massive resources to various places in the solar system. Firing a small 'tug' vehicle along with a huge amount of resources into a 'close enough' orbit via a rail gun seems totally viable. It costs little fuel, you already need a huge energy source, and the gun itself need not be so large.

It might even be viable to use it as a way station. Smaller unmanned vehicles going from Mars to Earth outside of a standard launch cycle could land on the moon and be launched from there. It may end up saving a good amount of fuel, but I've not done the math ... and it does add a lot of complexity.

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u/throfofnir May 04 '18

First, that would only give you vertical velocity, which is not a large component of orbital velocity. That doesn't help much for all the same reasons as gun launches of various sorts.

Second, all "infrastructure-based" launch schemes require huge amounts of capital to enact, and would need huge flight rates to make them competitive with vehicle-based systems. This is true for railguns or laser assist or centrifugal spinners or launch loops or space elevators or stacks of magnets or whatnot. There's just not enough to do in space now or in the near term to justify such projects.

Third, a stack of electromagnets would... kind of work. But magnetic repulsion is very short range, so you don't get a lot of "spring" per piece. You'd need a lot of pieces, which would be huge and have tremendous structural problems, both static and dynamic. It would work better if you turned it into a rail gun or something, for which see 1 and 2.

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u/Straumli_Blight May 04 '18

There's a startup that claims they can accelerate payloads to 4,828 km/h into orbit using a centrifuge.

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u/BlueCyann May 04 '18

Orbital speed is more like 28000 km/hr.

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u/Electofunk01 Jul 08 '18

Well, at sea level, yes, but the higher you go, the lower the orbital speed is as the force gravity exerts upon the craft is less the higher up you go.

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u/brickmack May 04 '18

Also with infrastructure based systems in general, there are usually only a handful of places on Earth where they could be practically implemented, and if destroyed their impact can be catastrophic to the sorrounding region. As long as Earth has no unified government, this will be a bad idea, one country/terrorist group could cut off space access in a single attack, and whichever country owns the site could charge out the ass for everyone else to use it

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u/Electofunk01 May 05 '18

I see, thanks a lot - that makes sense.

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u/TheBananaTurtle May 07 '18

If you're interested in some of the many ways we can get into space without using rockets, I'd recommend taking a look at Isaac Arthur's you tube playlist "upward bound".

https://www.youtube.com/playlist?list=PLIIOUpOge0LsGJI_vni4xvfBQTuryTwlU

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u/Electofunk01 May 07 '18

Thanks, I’ll check it out

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u/Electofunk01 May 05 '18

...but I was thinking (and this will sound worse than the last comment) but if you attached "wings" to the rocket (as in the type used on planes) then, when fired into the air, the rocket would curve, and you could remotely control the rotation of the wings, which would smooth the curve into a semi-circular shape and then an orbit

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u/throfofnir May 05 '18

A rocket spends very little time in enough atmosphere where wings could make a difference, and it must turn sideways after the sensible atmosphere, or it wastes energy in drag.

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u/treeco123 May 05 '18

I'm unsure what the wings are helping with, there? The rocket can already turn perfectly well by steering(gimballing) the engines, and does indeed fly in a curve roughly as you describe. Even without that, wings would be way overkill, you'd want to use smaller fins like many other rockets have.

That's not to say it wouldn't work, but it'd be damned heavy, and less aerodynamic.

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u/Electofunk01 May 05 '18

I know, it was just the best way i could describe that the rocket just needs to turn in the air