adzling
Cosmic Mongoose
It can be very challenging to adjudicate a starship chase across multiple systems due to the large number of variables and the rules being spread out across 2 books (Core & Companion).
Collecting all these disparate rules is almost impossible to do in-game and is a core failure of many RPGs including Traveller.
IMHO Traveller would benefit greatly from a collection of “how-tos” for GMs so I built this tutorial on Starship Chases.
“How to Steal a Starship” will be my next guide. If you’ve got any ideas on other how tos please let me know!
1). Transit from Jump to Refueling Point:
This is affected by various factors:
The effect of the Astrogation check can alter where you arrive in relation to the gravity well you’re targeting (Traveller Companion p.142). While the default aim point is 105 Diameters there is a small variance depending upon your Astrogation check. A perfect check will drop you precisely at the 100D limit and a bad check can throw you significantly off course even result in a bad jump.
High-port, down-port and Gas giants all have very different times to reach from the standard 100 diameter entry point due to the varying size of their jump shadows and whether the ship needs to transit from orbit to the planet.
Due to their large mass (and correspondingly large jump shadows) it can take days to reach a Gas Giant from their 100D limit, while it’s typically only a few hours to reach a high-port orbiting a planet (planets are much smaller and hence have a much smaller jump shadow). You would typically add @24 more minutes to reach a down-port from orbit (core p.153).
Core p.153 also has some transit times for various distances, note these times assume full burn at the noted G until the halfway point then constant deceleration until arrival.
This can also be stated with the following formula:
((sqrt ((2 x planet diameter in meters x 50) / (G x 9.8 )))2)/60* = transit time to refueling point.
*If refueling at a down-port don’t forget to add the time from orbit to surface.
2). Refueling:
Houserule: my table ruled that it takes at least 30 minutes after landing/ docking/ arriving in orbit to begin refueling. This represents the time to make arrangements and prepare to refuel.
It takes 1d6 hours to fuel a ship with water, unrefined fuel or refined fuel (core p.147).
Refueling with ice would take a lot longer as you have to melt it first (no notation on how long it takes to melt or what you would use, our table decided it’s at least as long as refining fuel)
Refueling via skimming also takes 1d6 hours (core p.147) but requires that you refine the fuel or suffer -2dm to your Jump check. You can reduce this time as you would with any other skill check.
Unrefined fuel (water or fuel from a gas giant) takes hours or days to refine once it is loaded on the ship. This refining time is governed by the capacity of the craft’s Fuel Processors (example: a typical far trader can process 40/ tons of fuel per day).
3). Transit to jump point:
This can be done faster than arrival as you can accelerate all the way to the jump point without breaking (you cannot use the transit times in the core book for this as they assume constant deceleration from the halfway point).
This can be calculated using the following formula:
(sqrt ( (2 x Planetary Diameter in meters x 100) / (G x 9.8 )))/60* = time to jump point under constant acceleration.
*If refueling at a down-port don’t forget to add the time from surface to orbit.
4). Reducing Transit Times:
This is mostly a factor of your ship’s max G and the size of the gravity well/ 100D limit.
However you can significantly reduce transit times by overloading the M Drive (Core p.160) at the start of your transit. Because there is no friction to reduce speed in space, increasing your M drive output just one G can significantly reduce transit times (math tbd, stay tuned).
Alternately you can jump early, while within the gravity well’s 100D limit. This can get very risky however (DM-4 to J-drive check if within 100D limit, Core p.148 OR DM-8 if within 10D limit, Companion P.140).
Note: you can never jump INTO a gravity well on purpose, you will just precipitate out of jump at the edge of the 100D limit.
5). Jump Prep Times:
While plotting a jump course requires 1d6x10 minutes to complete the Astrogation check this is almost always irrelevant as they are typically performed during the transit out-system to the jump point (core p.148)
In order to initiate a Jump a J-drive check is required (core p.148). This takes 1d6x10 minutes to perform. You can reduce the time to perform this check to minutes or even seconds (Core p.60).
6). Jump Times:
Jumping takes 148+6d6 hours (core p.148)
This can be reduced by comparing the effect of the engineer’s J-drive check when he initiated jump, (Traveller Companion p.142).
A perfect jump will put the ship on target at exactly 160 hours.
Note 1: Velocity on entering and exiting Jump
Although it is not stated anywhere in MG2e that you exit jump at the same velocity you entered, this was the case in earlier Traveller versions.
Retaining velocity after exiting Jump is a huge lore/ setting problem as it would enable any terrorist to use a 100 ton scout ship to wipe out an entire planet with close to zero chance of being stopped (accelerate to relativistic speeds, jump, enter system at 100d limit and hit the planet with only a few minutes warning/ no time to react for any system defenses).
MG2e implies that you exit jump with zero velocity as the transit time tables on Core p.153 assume a starting point of 0 velocity.
So unless someone can point to something within MG2e rules that stipulates conservation of momentum on exiting Jump we are going to assume that all ships exit jump with zero velocity regardless of how fast they were going when they entered jump (the excess energy would just be used to inflate the jump bubble).
Note 2: How to determine where a ship is jumping to
It is possible to determine the destination of a ship you observe initiating a jump by making a Sensor and Astrogation check.
See PoD p.109.
—
I think that’s it, if you find any errors or have additions/ changes please let me know!
Collecting all these disparate rules is almost impossible to do in-game and is a core failure of many RPGs including Traveller.
IMHO Traveller would benefit greatly from a collection of “how-tos” for GMs so I built this tutorial on Starship Chases.
“How to Steal a Starship” will be my next guide. If you’ve got any ideas on other how tos please let me know!
1). Transit from Jump to Refueling Point:
This is affected by various factors:
The effect of the Astrogation check can alter where you arrive in relation to the gravity well you’re targeting (Traveller Companion p.142). While the default aim point is 105 Diameters there is a small variance depending upon your Astrogation check. A perfect check will drop you precisely at the 100D limit and a bad check can throw you significantly off course even result in a bad jump.
High-port, down-port and Gas giants all have very different times to reach from the standard 100 diameter entry point due to the varying size of their jump shadows and whether the ship needs to transit from orbit to the planet.
Due to their large mass (and correspondingly large jump shadows) it can take days to reach a Gas Giant from their 100D limit, while it’s typically only a few hours to reach a high-port orbiting a planet (planets are much smaller and hence have a much smaller jump shadow). You would typically add @24 more minutes to reach a down-port from orbit (core p.153).
Core p.153 also has some transit times for various distances, note these times assume full burn at the noted G until the halfway point then constant deceleration until arrival.
This can also be stated with the following formula:
((sqrt ((2 x planet diameter in meters x 50) / (G x 9.8 )))2)/60* = transit time to refueling point.
*If refueling at a down-port don’t forget to add the time from orbit to surface.
2). Refueling:
Houserule: my table ruled that it takes at least 30 minutes after landing/ docking/ arriving in orbit to begin refueling. This represents the time to make arrangements and prepare to refuel.
It takes 1d6 hours to fuel a ship with water, unrefined fuel or refined fuel (core p.147).
Refueling with ice would take a lot longer as you have to melt it first (no notation on how long it takes to melt or what you would use, our table decided it’s at least as long as refining fuel)
Refueling via skimming also takes 1d6 hours (core p.147) but requires that you refine the fuel or suffer -2dm to your Jump check. You can reduce this time as you would with any other skill check.
Unrefined fuel (water or fuel from a gas giant) takes hours or days to refine once it is loaded on the ship. This refining time is governed by the capacity of the craft’s Fuel Processors (example: a typical far trader can process 40/ tons of fuel per day).
3). Transit to jump point:
This can be done faster than arrival as you can accelerate all the way to the jump point without breaking (you cannot use the transit times in the core book for this as they assume constant deceleration from the halfway point).
This can be calculated using the following formula:
(sqrt ( (2 x Planetary Diameter in meters x 100) / (G x 9.8 )))/60* = time to jump point under constant acceleration.
*If refueling at a down-port don’t forget to add the time from surface to orbit.
4). Reducing Transit Times:
This is mostly a factor of your ship’s max G and the size of the gravity well/ 100D limit.
However you can significantly reduce transit times by overloading the M Drive (Core p.160) at the start of your transit. Because there is no friction to reduce speed in space, increasing your M drive output just one G can significantly reduce transit times (math tbd, stay tuned).
Alternately you can jump early, while within the gravity well’s 100D limit. This can get very risky however (DM-4 to J-drive check if within 100D limit, Core p.148 OR DM-8 if within 10D limit, Companion P.140).
Note: you can never jump INTO a gravity well on purpose, you will just precipitate out of jump at the edge of the 100D limit.
5). Jump Prep Times:
While plotting a jump course requires 1d6x10 minutes to complete the Astrogation check this is almost always irrelevant as they are typically performed during the transit out-system to the jump point (core p.148)
In order to initiate a Jump a J-drive check is required (core p.148). This takes 1d6x10 minutes to perform. You can reduce the time to perform this check to minutes or even seconds (Core p.60).
6). Jump Times:
Jumping takes 148+6d6 hours (core p.148)
This can be reduced by comparing the effect of the engineer’s J-drive check when he initiated jump, (Traveller Companion p.142).
A perfect jump will put the ship on target at exactly 160 hours.
Note 1: Velocity on entering and exiting Jump
Although it is not stated anywhere in MG2e that you exit jump at the same velocity you entered, this was the case in earlier Traveller versions.
Retaining velocity after exiting Jump is a huge lore/ setting problem as it would enable any terrorist to use a 100 ton scout ship to wipe out an entire planet with close to zero chance of being stopped (accelerate to relativistic speeds, jump, enter system at 100d limit and hit the planet with only a few minutes warning/ no time to react for any system defenses).
MG2e implies that you exit jump with zero velocity as the transit time tables on Core p.153 assume a starting point of 0 velocity.
So unless someone can point to something within MG2e rules that stipulates conservation of momentum on exiting Jump we are going to assume that all ships exit jump with zero velocity regardless of how fast they were going when they entered jump (the excess energy would just be used to inflate the jump bubble).
Note 2: How to determine where a ship is jumping to
It is possible to determine the destination of a ship you observe initiating a jump by making a Sensor and Astrogation check.
See PoD p.109.
—
I think that’s it, if you find any errors or have additions/ changes please let me know!
