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Supplement Four April 26th, 2009 12:23 AM

Perspective on Traveller Space Combat
While participating in this thread, , I wrote the post below. It's a bit of a detour from the OP in that thread (which centered around High Guard and not Book 2 space combat), and I think some of the concepts I mention about the reality of Traveller space combat may be worth further discussion.

I'm guessing that not every Traveller GM has thought about Book 2 space combat in quite this way.

The remark I was replying to stated that ship "facing" is not an issue in Book 2 combat. I agreed, with these comments....

Yep. They figure 1000 seconds is enough time for the ship's thrusters to angle the ship in any direction, so facing is not an issue.

Plus, a ship can roll (which is probably what's done) without actually changing facing, bringing weapons to bear.

For example, a ship is traveling left to right across your bow. The weapons turret is on the dorsal side of the vessel, but you are observing the ventral side. All the ship needs to do is roll along its axis, bringing the dorsal side to bear on you, and the vessel's vector is never really changed. It's still moving in the same direction at the same speed.

Things get a little more dicey when the ship coming at your, bow on, or you are chasing a vessel, observing it's aft section. Still, the way most Traveller designs I've seen in illos. shows a turret that has a good field of vision fore and aft.

For this reason, actual ship's facing is a detail that isn't worth the trouble during Book 2 space combat (with Range Bands).

I would like to note, though, that when space combat is carried out, it is usually carried out at a low vector (low speed).

For example, using Range Bands, a ship with a Vector of 3 is moving 3 Range Bands (30,000 km) per turn. Let's say the ship's Captain decides to reverse course and return to where it came from. If that ship is rated with a M-1 drive, it will take that vessel just 3 space combat turns to bring the ship to velocity 0 and another turn to accelerate to velocity 1. (4000 seconds to "slow down" from traveling 30,000 km in one direction, reversing course, to a speed of 10,000 km per turn in the opposite direction.)

Just think of a combat scenario where the ship becomes engaged with an enemy when the ship is at a very high velocity.

For example, let's say a ship, with an M-1 drive, is done with its planetary duties and heads out to the nearest gas giant to refuel before jumping to the next world.

Just using the easy numbers from the Typical Travel Times chart, a close gas giant is 600,000,000 km away. It will take the M-1 ship 136.1 hours to make that journey.

Consider that, for 68.5 hours, the ship will be accelerating at maximum thrust, then, it will flip around, and travel "backwards", using it's drives to decelerate for another 68.5 hours (GMs should remember that it shouldn't be uncomon at all to see vessels traveling "backwards" in systems).

Let's say that the ship is attacked at 60 hours out from the main world. Just how fast is the ship traveling at that point?

A space combat turn is 1000 seconds. 60 hours is 216,000 seconds. So, what we're saying is that the ship has accelerated, constantly, in a straight line, for 216 space combat rounds.

That means the ship's velocity, in space combat turns, is 216 at that point (provided the ship started at velocity 0): That means the ship is traveling 2,160,000 km per turn. Guess how long it will take this ship to decelerate to a relative stop and start accelerating in the opposite direction (as I used in the example above)? That's right. 60 hours. Meaning: It ain't gonna happen any time soon.

(To put this speed in perspective: The farthest Earth-Moon distance is 405,696 km. The ship, with an M-1 drive, will be traveling over 5 times this distance in just over 15 minutes. Now, go outside at night. Look at the moon. See how far away it is. Then imagine 5 times that distance. NOW you get a grasp on just how fast our little M-1 drive ship is traveling after 60 hours of thrust.)

That's a hell of a speed. And, an M-1 drive can only alter that course by 10,000 km each 1000 second combat turn.

Effectively, if the ship is attacked 60 hours into its journey, the ship is traveling basically in a straight line, and there's not much the crew of the ship can do about it even if they wanted/had to.

That's the bad news.

The good news is that any pirate vessel looking to intercept the ship will have to match vectors, using its drive, and will essentially be traveling in a straight line also at this high rate of speed. More good news is that the ship will see the pirates coming on sensors long before the pirates accomplish their task of matching vectors.

On the other hand, the ship will be able to do little to stop the pirates from coming even though the pirates have been detected.

In this sense, Traveller space combat is a lot like 17-18th century sailing ships. They see each other coming for a long time, and then they start firing on each other when either reaches weapons range.

If you think about the above scenario, the ship and the pirate vessel will match vectors and just take pop shots at each other, just like going "broadsides" with old sailing vessels.

Maneuverability and weapon class are key to Traveller combat. If the pirate vessel is rated at M-3, and the ship is rated at M-1, this gives the pirates the ability to approach quicker (they'll still be seen coming) and get out of the situation quicker (as they should, the pirate vessel is 3 times more maneuverable).

As far as "facing goes", the ship can just shut off the drives, and use the attitude thrusters to face the ship in any direction desired (so, facing, again, is not an issue), but the direction of thrust and speed of the vessel will remain the same, no matter which way the bow is facing.

So, yes, really, "facing" is not really a factor. Range Bands do handle it well because, well, Range is all that we're really talking about. You don't need plots, 2-D or 3-D, because it's all about range.

aramis April 26th, 2009 01:04 AM

It's only 1 dimension of range when only 2 ships are involved. At 3 ships involved, if there are 3 sides, it's 2d; if only 2 sides, the two ships on one side are both relative to the target, and that's still a reduction to 1D for most purposes.

At 2+ ships on each side, you get the off-travel thrust being relevant, by two targets being able to separate and pull the pursuit to either one, or to split the pursuit force.

at 5-6 ships on a side, 2d becomes a real relevant handling, if the ships are not flying formations.

As S4 notes, the higher thrust ship can pick and choose it's range, given enough time. That's not always possible, but that's because of constraints of either intercept or escape.

On another tangent: One should note, however, that Traveller laser, Plasma, Fusion, and PA ranges are absurdly long; lasers in 1Td turrets should be at most a few (single digit or low double digit) million meters of effective range... not the 1-2 LS of Bk2 designs. Plasma and fusion far less.... Realistic weapons fire is a few G-minutes of acceleration separation, not 30+... Missiles, much further, IF they have the endurance. (One should also note that at realistic ranges, one also has almost no significant chance to not be where they think you're going to be when their fire hits where they think you will be; at ranges over 0.2 LS, there's a significant chance of missing small ships by virtue of exact position being uncertain due to light lag.

Supplement Four April 26th, 2009 01:56 AM


Originally Posted by aramis (Post 315404)
One should note, however, that Traveller laser, Plasma, Fusion, and PA ranges are absurdly long; lasers in 1Td turrets should be at most a few (single digit or low double digit) million meters of effective range... not the 1-2 LS of Bk2 designs.

On what do you base this? I think a laser firing at ranges given in Book 2 are realistic given the tech of the Traveller universe.

You've got to consider, unless you're very close to a destination or start point in a system, combat will generally take place at extreme velocity (as I demonstrated in the OP). This means ships, relative to each other, are traveling in straight lines with no maneuver altering of course realisticly possible (remember, it would take mucho hours for our M-1 ship to effect any type of maneuver, and the enemy who matched vectors could easily follow).

Thus, targeting for lasers in Book 2 Traveller is pretty simple for their targeting computers...predicing where the ship will be when the lasers hit is elementary. Since the ships are traveling in straight lines--just calculate where the ship will be in the time it takes the laser to strike.

Plus, it is generally assumed in CT (and confirmed in other versions of Traveller) that the to-hit roll for a laser doesn't necessarily represent a single laser shot. The attack roll represents multiple laser shots, shot gun approach, hoping that one or a few will hit. I remember seeing rate of fire figures of (what was it) several hundred in T4.

So, if you've got a laser firing 200 or 800 times per laser weapon at target you know will be in a certain spot at a certain time, your only problem would be (A) to make sure the laser delivers a powerful punch when it strickes and (B) you can actually hit the target at the fantastic range.

Visually, a Traveller starship should look more like something out of Star Wars when in combat (with respect to the laser weapons...not the maneuvering).

You should see the attacking ship, accelerating in one direction, it's laser weapons repeatedly firing as fast as their capacitors can recharge.

But, you wouldn't see the vessel's target. It would look like the ship is just firing its weapons out into the blackness.

That is, you'd see the lasers firing like that...if the beam was in the visual spectrum. Lasers in the UV band, would, of course, not be seen.

Interesting note: A target ship hit by lasers in the UV band would look like: A ship crusing along on course, and then explosions start appearing on the hull as if by magic.

Your objection may be to the power cost? To that I would bring up the enormous power a Traveller craft can manage using the J-Drive drive to rip a hole in space/time so the ship can pass through to Jump Space. It's not out of reason to think that a ship's powerplant can power the lasers effectively.

I've mentioned before in other posts that, in most cases, when pirates attack, everybody in the entire system knows it. The victim should, in most cases, detect the pirate craft early, with the problem being: The target ship cannot do anything about the approaching pirate vessel. It's like the 16-17-18th century sailing vessels, where a pirate ship may chase a target for several hours to several days, and the target unable to do anything about it except delay the attack by running and prepare for combat or boarders.

Except, in Traveller, there's radio communication. So, the target vessel will have plenty of time to send out Signal GK's, Last Will and Testaments, Sensor Data, or any other type of broadcast that they wish to make. The pirates can do little to stop this, but they probably don't care.

Pirates will have to deal with their ships being "known" to authorities from being reported and viewed (via broadcasted sensor data) so many times.

Other ships in the system can do little to prevent the attack. Even if there's an Imperial Battleship in orbit around the main world, it won't help a pirate victim that's 3 days thrust away from the main world.

All the authorities can do is try to post deterrents at "hot spots" within a system.


That's not always going to do the trick, either.

Let's say a "hot spot" is 60 hours away from the main world, as I mention in the OP. If the IN posted a SDB in that area, along that route, there's a good chance the SDB would not be able to help a victim running through that area.



The SDB would have to keep to a certain velocity or its patrol would take it out of its patrol range.

Yet, vessels moving through that area, on their way to the GG, would be hauling some butt (remember how fast the vessel in the OP example is moving).

So, in effect, what would happen is that the IN SDB would pick up the pirate attack early and do what it could to match vectors, but there probably wouldn't be time to get to the extreme vector of the attacked ship (see the OP). If the IN SDB is very, very lucky, it could possibly maneuver itself to a position and speed where it could engage in exactly one round of space combat before the victim vessel and the pirate vessel zip by, out of range.

It'd be like the IN SDB was a bicycle on a side walk next to a freeway, with the victim and pirate represented by the speeding freeway cars. They're there. Then, they're gone.

Of course, it's not so easy for the pirates, either. They've got to be in a position and have enough unmolested time to match vectors with a target vessel, all the while knowing that they will be detected.

I think successful pirate operations probably work with a person planet side who tight beams a message to the pirate vessel about a prospective target. The pirate vessel can then start to match vectors, hopefully having enough time to reach the target. But, it can't do this if other ships are in range to do the same thing.

One would think the pirate could just find a place along a well traveled route (say....the direct line between the closest GG and main world) and sit there at relative stop, going cold so that it won't be detected. This is fine...but the pirate will have the same problem the IN SDB did above. The target would fly by at extreme speed, be at the GG, refueled, and jumped outsystem before the pirate could match vectors.

Piracy must be tricky. "Normal" points, like in orbit of the GG, would be typically patrolled, and if not patrolled, then likely to have more than one civilian ship there (running the risk that the pirates would be fighting more than one vessel). Points farther away have the "speed" problem I mentioned above. Add to this the fact that it's almost impossible to approach a ship without being detected--and your pirates have to really think out their attacks.

But, it can be done. And, it may even not be as hard as what I'm saying here, depending on the system dynamics.

Supplement Four April 26th, 2009 02:19 AM

The logical questions the births out of these types of discussions have to deal with sensors. How far can a ship detect...?

CT gives us ranges, but let me remind you that sensors don't have cut-n-dried range numbers. It depends on what you're trying to detect and how much time you have to try detecting it.

When I see the CT sensor ranges, my assumption is that's a guideline for detecting other vessels. But, a basic sensor package on a tramp freighter should be able to detect light from other solar systems, maybe even other galaxies, given enough time.

Size of the object matters, and effects sensor range. A Gas Giant is easier to detect than a starship.

Distance to the object matters, and effects sensor range. A starship in orbit around the moon is easier to detect than a starship in orbit around Mars.

Signature of the object matters. Stars are easier to detect than planets.

Line-of-sight Obstacles matter. Sun spots. Dense gravity. Magnetic anomalies. Debris. And, of course, solid objects all decrease distance.

So, the next time the players try to detect something, and you look at the rules and say, "Well, your sensors don't have that kind of range," consider what that something is. If it's a ship, then it's probably not being detected. But, if it's a star, then the players just may very well detect it (heck, we can see 'em with our naked eyes), even if the star is 300 parsecs away.

The players can't tell much about a star system 1 parsec away, except, maybe, the number of stars (and possibly stellar class) in that next system, if they only use one space combat round to check (15+ minutes).

But, if the players spend six months, with their ship in optimal position, to observe the nearby system, some details, such as the number of planets, may be discovered.

More sophisticated sensor packages, and sensors designed for this purpose, can delever better results in a more timely fashion.

The point is: It's possible. The next system (and other objects closer) are not necessarily "out of sensor range".

It just depends...

Your eye is a passive sensor. With it, you can detect stars that are several parsecs away. On some nights, you can detect details on the moon, which is just 300,000-400,000 km distant. Sometimes, you can see satellites in orbit, some 5,000 km away.

But, the same set of eyes won't allow you to detect a chair, 15 feet away, on the other side of a dark room, or details of a man walking toward you from a mile off on a sunny day.

What your ship's sensors can detect...also depends.

aramis April 26th, 2009 02:59 AM

My objection to the ranges is due to simple physics, as noted in the TNE rulebook Fire Fusion and Steel, wherein they resort to gravitic focussing (which, per physics, means localizing 20+G's to accomplish the lensing needed... making same said rulebook's 6g compensation limit seem out of place.) It's the exact same physical limits of the laws of optics that nerfs sensor resolution... you can't get a tight focus at huge ranges.

mike wightman April 26th, 2009 03:33 AM

To focus light by bending it due to gravity would take a lot more than 20g. The reason I never liked the g focusing tech is that if such high g fields can be made how come they aren't used in other applications?

Supplement Four April 26th, 2009 04:01 AM


Originally Posted by aramis (Post 315407)
My objection to the ranges is due to simple physics, as noted in the TNE rulebook Fire Fusion and Steel, wherein they resort to gravitic focussing (which, per physics, means localizing 20+G's to accomplish the lensing needed... making same said rulebook's 6g compensation limit seem out of place.) It's the exact same physical limits of the laws of optics that nerfs sensor resolution... you can't get a tight focus at huge ranges.

So...don't follow FF&S. Yes, it's Traveller, but no, it's not CT.

I wouldn't argue with someone who wanted the laser weapons attack throw to represent one actual laser burst (instead of going with a volley, as I think is logical).

CT gives us that it works. Use another handwave that will satisfy you.

This is not unlike strange UWP results. Don't fix 'em, as Hans says. Figure how the world go so cool, as Marc says.

In a universe where "lanthanum" is absolutely needed for the inner coils of the jump drive, I'm sure there's something that can make the lasers kosher for you.

Or, maybe not. :(

Icosahedron April 26th, 2009 04:06 AM

Another difficulty for long-range laser fire is angular diameter of the target. Vibrations from your own drives could be enough to displace the far end of the beam miles away from your target, just as your own muscle tremors can prevent you focussing a pair of binoculars on Saturn.
Aim a laser ponter at a dartboard at 10m, then 100m, then 1000m, then...

Zparkz April 26th, 2009 05:14 AM

Regardless of which rulesystem you use, the laser rules are written so that they become playable. Which is far more important to realism in most cases.

Lasers are probably the one item in Travelelr that creates much controversy and handwaving. If you follow FF&S and drops grav focusing you effectively make TL 13 X-ray lasers the winners of the battlefield. A TL 13 X-ray laser outperforms a grav focus laser at any range up to 10LS (Hexes). It is cheaper and got more damage pr MW.

I have been toying with dropping lasers on ships and go for a more "Battlestar Galactica" approach fitting crafts with mass drivers and missiles. Ranges will go down to a few hundred kilometers. Combat turns will be correspondingly shorter. Any rolling of the craft t get all batteries to bear will be moot as the combat turn will be less than a minute long.

However, missiles will be the main armament as they can strike target well outside effective mass driver range. This means that there will be need for two combat scales. One scale for the missile fire, and then one for the close in brawling, which may make the whole game unplayable.

The lower effective range and reduced timescale will also force the combat to be performed at slower velocities close to points where crafts gather for jump, orbital approach and so on. Deep space battles may be of a rare occurence, and only with missiles.

RKFM April 26th, 2009 10:11 AM


Originally Posted by Zparkz (Post 315414)
Regardless of which rulesystem you use, the laser rules are written so that they become playable. Which is far more important to realism in most cases.

Exactly. You can't try to coax reality into Book 2 space combat.

Not to mention the anachronistic computers and the Star Wars/WWII 'Gunners' manning the laser turrets.

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