[Spaceships] Starfire to GURPS conversions? (revisited)

[DaltonS]

System Mapping

From GURPS Spaceships 5, page 31;

Starships that don’t travel through normal space but use jump drives or hyperdrives can appear in a system they haven’t studied at all. If so, it’s still possible to use any of these out-system procedures from within the star system itself.

Two elements should be added to the data collected by standard system mapping, whether it's done in game or before by the GM:

1. the game date of the system survey.
2. the position of each world in its orbit as of that date. This should be done as per Step 4 of Generating Jump Points above.

This data is needed to calculate future planetary positions and thus travel times between worlds and jump points.

Gravimetric Survey
When entering a system for the first time, a survey is required using a Science or Multipurpose Sensor Array’s gravimetric sensors to find any existing Jump Points. This is a long task that takes eight hours per attempt, during which the ship will rotate 45°/hour for full sensor coverage. Careful explorers can take full advantage of extra time and spend as long as 240 hours per attempt (at +5 to skill). (Note: This is separate from System Mapping.)
For best results, each attempt should be made with the drive field Off or on Standby Mode and its location (distance and bearing from system center) noted; subtract 1 from each Survey Roll if the drive is on Standby (due to the drive’s sensor “blindspot”). At the end of each attempt, the GM must do a Survey Roll for each JP using its Visibility, adding the Array’s scan rating (TL+SM-9) and subtracting the Distance Roll on the Table 2 inGenerating Jump Points above for the range from the ship to the JP. A normal success locates the JP within one light-minute of its actual position, while a critical one locates it within one light-second. On an ordinary failure the JP is missed by the survey, but a critical failure creates a false positive at a random location (use Table 2 and step 4 in Generate Jump Points above).

Example: A SM+9 survey ship with an Early TL10^ array and its drive Off can detect an Open JP at 3AU (25 light minutes) away on a roll of 15+10-11=14 or less. The same ship could detect a Concealed JP at the same range on a roll of 13 or less, but could not find a Hidden, Secret, Top Secret or Undisclosed JP at any range without a more advanced gravimetric sensor. At 12AU (100 light minutes), an Open JP would be found on 10 or less (a 50% chance) while a Concealed one would be found on 9 or less (a 37.5% chance).

As you can see, a comprehensive Gravimetric Survey of the system would require multiple tasks from different locations. Rather than rolling for each JP at every survey point, do one roll at the end of the comprehensive survey for each JP using a decided on bonus/penalty. To determine the number of survey points required to completely cover the system;

1. Determine the scan bonus/penalty you are willing to accept. (This should include the -1 penalty for scanning with the drive in Standby Mode if applicable.) Subtract this from the scan rating of the sensor array (TL+SM-9) to get its effective scan.
2. Look up the effective scan in the “Roll” column of Distance Table and use the corresponding distance in light-minutes as the mean separation of survey points s.
3. The number of survey points is N = (350/s)^2 rounded up.

Given that v is the speed of the ship (use Strategic Mode if the survey is overt or LOD Mode if it’s covert), (2×s/v+8)×N hours is the absolute minimum time for the complete survey by a single ship. This time can be reduced by using multiple survey ships and consolidating their data. A normal success locates the JP within one light-second of its actual position, while a critical one means a “transit signature” was observed for that JP which was used to calculate (takes 1 day) an exact position (within a 20-second hex or 31,000 miles) and transit information.

Example: Without any bonuses or penalties, the above ship would require (350/15)^2 = 545 survey points to cover the system. If the ship has a 2nd generation Inertialess Drive with a Strategic Mode speed of 1.5, it would take (2×15/1.5+8)×545 = 15260 hours (1.74 years) to complete the survey. By accepting a 1 point penalty, we can reduce the number of survey points to 196 and the survey time to 8101? hours (337.6 days or about 11 months), a reduction of 46.9%. This will still find an Open JP on 14 or less (90.7%) and a Concealed one on 13 or less (83.8%).

Dalton “getting there may be half the fun, but knowing where to go is the other half” Spence