## JTAS 4 Sensor operations

Discuss the Traveller RPG and its many settings
Linwood
Lesser Spotted Mongoose
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### Re: JTAS 4 Sensor operations

I like that house rule. I may steal it for my campaign....
phavoc
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### Re: JTAS 4 Sensor operations

Feel free. Here's what I have on this:

Jump flashes
Affected by tonnage, exit speed and jump distance from the origin. Detection is doubled in the direction of travel, and normal in all other directions. The larger the ship that is jumping, the more tonnage that it has and the speed upon which it is travelling all combine to determine the size of the exit flare (e.g. jump flash) of the ship.

Jump flash = (ships tonnage * jump distance * speed in G’s of exit velocity) * 100. If exit speed is zero, then substitute 1 G in the equation to eliminate multiplication by zero. The minimum flash distance is 10,000km, regardless of size or other methods to reduce the jump flash.

Ex – An Imperial 100ton scout has performed a 1 parsec jump, with an exit speed of 1G. ((100 tons * 1 parse * 1G) * 100) = 10,000. The scout’s jump flash can be detected at 20,000km if the ship emerges from jump in the direction of a detector, or 10,000 km if it does not.

Ex – A 600ton subsidized liner has performed a 3 parsec jump, with an exit speed of 2G. ((600 * 3 * 2) * 100) = 360,000km jump flash (720,000 if facing a jump detector).

Ex – A 5,000ton Imperial Destroyer with a stealth coating performs a 2 parsec jump and emerges with an exit speed of 0 G ((5,000 * 2 * 0) * 100) = 1,000,000km jump flash, which is halved by the stealth coating down to 500,000km.

Ex – A 50,000ton Imperial cruiser executes a 5 parsec jump and exits jump space at 9G (50,000 * 5 * 9) * 100) = 225,000,000Km (or 500,000,000 if the ship emerged in the same direction as a detector). Had the cruiser done the same jump with an exit speed of zero the detection range would have been reduced to 25,000,000Km.

Ways to reduce jump flash:
Stealth coating of a ship’s hull will reduce the jump flash by 50%.
Jump with a speed of zero to minimize exit flash.

Jump tracking
A ship with military-grade sensors or better that is within 100,000km of a ship that jumps is able to estimate the line along which the ship may emerge. It can even estimate, within an hour, of the estimated transition time back to realspace.

Fleet Jumping
Ships may jump in tandem by synchronizing their jump navicompters. The timing and accuracy is enhanced if the ships are at a relative rest to the system they are jumping from. If they are travelling at speed the chances of mistiming increase for any of the ships attempting a tandem jump. The systems are all fed the same jump coordinates and tied together. The master controller ship determines when the synchronized jump will take place and sends a signal with the exact instance the ships should initiate jump sequence. This is all automated, humans attempting to do it by voice command will emerge 1D6 hours different from each other. Ships using the automation will emerge with 1D6 turns of each other, assuming no extenuating circumstances. For each G of speed the ships are under roll 2D6, multiply by their G speed and that is the emergence timing difference.
Moppy
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### Re: JTAS 4 Sensor operations

What does the speed mean?

Speed must always be measured relative to something. What is that something? How do I calculate my speed? The question is like "which way is is up in space where you feel no noticable gravity?".

1 g is an acceleration, not a speed. Say your acceleration is 10 meters/second^2 (1 g after rounding). You could be moving 1 or 100 meters per second, and still apply 1 g acceleration. This case, after 2 seconds of acceleration your speed relative to your old one, would be 21 or 120 m/s respectively.
phavoc
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### Re: JTAS 4 Sensor operations

Well, Traveller doesn't really track absolute velocity, just your drive rating. For figuring out time between destinations in real space it uses acceleration, changeover, then deceleration. Space combat is just G-ratings.

Your speed will be dependent upon how long you have been accelerating. I'm not wanting to keep track of all that. To keep things simple and not have to keep recalculating on the trusty TI-994a calculator, just use G-ratings and be done with it.
Condottiere
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### Re: JTAS 4 Sensor operations

While I tend to be more than happy to figure out an algorithm to anchor a game mechanism, all I can say is that there must be some difference between a hundred tonne scout slipping into a system, and the arrival of a Tigress battle squadron.

I would tend to calculate detection primarily on the energy used in the transition.
Moppy
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### Re: JTAS 4 Sensor operations

phavoc wrote:
Wed Jul 31, 2019 1:23 pm
Well, Traveller doesn't really track absolute velocity, just your drive rating. For figuring out time between destinations in real space it uses acceleration, changeover, then deceleration. Space combat is just G-ratings.

Your speed will be dependent upon how long you have been accelerating. I'm not wanting to keep track of all that. To keep things simple and not have to keep recalculating on the trusty TI-994a calculator, just use G-ratings and be done with it.

G-rating measured when?

If it mattered you'd cut maneuver drive an instant before jump, and most ships have to because of power plant

Perhaps use maximum installed g-rating regardless of operating status?
NOLATrav
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### Re: JTAS 4 Sensor operations

Condottiere wrote:
Wed Jul 31, 2019 5:13 pm
I would tend to calculate detection primarily on the energy used in the transition.
This is how I handle detection, based on Power currently in use. Allows the heroes to “run silent” by powering down all possible systems and making detection harder. I know we’re discussing jump emergence and fleets but it’s created a nice cat&mouse scenario for in-system travel when players are on the prowl - or hiding.
phavoc
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### Re: JTAS 4 Sensor operations

Moppy wrote:
Wed Jul 31, 2019 6:36 pm
G-rating measured when?

If it mattered you'd cut maneuver drive an instant before jump, and most ships have to because of power plant

Perhaps use maximum installed g-rating regardless of operating status?
At the time of entry/exit - those two speeds are the same since you can't (or couldn't till T5) change your speed or heading once you entered jump. The idea being that if you want to be sneaky you need to enter slow, be small, and drop into normal space further out.

Jump flash = (ships tonnage * jump distance * speed in G’s of exit velocity) * 100. If exit speed is zero, then substitute 1 G in the equation to eliminate multiplication by zero. The minimum flash distance is 10,000km, regardless of size or other methods to reduce the jump flash.
Condottiere
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### Re: JTAS 4 Sensor operations

You can manoeuvre while you fall down the rabbit hole?
AnotherDilbert
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### Re: JTAS 4 Sensor operations

Condottiere wrote:
Thu Aug 01, 2019 9:21 am
You can manoeuvre while you fall down the rabbit hole?
T5.09, p339 wrote: Movement Vector Can Be Changed
A ship can change its speed and direction while in jump space. Vector change requires non-gravity-based drives or devices; gravity-based drives (due to their need to interact with gravity sources) are generally ineffective.
Moppy
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### Re: JTAS 4 Sensor operations

phavoc wrote:
Wed Jul 31, 2019 7:51 pm
At the time of entry/exit - those two speeds are the same since you can't (or couldn't till T5) change your speed or heading once you entered jump. The idea being that if you want to be sneaky you need to enter slow, be small, and drop into normal space further out.

Jump flash = (ships tonnage * jump distance * speed in G’s of exit velocity) * 100. If exit speed is zero, then substitute 1 G in the equation to eliminate multiplication by zero. The minimum flash distance is 10,000km, regardless of size or other methods to reduce the jump flash.
Sorry for being pedantic but maybe an example is needed as I don't understand when you're measuring the "speed".

I have a 2G ship taking off from Earth, heading to the 100D point and entering jump to a different system.

What "speed" would you use for it when it re-emerges, (a) assuming constant acceleration towards the jump point, and (b) assuming it turns around half way and decelerates the 2nd half?

edit: Changed ship to 2G as it makes the edge case of "1G if 0" mean that 1G is indistingihsable from no acceleration.
phavoc
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### Re: JTAS 4 Sensor operations

If you took off from the world at 2G and have been accelerating steadily to the 100D limit and jump, your speed would be 2G to estimate how large the jump flash would be upon emergence.

It's slightly interpretive since a rules lawyer would go "I stop accelerating, then jump, so my jump flash should be calculated to be the minimum". Whereas the GM should smack them over the head and point to their 2hrs of continuous acceleration at 2G and apply that to the formula.

The above explanation wasn't written to be published. It was just copied from my own notes.
baithammer
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### Re: JTAS 4 Sensor operations

You'd want to not be accelerating while jumping as you'd build up 2 weeks worth of acceleration within jump space.

I now see where Miller was going with reduction in g-drive / m-drive thrust for being further out than 10/100 diameter limit.

As for Jump sig, size isn't going to matter as it is detectable out to very distant with arrayed ship sensors in visual / thermal range. ( Grav Sensor Arrays are the game changer.)
I have a 2G ship taking off from Earth, heading to the 100D point and entering jump to a different system.

What "speed" would you use for it when it re-emerges, (a) assuming constant acceleration towards the jump point, and (b) assuming it turns around half way and decelerates the 2nd half?
You'd want to keep within acceleration / deacceleration of your thrusters in order to be able to avoid collisions and be able to avoid overshooting your post-jump location as there is the variance in jump emergence time.
Condottiere
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### Re: JTAS 4 Sensor operations

Mongoverse manoeuvre thrusters don't require a nearby gravitational well to function, unlike, apparently, Tee Five variants.

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