star trek - How does Picard choose a warp speed?

How does Picard, or anyone for that matter, decide at what warp speed to travel? Obviously there are times when they need to get somewhere in a hurry and he says, warp 9 or maximum warp, but the rest of the time he just seems to pick a number at random. He rolls a warp 6.5 Is there some guide as to recommended speeds that he's following? Is there a speed that is the most efficient?

Answer

One major consideration when determining the what warp factor to travel at is energy consumption: starships—even in the 24th century—did not have infinitely renewable sources of energy, requiring massive amounts of deuterium and antideuterium to power the matter/antimatter reaction assembly in the warp core.

A second consideration is the wear and tear on the warp drive: starships, for all their sophistication, are also fine-tuned instruments that will fail under stress, especially under the strain of sustained travel at high warp.

The final consideration, that you touched upon, is the urgency of the matter at hand. The captain must take the previous considerations into account and weigh them on the pressing urgency of the current mission.

So when a starship is commissioned, it's rated for different types of travel:

• Normal cruising speed until fuel exhaustion. On a Galaxy-class starship like the Enterprise-D, this would be Warp 6.


• Maximum cruising speed. Traveling at this speed would be tremendously inefficient, but should cause minimal wear-and-tear. For Galaxy-class starships, this is Warp 9.2.



• Maximum top speed. Traveling at this speed would be inefficient and would not be sustainable after 12 hours due to the damage it would cause to the propulsion system. Warp 9.6 on a Galaxy-class starship.

So when Picard commands Warp 6.5, he's not picking a number at random: he's considered the urgency of the mission and decided that it's worth traveling faster than the normal speeds to get to the destination.

Notes

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  In "Force of Nature", it's determined that high warp speeds harm the fabric of subspace, and the Federation issues a speed limit of Warp 5 unless in the case of a dire emergency. Naturally, Enterprise-D often broke or ignored that limit (episodes are rarely if ever about the non-emergency missions). By the time Voyager was commissioned, Starfleet was able to develop a warp system that overcame this problem by creating a substantial warp field (the movement of the nacelles).

  
  


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  A good engineer always knows how to push the engines beyond their rated speeds: it wouldn't be unheard of for the Enterprise-D to run consistently a notch or two above the rated speeds due to La Forge's engineering skill.

  
  
  


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  Source for the speeds is from the Star Trek: The Next Generation Technical Manual.