Alternate way to get the 100 diameter limit?

[Enoki]

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.

 

[whartung]

Hmm....Unlikely.

The point about the place between two stars is not that you're in zero gravity, rather you're at the equilibrium of two forces, so neither can "out pull" the other. You're still under influence of both bodies. You would need more power to leave such a point than if you were in actual "zero g".

 

[Kakistocrat]

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?

In CT, I don’t recall reasons being given for the 100d limit. If it was due to avoiding strong gravity fields, then I’d expect that one result of that would be that the starting point of 100d would be the center of mass of the astronomical object in question. (And since gravity is determined by mass rather than by volume, 100d presumably includes some margin of safety to account for variation in densities of astronomical objects, since e.g. the average density of Terra is nearly four times that of Sol.)

 

[Condottiere]

As I recall, Lagrange points are more likely to increase the chances for a misjump.

 

[kilemall]

The point of 100D is to define a map space where the edges are the planet and x distance out allows for a space battle to occur with definable target distance mods and an escape option.

Everything else is gear nerd fluff.

The interesting question to me is the shorter ranges particularly in MgTx detection and weaponry don’t really mesh with the old combat systems and 100D distances.

Should MgT be 10D to realign the old time of battle/escape ratio?

 

[Spinward Flow]

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.

The problem with that plan is that you're still inside the jump shadow.
Jump shadows are known to precipitate starships out of jump.
Hit a jump shadow and you drop out of jump.

In other words, what you're describing wouldn't even work as a micro-jump within a single parsec hex on the map.
Instead, you would experience a "nano-jump" ... in which it takes a week to move a distance away from the point of origin that could have been accelerated through on maneuver drive in a few scant hours (because you hit a jump shadow "so soon" in distance terms from where you started).

The circumstances you're describing is a bit analogous to being in the eye of a hurricane ... and still needing to move north/south/east/west to get anywhere useful. Rather than doing a ballistic sub-orbital maneuver (up out of the hurricane) you're instead going to be speeding up to hypersonic velocity and slamming into the storm horizontally in a maneuver that will ... tend to be Bad For You™, shall we say.

The key insight that you need to have is that 100D jump shadows ought to be thought of as "jump blockers" (in effect) and that your navigator (and computer!) are going to need to plot a course that has NO JUMP SHADOWS between your point of origin and your point of destination ... because if there is one, guess what ... you break out of jump somewhere OTHER THAN where you really wanted to.



So even if the gravity fields at the equilibrium point between 2 stars are "flat enough to jump" ... you aren't going to "get too far" before that condition is no longer the case and you may have the 100D jump shadow of either (or both) star(s) "blocking your path" along your jump trajectory ... and if that happens, you don't "get very far" for a week of jump time and a whole lot of fuel burn (relative to trying to jump from somewhere else, successfully, in the star system).

In CT, I don’t recall reasons being given for the 100d limit.

It was a convenience, really.
Fun part was that because there weren't enough "tools" at the time of CT to properly model planets and orbits (computers were primitive back then, unlike now), a lot of Referees just kind of "ignored" the 100D limit details and just elided past stuff, saying things like, "After a few hours of maneuvering you reach the jump point and jump" without worrying about calculating exact times, distances, where all the jump shadows in a star system could be ... etc. etc. etc. (you know the drill).

Another fun thing about the CT era is that white dwarfs, neutron stars and black holes weren't as well studied or understood back then as they are now. Stuff like contact binaries with any kind of white dwarf is now understood to result in the fusion powered star losing mass "on the regular" to the white dwarf ... until the white dwarf reaches a critical mass limit and ... you get a Type Ia supernova (which tends to "smash stuff" in that star system and is used as a "standard candle" is astronomy).

Sorry, Regina/Regina/Spinward Marches ... according to LBB6, p55 ... Lusor (F7 V) is a contact binary with a DM white dwarf with a mass of ~1.11 solar masses. Once Speck siphons ~0.33 solar masses away from Lusor ... there's going to be an extremely BRIGHT LIGHT all of a sudden (see: Type Ia supernova) ... so Regina as a "habitable moon" of the gas giant Assiniboia is a decidedly TEMPORARY condition (no Darrian Maghiz Star Trigger tech necessary).

 

[sudnadja]

As I recall, Lagrange points are more likely to increase the chances for a misjump.

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)

 

[sudnadja]

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.

If you take the somewhat typical extension that you need relatively flat space (gradient or tide being below a particular value) a gravity balance point or barycenter might work, but the ship would almost immediately precipitate out of jump as it is within a '100 D' volume.

 

[Badenov]

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.

 

[G. Kashkanun Anderson]

Another fun thing about the CT era is that white dwarfs, neutron stars and black holes weren't as well studied or understood back then as they are now. Stuff like contact binaries with any kind of white dwarf is now understood to result in the fusion powered star losing mass "on the regular" to the white dwarf ... until the white dwarf reaches a critical mass limit and ... you get a Type Ia supernova (which tends to "smash stuff" in that star system and is used as a "standard candle" is astronomy).

Sorry, Regina/Regina/Spinward Marches ... according to LBB6, p55 ... Lusor (F7 V) is a contact binary with a DM white dwarf with a mass of ~1.11 solar masses. Once Speck siphons ~0.33 solar masses away from Lusor ... there's going to be an extremely BRIGHT LIGHT all of a sudden (see: Type Ia supernova) ... so Regina as a "habitable moon" of the gas giant Assiniboia is a decidedly TEMPORARY condition (no Darrian Maghiz Star Trigger tech necessary).

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.

 

[Condottiere]

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

Currently, you can jump from anywhere, even sea level; it's just inadvisable.

Emergency jumps from ten diameters out are somewhat viable.

 

[Grav_Moped]

so Regina as a "habitable moon" of the gas giant Assiniboia is a decidedly TEMPORARY condition (no Darrian Maghiz Star Trigger tech necessary).

What if you can run the Darrians' Star Trigger backwards? And then the Darrians loaned that device to Regina for some compensation that nobody really talks about.

(Without, of course, telling them that the Reggirt Rats device could itself be run backwards.)

 

[Grav_Moped]

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

Currently, you can jump from anywhere, even sea level; it's just inadvisable.

Emergency jumps from ten diameters out are somewhat viable.

In Classic? Absolutely. Probably won't vaporize you outright, and if you get out of Jumpspace with J-1 fuel remaining you're almost certian to be able to reach a fuel source and get yourself home. Ran the numbers once, but that was years ago and I'm too tired to look them up. How it works in later rules systems, I don't know.

 

[mike wightman]

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?

Interstellar Travel: Worlds orbiting different stars are reached by interstellar travel,
which uses the jump drive. Once a starship moves to more than 100 planetary
diameters from all worlds, it may activate its jump drive and move to another star
system. Jump drives transfer ships from one star system to another in about one
week per jump.
Interstellar distance is calculated on the basis of jumps, which range in size from
one to six. Some worlds are inaccessible with the use of lesser size jumps, while, in
other areas of the universe, large clusters of worlds are all situated within one jump
of each other. Different ships are also equipped with jump drives of different capabilities,
which determine the jump distance each ship is capable of. Actually making a
jump takes about one week of elapsed time, which includes navigational and pilot
support, and normal preparation as necessary. Transit time to a point at least 100
planetary diameters out adds a total of approximately 20 hours to the whole trip.

 

[mike wightman]

The rules on misjumps were one of the things revised, cpmpare 77 with 81:

For all jumps (in any situations) throw 12+ for a misjump to occur. DM: +5 if
within 100 planetary diameters of a world or star; +3 if using unrefined fuel (except
military and scout ships); –1 if using refined fuel; +2 if operating beyond the required
date for annual maintenance.

Each time the ship engages in a jump, throw 13+ for a misjump: Apply
the following DMs: +1 if using unrefined fuel (and not equipped to do so), +5 if
within 100 planetary diameters of a world, +15 if within 10 planetary diameters of
a world. If the result is 16+, then the ship is destroyed.

 

[Grav_Moped]

And on the original post? I'd allow a jump from a LaGrange point within 100D -- but only as a high-risk option, and with limited choice of destination. In "real life" you'd jump out on the plane perpendicular to the line between the planets' centers of mass -- which resolves to a line on the Traveller hex map. That line may well not be pointed at the center of a hex grid... so yeah, it gets you out but you exit at your referee's choice of two exit points*, at [Jn] hexes away -- somewhere near an edge of the target hex, not at any world that's in it.

-----------------
*High astrogation skill might let you "time" the jump (with suffient lead time, depending) so as to choose a more useful exit point by waiting for the planets to align in a favorable direction. Might take a few weeks (where a moon is involved), might be months (where it's a star that's affecting things).

 

[mike wightman]

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.

In the Third Imperium et al - probably not.
IYTU and in MTU, most definitely

People have noticed that the equations for tidal forces are the closest to giving a 100D equivalence, but there are other ways to look at gravity. Spacetime, quantum gravity, potential energy, Newtonian-Lagrangian-Hamiltonian etc mechanics...

and then there is the magic of Traveller gravitcs and jump drives.

 

[mike wightman]

And on the original post? I'd allow a jump from a LaGrange point within 100D -- but only as a high-risk option, and with limited choice of destination. In "real life" you'd jump out on the plane perpendicular to the line between the planets' centers of mass -- which resolves to a line on the Traveller hex map. That line may well not be pointed at the center of a hex grid... so yeah, it gets you out but you exit at your referee's choice of two exit points*, at [Jn] hexes away -- somewhere near an edge of the target hex, not at any world that's in it.

-----------------
*High astrogation skill might let you "time" the jump (with suffient lead time, depending) so as to choose a more useful exit point by waiting for the planets to align in a favorable direction. Might take a few weeks (where a moon is involved), might be months (where it's a star that's affecting things).

'Bout time those Navigators did something for their money instead of just making coffee and carrying computer cassettes.

 

[Grav_Moped]

'Bout time those Navigators did something for their money instead of just making coffee and carrying computer cassettes.

It's that pencil skill that's critical to recover from malfunctions. C30-C60-C90 Go! (Youtube -- it's Bow Wow Wow from 1980.)

 

[Grav_Moped]

The rules on misjumps were one of the things revised, cpmpare 77 with 81:

in the '81 rules, a Type S (with current maintenance) had an 83% survival rate for a jump in the Hazard Zone between the 10D Line of Death and the 100D Safe Space, if it has J1 fuel left over on exit.

50% chance of a normal jump, 23% chance of a misjump exiting within J-1 range of a world with a fuel source (I checked, and checking that is a bloody tedious process). That J-1 range is why (IMTU) the Type S has 20Td of power plant fuel -- 10Td of it is actually a jump-1 reserve.