Thoughts on a TU w/o captal starships

[AnotherDilbert]

A 5 kDt ship has a diameter of about 50 m. The safe distance to jump out is 100 d or ~5 km.

When you arrive you will gently be pushed out of jump space at the 100 d limit if you encounter a mass, so will not crash into another ship.

 

[Reynard]

An object with a significant gravity influence will cause a ship to precipitate out of jump space. Even your largest Traveller ship don't naturally produce a gravity well.

Space is still big even in the 100D limit so exiting into the path of another ship is.... very small. That's why one sensibly does not come into a busy system under power, just in case.

 

[baithammer]

The safe limit in the original post is the clearance needed to account for the possibility of a ship jumping into another ship transiting out of the safe limit. ( 148 - 184 hrs of travel and given the ship can't communicate with normal space to plot out entrance and exit.)

This gets more complicated with both the raw number of ships incoming and exiting as well as coordination of convoys.

Also given most commercial vessels tend to top out with 4 wks operating time with 2 jumps per month and only 2 weeks available for transit.

 

[AnotherDilbert]

An object with a significant gravity influence will cause a ship to precipitate out of jump space. Even your largest Traveller ship don't naturally produce a gravity well.

The T5 crows seems to maintain that a ship produces enough gravity to prevent another nearby ship to jump. Presumably the same goes for exiting jump.

Interference with Exit is virtually impossible. If the Exit Point is within a 100 Diameter sphere, the ship automatically exits where the straight line course intersects that sphere.

100 Diameter Sphere. 100D Sphere. 100D limit. A sphere centered on a gravity source with a radius equal to 100 times the diameter of the source.
Blockage. The presence of an object (or the 100 D sphere of that object) on a jumpline. Blockage occurs if the object is larger than the ship in jump.
...
Gravity Source. An all-inclusive term for a mass (or an operating gravitic device). The diameter of the source is the distance across its longest dimension (some exceptions apply to very long and narrow objects).

So any gravity source larger than your ship seems to block (and presumably cause exit from) jump.

The safe limit in the original post is the clearance needed to account for the possibility of a ship jumping into another ship transiting out of the safe limit. ( 148 - 184 hrs of travel and given the ship can't communicate with normal space to plot out entrance and exit.)

Jump exit is rather precise in space, if not in time:

Over a jump distance of one parsec, the arrival point of a ship can be predicted to within perhaps 3,000 kilometers (on larger jumps, the potential error is proportionally larger)

The 100 d limit of Earth is ~1 260 000 km or a sphere with a surface of ~20 × 10¹⁸ m². The odds of arriving within 100 m of another ship at that exact radius is something like 1:10¹⁵. If you add in that ships arrive within ~10 000 km of the limit or so, the odds is lowered to ~1:10¹⁹. So if a billion ships jumped a billion times it might possibly happen.


The risk of reappearing into something is vanishingly small or non-existent. You might crash into something after you have reentered normal space, which is why civilian ships generally translate at low speed relative to the star systems.

 

[baithammer]

The odds of arriving within 100 m of another ship

Not taking into account the time deviation for jumps and the possibility of other vessels moving into the target area, which like airport runways require more area than the aircrafts footprint. ( Also isn't helped with communication being blocked for the entire jump space transit.)

Further complicating this situation is the average vessel only has 4 weeks total fuel for systems and m-drive with 4 weeks being used for 2 jumps and 2 weeks total of transit between the target diameter limit and the safe jump area that creates a far more finite area to parcel up.

Add to this a combination of individual vessels transiting over a week through that band, not to mention coordinating convoys for larger flows that seriously increases the amount of safe space required.

 

[AnotherDilbert]

Not taking into account the time deviation for jumps and the possibility of other vessels moving into the target area, which like airport runways require more area than the aircrafts footprint.

Spreading ships out in time would further decrease the odds.

Other ships in the volume is kind of a prerequisite for collisions? Yet each other ship would only spend less than an hour in the volume since it is only 10 000 km thick.

 

[h1ro]

So, originally in CT, starships were limited in size to 5000 tons.

<snip>

What else might be different in this sort of TU?

Heron61, did the thread answer your question? Where do you think you might be going with this?

 

[baithammer]

Not taking into account the time deviation for jumps and the possibility of other vessels moving into the target area, which like airport runways require more area than the aircrafts footprint.

Spreading ships out in time would further decrease the odds.

Other ships in the volume is kind of a prerequisite for collisions? Yet each other ship would only spend less than an hour in the volume since it is only 10 000 km thick.

Which given the time delay for communications and not all traffic is from the same system, your looking at a bigger safe zone than 10,000 km and in a spherical volume.

 

[h1ro]

Maybe, just maybe, with an established method of transport and centuries of travel, known astronomical data and all that stuff, someone has figured out a way to drop a ship from J space into N space safely?

As AD pointed out, the location a ship exits jump space is known, the time it drops out is predictable but not precise. Before you jump, you log a flight plan with system traffic control and you're given a point to aim for. A little bit of coordination would make this safe and easy to do. The info would be secure but obviously the departure and arrival traffic controls have worked this stuff out ahead of time. It's no more difficult than the logistics we have today for commercial air liners arriving at the planet's busier airports.

I know we're thread drifting but I don't get how this is part of the discussion.

 

[baithammer]

the location a ship exits jump space is known, the time it drops out is predictable but not precise.

And creates more uncertainty with ships transiting in normal space in the same area.

Before you jump, you log a flight plan with system traffic control and you're given a point to aim for.

Which takes two weeks for 1 ship to get clearance if that ship is the only ship in play, not really feasible with the scale needed to support colonies or commerce.

It's no more difficult than the logistics we have today for commercial air liners arriving at the planet's busier airports.

Which is not an apples to oranges comparison as aircraft can communicate within seconds with traffic control and respond to changes mid flight. Thats not possible with jump travel as jump space prevents normal space communication and would be half-duplex in nature as the directionality of the communication traffic is one way and requires an average of two weeks for submitting and responding.

I know we're thread drifting but I don't get how this is part of the discussion.

Its a fundamental limitation that is exasperated by the displacement limitations while maintaining the big ship universe scale.

 

[h1ro]

And creates more uncertainty with ships transiting in normal space in the same area.

Using Earth as an example, it's moving at 29.8km/s on it's orbital path, it's also orbiting a star that's moving thru space. The space at the 100D sphere of a planet is changing massively every minute.

Which takes two weeks for 1 ship to get clearance if that ship is the only ship in play, not really feasible with the scale needed to support colonies or commerce.

The point in time/space you drop into and out of J space at the departure and arriving systems is preallocated. There's no need for real time communication.

Its a fundamental limitation that is exasperated by the displacement limitations while maintaining the big ship universe scale.

No it's not. To quote a smarter and much funnier man than me: "Space is big. Really big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist, but that's just peanuts to space."

 

[Jeraa]

Before you jump, you log a flight plan with system traffic control and you're given a point to aim for.

Which takes two weeks for 1 ship to get clearance if that ship is the only ship in play, not really feasible with the scale needed to support colonies or commerce.

What he means is that the system of departure assigns the location, not the system of arrival. He is saying that the two worlds have agreed on sending ships to a specific area of the 100D destination. All ships traveling to Planet X from Planet Y arrive in area reserved for them. Ships traveling from Planet Z to Planet X have their own destination area, and so on. Ships leaving Planet X would have their own area they are allowed to jump from (having multiple areas for departing ships isn't really needed).

It would involve setting up a system with every other world within 6 parsecs, but is possible.

 

[AnotherDilbert]

A little bit of coordination would make this safe and easy to do. The info would be secure but obviously the departure and arrival traffic controls have worked this stuff out ahead of time.

We could do something like that, but is even worth the trouble?

According to T5 even the most busy systems only see about ~100 ships a day or ~5 ships per hour, spread out over say 10²⁶ m³. You won't hit anything...

 

[h1ro]

We could do something like that, but is even worth the trouble?

Absolutely not, it is not worth the trouble! It's one of the assumptions of the game.

I just don't understand why Baithammer is making a thing of it! I'll post no more till we get back to the thread.

 

[baithammer]

I just don't understand why Baithammer is making a thing of it! I'll post no more till we get back to the thread.

The thread is about the effects of imposing a 5kdt limit on jump ships, this has a knock on effect up and down the universe.

According to T5 even the most busy systems only see about ~100 ships a day or ~5 ships per hour, spread out over say 10²⁶ m³.

Assuming a big ship universe where ship cargo volume is at the tipping point that 100 ships a day is reasonable, that is with ships around 100kdt+ and assuming that colonies can be supplied to get them relatively self sufficient and not being as constrained on what worlds are suitable for colonization.

If we want to simplify this without having to play jump checkers we can get around this by dividing commerce between non-ftl bulk transports with a massive buffer to account for the time delay and use faster jump capable transports for time sensitive cargo.

To further tone the setting, you can consider reducing the spread of inhabited space and requiring a higher standard of world required for colonization.

I hope I'm not coming across as trying to say this is impossible, it just needs some careful consideration of the limitations.

 

[phavoc]

Maybe, just maybe, with an established method of transport and centuries of travel, known astronomical data and all that stuff, someone has figured out a way to drop a ship from J space into N space safely?

As AD pointed out, the location a ship exits jump space is known, the time it drops out is predictable but not precise. Before you jump, you log a flight plan with system traffic control and you're given a point to aim for. A little bit of coordination would make this safe and easy to do. The info would be secure but obviously the departure and arrival traffic controls have worked this stuff out ahead of time. It's no more difficult than the logistics we have today for commercial air liners arriving at the planet's busier airports.

I know we're thread drifting but I don't get how this is part of the discussion.

Not hard at all. The key is at the departure world. Essentially you take your arrival destination and chop it up into arrival zones. Obviously these zones change every hour since a planet rotates around a sun. So each world (or worlds, if multiple departure points are in a system) gets a specific number of arrival zones assigned to it. Each ship that departs requests a departure zone assignment from traffic control. The zones would be something relatively big to allow for errors and orbital drift and the vargaries of jump travel arrival times. So they could be like 10,000 x 10,000 km in size, or even larger. It's not like there is going to be a shortage of real estate at the 100D limit.

For ships that depart worlds or areas with no departure control, much larger zones would be alloted to an entire system, further out of course. And you could assign the arrival zones to be, for example, time-based. For low-amounts of traffic the risk is pretty slim of a problem. And if necessary you simply make them rather large and further distant. All of this could easily be kept updated via normal mail service with any changes. And arrival worlds would fine ships that violate this rule - easily resolved by having departing worlds create a time-stamped authorization code you have to transmit before docking.

Of course any ship doing this would need to essentially halt it's momentum, ideally relative to the ARRIVAL system, so that it is at a stop when it arrives, making it less likely for ships to have a collision. Though this is somewhat tied to the other handwavium going on that allows for ships to 'dogfight' using inertia-based drives.

To keep this with the idea of the thread, such a traffic control concept (or any other) would be wanted in a smaller ship universe that has more traffic in it, thus more possibilities of ships colliding.

 

[Reynard]

Once again why Traveller ships have such incredibly powerful ship computers just to store and constantly update so many system parameters so you can try to come as close to bullseyeing a destination exit as safely as possible. The biggest X factors are the chaotic nature of jump space, systems with little to no system traffic control and rogue spacecraft reflected in the ship encounter table and sensor checks for encounter distance upon leaving jump space.

"However, spacecraft tend to crowd to just a few places in any given system, such as the hundred diameter jump limit of colonized worlds, industrial belts in orbit, and gas giants and settled moons."

Yeah and then there's that issue.

 

[AnotherDilbert]

"However, spacecraft tend to crowd to just a few places in any given system, such as the hundred diameter jump limit of colonized worlds, industrial belts in orbit, and gas giants and settled moons."

Yes, the 5 ships an hour are crowded into the 10²⁶ m³ shell around the main world. If we assume the average ship spends half an hour in the thin shell just outside the 100 d limit, there would on average be 2.5 ships there for a total density of 1 ship per 4 × 10²⁵ m³ or 40 trillion trillion m³. Crowded indeed!

 

[Reynard]

Why would ship exit on the other side of a mainworld from a starport. It might seem suspicious your vessel is going to waste all that time. Most want to exit at the most optimal location to their final destination barring minor misjumps.

 

[Jeraa]

Why would ship exit on the other side of a mainworld from a starport. It might seem suspicious your vessel is going to waste all that time. Most want to exit at the most optimal location to their final destination barring minor misjumps.

Due to jump masking*, maybe the ship couldn't come out above the starport as the planet was in the way.

And since the time spent in jump is random, you don't know when you are going to come out, so you don't know just where the starport is going to be. On Earth, a mere 12 hours difference means the starport my be on the opposite side of the world from your target coordinates while the randomness of a jump gives a 30 hour window in which the ship can arrive. You can try to plot a destination in the most optimal way, but due to the randomness of jumping, it doesn't always work out.

*Jump masking is canon in MgT, GURPS Traveller, and T5. 2e core rulebook page 148 (or 1e core rulebook page 141):

Gravity can cause a jump bubble to collapse prematurely, bringing a ship back into normal space early – so, if a ship tried to jump from Earth to Mars when the Sun was between the two, the vessel would fall out of jump space as soon as it came within one hundred diameters of the Sun.