Can you accelerate during jump?

[rancke]

True. I was a bit surprised by Hans' alternate take on the jump drive necessity once into jump space...

Um, what do you mean, alternate? From the very beginning (almost) it was established that the jump drive used up ALL its fuel before entering jump space. It's always been obvious to me that the drive had done its job by the time it had used up its fuel. How do you keep a machine working without fuel?

I know later versions have tried to mess around with keeping some of the fuel aboard for the duration, but I've always considered them misguided. They're the alternate version, IMO.


Hans

 

[JAFARR]

For game purposes, I can live with this but for players who look for scientific accuracy, how do you explain what happens to the force exerted by the maneuver drives?

Next,
What happens if the jump drive goes down once you've entered J-Space?

To be totally accurate from the point of our present scientific knowledge, they (m drives) don't exist. HOWEVER, for game purposes my interperation would be that your m drive works in real time space, and that your J drive places you temporalry outside of real time space for the duration of the jump and, THEREFORE, your m drive ceases to function.

 

[JAFARR]

As to your vector on emergence from J space: I thought that this was part of the idea of the navigator's job, ie. "Set us up so that when we exit J space our vector is aiming where we want to go." IIRC, that was the idea of the pre-recorded jump tapes. They gave you a set of parameters to meet when you went into J space so that you could exit J space with the correct vector and not waste time correcting it.

 

[Commander Truestar]

I have always thought, and run MTU that way, that vector and vee were an absolute match from when yo entered J space.
The navigator's skill determined how close you emerged to where you wanted to. If you wanted to jump into a system and hit exactly the 100d limit(to minimize transit times) then you had to roll well enough. Bad rolls brought you intide the 100d limit of either the destination world or a moon and caused positive DM's for misjump effects.

Also, and this is strictly IMTU, I allow "pirate point jumps"

If a crew feels they have up to date and very accurate data on a destination system the Navigator can attempt to determine where a Trojan point will exist or develop at the time of intended emergence. Once they make the skill rolls for that, they can then make the much more difficult skill roll to plot a jump to hit that point.

If they succeed, they can arrive at a world much faster. Arriving at the unstable* Lagrange 1 of a system instead of it's red giant star's 100d limit allows you to emerge much closer. An example would be my current campaign where my players arrived in the
Risek system(Rhylanor Subsector/Spinward Marches) The world holds a solar orbit of .2 AU so the star's side comes into play forcing any ship jumping in-system to make an ~48 hr transit to the planet. Use a Lagrange jump and, if you succeed, you get there in hours once you emerge from jump.

So a high Navigation(Astrogation) skill has many advantages and allows the players a new way to gank themselves if they are not careful

Marc

* The Lagrange points 1 thru 3 in a three body system are notoriously unstable

 

[Icosahedron]

Interesting idea there, Marc, I'll file that one away...

 

[Frankymole]

There's also the rather important point of the (occasionally huge) proper motion of stars relative to each other.

If we use the "conservation of momentum" idea that ships come out with the same velocity they went in (relative to what? The galaxy? The jumped-from previous star system?) then a star system that's hurtling at thousands of kmph in another direction could make a mess of any carefully-planned trajectory.

 

[Commander Truestar]

Interesting idea there, Marc, I'll file that one away...

Don't credit me with that one.
As I said, it comes form the universe FASA built for Battletech. I just morphed it for Traveller. I should also add that it remains color for now IMTU. None of my players has ever felt the need to risk that dangerous a jump manuver

Marc

 

[Commander Truestar]

There's also the rather important point of the (occasionally huge) proper motion of stars relative to each other.

If we use the "conservation of momentum" idea that ships come out with the same velocity they went in (relative to what? The galaxy? The jumped-from previous star system?) then a star system that's hurtling at thousands of kmph in another direction could make a mess of any carefully-planned trajectory.

There was an interesting "sideline" novel put out by FASA(Again referencing the Battletech Universe) when FASA was considering the idea of adding Aliens to that universe. In that novel a mega-Cosologic event was used to create an "epic" mis-jump(when put in Traveller terms).

What happened was that(IIRC) the gravitational effects of two galactic clusters moving away from each other created a region of extreme gravitational effects. The effect just happened to "flex" itself in the system just at the very moment the jumpship initiated its jump.

The novel is named "Far Country" by Peter L Rice if you want to read it for yourself

Marc

 

[rancke]

If we use the "conservation of momentum" idea that ships come out with the same velocity they went in (relative to what? The galaxy? The jumped-from previous star system?) then a star system that's hurtling at thousands of kmph in another direction could make a mess of any carefully-planned trajectory.

I've always assumed that "in reality" this is the case and astrogators compensate for that when they calculate a flight plan, but that the rules ignore this as too complicated to simulate.


Hans

 

[Whipsnade]

There's also the rather important point of the (occasionally huge) proper motion of stars relative to each other. If we use the "conservation of momentum" idea that ships come out with the same velocity they went in (relative to what? The galaxy? The jumped-from previous star system?) then a star system that's hurtling at thousands of kmph in another direction could make a mess of any carefully-planned trajectory.

Frankymole,

Relative to the system in which the jump originated is usually the less messy choice.

Vector retention is canon. It's right there, stated explicitly, in Mr. Miller's Jump Space essay in deadtree JTAS. It's a part of several MT adventures and is extremely important in the fuel hungry HEPlaR-using TNE setting.

However, as Hans has already pointed out, ignoring both vector retention and the movement of stars relative to each other is nearly always done in order to ease/speed play. GMs can apply or ignore the concept as they see fit.


Bill

 

[Commander Truestar]

Frankymole,
ignoring both vector retention and the movement of stars relative to each other is nearly always done in order to ease/speed play. GMs can apply or ignore the concept as they see fit.

Bill

I always felt that vector retention was upheld in the game though on a level of rules ment to support playability. As for conservation of momentum on the interstellar(or even cosmological scale) I felt that was folded into the Navigation(or astrogation in some game versions) skill.
I always felt that it was not just plotting a ling from A to B while avoiding things in the way. I felt it included calculations based on everything(as in my suggestion of pirate points earlier in the thread) from distance and obstructions to the movement of the end-point and intervening solar systems, the over all effects of the known galactic gravitational fields, etc...

This was why I saw Navigation/Astrogation as properly separated from Starship piloting.

Marc

 

[coldwar]

No as it would take power away from the Jump drive, Comprimising the ship. Plus if you did have a large enough power plant to power both drives it would not have any effect what so ever.

Secondly if it was possible, you still would not want to do that as when you come out of you jump you are still unsure which direction you will be facing, so it would not be a good idea using that rule without changing the randomness of emerging from jump space first.

Secondly If Both rules were in place, the defending planetary forces would have a few ships of High acceleration around the typical emergance areas, which many security vessels will do even in peace time go that far to surprise vessels emerging for sudden surprise inspections as they would want to catch smugglers out as much as possible.

 

[Icosahedron]

Frankymole,

Relative to the system in which the jump originated is usually the less messy choice.

Vector retention is canon. It's right there, stated explicitly, in Mr. Miller's Jump Space essay in deadtree JTAS. It's a part of several MT adventures and is extremely important in the fuel hungry HEPlaR-using TNE setting.

However, as Hans has already pointed out, ignoring both vector retention and the movement of stars relative to each other is nearly always done in order to ease/speed play. GMs can apply or ignore the concept as they see fit.


Bill

That's another bit of canon I tend to ignore. It's much easier to rule that ships always enter a system with a zero vector - gets rid of the near-c rocks, too.
What happens to the momentum? Well, that's where some of your fuel goes, and it adds to the uncertainty in your four-dimensional exit point.

Not that it's ever been important in any of my games yet.

 

[Commander Truestar]

No as it would take power away from the Jump drive, Comprimising the ship. Plus if you did have a large enough power plant to power both drives it would not have any effect what so ever.

Secondly if it was possible, you still would not want to do that as when you come out of you jump you are still unsure which direction you will be facing, so it would not be a good idea using that rule without changing the randomness of emerging from jump space first.

Secondly If Both rules were in place, the defending planetary forces would have a few ships of High acceleration around the typical emergance areas, which many security vessels will do even in peace time go that far to surprise vessels emerging for sudden surprise inspections as they would want to catch smugglers out as much as possible.

Coldwar,
Were you responding to me?
If I was unclear, I am agreeing with you. IMTU the M drives are shut down as useless while in jump and (also IMTU) Imperial Interstellar Travel laws mandate an amount of engineering recalibration and systems certification of the M drives during that time.

As for your second point, my opinion is different than yours(which is par of the enduring elegance of Traveller). Even with specified emergence areas in each system there is no guarantee all law abiding ships will heed those restrictions. Nor will any attackers care for the emergence restrictions. So any system with local or Subsector/Sector/Imperial naval assets will have patrols throughout the system. This provides the ability to respond to those who will enter those systems illegally.

Marc

 

[Brian Smaller]

Next,
What happens if the jump drive goes down once you've entered J-Space?

There have been a lot of good ideas here. I rule that the drive failing(or the powerplant component of it) precipitates the ship out of jump and into normal space. Given that Traveller ships have 30 days fuel for routine manouvre and life support (as a rule), that usually means the crew are dead unless they find a wayward comet, a rogue planet or some other adventure hook on the edge of their sensors and life support..

I use things like this as an opportunity to game rather than try to explain it away with technobabble.