Weapon systems, part 0001

[Jeremy Buloch]

Yes Good to see you Gateway. I wish you an easy time.
By the way, Blake you dont talk too much.


Now about this topic of ours...

The energy Weapons would be much more beneficial in stellar combat. The energy pulses would hit the vessel and if it misses then the energy slowly disipates. A projectile would have too many risks involved that would make it unsafe.

If we were to use projectile based weaponary then we would have to devise some sort of working system that would go as follows:

Two vessels are in combat and one vessel fires a projectile which misses the other vessel. Later after the battle another innocent vessel is passing through space and is hit by a stray projectile(s). This would have to be implemented into the game in order for it to be realistic, would it not?
-J.B.-

[Blake]

Two vessels are in combat and one vessel fires a projectile which misses the other vessel. Later after the battle another innocent vessel is passing through space and is hit by a stray projectile(s). This would have to be implemented into the game in order for it to be realistic, would it not?

Space is big, spaceships are tiny. The only time that stray shot has even a remote chance of hitting something that feels it (ie not a star or blackhole) is when it's locked in orbit, hence prehaps a "Space Junk" variable would be useful.
- keep a count of the total number of particles in orbit
- calculate the volume of space in the orbit
- from that, determine the chance of a spaceship hitting 1 particle
- use some sorta probability distribution to determine if, and how many particles the spaceship hits.
- throw all that out the window, and use an approximation that works
In practise have some variable that increases each time a spaceship gets blown up in orbit of the planet, it should reduce slowly due to junk falling into the atmosphere. Use some sorta probablistic method to determine how many hits orbiting ships get....

In principle a whole solar system could start getting dangerous if entire planets start getting blown up (a planet worth of debries scattered in a belt around a star presents a significant danger to spaceships). But when talking a single stray shot, nah.

[targon]

Hey, IMHO, your "space junk" fears are fairly irrelivant, as high-tech projectiles will surely leave this humble solar system as they velocity will be reasonable high (~30km/s will do). Missiles even now employ self-destuction if they can't hit the target.

[targon]

I've forgot about some more weapon stuff:
Discharge cannon. Atmosphere only (possible hydro). Employs massive discharge generator coupled with pulse laser. Laser beam forms conductive "thread" that is later used to fry enemy electronics and even armour via strong discharge. Laser may be substituted with some other beam, but electrons, protons and especialy heavy ions tends to deflect and change its directions.

[Blake]

Nah I mean junk leftover from battles, like when a ship explodes, sure some of the debries would escape the orbit, or hit the atmosphere, but some would remain in orbit.... (assuming the spaceship was in stable orbit)

I assume a discharge cannon would only work in atmosphere? ie the laser beam ionizes atmosphere to make the conductive thread.

[targon]

Blake,

Originally posted by targon
Discharge cannon. Atmosphere only (possible hydro).

In fact, I saw its working prototype, so it is't my pure imagination... there are some problems, but we speak about future, right?

Originally posted by Blake
Nah I mean junk leftover from battles, like when a ship explodes, sure some of the debries would escape the orbit, or hit the atmosphere, but some would remain in orbit.... (assuming the spaceship was in stable orbit)

Yep, you're right. Assuming the spaceship was in stable orbit, center of masses of its debris must remain the same orbit (w/o light pressure, atmsphere and other subtile ways of momentum transfer)

[Gateway103]

Originally posted by Blake
Good to see you gateway

Well regarding turnrate you are mostly wrong (but it's a common mistake/misconception that I've seen before by people who really, should know better...). Turning doesn't make much sense in the absence of friction, the only thing that really matters is change in velocity, it doesn't matter if your going at 0.2c or 20m/s, if someone fires a bullet *to intercept you* then all you need to do is accelerate in some direction so that the bullet hits empty space.

Well, it actually does depend on your velocity. Let us assume your ships can produce a constant maximum X amount of lateral acceleration (used for turning), and the linear velocity is constant at V.

Now, the lateral acceleration is your centripetal acceleration, which we assumed to be constant and equal to X. Therefore, by the formula, F = MV^2/R = (4 Pi^2 R M) / (T^2): we see the following,
(1) Since F (i.e. X is constant), then the relationship between V and R (turn-radius) is R = MV^2/X
(2) Also, T^2 (square of period) = 4 Pi^2 R M / X
(3) by (1) and (2) then, T^2 = (4 Pi^2 M^2) / (X^2 V^2), or in otherwords, T is proportional to V (M and X are fixed if linear velocity is constant, and X fixed).

By result (3) then, if the period required to complete a full turn (i.e. 360 degrees) is proportional to V, then the turn-rate, measured in radians/second, is 2Pi/T or proportional to 1/V. In otherwords, if velocity increases, turn-rate is lowered.

This should be intuitive, because if you think about it, turn-radius definitely increases with increasing in linear velocity. And unless your ship is capable of generating and withstanding any arbitary lateral acceleration (providing you, the passenger, can withstand it too), you must move across a longer arclength (i.e. longer path) at the same initial velocity you were in (again assuming only lateral acceleration). So since T = D / V, increasing in D, while keeping V constant, will surely result in increasing in T, and subsequent lower turn-rate.

Now I hope I have illustrate that turn-rate and turn-radius are indeed affected by your initial linear velocity, I wish to discuss more about space combat.
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You are nevertheless correct in that actual space combat at long range (read: lightsecond and upwards) is problematic. However, long range weaponary tend to have short-comings.

1) Beam Weapons
With lasers or other beam weapon capable of luminal speed, there exist the problem of energy dissipation over distance. This is not a trivial matter, and does exist in vacuum. But for 1 light-second, this may be alright (given you have centuries to refine this tech perhaps)

The more serious concern is the energy output of the beam weapon. In your thought experiment, just because the defender is hit with the laser, it doesn't mean it is destroyed. Beam weapons is like a conduit, depositing energy from the attacker to the defender. Therefore, the amount of energy you can put on the defender depends not only on the energy output of the beam (ignore dissipation for now), but also the duration. Just grazing the defender's ship for a fraction of a second probably isn't enough to do much damage, unless you got one very-powerful lasers (probably not on ships due to power generation constraint; but with orbital weapon platforms such as space stations, this is feasible)

And foreseeably, because of movement, energy deposition is spread over an area of the hull, thus lowering the energy density and most likely damage incurred. Also, armouring materials at the surface of the hull would likely to be designed to spread incoming energy as quickly as possible across the entire outer-hull, so again minimize damage. Therefore, beam weapons at long range isn't going to be very effective against agile defenders.

However, if the target is immobile, well, then you may be able to do some serious damage there.

2) Missiles-type
Missiles are more capable of delivering a concentrated energy blast to defender, either via actual impact detonation (difficult against agile target) or proximity detonation (via sharpenal or other means). Missiles are limited to travel at sub-light speed, although they may indeed be faster than ships. Nevertheless, at long range, enemy would have time to pick them off with point-defense weapon platforms (e.g. PD lasers, or more agile escort/picket vessels, including fighters).

Now for closer range however, missiles can be devastating, provided you the attacker isn't too close either.

3) Projectile of sub-light speed
Projectile of sub-light speed suffers the same accuracy penalty as luminal speed beam weapons, and even worse. However, due to the absence of pretty much anything in space, damage potential dissipation due to travelling distance is not significant for moderate range. Therefore, these are most suitable for close-range combat.

Conclusions:
1) Long range combat is feasible, especially against immobile target and/or larger/slower targets. However, against small and agile target, this isn't going to be productive.

2) One possible tactic, however, is to throw long range offensive fire against enemy via larger/slower capital ships, while sending in smaller escort/picket vessels (including fighters) to destroy/harass enemy at mid- to close-range.

3) To counter the battle tactics in 2), enemy must also need to have small escort/picket vessels, to protect their larger/slower capital ships from approaching vessels and missiles (long to close range ones). This is akin to modern naval warfare, whereas you see lots of smaller escort vessels for the core ships (e.g. carriers, troop transports, etc.)

4) From 1) to 3), it is feasible that battle would occur in all ranges, depending on the fleet composition and weaponry of each side. And recall velocity affects manuverability, which is very important in mid- to close-range, conventional weponary (e.g. projectile, beam weapon, and missile-type) would then be adequately effectively (of course if you got some better alien tech, by all means use it).

To close it off, battle only at long range isn't going to be common or productive in general, especially if you want to invade planets and attack orbital platforms (while they are immobile, they have much better defense capabilities, not to mention the likelihood of a local defense response fleet). So the general categories of beam, projectile, and missile weaponries can be useful, at various stages/ranges, depending on the sophistication of the relevant technology as well as opposing defense capability.

-Gateway103

[Leland]

Originally posted by Gateway103 Well, it actually does depend on your velocity. Let us assume your ships can produce a constant maximum X amount of lateral acceleration (used for turning), and the linear velocity is constant at V.

...

Uh, it seems like you define "turning" in space as a change in velocity V to -V. In that case, of course the time spent in the manouver is proportional to the initial velocity. I'm not much of an expert in this stuff, but I don't really see the relevance of this in evasive action... to dodge a bullet/missile/beam, all you have to do is to avoid being in the same place at the same time, and this you can achieve by accelerating in any direction (assuming the guys who shot you assumed you won't accelerate at all). If the shooting algorithm takes into account your initial acceleration at the time they pull the trigger, then the situation gets too complicated for my puny brains though...

Hmm, how come I get the picture that the best way to dodge lasers and dumb projectiles would be to set your ship's engines accelerating in random directions, and then hoping for the best? That might be an interesting thing to see.

[Martin the Dane]

Well I must ask what is the point of turning ratio and radius for a spaceship in combat?

In caombat you want to avoid being hit. So how do you acieve this.

For grund combat you don't use evasive manuvers very much you use trerain for cover, and expose as little as possible of yourself for the shortest possible time. Only when it is not feasible to take cover you use speed and acceleration to dodge bullets.

For naval combat, there is seldom much terrain to use for cover, and since naval vessels generally dont have much in way of acceleration evasive manuvers arn't overly effective.

For air combat, even less cover but you have quite good accelerations, and due to aerodynamics you have to maintain a certain minimum speed relative to the air (airspeed). Traditionally planes have only been able to apply thrust in one direction (ecxept the harrier) so they have use control surfaces to generate lateral acceleration, so the grater airspeed the greater lateral acceleration, for modern aircrafts the turnratio is limited by the ammount of acceleration the pilot can cope with.

Now for space combat, there is still nothing to take cover behind, so the only way to avoud being hit is, as Leland correctly points out, not to be where the projectile/beem/misile "hits", so we have to rely on evasive action, or active defence.
In space there is no airspeed, so unless we operate at relativistic speeds, the absolute velocity is completely irelevant (except for calculating travel time for lightspeed weapons). What is interresting is the relative speeds of the combatants. If they are traveling on a converging cource, thy will for all practical pourpouse be traveling straight for each other, at a given speed, and since spaceships don't have to take drag into account they can be orientated in any direction, so turnratio is irelevant for the purpouse of evasive action. If the aim is to pursue the oponent or escape him, the acceleration is best used either directly towords or away from the oponent, (or rather where the oponent might be at the time of intercept, relative to the current system of coordinates that is) depending on wether you want to prolong or shorten the encounter.
Since the oponent is most likely to use his acceleration to his own advantage, it becomes a question of who has the best acceleration. Here it is interresting to note that if you want to run from an encounter the best cource might be to accelerate more or less straight for you oponent. This might get you closer to him, but since you will then have the greater speed relative to him, you will spend less time inside his sphere of attack. An added bonus is that if he causes you to explode he will moste likely be hit by the debree, so he will be more reluctant to shoote.

Oops there I got into my speculations on space tacktics, and not the dynamics of space combat. Well my point is that turnrate has no meaning in space combat.

As you have no fixed system of coordinates, and don't have any aerodynamics to take into account tactics changes and becomes a question of being where _you_ want to at the time _you_ decide - relative to your oponent. The same goes for your weapons, being it projectiles, misiles or beams.

[Gateway103]

Let's me try again.

Space Combat
-no cover
-no fricition

To dodge incoming fire
-random bursts of acceleration in various direction (i.e. evasive manuvering)

Note about hitting target
-Space is big, difficult to hit directly with projectile/missile/beam weaponry.
-Solution? use proximity/pre-set detonation for missiles. And use a boresighted projectile/beam emitter.
---proximity detonation: the warhead detonated if it is within certain distance away from the target.
---pre-set detonation: more like bombs, it'll travel a certain distance, pre-set by the attacker, then detonate. This works in the hope that enemy will be near when it detonates (like depth charge against submarines)
---boresighted cannon: guns and cannons don't concentrate all their firepower on a single point, or a small area. Surely the damage potential is higher for concentrated fire, but it is much easier to completely miss the target that way. Hence, modern cannons/guns (not hand guns, more like guns on aircraft) has a larger envelope area in which they funnel their projectile into. For example, F-16 is boresighted to about 6 foot, meaning the gun is adjusted to fire a burst that will put 80% of the rounds inside a 6 foot diameter circle. This makes it easier to hit if you aim correctly, despite enemy manuvering. Beams are a bit different, but that's not within the scope of this post
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Now, turn-rate and turn-ratio
-On the surface, many seems to think it has little or no impact in space combat. However, as noted above, direct hit is difficult, thereby you are trying to just put your firepower near where enemy may be.
-Attached in the zip file are 2 files, a diagram and an avi, please load the diagram first.

Diagram
In the diagram, you see two sets of attack. The upper one involves a fast moving target, the lower one involves a slower moving target. Both frames are considered to be relative to the attacker, therefore the attack is considered fixed.

Both target starts out at the same initial position. As indicated before, turn-rate and turn-radius is larger for faster moving vessels, and slower vice versa.

edit: Note, the faster moving vessel, because its higher momentum, would have higher structural stress when accelerating, relative to the slower vessels at the same acceleration. And this diagram assumes the ships are accelerating at their respecitve maximum possible acceleration, hence everything else being constant (ship size, geometry, thrust, mass), the faster ship would have a lower max acceleration than the slower ship. I forgot to mention is earlier, sorry for the inconvenience.

In the upper depiction, Target is moving quickly away from the Attack, but because of its high linear velocity, after some arbitrary time, the probability envelope is as indicated. The probability envelope is given the initial velocity of the target, and the maximum lateral acceleration it can generate, where the target can be in. I.e. , the target may not carry out acceleration in only one direction, but rather doing something, in that case, it'll be inside the boundry of the blue area (actually a volumn if you rotate it about the yellow axis, but drawing 3D is a bit harder on Paint)

Similarly, in the lower depiction, Target is a slower moving target, but with better turn rate and turn ratio. The probability envelope is again depicted.

Ok, now recall that we are not really trying for a 100% direct hit (too difficult), but rather near the target. Assuming your missile detonation kill radius is fixed, and your boresighted cannon a fixed damage envelope. Now consider a missile fired along the yellow axis and detonated somewhere on the axis inside the probability envelope (pre-set or proximity). Due to the shape of the probability envelope, the target can not be very far away from the axis, as oppose to the lower example. Therefore, the target in the upper case is more like to be damaged.

Similar effect works for beam weapon too.

movie
For a hopefully clearer demonstration, please load up the avi movie file.

In the movie file, two defenders started at the same location, but with different linear velocity, travelling directly away from the attacker. Again, all the motion is relative to the attacker, and let's assume the attacker to be stationay. The orange ball you'll see appearing are missiles, where cyan lines are beam weapons. Blast radius is indicated as enlarging balls, (should be sufficiently obvious which is which, despite my poor skills).

Just look at the movie and you'll see that turn-rate and turn-ratio does affect combat survivability, and in an important way.

Of course, this is a very crude model, in actual combat between two armed sides, both parties are doing evasive manuvering, travelling towards/away/passby each other, carrying out counter-measures, as well as firing against each other, making the calculation that much more complicated. Nevertheless, the same principle holds.

-Gateway103

[vovan]

I figure it would be easier for the people to see if they didn't have to download the large file. So, I converted it into a much smaller animated gif (hope you don't mind )

[vovan]

And, of course, the diagram:

[Leland]

This is so counter intuitive that my brains won't accept it. I mean, if the slower ship can accelerate "upwards", why can't the faster ship do the same? After all, in their own frames of reference boths ships have zero velocity. furthermore, since the pursuing missile has lower velocity relative to the faster ship, I would expect it to be able to dodge it.

Uugh.

[Gateway103]

First, thanks to vovansim for convertin the diagram and avi file , I wonder why I didn't think of that

Second, to addreadd Leland's inquiry.

You are right that in their own reference frame the individual ships have zero relative velocity to themselves, so intuitvely they should both be able to dodge the missile.

But an underlying assumption I made, which I forgot to state (sorry, sorry, don't lock me up ), is that there are more structural stress on the faster moving vessel, hence its lateral acceleration must be slower than the second slower vessel so as not to break itself apart (sorry, I factored it in during render, but forgot to mention it in either post... guess that's what happen when you start rendering near 1am in the morning...) So that's actually what is depicted in the movie, the faster vessel having a necessarily lower lateral acceleration.

[I'll edit the above post to include this assumption sorry]

And you are right, if they are of same lateral acceleration (say with some tech to reduce stress), you would intuitvely expect the faster ship to doged as well.

Once again... I am very sorry for the confusion

-Gateway103

[Martin the Dane]

Well I must admit it Gateway you have a point, but it does not hold.

First speed in zero-g and zero-athmosphere does not result in stress, only acceleration does that. So the only important factor here is the acceleration, and we have setablished that it is applied lateraly to the ships current movement.

Let's take an example:
One Attacker A and two targets B1 and B2.

Initial state:
A is moving at Va=10km/s B1 is moving at Vb1=14km/s B2 is moving at Vb2=12 km/s all in the same direction.

We transform the coordiane system to A, so now we have Va=0, Vb1=1 Km/s, and Vb2=2 Km/s.

Since A is clearely loosing ground A fires 2 shots running at 10 Km/s relative to A. The distance to both targets at firing is 1000 Km so the shots will take ~111 seconds to catch-up with A1 and ~125 seconds to catch-up with A2.

If both targets keep going as they did they will then have ~111 and ~125 seconds to live respectively.
And due to the speed of the shot they canot outrunn it by accelerating.

So both B1 and B2 accelerates laterly at full trhust 10g (close to the limit of the pilots I dont think we have to consider stress on the ships, as they can most likely tolerate far more than the crew).

When the shots get to where B1 would have been it has moved ~111*111*10m=~123 Km sideways.

When the shots get to where B2 would have been it has moved ~125*125*10m=~156 Km sideways.

If both shots explodes when they reach the spot where the targets should have been (T1 and T2) B2 has the best chance of escape. since he has put ~26 km more between himself and the blast than B1 has.

Since the attacker most likely knows this, he will probably use multiple spreading shots so now the angles O# between the lines A-B# and A-T# comes into play. (See the attached image)

If I remember my trigonomy-lessons right, O1 is 6.3 and O2 is 7.1 degree, so the faster ship not only gets the benefit of distance but also of the greater angle.