Acceleration times

[sudnadja]

Sorry, another perfect spring day. I've never seen my local promenade by the beach so crowded...

Given your work, perhaps the best I can hope for is proving there is no solution.

Going back to the original point of this thread, I think it is more damaging to game physics (in terms of coming up with an orbit) that 1/2 a t² isn't respected. Gravity applies a change to the position as if acceleration were twice as high as it is while applying a change to the velocity vector as if acceleration is as written. You can't double integrate acceleration and get position, you can't take the second derivative of position (wrt time) and get acceleration.

While doing all of this I have now realized that a lot of my helper functions, written to work in the real world, do not work in Traveller LBB rules. An optimum intercept method (you want to have the same velocity and position of the target at the minimal time given some acceleration) that works in the real world doesn't work here.

My work above has all been presuming LBB rules, and I think there is still a geometric proof possible that will show no orbit is possible within the rules, but I think I've become a little disenchanted with LBB movement rules. Everyone can be expected to be able to work basic kinematics and the LBB movement rules were an unneeded abstraction.

 

[aramis]

Everyone can be expected to be able to work basic kinematics and the LBB movement rules were an unneeded abstraction.

Not even close to true. Vector movement is so counter-intuitive that most people find even the simplification into Bk2 to be a hassle bigger than they can cope with. Which is why the even more abstracted Mayday was such a blessing; it quantizes even more than book 2, but even then, it's hard going on many.

To be honest, from most of the games I've run, played in, or heard of, almost no one used the Bk2 movement rules, few used mayday; most just handwaved it all and avoided anything but simple pursuit combat.

 

[whartung]

To be honest, from most of the games I've run, played in, or heard of, almost no one used the Bk2 movement rules, few used mayday; most just handwaved it all and avoided anything but simple pursuit combat.

I know I'm a stick in the mud, but it's just the fundamental truth of space combat, especially with Traveller type weapons.

In the end, it's two ships, closing on each other (as to who's chasing who, is moot), with their lasers on HIGH the entire time.

Sure, there's missiles, perhaps, etc. to cloud up the target space. But in the end, that changes the outcome only marginally. If you're running away, you shoot at the missiles. If you have a Jump window you're trying to make, you run as fast as you can. If you don't have a Jump escape, and they are closing, then it's just a matter of time. It's arguably reckless to "turn and fight". The longer you are in the danger space, the more chance of you getting critically injured.

If you, indeed, overpower your opponent, then it may be worth "staying and fighting", but why even spend the money repairing the damage you will likely inevitably get? If you can end the fight faster, and in turn, taking less damage, then it's worth staying.

The intruder, otherwise, is going to shoot, shoot, and shoot some more. Lasers are "free". Shoot early, shoot often. You might get lucky. And, if not, you're closing, and getting luckier.

So, yea. Two riflemen in a bull ring, whether one is running for the exit or not is situational.

At that level, it's a one dimensional game -- distance, and how fast it's closing.

 

[Grav_Moped]

Not even close to true. Vector movement is so counter-intuitive that most people find even the simplification into Bk2 to be a hassle bigger than they can cope with. Which is why the even more abstracted Mayday was such a blessing; it quantizes even more than book 2, but even then, it's hard going on many.

To be honest, from most of the games I've run, played in, or heard of, almost no one used the Bk2 movement rules, few used mayday; most just handwaved it all and avoided anything but simple pursuit combat.

And orbital mechanics is an entirely different can of worms. Even NASA got it wrong the first time they attempted an orbital rendezvous.

 

[sudnadja]

And orbital mechanics is an entirely different can of worms. Even NASA got it wrong the first time they attempted an orbital rendezvous.

The whole orbit within LBB rules discussion is more just trivia, it was just an attempt to answer if a ship in LBB rules could be in orbit aside from just declaring "It's in Orbit". I doubt that anyone (without computer support) would take the time or make precise enough measurements on a playing surface to actually put something in orbit if it were possible.

Even using real physics, orbital mechanics would be simplified compared to a real Earth orbit. Traveller planets are uniform objects, they are spheres and can be treated as point gravity sources due to that. No J2, etc terms. I think even when people do attempt a more realistic approach for orbits (which is rare), they are ok with Kepler.

 

[whartung]

The whole orbit within LBB rules discussion is more just trivia, it was just an attempt to answer if a ship in LBB rules could be in orbit aside from just declaring "It's in Orbit". I doubt that anyone (without computer support) would take the time or make precise enough measurements on a playing surface to actually put something in orbit if it were possible.

In my "simulations", orbit was a special case. When the ship got "close enough", it placed itself in to orbit. At that point, orbit was a velocity that the ship traveled in a circle, and was simply updated that way rather than playing with gravity and what not. The velocity was "accurate" but that's as far as it went.

 

[sudnadja]

In my "simulations", orbit was a special case. When the ship got "close enough", it placed itself in to orbit. At that point, orbit was a velocity that the ship traveled in a circle, and was simply updated that way rather than playing with gravity and what not. The velocity was "accurate" but that's as far as it went.

Judging by Aramis' comment above, even that almost never happens in most Traveller games. Having listened to a number of actual plays now, I'm starting to get to the opinion that all of the traveller rules are completely ignored in almost all play, aside from the character generation component. It is a little unfortunate that - 40+ years after the fact - what initially attracted me to Traveller isn't what Traveller turned out to be.

 

[aramis]

Judging by Aramis' comment above, even that almost never happens in most Traveller games. Having listened to a number of actual plays now, I'm starting to get to the opinion that all of the traveller rules are completely ignored in almost all play, aside from the character generation component. It is a little unfortunate that - 40+ years after the fact - what initially attracted me to Traveller isn't what Traveller turned out to be.

When I ran CT (and the last time I did was about 1996), the CGen, travel, trade, and ship construction were what I used; Ship combat was using the Starter Traveller range band system rather than Bk2.
The Skills chapter was "augmented" by the DGP task system.

Traveller is, and was, intended to be a modular framework. This is why there are two character generation modalities, two trade rulesets, two ship design rulesets (and three permutations of in-campaign use), an additional 12 careers in a supplement, and licenses for 3pp materials from about the time they realized the audience wanted expansions and adventures. Buried in various places are a bunch of specialized bits, like the space dogfights in Ship's Boat skill, the ATV combat rules in one of the double-adventures, and a setting with fluff that is close to what the rules generate, but with heavily skewed frequencies.

There are even a bunch of installables that one can reverse engineer to add to the ship construction systems if one reverse engineers the adventures and setting supplements.

Likewise, it's worth noting that, except for licensees to the OTU, Marc never lists canon as a whole, only by edition. That Don promulgated an attempt to reconcile it all is a noble, but ultimately, futile effort.

I know I'm a stick in the mud, but it's just the fundamental truth of space combat, especially with Traveller type weapons.

In the end, it's two ships, closing on each other (as to who's chasing who, is moot), with their lasers on HIGH the entire time.
[snip]

At that level, it's a one dimensional game -- distance, and how fast it's closing.

It becomes 2D eligible the moment you add a missile or 3rd craft. Especially if the missiles are ROVs, rather than seekers. A 4th item in the mix can justify 3d narratively, but play-wise, it just isn't worth it.

Also note: in T5, if the agressor is bigger than you and has more Accel and can match course... you cannot escape because you cannot jump.

 

[sudnadja]

It becomes 2D eligible the moment you add a missile or 3rd craft. Especially if the missiles are ROVs, rather than seekers. A 4th item in the mix can justify 3d narratively, but play-wise, it just isn't worth it.

Though any two points are colinear, if they have motion or can accelerate in any direction other than toward or away from each other they need as many dimensions as degrees of freedom of the acceleration, though I suppose the range band system is to get around that. The math becomes as complicated in 1 dimension as just adding a second dimension. ("ships are point A and point B, initially 100000 km distant. Ship B accelerates within the tangent plane at 10 m/s²". The distance at time t is then Sqrt[ 10¹⁶ + 25 t⁴] meters.

 

[sudnadja]

When I ran CT (and the last time I did was about 1996), the CGen, travel, trade, and ship construction were what I used; Ship combat was using the Starter Traveller range band system rather than Bk2.

For spaceflight, I only ever had the two extremes, LBB book 2 when I first was introduced to it and then not really even range bands, which isn't interesting to me, but seems to be the system preferred by the vast majority of players. Ship construction never seems to happen in game, but as some kind of side channel activity.

 

[kilemall]

I've pretty much NEVER done range bands, but I also don't do tabletop- I do graph paper maneuver and measure like minis for ranging. Pretty much do that for Harpoon too.


Doing a major fleet action with several subfleets, then I might do a Mayday scale for closing until in battle range.

 

[aramis]

Though any two points are colinear, if they have motion or can accelerate in any direction other than toward or away from each other they need as many dimensions as degrees of freedom of the acceleration, though I suppose the range band system is to get around that. The math becomes as complicated in 1 dimension as just adding a second dimension. ("ships are point A and point B, initially 100000 km distant. Ship B accelerates within the tangent plane at 10 m/s²". The distance at time t is then Sqrt[ 10¹⁶ + 25 t⁴] meters.

Until you get a third point involved, the degrees of freedom are literally irrelevant to overall movement.

Note that firing, due to light lag, at the ranges in CT, makes off-linear thrust relevant, but still leave the actual effect a reduction of effective range thrust in exchange for reduced chance of being hit.

As long as you don't have 3 maneuvering objects (or 2 and a gravity well of note), only the range and ability to accelerate matter. off-linear thrust literally only reduces the effective closure rate for the chaser, and only increases it for the target.

It's only in that space where the planet is relevant (<100 Diameters) that the standard CT encounter table result isn't just a line.

Remember: CT has no firing arcs, and, even in Bk2 detailed level maneuver, abstracts the off-vector-gaining thrust for evasive maneuvers. It even ignores the pivot speeds.

It's highly abstract, and still too complex for most. (try running SpaceMaster's 3d option, where facing is tracked, or TNE's Brilliant Lances, where facing does limit firing...)

 

[sudnadja]

Until you get a third point involved, the degrees of freedom are literally irrelevant to overall movement.

Note that firing, due to light lag, at the ranges in CT, makes off-linear thrust relevant, but still leave the actual effect a reduction of effective range thrust in exchange for reduced chance of being hit.

As long as you don't have 3 maneuvering objects (or 2 and a gravity well of note), only the range and ability to accelerate matter. off-linear thrust literally only reduces the effective closure rate for the chaser, and only increases it for the target.

It's only in that space where the planet is relevant (<100 Diameters) that the standard CT encounter table result isn't just a line.

Remember: CT has no firing arcs, and, even in Bk2 detailed level maneuver, abstracts the off-vector-gaining thrust for evasive maneuvers. It even ignores the pivot speeds.

It's highly abstract, and still too complex for most. (try running SpaceMaster's 3d option, where facing is tracked, or TNE's Brilliant Lances, where facing does limit firing...)

In Special Supplement 3 (I think it is, Missiles), the movement of missiles is supposed to duplicate the movement of ships. If a ship can only move in a single direction (toward or away) it makes the intercept solution simple for a player controlling a missile. With two dimensions, the intercept solution becomes more difficult and there is a better chance to evade or for an evading ship to force a missile overshoot or undershoot. The same for a pursuing ship - you don't head toward where the ship is, you head toward where the target is projected to be or at least such that you will have a vector that comes within a certain distance of the target - but for missiles with limited thrust turns available you certainly would want to be able to maneuver with two or three dimensions if you are evading, in my view, anyway.

 

[whartung]

The same for a pursuing ship - you don't head toward where the ship is, you head toward where the target is projected to be or at least such that you will have a vector that comes within a certain distance of the target - but for missiles with limited thrust turns available you certainly would want to be able to maneuver with two or three dimensions if you are evading, in my view, anyway.

The trick for missiles is to get them within the G maneuver limit of the target ship so they can burn their drives "all at once" and close.

So, if you have a 6G Missile (which most are), they need to get within 6 hexes (or whatever), then the missile engages the target.

It true you need to try and plot the missile to where the "ship will be", but it's not necessarily that difficult, especially against a slow (1-2G) ship.

You can also close the firing ship in "close" and fire all the missiles, and they arrive "all at once".

 

[sudnadja]

The trick for missiles is to get them within the G maneuver limit of the target ship so they can burn their drives "all at once" and close.

So, if you have a 6G Missile (which most are), they need to get within 6 hexes (or whatever), then the missile engages the target.

It true you need to try and plot the missile to where the "ship will be", but it's not necessarily that difficult, especially against a slow (1-2G) ship.

You can also close the firing ship in "close" and fire all the missiles, and they arrive "all at once".

It isn't as simple as that, a 6G missile not only has to be within 6 hexes (or 60 mm) but its velocity can't be such that the 6G is not adequate to make the interception. If the missile finds itself at {-10000 km, 0} and the ship is at {0,0} but the missile has a velocity of {-1,000,000 m/sec,0} it will not be able to make the interception. If the player that controls the missile is naive and just aims directly at the ship each turn and expends vector change that way you get situations like this:

which ends up being a double undershoot. If the player controlling the missile is a bit smarter and the player controlling the ship is not, they will presume the ship is accelerating at a constant rate and make an intercept prediction and follow that path. But then if the ship realizes that, it will vary its velocity and direction enough to make that prediction difficult. In the one-dimensional case, none of that needs to be done at all, the missile either has the velocity change available to make the interception or it does not, no other computation needs to be made.

 

[whartung]

You're doing that whole physics thing again, though.

This is a board game and missiles have special rules. The maneuver "last", simply have to cross the target hex. That's why if you're within the G rating of the missile, at the end of movement, the missile simply "maneuvers" to the target and "bang". In this sense, missiles can act as a space control device, like a mine. The target ships goal is to NOT breach that radius.

TNE broached that subject of simply having to have the missile "close" before it detonates in to a bomb pumped laser, eliminating the "last mile" problem of velocity matching. It just has to get "close enough" to get in a laser shot. It still strives for a "range 0" shot, but in TNE, that's still 30,000km.

The pumped laser also helps counter what should be almost impenetrable defensive laser fire against something "very slow" like a missile.

 

[sudnadja]

You're doing that whole physics thing again, though.

This is a board game and missiles have special rules. The maneuver "last", simply have to cross the target hex. That's why if you're within the G rating of the missile, at the end of movement, the missile simply "maneuvers" to the target and "bang". In this sense, missiles can act as a space control device, like a mine. The target ships goal is to NOT breach that radius.

I think the conversation is becoming confused because there are so many sets of rules we could be talking about. I'm talking about LBB2 and SS3, for which there are no hexes at all. It isn't real physics, but the game defines a set of rules that are kind of physics like and the same pitfalls can occur because of them, like naive steering of the ship or missile will result in too much velocity (length and direction of a vector) and make an interception difficult or impossible. In those rules, missiles don't move before ship movement, they are a part of the ship movement phase except for the turn that they were launched. An interception occurs if the missile passes within 25 mm (2500 km) of the target, and to the point of my making this reply, that is trivial in one dimension and harder in more than one dimension, even if the only two objects in the game are a missile and the target. In SS3, it is mentioned that it is worth firing unguided missiles only if the missile acceleration can intercept the target in the turn that they are fired, otherwise an interception becomes much less likely.

This is only true if there is more than one dimension that can be maneuvered in, in a single dimension an unguided missile is a better choice - less of the mass of the missile needs to be devoted to the propulsion assembly for continuous burn and more can go to the warhead, or use a larger continuous burn engine.

I think I'm going to drop this now, though. It's pretty clear no one is actually playing LBB2/SS3 rules and that's the only system I vaguely know.

 

[kilemall]

It isn't as simple as that, a 6G missile not only has to be within 6 hexes (or 60 mm) but its velocity can't be such that the 6G is not adequate to make the interception. If the missile finds itself at {-10000 km, 0} and the ship is at {0,0} but the missile has a velocity of {-1,000,000 m/sec,0} it will not be able to make the interception. If the player that controls the missile is naive and just aims directly at the ship each turn and expends vector change that way you get situations like this:

which ends up being a double undershoot. If the player controlling the missile is a bit smarter and the player controlling the ship is not, they will presume the ship is accelerating at a constant rate and make an intercept prediction and follow that path. But then if the ship realizes that, it will vary its velocity and direction enough to make that prediction difficult. In the one-dimensional case, none of that needs to be done at all, the missile either has the velocity change available to make the interception or it does not, no other computation needs to be made.

I think missile avoidance is part of the combat game, so I don't particularly care for writing it out. Big drama too, maybe risk drive burnout doubling G for a bit to get that extra 10000km to generate a miss.


The 'too-fast a missile' problem should also not be written out, although again needs trade-offs, you get hit with a missile going that fast and keeps the target ship in it's target window, it should HURT.



OTOH any missile driver has a computer telling him what intercept box to aim the missile for, a lot more accurately then most players will, so I don't know if I would always make the gunner navigate the missile in by hand. Probably the to-hit number in HG is partially about succeeding in getting the missile to that itty-bitty box.

 

[whartung]

I'm talking about LBB2 and SS3, for which there are no hexes at all.

No, but the differences aren't that stark.

In Mayday, you move by hexes. That certainly enforces some granularity to the movement over what LBB2 does.

In LBB2, you can move 100mm/G (10,000km). This isn't that different from saying that each hex is 10,000km. It's just easier to only move in increments less than "one hex".

In LBB2, the phasing player move his ships/ordnance.

If a target player has a ship within 600mm (6G) of a missile, at the start of the phasing players movement, that missile is going to strike at that target.

Simply, there is a 600mm bubble around a missile. Any thing that ends up in the bubble, it is going to get hit (attacked, again assuming a 6G missile).

Now, if a ship is moving quickly (800-1000mm / turn), it's simply difficult for a missile to catch that ship. The target is more likely to stay out of the 6G envelope.

The firing ship has great responsibility in setting the original missile vector.

Most of the Traveller missiles really only have 6G of movement, that's not a lot. It's a lot when your target has only 2G of maneuver. IF you can get the missile properly placed, even at high speed, the target can't turn fast enough to "get out of the way". That's the dance and ballet that has to take place.

I honestly have not played enough to discern how fast most battles fly at. Do the ships make continual high speed passes amongst each other, then spend several turns, turning and burning to re-engage? Or to they stay slow to keep it tight.

If you're deploying missiles, it actually behooves you to slow down so that their high maneuver can be effective. Otherwise, it's easy to have gaps of coverage because the ships are flying too fast and missiles are hopscotching over targets -- even stationary ones. Come flying in at speed 10 against an orbiting facility and it's easy to get there too early or too late. It may be "impossible" for a missile to hit the target, simply because of the turn phasing.

Later games lessened this relying on "closest approach" to help fill those gaps.

 

[kilemall]

If one has SS3 ruling what missile design is, the standard Cr5000 homing missile is 5Gx6 turns. That means they will crank up to potentially 30G additional vee. If the missile started from a zero vee ship and strikes a zero vee target, that's 10 extra CT hits if it makes direct contact.


Of course the firing ship will likely be in motion and so will the target, either adding closing target speed and thus damage or subtracting from the built-up speed of the missile- or negating the missile entirely if the missile can't 'catch up' before fuel runs out.


At final turn of maneuver, the missile can end up with 300,000km per 1000s turn, or if you like 300 km/s, not counting imparted vee from the launching ship. That's 3.3 seconds or so on that last approach, pretty nice closing rate.


That's one effect, the chasing ship would be inflicting less damage from their missiles while risking more from the chasee. OTOH the fleeing ship is imparting their own negative vee on their missiles, may take a couple turns before they even actually head towards the oncoming chaser.