JUMP - bearing and speed

[atpollard]

Response Moved to a New Topic to preserve old Topic.

Thanks for the feedback. It's funny how every time I post on this site, someone points out a whole new topic I hadn't thought about.

When you travel 100 diameters out to jump, is there any reason that should be directly "towards" your destination? I can see why the opposite direction might feel like a bad idea (because there's a planet in the way), but jump travel doesn't pass through real space, so why not? I guess the traffic management may be better if all ships avoid each other, so Icosahedron may be right that there could be a lot more traffic out there, just beyond range.

Standard practice is described as accelerating/decelerating to the jump point, coming to a complete stop, jumping to the destination point, arriving at destination at rest, and accelerating/decelerating to the port. This is the safest method and uses all of the standard accelerate to midpoint/decelerate to stop travel formula.

A more skilled pilot/navigator could shave time off the journey by accelerating continuously to the jump point (reducing the travel time to jump point), jump with the desired bearing and velocity to a carefully chosen exit point, and exit jump at a high speed on an intercept course with the port (reducing the travel time to the starport). Using the moon for a gravity sling (to change course at high speed) or the planetary atmosphere for braking could reduce the travel time further (but is not for the faint of heart or a luxury liner).

A great deal of this depends on the assumptions for “Your Traveller Universe” and jumpspace, but none of it is prohibited by Classic Traveller.

 

[aramis]

TNE specifically states the retained vector jump, as a fuel saing measure.

 

[Icosahedron]

Depends how much of this 'jump masking' stuff you take to heart, perhaps, Tinker. I've never given it much credence myself, but MTU is non-canon in many ways.

I can see what you're saying - you could take a ship heading on a bearing of 'due South', jump it 'North' by several star systems, emerge 'due North' of the destination world and continue your heading 'due South' to make planetfall. In fact you could do this with a jump in any direction, the only provision being that you must emerge 'due North' of your destination, so that your initial bearing takes you toward the planet.

It just helps our monkey brains if we do it the other way, I suppose.

The other way also ensures you can be followed...

 

[Fritz_Brown]

Jump masking is one part of it. But, it is also the assumption regarding retained velocity in jump. If you want the arguments, go searching for them on this board - they are definitely here. Basically, many interpret the CT rules as prohibiting n-space velocity retention through j-space. (YMMV, of course.)

 

[The Oz]

I've always assumed that velocity (relative to the star system of origin) was retained in jump. This makes Navigation skill worth having, both for calculating a "least-time" jump and for predicting/guessing where someone you're chasing might have jumped to.

 

[Spinward Scout]

Basically, many interpret the CT rules as prohibiting n-space velocity retention through j-space. (YMMV, of course.)

Which is contrary to what the Psionics rules say about Conservation of Energy/Momentum.

 

[Icosahedron]

Which is contrary to what the Psionics rules say about Conservation of Energy/Momentum.

Not necessarily, the momentum might have been 'used up' in transferring to and from j-space, or might result in an 'instantaneous' deviation from the predicted exit location/time.

 

[aramis]

Or might be one of the uses of all that LHyd...

 

[Fritz_Brown]

It's also not canon (at least not in the early stuff) that jump has anything to do with psionics. But, it only really matters if it makes your game fun. (I had to say that since Bill's not here.)

 

[tinker123]

In fact you could do this with a jump in any direction, the only provision being that you must emerge 'due North' of your destination, so that your initial bearing takes you toward the planet.

Given the LBBs' approach of jump-while-stationary, I'd go so far as to say that you could depart world-A due North, stop, jump 1 parsec to the South to arrive due South of world-B, turn around and travel North to make planetfall. Or even arrive due East; it makes no difference. If YTU lets ships carry over momentum through jump, this is just an inefficient way of jumping.

 

[BetterThanLife]

Actually CT (LBB5) implies that velocity and direction is and can be retained through Jump, even if it never states such.

Pg. 43: LBB5

Suppose, for instance, that a fleet were to jump into a system with its black globes on and its velocity set upon a predetermined course. It could drift unseen past any defending fleet and drop its screens at a preplanned moment, to bombard a planet or to engage enemy fleets by surprise.

Though that maneuver would require some very precise astrogation. Given the generally imprecise nature of Jump Astrogation jumping with a Zero velocity would be safer though. (Watch out for that rogue asteroid. )

Further since MT introduced the concept of 168 hours +/- things get rather dicey if you are retaining a velocity which could definitely be away from your target instead of toward it. If we assume an orbital period of 360 and an orbital radius of 90 million miles, so a day is a degree. If a second of an angle is an inch at 100 yards how far is half a degree at 90 million miles?

Is Jump emergence relative to the destination planet, the destination star, the destination starsystem, the starting planet, starting star, starting system, the galactic core, the center of the universe, or some other point? Kind of makes a difference as to how bad 168 hours +/- 10% can be.

 

[avi.hecht]

JUMP - Random time

[FONT=arial,helvetica]BTL said
"Further since MT introduced the concept of 168 hours +/- things get rather dicey..."

Does this imply random time? or that not all jumps are created equal?
Can a good Astrographer 'shave' off time or a fixed route will always have the same
jump time?

If the time is fixed or can be pre-calculated than ships can still use vectors to reduce time.
If not - jumping from 0 Velocity (relative to what???) would be the norm.

IMTU - civilians jump from 0 at 120 radai from planet (well I actually use g percentage)
Navy Jumps on the move at closer range and Scouts are the daredevils of the universe
jumping way to close with way to much velocity...
(No Jump-Masking IMTU)
Ships also cost differently - A scouts jump drive is more expensive and the ship needs
a stronger computer and better jump software.

I like the random factor, but I think it needs to be tampered.
Naturally a wide spread;
Some reductions in variance for Navigation; being a 0 velocity; Well known routes...
Some additions for short distance from planet; high velocity; quick jumps




[/FONT]

 

[BetterThanLife]

Depending on where the jump emergence point is based on, arriving early is just as bad as arriving late. The closer to your plotted arrival time you are the closer you are to where you want to be.

The most logical place that jump emergence is determined from, in an Astrogation skill sense, is your departure point. Remember though that Planets, Asteroids, Moons, Companion Stars and the system itself is all in motion. IN a fast moving system or if it is the wrong time of year, being early or late a day could put you on the wrong side of the Companion Star, or for a fast moving system cause you to wind up in the outer system instead of in the habitable zone. So a good astrogator will put you where you want to be and when you want to be there.

 

[Straybow]

Actually CT (LBB5) implies that velocity and direction is and can be retained through Jump, even if it never states such.

Pg. 43: LBB5

[FONT=arial,helvetica] Suppose, for instance, that a fleet were to jump into a system with its black globes on and its velocity set upon a predetermined course. It could drift unseen past any defending fleet and drop its screens at a preplanned moment, to bombard a planet or to engage enemy fleets by surprise.[/FONT]

Though that maneuver would require some very precise astrogation. Given the generally imprecise nature of Jump Astrogation jumping with a Zero velocity would be safer though. (Watch out for that rogue asteroid. )

It requires time and reasonable planning. First, move out to 100+ diameters. Then establish a movement vector perpendicular to the direction of jump. Now turn your ship to face the jump vector and plot the jump for the several AU distance from target you need for concealment.

Now when you come out of jump you the +/- puts you to the left or right of a dead-on course to target. Turn the ship to face the movement vector. From that distance only the tiniest of corrections need be applied to the initial vector to come in on target.

The main thing is whether a fleet can be synchronized to arrive much closer together than the overall +/- for jump.

[FONT=arial,helvetica] Is Jump emergence relative to the destination planet, the destination star, the destination starsystem, the starting planet, starting star, starting system, the galactic core, the center of the universe, or some other point? Kind of makes a difference as to how bad 168 hours +/- 10% can be.

[/FONT]

Now you understand why jump must preserve the movement vector. If it didn't, what "null vector" would jump "choose" to set?

As far as the universe is concerned you and your target system are both moving. The majority of the vector between the two is common (referenced to the center of the galaxy, for example, which is moving relative to other galaxies in the cluster, and the local group...).

 

[BetterThanLife]

It requires time and reasonable planning. First, move out to 100+ diameters. Then establish a movement vector perpendicular to the direction of jump. Now turn your ship to face the jump vector and plot the jump for the several AU distance from target you need for concealment.

Except if your jump is in relationship to the system or to where you left, your arrival vector is probably random and meaningless. Now obviously your vector in relationship to the region of the galaxy has to be retained.

Now when you come out of jump you the +/- puts you to the left or right of a dead-on course to target. Turn the ship to face the movement vector. From that distance only the tiniest of corrections need be applied to the initial vector to come in on target.

The main thing is whether a fleet can be synchronized to arrive much closer together than the overall +/- for jump.

Grandfleet almost covers it. (Squadron Jump) But it still scatters them within a couple hours of each other. So a Black Globed Jump might not make for a good Fleet Maneuver.

Now you understand why jump must preserve the movement vector. If it didn't, what "null vector" would jump "choose" to set?

As far as the universe is concerned you and your target system are both moving. The majority of the vector between the two is common (referenced to the center of the galaxy, for example, which is moving relative to other galaxies in the cluster, and the local group...).

Yet even if they move with the same general direction and speed there will still be a variation. At 3-20 light years distance even a minor variation is important. But apparently neither Jump Drive nor Astrogation is an exact science.

 

[aramis]

Straybow:

Your argument is exactly why I feel jump vector preservation does not exist in the OTU.

(I can hear the head banging already. Let me 'splain.)

Y'see, in the OTU, it's two weeks per jump. When you preserve a vector from one system, you now have one to several days burn to cancel the relative motions of even nearby stars... under TNE, if you are not on the exact right course, you're toast... so preserving the system's vector is NOT going to make the OTU turn around times possible. (After all, most TNE ships carry less than 2 days burn.

 

[Merxiless]

We always figured that all the velocity calculations were considered in the jump...

Solar orbital, with respect to the system, galactic rotation, relative destinations galactic vector, planetary motion.. all of it, including current realspace velocity.

 

[TheEngineer]

Hi !

IMHO it perhaps should be a regular method to adapt direction and velocity in a way, that the vessel pop out at the destination with a kind of null vector relative to the mainworld.
The relative velocity difference to next stars usually should be well below 100 km/s. This usually could be handled in around 2,5 hours even for a humble 1g ship and is included in the typical "out of the 100D limit" navigation.
Generally a desired vector in a target system is affected only a bit by the uncertainty of jump duration. So I would say 99.9 % of neccessary maneuvering can already be done in the departure system.

I dont see any negative effect on turn around times. In contrast the preserve vector thing is the chance to be a bit faster

Regards,

TE

 

[tinker123]

If a second of an angle is an inch at 100 yards how far is half a degree at 90 million miles?

Is Jump emergence relative to the destination planet, the destination star, the destination starsystem, the starting planet, starting star, starting system, the galactic core, the center of the universe, or some other point? Kind of makes a difference as to how bad 168 hours +/- 10% can be.

As a rule of thumb for pilots, 1 degree of error is 1 mile of drift in every 60 miles travelled. So your 1/2 degree error at 90 million miles radius is just 3/4 million miles of arc. Practically a bulls-eye to an astronomer It'll take you about 5 hours at 1G.

The other question of relative momentum has scary implications. Presumably you could jump "at rest" from one system, and find yourself in the new system travelling so fast toward the sun that your engines couldn't save you, just because of the relative movement of one system to the other.

That would mean you need to collect some serious momentum before certain jumps (depending on the end points), and so you have to head off-world to the jump-point in a very specific direction to achieve it. Maybe not facing toward the destination system; maybe even directly away from it; but in a direction that will allow you to arrive with a "safe" vector.

And the result of all that would be that anyone could track your jump by the kind of vector you used before jumping.

I never realised that was canon for CT

 

[BetterThanLife]

The 168 hours +/- 10% wasn't introduced until MT and has been canon ever since.

The retain your vector on the other hand is from LBB5.

The really scary implications of the +/-10% with a vector is jumping into a system like Glisten with everything flying about. You could emerge from jump in front of a fast moving asteroid with a nice high vector right toward it.

If you could precisely pinpoint your jump time and have an accurate and up to date chart of the system you are going to, then you could plot your jump carefully enough and arrive safely. But +/-16.8 hours? Things are moving on the other end and they aren't necessarily moving in a consistent manner. Your system data on the system you are jumping to is at least 2 weeks out of date by the time you get out of jump. You can't see where you are going until you get there. Guaranteed to not let people on the ship in Jump, sleep well.

Fortunately space is a fairly barren and desolate place but remember, you are actually trying to arrive in a busy part of it.