OTU Only: The Limits of Traveller Space Combat

[Supplement Four]

We've discussed this in various threads over the years. I think it a facinating topic. When you consider the OTU, there are only a few places where space combat can take place.

A ship spends most of its time in Jump Space. The only time it's in Normal Space is during the travel to the jump point or travel from jump exit to destination. If you don't have to mess with the 100 diam limit of a star, the J-points are relatively close--so only a small portion of the journey is spent in normal space.

Further, high TL, high pop, well traveled systems will benefit from system defense boats and be virtually pirate-free.

On worlds where the 100 diam limit of the system star comes into play, we're talking about a heck of a lot of space to cover. Space combat is more likely at the jump exit point.

But, long journeys from jump exit to destination, or long in-system travel, are not the Corsair free-for-all that they would seem at first. A ship accelerates at full speed to the half way point of the journey. Then, the ship will declerate for the last half of the journey.

Very quickly, ship's on long in-system trips achieve a velocity that makes them all but invulnerable to attack. If a Pirate waits out in deep space, somewhere along the route taken by a ship on a long in-system journey, the Pirate will be lucky to get in one shot at the speeding vessel that zips by. It's akin to standing on the side of a freeway with a hand gun, trying to hit a car as it zooms past at 70 mph.

Pirate vessels must match vectors in order to conduct combat. This most often means that a defender will see the pirate coming for a long, long time--not unlike in the 1800's with combat betweens ships-of-sail.

Surprise by a pirate vessel is very hard to achieve. Most often, the prey will see the enemy coming and comm in for help. If Corsairs do take on a vessel, it's likely that the starport and other system ships will only be able to watch as the attack takes place, unable to do anything about the attack. This also means that Corsairs will have a limited time table to get the job done.

 

[Putraack]

Something I was just thinking about myself; I will be starting a group new to Traveller next month, and I am relatively new to it, too.

I assume that to go into Jump space, a ship wants to be heading in the direction of its target system, and have some velocity already? That might make it easier for both pirates and patrollers: say a system in which there are two likely jump routes, both would want to hang out near the 100d limit between the ports along the likely exit/entry vectors, no?

 

[Supplement Four]

I assume that to go into Jump space, a ship wants to be heading in the direction of its target system...

I don't think that's necessary, but it may be arguable, depending on which version of the rules you use.

...and have some velocity already?

According to the SOM (which is questionable, since it is quasi-canon and written for MT), it's not like Star Trek or Star Wars vessels. They don't all of a sudden speed off so fast that you can see them to a space horizon.

A ship can be at relative stop or in motion when it jumps (according to the SOM, the correct thing to say would be, "...when it tumbles"). Whatever velocity and heading a ship had when it jumped is what it has when it re-enters normal space.

I haven't read it in a long time, but since this is a CT forum, you may want to read the article on J-Space that Marc Miller wrote in the JTAS. That's probably about as CT canon as it gets.

That might make it easier for both pirates and patrollers: say a system in which there are two likely jump routes, both would want to hang out near the 100d limit between the ports along the likely exit/entry vectors, no?

I use the term "jump point" in the OP, but that doesn't mean that there's a single point that the ship rushes to in order to jump. A jump point is jusst the place where the ship does jump.

To be safe, you want your jump point (your jumping off point) to be past 100 diameters of any massive body. Sometimes, this is just 100 diams of the world. But, with some systems--especially when the main worlds are in the early orbits (like Regina in the Spinward Marches, a moon of a gas giant close to that system's sun)--the 100 diam limit of the world is superceded by the 100 diam limit of the system's star.

If that's the case, travel to jump point can take days, even weeks. it depends on how far it is, and the orbit of the main world within that jump shadow.

"Jump points" can be any point on the 100 diam sphere around the largest massive body, sun or planet.

Either way, you're talking about a lot of "ground" to cover.

Even on a Size 8 world, you've got a jump point 100 diams from the North Pole. And, likewise, among a zillion other jump points, you can jump at 100 diams from the South Pole.

In between those two J-points a distance 200 diams long (longer because a ship travelign that would have to swing around the planet--it can't go through the planet's core).

I always picture a glass sphere that has the world/sun at its center.




Remember, too, that routes to a jump point may not always be a straight line. Usually it is, but a ship could launch from the US curve around the planet, heading for a J-point that is 100 diams from South America (although I can't think of a reason to do that at the momement--the ship would take the shortest route to the 100 diam limit).

There may be reasons, though (thinking, now, of some reasons). Different space jurisdictions (political limit on balkanized worlds) may be one reason. A country may not want enemy ships to be able to "get above" it's country for 100 diams or so.

Space hazards could be another reason--avoiding the world's moon (maybe it's got a lot of space traffic) or a dense part of an asteroid belt.

Heck, maybe a captain finds it easier to take a longer route to be nearer to wherever the SDBs are--in a high-risk system.

 

[leo knight]

The last time I ran Traveller live, I tried to deal with actual travel times, acceleration, radio time lag, etc. at least as well as I understood them. The PCs took a chartered launch to a gas giant in their starting system. I assumed it was about 5 AU out, like Jupiter. Travel time at 1g took about 7 days. A radio distress message would take about 40 minutes to reach the main world. If they got into trouble, rescue would be almost 3 days away, even at 6g. Of course, I had a ship full of bad guys on the way from the main world, with the PCs having a lead of a few days. The PCs detected them way out, and had plenty of time to prepare for their arrival.

I kept trying over the years to make Traveller more like Star Wars, instead of just letting it develop in its own way.

 

[whulorigan]

Remember, too, that routes to a jump point may not always be a straight line. Usually it is, but a ship could launch from the US curve around the planet, heading for a J-point that is 100 diams from South America (although I can't think of a reason to do that at the momement--the ship would take the shortest route to the 100 diam limit).

There may be reasons, though (thinking, now, of some reasons). Different space jurisdictions (political limit on balkanized worlds) may be one reason. A country may not want enemy ships to be able to "get above" it's country for 100 diams or so.

Space hazards could be another reason--avoiding the world's moon (maybe it's got a lot of space traffic) or a dense part of an asteroid belt.

Heck, maybe a captain finds it easier to take a longer route to be nearer to wherever the SDBs are--in a high-risk system.

The last time I ran Traveller live, I tried to deal with actual travel times, acceleration, radio time lag, etc. at least as well as I understood them. The PCs took a chartered launch to a gas giant in their starting system. I assumed it was about 5 AU out, like Jupiter. Travel time at 1g took about 7 days. .

Another consideration is that in space (in-system), origin and destination points are constantly moving relative to one another in their orbits. So just because two worlds are 5.0 AUs from one another at one time, does not mean they will not be significantly more or less than this at some other time, based on their positions in their respective orbits relative to one another. (e.g. the two worlds could be on opposite sides of their star in their orbits).

This has some implications for Jumps and Combat regarding ships traveling inbound or outbound for Gas-Giant skimming. A ship may not be travelling simply from world-surface to a jump point on the 100-dia sphere, but in fact may need to travel along a significantly longer trajectory to reach a gas giant first before (or after) the jump for refueling (presuming of course that they are not purchasing refined fuel at the port). This course trajectory will be different every time the ship is in that particular system, as the orbital positions of the end-points is always changing.

 

[HG_B]

I've had fun with all this since CT. It takes real planning to be a pirate. In backwater systems help can be DAYS away. I like it much better than the Star Wars fantasy stuff.

 

[Supplement Four]

Another consideration is that in space (in-system), origin and destination points are constantly moving relative to one another in their orbits.

The SOM (a book that I love) has a simple chart that shrinks or lengthens distance based on orbit positions using a simple dice throw and a chart. It's used for planet-to-planet travel in-system, but it's easy to use the chart for other things like space stations or points in an asteroid field.

It may not be completely scientific, but it's good enough for gameplay, I think.

 

[Supplement Four]

The last time I ran Traveller live, I tried to deal with actual travel times, acceleration, radio time lag, etc. at least as well as I understood them.

There's an encounter in the Traveller Adventure where a supply shuttle is overdue and the PCs are tapped to take supplies from point to point in-system. Along the way, they find the supply shuttle, drifting in space.

This encounter should probably take place close to the origin or destination points. If the shuttle is detected somewhere in the middle of the trip, then the players' ship has to decelerate for a number of hours or days equal to the amount that they've traveled since launch, then do a new trip to the shuttle (which will be drifting and not in the exact same spot it was when detected but can probably be computed and tracked with ship's sensors).




My point is: Even a simple encounter like coming across a wreck in space is not really that simple. It's not like most science fiction depicts the situation. A ship journeying in normal space is either accelerating or decelerating (and, I imagine it's common to see ships flying through space "backwards" as the ship is flipped around so that the main drive can be used to slow the ship down--for hours and hours or even days and days).

 

[whulorigan]

The SOM (a book that I love) has a simple chart that shrinks or lengthens distance based on orbit positions using a simple dice throw and a chart. It's used for planet-to-planet travel in-system, but it's easy to use the chart for other things like space stations or points in an asteroid field.

It may not be completely scientific, but it's good enough for gameplay, I think.

I hadn't remembered that chart. I'll have to dig it out and take a look.

But another interesting possibility might be that for certain orbital configurations (e.g. central star mostly interposed between origin and destination), if you position an attacking ship correctly, you can manage to be "unseen" perhaps for a good portion of the defending craft's course trajectory (due to stellar-interposition, and also perhaps some signature masking due to stellar background radiation as the ship emerges over the stellar horizon, for a time). It would depend upon how much the attacking ship's signature(s) would stand out against the stellar output, and for how long based upon detection angles.

 

[HG_B]

But another interesting possibility might be that for certain orbital configurations (e.g. central star mostly interposed between origin and destination), if you position an attacking ship correctly, you can manage to be "unseen" perhaps for a good portion of the defending craft's course trajectory (due to stellar-interposition, and also perhaps some signature masking due to stellar background radiation as the ship emerges over the stellar horizon, for a time). It would depend upon how much the attacking ship's signature(s) would stand out against the stellar output, and for how long based upon detection angles.

Yes but, the distances are HUGE. Think of Earth/Mars when on opposite sides of the Sun. Where would you place the attacking ship? (remember that the "victim" is at its mid-point, highest velocity when nearest to the Sun)

 

[whulorigan]

(remember that the "victim" is at its mid-point, highest velocity when nearest to the Sun)

That is a good point.

If feasible, I suppose the tactic would have to be to try and target the M-Drives on a called shot, and then take the time to match vectors.

Or, have advanced knowledge from an agent in port concerning the departures of various ships and try to swing around the opposite side of the star on a course trajectory that will roughly intersect and match the vector of the target at the right time, but that (as mentioned above) would involve a lot of advanced planning and some guess-work on the part of the hostile ship.

 

[McPerth]

Surprise by a pirate vessel is very hard to achieve. Most often, the prey will see the enemy coming and comm in for help. If Corsairs do take on a vessel, it's likely that the starport and other system ships will only be able to watch as the attack takes place, unable to do anything about the attack. This also means that Corsairs will have a limited time table to get the job done.

And they have to remember that to flee tehy must reach the 100D limit ASAP, and that the SDBs going for them, aside from usually having greater acceleration, as they don't devote space to Jump drivs and fuel, can accelerate the whole trip (uless they intend to board the ship), don't needing to match vectors with the feeing pirates. once in range, they can begin to deccelerate while firing at it, and, should they overpass but leave it crippled, other incoming SDBs will take care of them, or they would have to waint the return (this time matching vectors) of the first one(s).

 

[aramis]

My point is: Even a simple encounter like coming across a wreck in space is not really that simple. It's not like most science fiction depicts the situation. A ship journeying in normal space is either accelerating or decelerating (and, I imagine it's common to see ships flying through space "backwards" as the ship is flipped around so that the main drive can be used to slow the ship down--for hours and hours or even days and days).

Not true in all editions... TNE ships only carry 5-13 hours of reaction mass. They coast almost all the way. Which makes piracy both easier and harder.

 

[HG_B]

Or, have advanced knowledge from an agent in port concerning the departures of various ships and try to swing around the opposite side of the star on a course trajectory that will roughly intersect and match the vector of the target at the right time, but that (as mentioned above) would involve a lot of advanced planning and some guess-work on the part of the hostile ship.

I think the "inside knowledge" idea would be the best way to go. Intercept 'blind' so to speak. If you take out the M drive at mid point you have it made. It would take others too long to intercept the pirate.

 

[HG_B]

And they have to remember that to flee tehy must reach the 100D limit ASAP, and that the SDBs going for them, aside from usually having greater acceleration, as they don't devote space to Jump drivs and fuel, can accelerate the whole trip (uless they intend to board the ship), don't needing to match vectors with the feeing pirates. once in range, they can begin to deccelerate while firing at it, and, should they overpass but leave it crippled, other incoming SDBs will take care of them, or they would have to waint the return (this time matching vectors) of the first one(s).

This begs the question, where do you station your limited number of SDBs (considering poor backwater system)? The 100D sphere is HUGE. While the SDBs are fast, they aren't fast enough if something is going down far enough away on the spherical area...

 

[McPerth]

This begs the question, where do you station your limited number of SDBs (considering poor backwater system)? The 100D sphere is HUGE. While the SDBs are fast, they aren't fast enough if something is going down far enough away on the spherical area...

That's a very good question, and I guess a MAJOR issue still debated in most HQs of such planets, with no single good answer and (again my guess) several currents of thinking.

It will depend on many factors, such as posible targets in the world, world (or rather 100 D limit) size (as the 100 D size may not depend on the worls but the body it's orbiting, be it a sun or a GG), space traffic, and other factors I cannot think about right now.

And in this regard, asteroid belts pose another special problem (unless population is concentrated in just a small part) due to the posible targets dispersal...

 

[flykiller]

Very quickly, ship's on long in-system trips achieve a velocity that makes them all but invulnerable to attack.

most merchants will be m1, m2 max. any self-respecting pirate will be m3-4. overhaul will be a simple matter.

besides, speed limits. no-one anywhere will want ships moving at 20 miles per second anywhere in their system let alone anywhere near inhabited areas and especially never ever not while vectored towards a major port. ever.

I assume that to go into Jump space, a ship wants to be heading in the direction of its target system, and have some velocity already?

oh that's a winner. yeah, jump in with significant vector without knowing what's going to be in front of you when you precipitate. oh yeah, have the news cameras in the sky waiting for footage on that one.

If that's the case, travel to jump point can take days, even weeks. it depends on how far it is, and the orbit of the main world within that jump shadow.

imtu navigation skill applies to how accurate and precise a jump is. nav1 is routine and sufficient to put you at the star's 100d and often not much better. nav3 is expert and usually sufficient to put you just outside the target planet's 100d. nav2 is in-between.

 

[HG_B]

most merchants will be m1, m2 max. any self-respecting pirate will be m3-4. overhaul will be a simple matter.

Simple but TIME consuming. A 1G merchie going from Earth to Jupiter (closest approach) takes ~60 hours. A 4G Pirate, ~30 hours. Lots of time to call in a 6G SDB...

oh that's a winner. yeah, jump in with significant vector without knowing what's going to be in front of you when you precipitate. oh yeah, have the news cameras in the sky waiting for footage on that one.

Umm, you'll win the "Lotto", several times over before there is something right in front of you when you jump in. Space is WAY bigger than you envision. WAY bigger...

 

[flykiller]

oh that's a winner. yeah, jump in with significant vector without knowing what's going to be in front of you when you precipitate. oh yeah, have the news cameras in the sky waiting for footage on that one.

Umm, you'll win the "Lotto", several times over before there is something right in front of you when you jump in. Space is WAY bigger than you envision. WAY bigger...

yeah. but not all of it is a jump target, just those areas of maximum economic concern. everybody will be going for the same max profit therefore the same minimum runtime therefore the same precipitation spot. and the bigger the boat/bomb the more likely they'll have a crack navigator onboard who will hit that sweet exact spot ....

I say keep the cameras rolling.

 

[HG_B]

yeah. but not all of it is a jump target, just those areas of maximum economic concern. everybody will be going for the same max profit therefore the same minimum runtime therefore the same precipitation spot.

There is no SINGLE spot. Every second any "spot" changes. There is no jump accuracy measured in centimeters. Like I said, you have NO idea of how big space that is.