# Thread: How feasible is using railgun technology to launch space probes?

1. Navy's New Railgun Shoots at Mach 7, Can Hit Targets 100 Miles Away : 80beats

The article I linked above talks about the U.S. Navy's new successful railgun weapon test. It got me thinking about how feasible this technology would be in space to launch probes out past the inner planets, or even potentially out of the solar system. I thought it might be possible to have an orbital station powered by a combination of nuclear and solar energy. With less drag and gravity to slow down the probe, maybe they can get them going much faster. A drawback I see there though is that the probe would need to decelerate once it reached it's destination.

I admit I don't know the math of this, so that's kind of why I am posting it here.

2.

3. The orbital velocity of the ISE is around 7.7 km/s (or Mach 22.5 at sea level, give or take a bit) so I think we are going to need a bigger rail gun.

More importantly, current rocket tech uses relatively low acceleration but applies it for an extended period of time, this is important as this limits the structural stresses exerted on what ever you are trying to put into orbit. You do not have that luxury with a rail gun, going from stationary to full tilt in under a second.

Finally, why would you want to slow it down?

4. Originally Posted by river_rat
The orbital velocity of the ISE is around 7.7 km/s (or Mach 22.5 at sea level, give or take a bit) so I think we are going to need a bigger rail gun.
Oh definitely. I was thinking 10 or 20 years down the road.

More importantly, current rocket tech uses relatively low acceleration but applies it for an extended period of time, this is important as this limits the structural stresses exerted on what ever you are trying to put into orbit. You do not have that luxury with a rail gun, going from stationary to full tilt in under a second.
I hadn't considered that. I thought that being launched from space might have mitigated some of that.

Finally, why would you want to slow it down?
Well, if it's a space probe, they are probably sending it to a planet or a moon in the outer solar system. Uranus and Neptune are still somewhat mysterious places, and the Kuiper Belt and Oort Cloud are excellent places to study too. Pluto would be neat too, it's essentially a giant comet. Probes take over a decade to get that far now. It took Voyager about 10 years just to get to Uranus. So I was thinking they'd want to be able to slow it down or at least steer it to get it into orbit around something. Would it be possible to just steer it into orbit and use the planet's gravity to slow it down?

5. Putting a railgun on the moon would work better. (from a launching point of view)

6. Not sure how this could work, as some part of the item being launched touches the barrel. In other words, anything that isn't the same shape as the barrel would disintegrate.

7. Originally Posted by shlunka
Not sure how this could work, as some part of the item being launched touches the barrel. In other words, anything that isn't the same shape as the barrel would disintegrate.
A shell. Encase the item you're launching inside of a shell.

8. Junkieturtle, I had been thinking about something similar - for a while I thought I might try writing some SF (turns out I don't have the persistence or writing skills) and one storyline I played with had something like that; in the aftermath of global war orbital KE cannons (railguns) get converted to launching interstellar probes. Not large ones but very small ones. Still relatively slow by interstellar standards but they wouldn't be one off's; there'd be regular launches in long stretched out strings that would allow very low power signals to be relayed along the line, a multi-generational project.

I admit I wasn't too worried about how achievable that might be, imagining centuries in the future when all but one string had been abandoned, the last one run by a succession of school and university students without any real expectation that anything of value could result, perhaps the first probes of the string appearing to be dead - until enough solar energy warms the systems. I still like the idea but I doubt I'll ever write it.

I never thought the idea of launching manned or unmanned space vehicles that way could be considered original, but I'm not aware of anyone proposing strings of probes to be both relays and backups (although I wouldn't be surprised if I'm not original there either; it seems kind of obvious). Different ones would have different instruments and capabilities, perhaps some dedicated comm relays, sacrificing other capabilities for the ability to leapfrog communications along the line , others that are dedicated to specific instruments.

As for the launch 'guns' - what if there were two or more? Say one in Earth orbit to launch sunward, another, open both ends, in close solar orbit to boost it some more?

9. Current plans for a rain gun launch system call for a 1600 meter track and an acceleration of 1988 g's. 100 g's can detach your aorta artery from your heart, which is quickly fatal, definitely not for manned missions.

10. But with a railgun you can increase the length to reduce the acceleration.
It's an engineering trade-off and based on what you want it to do.
The one you mentioned was intended only [to] be used to launch sturdy materials, such as food, water, and fuel.

11. A large spaced based railgun (big enough to shoot telephone pole sized projectiles) could pick off anything in the solar system or select earth targets for massive destruction. These projectiles would be strictly kinetic energy impact weapons. Once launched there wouldn't be much of anything that could stop or deflect them.

Does anybody know how much mass a depleted uranium slug the size of a telephone pole would be? Or how much kinetic energy it would have at a speed of about one 10th of C when it impacted?

Note - If your going to talk about the benefits of something you must also consider the negatives.

12. Originally Posted by arKane
Does anybody know how much mass a depleted uranium slug the size of a telephone pole would be?
DU is ~18.95 gm/cm3

Or how much kinetic energy it would have at a speed of about one 10th of C when it impacted?
Lots.
There's a unit of measure used by the guys on sfcoinsim-l the rick and kilorick (named after one of their members Rick something-or-other, who pointed out that a difference in velocity of 5 km/sec at impact gives a 1 kg mass the same energy as 1 kg TNT IIRC).
Anything at 0.1c is going to generate a lot of kiloricks.

13. Can you imagine what 2000 g's of acceleration would do to the human body. There would just be a puddle left. I guess it would be like weighing 340,000 pounds for brief second. Ouch.

14. Originally Posted by MacGyver1968
Can you imagine what 2000 g's of acceleration would do to the human body. There would just be a puddle left. I guess it would be like weighing 340,000 pounds for brief second. Ouch.
That's easy, just make sure your inertial compensators don't go off-line while under acceleration, you'll be fine...

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