It appears from the rules about jump duration that ships which jump to the same destination will arrive at different times over a two day period. How then do you conduct a coordinated surprise attack on a star system if it takes a couple of days for all your ships to arrive? This has major implications for convoy, military, and other multi-ship operations. - C.B.
Good question! You have discovered what amounts to a "hole" in the rules - a hole that needs filled. These types of problems are the most fun to solve because we need to come up with an answer that does not conflict with prior Traveller material. (Contrary to what some of you may think, we haven't thought of all the implications of everything!) At any rate, after discussing this problem with Marc Miller, we offer the following solution.
When a group of starships know they have to arrive in unison, they elect to spend significantly more time at the start computing and sharing jump vector computations. This leads to a much more accurate jump exit at the other end, with the errot dropping significantly.
The formula in the Starship Operator's Manual for normal jumpspace exit is:
124 hrs + (2D x 6 hrs)
yielding a result of 136-196 hours
(that is, 5.7 to 8.2 days)
If double the jump preparation time is spent with all the affected ships in computer link via tight beam communication, use the following formula instead:
167 hours + (2D x 0.1 hr)
yielding a result of 167.2 - 168.2 hours.
Most ships will now arrive within minutes of each other, with the worst spread being up to 60 minutes apart (and this only happens in about 1 out of 20 jumps). Considering the vast distances found in a star system, starships arriving minutes apart would not spoil a surprise arrival.
Constant communication during the jump vector generate[sic] is essential for this to work, and double the normal vector generation time must be observed. But when getting there "on a dime" timewise is essential, then this technique is the key. Most civilian vessels don't need this level of schedule precision, so they don't bother. - Joe D. Fugate Sr.