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posted by
cmn32480
on Saturday November 14 2015, @07:45PM
from the i-so-want-to-try-this-at-home dept.
from the i-so-want-to-try-this-at-home dept.
This is the most powerful mobile electromagnetic railgun built by a non-government. A railgun is a device that accelerates a conductive projectile using extremely high current and electromagnetism. No explosive powder required. Just batteries. This page shows many of the steps required to make one.
The gun is portable, but the power supply is not. Still, cool project.
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DIY 250 lb Giant Mobile Railgun, 27,000 joules.
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Life is to you a dashing and bold adventure.
(Score: 2) by deadstick on Sunday November 15 2015, @03:13PM
...and if you launch straight up, once you reach orbital altitude you'll have to deliver a very large injection burn to reach orbital velocity -- otherwise you're coming right back down. With a low-angle launch you'll still need the injection burn, but not as much.
(Score: 2) by AnonymousCowardNoMore on Sunday November 15 2015, @05:12PM
No, that is penny wise and pound foolish if it can even be done. You need to compensate for drag by adding initial speed, which means increased drag—leading also to more gravity losses. You'd need an unrealistically thick heat shield, an unrealisitcally big launch rail, etc. where you could simply have added a bit more fuel to the rocket. If what you said were true, we'd launch rockets horizontally. Launch systems must optimise for total cost, not orbit insertion stage mass. Thus the goal should be to replace the first and heaviest stage, getting the rocket above the worst of the atmosphere (with some potential energy gain also associated) as cheaply and reliably as possible. The horizontal speed that is also imparted is gravy.
(Score: 2) by deimtee on Monday November 16 2015, @12:06AM
If you watch any NASA launch, pretty soon after they clear the tower they start to lean over and get some lateral velocity. I assume NASA knows what they are doing.
The optimum efficiency is not straight up to altitude, then sideways burn to orbital speed.
If there was no atmosphere, optimum launch angle would be horizontal, and just keep accelerating to enlarge the orbit. But since there is an atmosphere, It is always a trade off between hanging around fighting gravity and air resistance if you go fast.
If you built a 100 km railgun up the side of Kilimanjaro, and then pulled 10g all the way, you would exit above half of the atmosphere, with a speed of about 4000 m/s.
Review the rocket equation to see how beneficial cutting your required delta-V in half would be.
If you cough while drinking cheap red wine it really cleans out your sinuses.
(Score: 2) by AnonymousCowardNoMore on Monday November 16 2015, @03:25PM
Kindly mind your tone.
Rockets turn sideways but not very quickly. Your solution is physically impossible. The projectile will be stopped by drag at any speed [wikipedia.org]. It cannot be made sharp enough to avoid this because the shock wave would stick to the surface and burn through the whole rocket no matter the material it is made of.
(Score: 0) by Anonymous Coward on Monday November 16 2015, @08:03PM
https://en.wikipedia.org/wiki/Gravity_turn [wikipedia.org]
What goes (straight) up, comes back down.
(Score: 2) by deimtee on Tuesday November 17 2015, @09:34AM
4000 m/s is, at sea level, about Mach 12. At 6000 m altitude it might be closer to 13.
That is nowhere near fast enough to invoke Newtons impact penetration formula when using an aerodynamic craft.
If you cough while drinking cheap red wine it really cleans out your sinuses.