Alternate way to get the 100 diameter limit?

[G. Kashkanun Anderson]

Edition specific.
According to MWM's Jumpspace article in JTAS 24 repeated in MgTJTAS 2 a ship must be entering jump space or leaving jump space to be affected by "gravity". You do not get pulled out of jumpspace for the simple reason you are not in our universe anymore.

What?!

No.

The perturbing effects of gravity preclude a ship from exiting jump space within the same (100 diameter, ed.) distance. When ships are directed to exit jump space within a gravity field, they are precipitated out of jump space at the edge of the field instead.

-- 'Jumpspace', JTAS 24, pg. 34

And a bit later:

... there seems to be a built-in safety feature for ships trying to leave jump space within 100 diameters of a world. Ships naturally precipitate out of jump as they near the 100 diameter limit.

-- 'Jumpspace', JTAS 24, pg. 35

I can't speak for whatever Mongoose's source has to say about it, but MWM was pretty clear on the matter: If you attempt to direct a jump path into or through a gravity well, you will get kicked out at the established horizon.

 

[mike wightman]

Yes.

You actually quote it yourself:

When ships are directed to exit jump space within a gravity field, they are precipitated out of jump space at the edge of the field instead.

there seems to be a built-in safety feature for ships trying to leave jump space within 100 diameters of a world. Ships naturally precipitate out of jump as they near the 100 diameter limit.

So unless you are trying to leave jump space the 100D limit does not apply.

It's where the whole jump shadow/masking thing started, people ignore the bit they don't want to see...

 

[Condottiere]

And we're back to if you can jump through the middle of a star.

 

[mike wightman]

There are no stars in jump space, jump space is a series of hyperspaces outside of our universe.

 

[Condottiere]

Has anyone tried jumping from Earth to Mars, while they're on opposite sides of the Sun?

 

[whulorigan]

Remember that Lagrange points come from the sum of real and fictitious forces in a rotating frame. It's the viewpoint within the rotating frame that the forces seem to cancel, I don't think it'd work with the way the jump drive works (at least in spirit)

I would generally go with SpinwardFlow's explanation above about Jump Shadows, but as far as real and fictitious forces go in an accelerated reference frame, recall that according to the Equivalence Principle in General Relativity, gravity and an accelerated reference frame are formally indistinguishable.

 

[whulorigan]

I agree with all of the above reasons for Lagrange points not being a valid jump point.

If you want technobabble, call it a matter of the curvature of space at that distance from a body. So you can't jump from space with too steep a gravity gradient and the approximate distance is 100 diameters where the gradient smooths out. (The actual distance would depend on the density of the body and a host of other factors, making the calculation cumbersome, so everyone uses the approximation.) So a lagrange point would be a very small null where jumping is possible surrounded by too steep a curvature. As has been said, you could jump out if you were there, but the gravity well would pull you out of jump in a matter of km rather than parsecs. And the ability to jump in is way too imprecise to catch Lagrange coming in.

Random idea: So, maybe a TL16+ advance in Jump drives can transcend this, or can push down the gradient, allowing jumping from closer to a mass.

At TL17+ we have the introduction of the Hop Drive which is more powerful by an Order of Magnitude and requires 1000D clearance.
So perhaps with this advance in understanding and capability from TL17+ onward, Jump Drives might be fine-tuned to respond better at larger gradients?

 

[Spinward Flow]

And we're back to if you can jump through the middle of a star.

Shhh.
He's trying to sound clever.

Trying ...

Has anyone tried jumping from Earth to Mars, while they're on opposite sides of the Sun?

You mean, without impacting Sol's jump shadow that extends out to 2.9 AU and would completely block a LOS between Terra and Mars when Sol and Mars are in conjunction as viewed from Terra.

Semi-transparent 2.9 AU jump shadow of Sol added to the image below to help illustrate the problem.

 

[whulorigan]

Nah, you can still lay the blame directly on GDW for that clinker. Cataclysmic binaries were known about at the time that LBB6 came out. Messrs. Chadwick, Harshman & Wiseman just didn't dig deeply enough into their cosmogony manuals to find that out and cover for it.

Though, to be fair, there was no internet back then, so it was exponentially harder to research every little sidebar of stellar physics.

Fortunately, the Traveller Gods have figured it out since then, and Speck has been magically transmogrified into a brown dwarf. This also has its own potential problem (see: Brown Dwarf Desert), but that's not nearly as severe an issue as having to explain away one of Traveller's most famous T-Prime worlds somehow muddling through a system sterilizing event every few hundred thousand to million years.

Well, the other issue was that the original mechanic used to generate secondary and tertiary stars in SysGen generated an extremely high anomalous number of white dwarfs (and excessively cool ones at that ("DM"), based on the standard notation used in Book 6). That is why the T5SS project transformed most of them into Red Dwarfs ("M_ V"), for which there are in fact a large number of such stars in observational evidence.

 

[whulorigan]

If in jumpspace, and you pass within a hundred diameters of a gravity well, you exit.

Unless you get stuck in the roundabout . . .

 

[Badenov]

At TL17+ we have the introduction of the Hop Drive which is more powerful by an Order of Magnitude and requires 1000D clearance.
So perhaps with this advance in understanding and capability from TL17+ onward, Jump Drives might be fine-tuned to respond better at larger gradients?

Ah, that's super interesting. I don't have any access to source material for above TL15 other than tidbits in the main books, so anything beyond that is pure speculation for me. What does a Hop Drive do, and how long does it take to get to 1000D?

 

[Condottiere]

Unless you get stuck in the roundabout . . .

Slingshot.

However, only straight lines in jumpspace.

 

[Enoki]

Edition specific.
According to MWM's Jumpspace article in JTAS 24 repeated in MgTJTAS 2 a ship must be entering jump space or leaving jump space to be affected by "gravity". You do not get pulled out of jumpspace for the simple reason you are not in our universe anymore.
I may be missing it but where in CT 77/81 does it state you arrive at a 100D point?

The way I interpret how jump works is it's gravity based. You are opening a sort of 'gravity well' that the ship 'falls' into and is pulled to the far end. Any outside influences of gravity will distort the well and that compensating for anything other than a sort of background micro-gravity is difficult to do. A skilled crew can make the compensations manually or with computer assistance, but the normal jump programs used only compensate for that all-present micro-gravity. Any outside source not accounted for between where you jump and where you end up can also distort the jump well resulting in a mis-jump.

At least that's how I see it.

 

[Enoki]

Unless you get stuck in the roundabout . . .

A left-hand, or right-hand roundabout...?

 

[Spinward Flow]

At TL17+ we have the introduction of the Hop Drive which is more powerful by an Order of Magnitude and requires 1000D clearance.
So perhaps with this advance in understanding and capability from TL17+ onward, Jump Drives might be fine-tuned to respond better at larger gradients?

Mongoose 2e HG, p48 ... one of the advantages you can add to a jump drive is being able to jump @ 90D instead of the more typical 100D.

There is no mention of "Hop Drive backports into Jump Drive Tech in 'such and such a way'" like you're describing. At best, because you need to be "high tech" in order to have Hop Drive at all, it becomes possible to have "high tech jump drives" with sufficient Advantage points built into them to enable choosing this option ... but that's a function of +TL above requirement, rather than being something unlocked by the existence of Hop Drive like you are asking with your question.

Same outcome, but for entirely different reason(s).

 

[whulorigan]

Ah, that's super interesting. I don't have any access to source material for above TL15 other than tidbits in the main books, so anything beyond that is pure speculation for me. What does a Hop Drive do, and how long does it take to get to 1000D?

A Hop-Drive produces a "Hop" of 10.0 pc per Hop#, with a Hop requiring 1 week standard. Hop-Space can only be safely entered at greater than 1000-D from any massive object. 1000-D is typically the extreme operational range-limit of the standard M-Drive and is about the orbit of Saturn in the Sol-System, so it is like a Gas-Giant fuel-skimming run.

Hop-1 is TL-17
Hop-2 is TL-19
Hop-3 is TL-20
Hop-4 is TL-21
etc.

And at TL-21 is the Skip Drive with each Skip# producing a Skip of 100.0 pc per Skip and requiring 10,000-D safe entry distance (~ Kuiper Belt), each Skip thru Skip-space taking 1 week and subject to a non-negligible "skip-scatter" at the destination which is the uncertainty error in the emergence point.

Skip-1 is TL-20
Skip-2 is TL-22
Skip-3 is TL-23
Skip-4 is TL-24
etc.

 

[Badenov]

A Hop-Drive produces a "Hop" of 10.0 pc per Hop#, with a Hop requiring 1 week standard. Hop-Space can only be safely entered at greater than 1000-D from any massive object. 1000-D is typically the extreme operational range-limit of the standard M-Drive and is about the orbit of Saturn in the Sol-System, so it is like a Gas-Giant fuel-skimming run.

Hop-1 is TL-17
Hop-2 is TL-19
Hop-3 is TL-20
Hop-4 is TL-21
etc.

And at TL-21 is the Skip Drive with each Skip# producing a Skip of 100.0 pc per Skip and requiring 10,000-D safe entry distance (~ Kuiper Belt), each Skip thru Skip-space taking 1 week and subject to a non-negligible "skip-scatter" at the destination which is the uncertainty error in the emergence point.

Skip-1 is TL-20
Skip-2 is TL-22
Skip-3 is TL-23
Skip-4 is TL-24
etc.

If you can't jump less than the 10Pc amounts, then such a ship is only useful for courriers in a sort of hub and spoke arrangement, with regular jump ships on the spokes taking the bag out to individual systems while the main mail runs in 10Pc hops, skips, and jumps through the comm lanes. And maybe some warships will have a both a hop and regular jump drive to be part of a fast reaction force. But not being able to jump less than 10 would kill most of the missions my group has been on.

 

[whulorigan]

If you can't jump less than the 10Pc amounts, then such a ship is only useful for courriers in a sort of hub and spoke arrangement, with regular jump ships on the spokes taking the bag out to individual systems while the main mail runs in 10Pc hops, skips, and jumps through the comm lanes. And maybe some warships will have a both a hop and regular jump drive to be part of a fast reaction force. But not being able to jump less than 10 would kill most of the missions my group has been on.

Yes, but remember that you can deliberately plot a jumpline intersection course with an intervening body to force-precipitate out of jump prior to the nominal jump-number range.

 

[sudnadja]

I would generally go with SpinwardFlow's explanation above about Jump Shadows, but as far as real and fictitious forces go in an accelerated reference frame, recall that according to the Equivalence Principle in General Relativity, gravity and an accelerated reference frame are formally indistinguishable.

What I am trying to say is that if you sum up the gravitational forces in a system, you don't get equilibrium at the lagrange points. The Earth-Sun L2 point isn't where Earth and Sun's gravity balance out, it's where Earth and Sun's gravity with centrifugal force as viewed from a frame co-rotating with Earth balance out, and it is exactly the same viewpoint that places an object in orbit - gravity is balanced out by centrifugal force in a frame co-rotating with the satellite. If jumps from a lagrange point are allowed, jumps from orbit (any orbit) should also be allowed. (attached: force plot of the sum of real and fictitious forces for and Earth size and mass object in a frame rotating at 0.001144 radians/sec - orbital velocity for an object at 350 km orbit altitude. The gravitational and centrifugal (and coriolis and euler) forces balance out.


If you do a similar two body plot, for example Assiniboia and Regina, summing up forces as viewed from the frame co-rotating with Regina, the L1 and L2 points pop out as expected:


Of course, those points don't pop out if you simply sum the gravitational forces of the Assiniboia-Regina (et al) system:



Where I'm going with that is if you allow jumps from "sum-of-real-and-fictitious-forces-is-zero", a jump from a very low orbit is just as valid as a jump from a lagrange point.

 

[Marcatlas]

The 100d limit needed for a jump is--at least I've always thought--based on the need to avoid strong gravity fields. So, it should be possible for a ship to use alternate points where there is a lack of gravity due to canceling sources, like two planets where the gravitational fields are equal and opposite. Is this doable? Because if it is, it opens possibilities for jump in locations that would previously not have been possible.
For example, in a binary star system it might be possible to make a jump where the two gravity fields of the stars are equal and opposite leaving the point at zero gravity.

Not really as it isn't a lack of space distortion but a balanced distortion you are talking about. So the distortion (gravity) is still there.