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Realism of ksp mod idea: orbital rail guns for cargo?


Buster Charlie
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I'd suggest this as a mod but  I'm not even sure how realistic this is. There is a nice mountain range near KSC, if you had a nice big nuclear reactor and plenty of energy... how realistic would it be to launch non God sensitive  cargo into orbit using electromagnetic acceleration?  I realize you'd be talking about hypersonic speeds near sea level, so as a offshoot how about just an initial boost with SRB providing sustaining thrust and orbital circulation?

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So optimal efficient velocity is when drag roughly equals the force of gravity which results in 4200 dV to reach space, about 1200 dV used basically to counteract drag.
This is a speed profile of 100 (0), 160 (5000), 256 (10000) to about 18000 (Mach perterbations limit) meters (safely) then 1000 to about 32000, 1500 to about 45000 alt.

If you doubled that speed you would triple the force of drag so instead of needing 1200 dv you would need 3600 dv again at low altitude at Mach you would have restrictions the went up very rapidly

If you doubled that speed again it would be more like 14400 dv required. Since that dV is all going into heating you have to consider that this is going to translate into heat on the surface, explosive heat.

Second, shooting an object into space does not place you in orbit, either you escape SOI or you are on a hyperbolic trajectory that intercepts the planet.

Third, So lets say we apply 20000dV, lets say the viability limit is 300 m/s OK 20000/300 = 66.66 seconds and so distance is 1/2 a t 2 = 667km. IOW you would need to have a hole through the center of mass of kerbin and 67km the other side to have enough distance to accelerate the object to reach the surface.

Flat answer no, you cannot do this from KSC. To determine which altitude you could do this see how much dV it takes starting with 0dV at a given altitude to reach space, the determine the energy diffeential between orbit (apo = peri = 671000, Vo = SQRT(u/671000)  and sitting on kerbin (apo = 600km radius, Vo ~ 175 m/s, peri = 1 or 2 km, calculate the semimajor axis, the keplars area rule can be used to determined)), this then defines the energy between the two states and can be used to calculated dV. The dV not used is a combination of waste 'hoovering' and drag. 

I might be possible to do from KSC if you reduced the coefficient of drag on the parts, but to be fair you would have to make much longer parts which are much heavier. Drag is composed of two parts, the part caused by collisions and the part caused by sliding. You can reduce the collision drag, but not the slide friction, some propose ejecting hot gas along the surface of an object to reduce sliding drag. You would have to make the parts extremely resilent to heat and you could not turn after launch below 36000.

 

 

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I did see one interesting light gas gun idea which involved a long floating underwater gun under water so they could change the angle of launch. 

 

From a game play standpoint,  I think it would be interesting to basically have a launch sled as a root object, and treat it like a fairing base.  Anything you launch would have to attach to the launch sled object and  fit within a fixed fairing envelope.

 

As you said you'd need a rocket stage of some sort to complete the orbit so maybe this would still  be worth looking into as a first stage replacement. 

 

As far as heat and shielding, maybe the gun is only designed to get the launch sled above 32k, at which point it sheds it's fairing and air brakes away from the ship itself  (optional parachutes for stage recovery? )

 

Dowsnide would be the payload would need to withstand launch get forces and fit within a fixed size envelope.

 

Plus side is it would provide a fast and reliable way to get the payload to 32k?

Edit: I suppose one could make a launch clamp like part that provides a single impulse of thrust to the sled part, maubergine borrow the code from the orion nuclear engine but make it one shot and insanely powerful. 

 

The realism issue is these guns would tend to be longer than is practical to render in game. Although part of me would really like to see a portable nuclear powered space cannon you could assemble on low gravity moons and such. That might be and bit more practical,  and maybe you'd be able to you use KAS  to build it in sections 

Edited by Buster Charlie
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I think there is / was a rail gun mod. I like those light gas gun proposals, but they are only talking about shooting 1000 kg 'payloads' (which have an engine to circularize). To be 'practical' in the game you'd like the gun to lay down a maneuver node that you could play with (it would have model the drag effect, drag proportional to velocity^2 but high velocity also reduces the time under drag) a light gas gun could 'easily' shoot something from Mars surface to Earth.

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In theory, a shield could be placed at the front of your projectile which ablated readily and shed gas in a sheath around your projectile to cancel compressive and form drag.

If you don't want to bother with an engine to circularize, simply place a 10-mile-long space station in orbit with a large maglev track on it, then build an alectromagnetic launcher on the surface to fire your payload up and outside of the atmosphere such that it intersects the front of the space station as it passes overhead. Then the orbiting space station can maglev the projectile/payload up to orbital velocity.

Edited by sevenperforce
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1 hour ago, DBowman said:

I think there is / was a rail gun mod. I like those light gas gun proposals, but they are only talking about shooting 1000 kg 'payloads' (which have an engine to circularize). To be 'practical' in the game you'd like the gun to lay down a maneuver node that you could play with (it would have model the drag effect, drag proportional to velocity^2 but high velocity also reduces the time under drag) a light gas gun could 'easily' shoot something from Mars surface to Earth.

Now that you mention it, it's beyond what I ever could dream of doing, but it would be neat to integrate it with the trajectories mod, if you required all payloads to fit inside a cargo pod, and you know it won't have any maneuvering during its atmospheric flight, then I figure it would be pretty easy to use that mod to calculate an escape trajectory out of the atmosphere.

 

The way I would do it, if I had the ability, would basically treat it like a 3rd lahnchpad, give it 3 tiers of upgradeability and make it an endgame money sink so that players who pretty much unlocked everything else have an expensive project to build.

I think building in the water facing east from the KSC word be best since it's close enough you could do a access building on the shoreline, but the vehicle would spawn loaded in the gun, which is located under water and angled upward.

 

Tier one could have a fixed charge and angle, suitable only for 1.25m payloads that can handle super high g loads and heat because the gun is small and has to accelerate faster. Suitable for launching raw resources into Low orbit with a booster or maybe a carefully tuned sub booster on a timer, something very primitive and simple to survive launch.

 

Tier 2 could be maybe 2.5m payloads or just heavier 1.25m, and this would have a longer barrel and allow for slower accelleration, and maybe simple angle adjustment  or power adjustment. 

 

Tier  3 would be even larger payload, and full maneuver node placement, so as you mentioned you could launch a supply payload directly on an intercept  course with no booster stage, just whatever landing provisions you need. I'm thinking hardened supply pods for colonies.

 

 

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8 hours ago, Buster Charlie said:

Now that you mention it, it's beyond what I ever could dream of doing, but it would be neat to integrate it with the trajectories mod, if you required all payloads to fit inside a cargo pod, and you know it won't have any maneuvering during its atmospheric flight, then I figure it would be pretty easy to use that mod to calculate an escape trajectory out of the atmosphere.

 

The way I would do it, if I had the ability, would basically treat it like a 3rd lahnchpad, give it 3 tiers of upgradeability and make it an endgame money sink so that players who pretty much unlocked everything else have an expensive project to build.

I think building in the water facing east from the KSC word be best since it's close enough you could do a access building on the shoreline, but the vehicle would spawn loaded in the gun, which is located under water and angled upward.

 

Tier one could have a fixed charge and angle, suitable only for 1.25m payloads that can handle super high g loads and heat because the gun is small and has to accelerate faster. Suitable for launching raw resources into Low orbit with a booster or maybe a carefully tuned sub booster on a timer, something very primitive and simple to survive launch.

 

Tier 2 could be maybe 2.5m payloads or just heavier 1.25m, and this would have a longer barrel and allow for slower accelleration, and maybe simple angle adjustment  or power adjustment. 

 

Tier  3 would be even larger payload, and full maneuver node placement, so as you mentioned you could launch a supply payload directly on an intercept  course with no booster stage, just whatever landing provisions you need. I'm thinking hardened supply pods for colonies.

 

 

Wait, KSC had 2 launchpads? Where's the 2nd one?

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I think that this would not fit very well in KSP's current scope. Railgun would be optimal for very frequent launches of hundreds of payloads, for example automated supply transports to colonies or sending automated mining systems to bring resources from asteroids to kerbin. But there is not such possibilities in KSP. KSP concentrates to earlier phase of space technology where single missions are important and player plan them and execute them. Railgun would fit better to game where basic piloting is automated and player manages larger scale logistic operations in solar system.

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Btw it's a nice idea about the mountains.
Not for a launching cannon, but for another thing.
(I would in any case suggest another mountain though: about 200 km or so to east-north-east from KSC, right to the north from a big island. It's higher and more flat, iirc.)

An Evil Scientist's Dark Castle on the top of mountain.
An alternative launchpad placed with KerbalKonstructs or ExtraplanetaryLaunchpads. Much less drag, more close to sky, some place to land.
The mountain perimeter is defended with BD Armory turrets.
A grim castle with smelters and a green(black?)house to feed your army.
A giant smoking pipe and roaring steam boilers from VerticalPropulsionEmporium mod.

(Maybe a giant cannon too - not for launching, but for throwing fireballs).

Feel yourself a Dark Lord of Kerbin!
 

Edited by kerbiloid
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6 hours ago, fredinno said:

Wait, KSC had 2 launchpads? Where's the 2nd one?

From a gameplay mechanic, the runway is a launchpad, because as far as I'm aware you can launch rockets from the runway, and you can launch aircraft (albeit possibly short lived) from the rocket launch pad. Sorry I typed most of this on my phone so it's not expressed the best way. I was just saying If you did a space gun, instead of it being a pure craft, because of the potential length it should probably be handled as a KSC building, and the bonus of that is it's capabilities and cast can progress at a rate to keep it from being 'easy mode'. SO if the first tier cost 12,000,000 and the second tier cost 125,000,000 and the third tier was 5,000,000,000 or whatever then that would make sure people fully explore the fun of traditional rockets, before they could just fire a supply mission on a ballistic course to Duna.

 

I really like the electromagnetic orbiter, but either it would have to be in geostationary orbit, or you'd have to have an easy or automatic way to synchronize it's orbit with your projectile. Also, IIRC planets are not movable in this game, just asteroids. So in theory if you could tie the KSC build upgrade mechanic to actually inserting a new planet... Then in theory Tier 3 of the space gun could spawn a new 'planet' in geostationary orbit at the right phase angle for space gun intercept at that altitude (Since it would be rather high up). The planet could be very small and basically be a place to stick your orbital magnetic circularizing device. And I guess you would have to make it so if any object enters it's SOI then it gives it a enough boost to circularize it's orbit somehow. 

 

5 hours ago, Hannu2 said:

I think that this would not fit very well in KSP's current scope. Railgun would be optimal for very frequent launches of hundreds of payloads, for example automated supply transports to colonies or sending automated mining systems to bring resources from asteroids to kerbin. But there is not such possibilities in KSP. KSP concentrates to earlier phase of space technology where single missions are important and player plan them and execute them. Railgun would fit better to game where basic piloting is automated and player manages larger scale logistic operations in solar system.

I agree, but being that this would be a mod, it would fit in with say USI or other colonization mods, or anything with life support or in space launchpads. That's why I acknowledge it should be a very expensive end game goal, not something you unload right away.

 

But I asked it here because I just wanted peoples thoughts on how 'realistic' it was as a concept, I know nobody has done it on earth (although there have been some 'scale model' attempts), but I'm just curious how close to reality it is vs how much is just science fiction. But I like also to discuss how it would fit into KSP as a game too!

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3 hours ago, kerbiloid said:

Btw it's a nice idea about the mountains.
Not for a launching cannon, but for another thing.
(I would in any case suggest another mountain though: about 200 km or so to east-north-east from KSC, right to the north from a big island. It's higher and more flat, iirc.)

An Evil Scientist's Dark Castle on the top of mountain.
An alternative launchpad placed with KerbalKonstructs or ExtraplanetaryLaunchpads. Much less drag, more close to sky, some place to land.
The mountain perimeter is defended with BD Armory turrets.
A grim castle with smelters and a green(black?)house to feed your army.
A giant smoking pipe and roaring steam boilers from VerticalPropulsionEmporium mod.

(Maybe a giant cannon too - not for launching, but for throwing fireballs).

Feel yourself a Dark Lord of Kerbin!
 

On a slightly related note about alternative mountain launchpads, I was reading on the real life possibility of Project Orion type rockets, and pretty much the best way to control irradiation and other side effects would be to launch from near the poles, apparently the magnetic poles would help control any lingering radiation, and you have the benefit from being away from civilization anyway, in case you had to do a launch abort and detonate the payload to avoid them from falling into the wrong hands (not a issue in KSP).

So maybe for the project Orion Mod you'd want a special launchpad in high latitudes, that thing has so much delta-v that launching from a weird inclination isn't really a big deal. 

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5 hours ago, Buster Charlie said:

On a slightly related note about alternative mountain launchpads, I was reading on the real life possibility of Project Orion type rockets, and pretty much the best way to control irradiation and other side effects would be to launch from near the poles, apparently the magnetic poles would help control any lingering radiation, and you have the benefit from being away from civilization anyway, in case you had to do a launch abort and detonate the payload to avoid them from falling into the wrong hands (not a issue in KSP).

So maybe for the project Orion Mod you'd want a special launchpad in high latitudes, that thing has so much delta-v that launching from a weird inclination isn't really a big deal. 

Also because the Mag. feild is a lot weaker at the poles-thus auroras.

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4 hours ago, fredinno said:

 

But you know if the launch pad had a pneumatic mass accelerater builtin that could give a ship 30m/s of bump for the following reasons.

Smaller or fewer boosters. Allow higher loading of LfOx, and particularly some of my so-and-so wants to friggen go to mars solar powered stuff, I don't need alot of power at launch, high T/W ratios are the dreaded enemy of things that create alot of drag, and you get T/W with altitude, anyway so if you simply had something to get you close to maximum safe dynamic stress, then that's all you need. Or to state simply, a hoovering verticle ascent above the launchpad below maximum safe dynamic stress velocity is as wasteful as can be (just look at the dm/dt). One of the biggest problems in launching ships where T/W is close to m*g is that they are not very stable over the launch pad, they tend to want to roll and there is no steering currents around the ship. As has been discussed here before, also raise the atmosphere to say 5000 meters also improves the performance of draggy loads, they are trying to gain speed as the atmosphere thins.

 

Edited by PB666
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