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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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It's raisins that make Post Raisin Bran so raisiny ...
(Score: 2) by MichaelDavidCrawford on Sunday November 15 2015, @12:29AM
You wouldn't want to reach orbital velocity at low altitudes but you could use the railgun for what otherwise would be the first stage. Because the railgun itself would not require lift, the actual vehicle could be a lot smaller and lighter than conventional rockets.
Surely someone has studied this, I couldn't possibly be the first?
Sounds like a project for Burning Man - fire myself into the air with a railgun, land with a parachute.
Yes I Have No Bananas. [gofundme.com]
(Score: 1, Informative) by Anonymous Coward on Sunday November 15 2015, @02:01AM
It would be too many g forces for a human to survive though.
(Score: 0) by Anonymous Coward on Sunday November 15 2015, @03:19AM
Cheaper resupply runs to LEO are still a major benefit.
(Score: 0) by Anonymous Coward on Sunday November 15 2015, @03:30AM
Also, if you watch the video you'll notice a lot of liquid metal flying everywhere and one time the whole Al block turns almost completely into a mist
(Score: 2) by captain normal on Sunday November 15 2015, @03:50AM
That's because they used aluminum projectiles. The heat blew the material apart as if it had been hit with a plasma torch. Use ferrous projectiles and see what happens.
Everyone is entitled to his own opinion, but not to his own facts"- --Daniel Patrick Moynihan--
(Score: 2) by Phoenix666 on Sunday November 15 2015, @01:45PM
My late father was a dreamer and once took me and my brother out to Porcupine Butte [geomorphologyresearch.com] (see lower down the page for the topo) to check it out because it had a long flat separation between the main spine of the Rockies and a gentle rise up the western face of the Butte, with a long drop-off to the East. He thought it was perfect for a long gentle slope for a rail gun to launch payloads into space. He thought it would be best suited for getting bulk supplies like food, water, girders for constructing space stations and interplanetary ships into orbit. I have no idea if it would be suitable for humans.
Washington DC delenda est.
(Score: 4, Informative) by AnonymousCowardNoMore on Sunday November 15 2015, @10:55AM
Both rail launch and gun launch systems have been studied. There are several problems that need to be addressed by such systems, although they are not insurmountable.
High acceleration is, as the AC mentioned, one of them. A system which accelerates humans to orbital velocity must do so at less than, say, 12g. This means the rail/barrel must be kilometres tall. (No, you can't just accelerate horizontally and then turn up. Being accelerated upward by a turn in the rail is no better than being accelerated in any other way.) Taking only unmanned craft improves the situation but of course every cargo has its limits and the higher the g-force, the fewer the launches over which the fixed operational and capital costs can be amortised.
Another big problem is drag. Such a vehicle would be at its fastest while in the thickest part of the atmosphere, near sea level, where drag is highest. In addition to needing a much higher initial speed to compensate for drag, a very large heat shield would be required. The g-force from atmospheric drag may also be highly significant, see above. Keep in mind that this g-force is opposite that from the initial launch, which means that any occupants would probably need to be seated on their sides. (Which as an acceptable—in fact optimal—axis for the g-force but may present unique challenges for operating the controls.)
Reducing the fraction of total delta-v supplied by the rail can bring all of these factors down to feasible levels. But doing so reduces the savings, which makes it difficult to justify such a complex system. (Something like 5% of all launches fail. Increased complexity is not a good thing.)
The prospect of using such a system suffers due to economies of scale. It is probably a good idea for any civilisation with a very busy launch site. But the capital expenditure and upkeep of such a system can almost certainly not be justified with the number of launches we make, especially considering that many nations have their own launch sites for military/political reasons.
Lastly, neighbours get nervous whenever someone builds a big intercontinental cannon. Look up Project Babylon for an actual example.
(Score: 2) by deimtee on Sunday November 15 2015, @12:01PM
If you extend the line long enough, any direction that doesn't hit the ground is heading out into space. However, your point about air resistance and G forces is well taken. The optimum launch cannon would probably start one to two hundred kilometres west of Kilimanjaro, angled up at an angle just sufficient to clear the peak. (This may necessitate building quite a bit of supporting structure over the middle sections.)
If you cough while drinking cheap red wine it really cleans out your sinuses.
(Score: 3, Insightful) by AnonymousCowardNoMore on Sunday November 15 2015, @12:23PM
No. When you aim straight up, you have to clear a hundred kilometres of atmosphere. When you aim at the horizon, it becomes thousands.
(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.
(Score: 1) by Kenny Blankenship on Sunday November 15 2015, @01:35PM
Check out "Startram"
Someday, even Killer Meteors must fail.