Spaceship combat

Alright I’ll make it short and sweet. First though, thanks for taking a look at this post!

I’m mostly wondering how weapons, projectile weapons specifically, might work. Would they still have an arc in space like bullets here on Earth? Would they lose their power quicker or slower? What kind of round should I make “standard” or should I just use railguns?

I’m thinking frigate sized ships relatively close to what EVE online uses. I think their biggest one is the length of a Boeing 747. So I imagine the weapons would be like the Mark 45 5 inch gun the US navy sometimes uses.

 

Bullets in space would follow what’s called a “geodesic.” It’s a straight line through curved space. So, yes, and arc. They would it slow down at all, an object in motion will remain in motion unless acted on by an outside force.

We’d have to make some significant improvements to our projectile weapons. Something like a naval canon would be completely useless, they’re just too weak and slow.

I see that a US military rail gun fires a projectile around 5000mph. That’s nothing, like in a scientific sense that might as well be standing still. You’ll probably want your projectile moving about a million times that speed (a tenth the speed of light.)

At that speed if you fired from Earth orbit, the projectile would hit the moon after about three seconds.

 

I figured they might be to weak but, I didn’t think they’d be THAT weak. So I’d basically need a super charged version of our modern railguns/cannons. I imagine railguns would be the better way to go in this case. Do you think depleted uranium rounds would add to the penetration power like they do for our modern tanks?

 

Yeah, a railgun would probably be the only thing possible of creating speeds required. Explosives just aren't powerful enough so you'll need some type of electromagnetic accelerator.

I'm not sure how useful adding uranium to it would be. I just did the math and the kinetic energy of 1kg projectile hitting at 1/10 the speed of light is equivalent to a 100 kiloton nuclear weapon. With that much energy, you might as well just make them out of the cheapest material you can find (likely iron since it's floating around out there in bulk.)

 

I’m actually interested in how you do this calculation. It seems like something handy to know in my case. Plus I think I’m doing it wrong when I just use google. I got 190,368,210.83 Newton’s at 1/50th the speed of light.

Edit: my weight was 31.75 kg

 

In the "Forever War" which I totally recommend, spaceship combat reads something like, "We entered our stasis pods on May 10th at 0600 in preparation for the high G turn. The enemy vessel approached us at .8 light speed. At 1900 hours, the alien ship deployed a secondary object moving at point .88 light speed, forcing our ship's computer to deploy countermeasures. We pulled a 20G turn and launched 2 nuclear warheads which found their targets at 0100 on May 11th, destroying both the ship and the secondary object."

 

Projectiles will be acted upon by gravitational fields. If you fire them down into a gravity well, they will accelerate (but if they encounter significant atmosphere, they will slow down AND heat up). If you fire them out of a gravity well, they will slow down. In open space, they will travel in a straight line (newjerseyrunn is correct about geodesics), and will not slow appreciably for a long time. If the gun imparts enough momentum to pierce a hull at 20 feet, it will still pierce hull a million miles away - IF you can hit a target at that distance!

Projectile weapons are detectable with radar, so the target may have the opportunity to move out of the path, depending on detection range, how fast the ship canaccelerate, and how long it will take for the projectile to arrive.

Beam weapons are invisible until they strike something large enough to scatter the light emitted by that intersection. Unless the local space has a lot of dust or gas particles, the target will never see the attack coming intil it hits the target. However, beam weapons do spread over distance, obeying an inverse-square law from the virtual origin, which can be anywhere from the actual beam projector to somewhere rar behind it. A, s the beam spreads, the energy density at the target drops proportionally, so the damage inflicted falls off with distance.

 

Yeah, you must have done something wrong because you didn't end up with the correct units. Energy is measure in Newton Meters, not Newtons.

The formula is:

Energy = ((mass * c^2) / sqrt(1 - (velocity ^ 2 / c ^ 2)) ) - mass * c^2;
mass is in kilograms
velocity is in m/s
Energy should end up in Newton meters

This formula accounts for special relativity, which is why it looks different than the KE = mv^2 that you probably learned in school. Relativity becomes relevant around 10% the speed of light.



Beam weapons do not spread in an inverse square relation. A laser is produced by aligning all the outgoing photons to be parallel to each other. The spread would be relative to the precision of the laser. Also, at these kinds of speeds, the distinction between beam and projectile becomes pretty mute. We call alpha particles being shot around LHC the "beam" even though it's projectiles. Beam weapons would likely not even be light, as photons can't really do much damage on their own, where hadrons can hit really hard. Even a large hunk of metal would likely turn almost beam-like as spacetime has some strange properties around objects that are accelerating very quickly. A bullet would likely be ripped to shreds and be launched as a stream of disjoint atoms by it's own hawking radiation before it even left it's firing system.

 

Here's a thought.... is there any way in 1905 (or even today) that old Al could have known what the speed of light was? He knew the approximate speed of reflected light within the Earths atmosphere and magnetic fields was... kinda sorta. If you're going to square a big-assed number and put it up for all the world to ponder, it should be closer than kinda. This is science fiction after all.

 

The speed of light was discovered by Maxwell in 1864. It was not measured, but calculated exactly. It had also already been measured to fairly high degree of certainty. Here's how: Using Newton's laws of gravitation we calculated the relative distance to each of the planets. After we watched Venus cross in from of the sun, we could actually calculate distance to it and thus the rest of the solar system. We also noticed that the moons of Jupiter did not fit Newton's predictions exactly, they were up to 8 minutes ahead or behind of where they should have been. This delay was due to the time it took for light to make the trip and depended on which side of the sun we were on. It allowed for very precise measurements of the speed of light.

Maxwell's calculation was actually a huge disaster in physics because it threw Galilean invariance completely out the window. Until that point, Galilean invariance meant that if you measured something coming towards you, the perceived motion was going to be relative to your own motion. (If you are running towards a ball at 5mph and your friend is moving towards it at 10mph, you disagree about the relative speed of the ball.) Maxwell discovered that no matter how you moved relative to a light wave, you'd always measure it at the same speed. It fucked everything up for 50 years.

 

Well I guess my only other question at this point would be about rockets and the like. Seems inconsequential considering the power of a 2 pound weight at high speed...

 

Side Note On Rail Guns:
More power output for acceleration of the projectile
will create plasma at those higher velocities, which
will degrade and/or warp the rails over time. So
pack extra rails if you go that route, unless you don't
plan on using them all that much.

Coil Guns don't suffer the effect since the projectile
does not interact with the coils directly.

 

I would assume whatever would fire such a projectile would be essentially frictionless like the LHC.

I’d be more concerned with the heat generated by Uhruh (Hawking) radiation. I didn’t do any math but I’d guess that accelerating to a fraction of the speed of light in a fraction of a millisecond would probably increase the local vacuum temperature to hundreds of thousands of degrees. The projectile would be plasma by the time it got out of the gun.

 

That would be an interesting one to know. I mean it makes sense I guess since you’re going from zero to 1/10th light speed basically instantly. That raises the question of heat dissipation though because those temperatures would be insane for anything to handle even once.

 

I haven’t heard much about coil guns. Rail guns seem to be the hot topic in all things sci-fi and modern. Are they on par with rail guns?

 

Most of the time when someone says "rail gun" oddly, they are thinking of a "coil gun."

 

Technically, you could still use conventional weapons- missiles, railguns, chemically-propelled rounds etc.- but it would mean that, in space terms, combat would be rather like that of the Age of Sail, with ships having to get in close to minimise the effects of range on the effectiveness of their weapons.
While that would be a bugger against an enemy who doesn't want to engage- killing your enemy in a fight wouldn't be the hard part; sneaking up on him in the first place would be- it does get rid of the issue presented by targets so far distant that no kind of scanner or detector can accurately plot their current position due to the limitations of light speed, ie. even if your radar picks him up, that return took five minutes to get to you, so where is he now?

That's where your space fighters come in; small, stealthy, fast-moving craft that can sneak up more easily on an enemy vessel. Of course, they'd need to be able to do it at ranges over which signal delay would render remotely-piloted drones useless, so then you get human pilots involved and all of a sudden you're not refighting Trafalgar in space but Midway, with carrier-centric fleets groping around for each other in the darkness of space and other ships being largely there to defend the carriers and support planetary ops.

 

Three of the main issues you’ll have to square are distance, stealth, and inertia.

At long enough distance, communication and radar will be delayed.

Ships are incredibly easy to detect because of the huge amount of radiation emitted by their thrusters.

Course and speed corrections could produce devistating g-force that will splatter your crew. Without devastating g-force for a long period, how would you catch another ship?

 

As people soup.
But yeah you can't go from 1G too fast without becoming one with the bulkhead.

 

I was just thinking about this. How fucked would you be in a battle against aliens from a planet with 1.5-2G? You'd never catch up, never escape, without breaking your neck.

 

Oh, folks do love their facts! My favorite fact is that there are no facts,, but nobody likes that one.

 

This frightens me slightly.