Real-universe jump distances

[Adam Dray]

I built a spreadsheet of the 54 closest stars (including known brown dwarves) off Wikipedia's page and then added 14 additional near systems with known exoplanets within 31 LY.

I did some Excel magic to convert the right ascension, declination, and distance to X, Y, Z coordinates with Sol at 0,0,0.

I turned that into a matrix that shows the distance from each of those stars to each other, in parsecs.

I applied highlighting rules to call out the stars that were within 1 parsec of another star. With some COUNTIF rules, I was able to make a column for each star to show how many stars it could reach within 1.0, 1.5, 1.7, 1.9, 2.0, and 3.0 parsecs.

Of the 66 stars on my chart (including Sol), there are 2145 pairs of stars.

I can calculate how many (what %) of stars have a pair within a given distance. Furthermore, I can count how many stars are entirely unreachable.

12 pairs (0.56%) are within 1 parsec of one another. 55 (83%) are unreachable.

32 (1.5%) are within 1.5 pc. 40 (61%) are unreachable.

46 (2.1%) are within 1.7 pc. 35 (53%) are unreachable.

52 (2.4%) are within 1.8 pc. 33 (50%) are unreachable.

141 (6.6%) are within 2.0 pc. 0 (0%) are unreachable.


It's like our galactic neighborhood was built for jump-2.

 

[Orr]

It's like our galactic neighborhood was built for jump-2.

Or jump-1 with tanks just like GDW wrote way back in 1986 in Classic's Solomani Alien Module.

 

[wellis]

Also doesn't Near Stars use some sort of hypothetical dim stars or something to allow for Jump-1 usage?

 

[aramis]

Also doesn't Near Stars use some sort of hypothetical dim stars or something to allow for Jump-1 usage?

No. Not in the original one T:2300 NSL. They used a 7.7 LY limit for the drive. Avoids that.

It's out on the fringes that they added some in a supplement - but it was because they wanted a Kafer arm

 

[aramis]

Or jump-1 with tanks just like GDW wrote way back in 1986 in Classic's Solomani Alien Module.

Not tanks, a refueling station in the Oort.

 

[Taythorian]

Hiya

Would you mind sharing your spreadsheet?

I was thinking of doing something similar but you beat me to it.

Cheers

 

[Adam Dray]

I posted it in the files section: http://www.travellerrpg.com/CotI/Discuss/showthread.php?p=585007

 

[Orr]

Not tanks, a refueling station in the Oort.

No. The Classic Alien Module states: It took several years before a US Space Force team based on Luna tried a mission which, in several trips, established an intermediate stopover and refuelling point about one parsec out.

"About parsec out", not in the Oort.

 

[kilemall]

No. The Classic Alien Module states: It took several years before a US Space Force team based on Luna tried a mission which, in several trips, established an intermediate stopover and refuelling point about one parsec out.

"About parsec out", not in the Oort.

The Oort can stretch out a parsec.

https://en.wikipedia.org/wiki/Oort_cloud

 

[kilemall]

It's like our galactic neighborhood was built for jump-2.

Evidence of Grandfather's manipulations!

 

[JimMarn]

The Oort can stretch out a parsec.

https://en.wikipedia.org/wiki/Oort_cloud

According to 'How the Universe is Made' on Discovery Science channel, the Oort Cloud could go out to 1 or 2 parsecs. And it could be near, physically or gravitationally, to the same cloud around Alpha Centauri A-B.

I don't remember if they said Alpha Proxcima was inside the A-B cloud, or if thier cloud was around all 3 stars.

The problem is the bits out there don't reflect much sunlight and are rather difficult to pick up in telescopes.

 

[aramis]

According to 'How the Universe is Made' on Discovery Science channel, the Oort Cloud could go out to 1 or 2 parsecs. And it could be near, physically or gravitationally, to the same cloud around Alpha Centauri A-B.

I don't remember if they said Alpha Proxcima was inside the A-B cloud, or if thier cloud was around all 3 stars.

The problem is the bits out there don't reflect much sunlight and are rather difficult to pick up in telescopes.

The strongest evidence (and most widely accepted) is 0.5 to 1 LY radius shell. 1 LY in the right place puts P Centauri in reach.

1.5 LY puts all of the Centauri cluster fully accessible by 2 jumps.

2 LY puts the two oorts merging.

 

[Taythorian]

Many thanks for sharing the spreadsheet

 

[bjjones37]

Just out of curiosty, is there any theoretical basis for a jump drive, or is it simply assumed future tech?

 

[Grav_Moped]

No, it's strictly assumed future tech.

Lots of window-dressing about how it works and some rationalization of its characteristics, though. Keep in mind that the limitations on Jump Drive were specifically established to shape the nature of the Traveller fictional universe and facilitate game play.

If you're using real-universe inter-stellar distances in your game, there's nothing dictating that Jump-1 in your universe has to be exactly 3.26 light years (1 parsec). It could be greater or less, whichever works better with your map -- but should be approximately the distance between the closest pairs of stars on your map. That is, it's still a 1 hex range, but you should scale the hex grid to best fit the distances between stars.

Also, the actual galactic plane averages about 1000 LY thick; Traveller compresses this to a two-dimensional plane for playability.

 

[Condottiere]

You also don't have much chance of randomly encountering anything there.

Convenient for the dungeon master.

 

[bjjones37]

You also don't have much chance of randomly encountering anything there.

Convenient for the dungeon master.

"It is known that there is an infinite number of worlds, simply because there is an infinite amount of space for them to be in. However, not every one of them is inhabited. Therefore, there must be a finite number of inhabited worlds. Any finite number divided by infinity is as near to nothing as makes no odds, so the average population of all the planets in the universe can be said to be zero. From this it follows that the population of the whole universe is zero, and that any people you may meet from time to time are merely the products of a deranged imagination."

 

[aramis]

No, it's strictly assumed future tech.

Lots of window-dressing about how it works and some rationalization of its characteristics, though. Keep in mind that the limitations on Jump Drive were specifically established to shape the nature of the Traveller fictional universe and facilitate game play.

Having asked Marc about this when doing some math workups for him...

In the OTU, jump really is a 2-D plane. It has no Z-axis to it. Not all systems are on it. It's generally pretty close to mapped 3D distances.

The big limits:
FTL comm goes by FTL craft
Minimum 100Td jump craft
Quantum steps on drive performance; there is no J1.1. There is J1, J2, J3 ... J9, ..., J∞, but never a decimal. A J0 drive fails to jump, but otherwise acts normally.
Astrogation requires a sufficiently large (but not of need sophisticated) computer... a 1950's era 20Td model 1 (comparable to ENIAC) can do the needed calculations, which implies that some sensor is included, more than "the math is hard".
The time is known as jump commences, but not until.
A course plot is 162:00:00±16:12:00 H:M:S
Ships sharing a course plot vary by ±1:37:12 from each other.
Courses can be reverse engineered in a few hours if the exit flash is captured on sensors.
Everything bigger than the ship can pull it out of jump.

That last, I've tried to pin Marc down on a few details, but have gotten cryptic answers. ( "" is typical)

 

[whulorigan]

In the OTU, jump really is a 2-D plane. It has no Z-axis to it. Not all systems are on it. It's generally pretty close to mapped 3D distances.

@Aramis: Did you get the impression that he meant that not all systems are on it because some systems are unimportant (i.e. nobody generally has a reason to go there, so they are no on the map), or that some systems are not on it because they are unreachable by Jump? If the latter, is there only a single "Jump Plane", or are there effectively a large number of planes based upon the angle of Jump initiation relative to the galactic plane (i.e. are there alternate distinct Jump planes, for example, along perpendicular or 45^o angles to the galactic plane as compared to the "standard plane" parallel to the galactic plane?

 

[mactavish]

Objects larger than the ship can pull it out of jump...

So I'm going to guess that this doesn't mean larger ships, as that would really mess up jump travel throughout the galaxy, particularly if a 100-ton Scout and a 2,000-ton Carrier were headed to the same place at the same time.

I'm assuming that this means astral bodies not known to be between the entry and exit points: a comet with a particularly long orbit, an asteroid knocked into a previously-clear jump route, a rogue planet, a stellar ignition or collapse, and so on.

I've played this up before, having Travellers on the way to a given system only to "fall out" of jump because of high-energy spatial anomalies, a rogue planet, and even an previously unknown Dyson shell.

Now I don't claim to know if that's actually what Mr. Miller meant, but it works well in my games, particularly when you want to introduce something to temporarily sideline the Crew (for whatever reason).

Just a thought.

mactavish out.