"Group B" has acquired [Plot-device] and it is able to deliver over time infinite energy of the type needed for the story to work.

They decide to place it on the most powerful space engine known to man Anno Domini 2017, place it on max thrust for 2 light years, turn the rocket around and then brake for 2 light years.


  • The ship is optimized for best case scenario and does not weigh more than what is needed for the duration of the trip (size of crew compartment is depending on the travel time), the longer the travel time the more weight is needed.
  • [Plot-device] weighs roughly the same amount as the motors will do.
  • [Plot-device] has enough energy to deliver power to any kind of motor existing, (depending on configuration - several motors can be used)

how long time would it take to get there?

  • 2
    $\begingroup$ You may need to edit your question. A light year is a measure of distance not time. You do realize engines can wear out. Even with access to infinite energy powerful engines will wear quickly. $\endgroup$ – a4android Feb 6 '17 at 12:30
  • 2
    $\begingroup$ @a4android I think he knows it's a measurement of distance, because he asked for travel time in the title. So I'm guessing he wants the acceleration of the fastest engine and use simple math to calculate the time to get to 2LY and the multiply by 2 which would be the deceleration to get at a reasonable speed to proxima centauri. $\endgroup$ – user31746 Feb 6 '17 at 12:33
  • $\begingroup$ @Mas Yes. Accelerate half the distance and break half the distance. Though it isn't enough with the fastest engine, you need to get some weight of the ship in there also right ? $\endgroup$ – Magic-Mouse Feb 6 '17 at 12:35
  • $\begingroup$ @a4android Engines wearing out is probably the main limiting factor; after all with infinite energy and unbreakable parts a particle drive can accelerate to arbitrary speeds. $\endgroup$ – IndigoFenix Feb 6 '17 at 12:39
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    $\begingroup$ Assuming that acceleration 'A' is constant: V = At and S = 0.5 A *t^2 which can be rewritten as t = sqrt(2*S/A). Multiply that by 2 and you get t = 2*sqrt(2*S/A), where S is a lightyear in meters and A the acceleration in m/s^2 $\endgroup$ – Ezra Feb 6 '17 at 12:42

The answer is 5 years. This answer will ignore all the practical problems associated with an infinite energy power source and the probability that no known engine could continue running for the necessary time period.

The spacecraft has a crew of human beings. If the spacecraft accelerated at infinite or extremely high acceleration the humans would be crushed to a thin red smear. Humans can survive an acceleration of one gravity indefinitely. A spacecraft accelerating for this long will only accelerate at one gee.

It will take approximately one year to accelerate to near-lightspeed, and travel half a light year. Even continuing to accelerate the spacecraft will only travel close to lightspeed for the next three light years. Until it is half a light year from its destination, then it will decelerate for another year. A total travel time of five years.

Actually since the distance to Proxima Centauri is 4.1 light years. The travel-time will be 5.1 years.

This answer has ignored the time dilation experienced by the crew.

  • $\begingroup$ I think this is good knowledge for folks who want a non-FTL interstellar science fiction story but are willing to have infinite remass engines or whatever that could generate 1 gee of thrust forever, or at least for the 2 years of acceleration/deceleration. $\endgroup$ – Jason K Feb 6 '17 at 19:11
  • $\begingroup$ I see there is a downvote. Would the downvoter like to uncloak? Always willing to have a meaningful discussion, if there are issues you'd like to raise. $\endgroup$ – a4android Feb 7 '17 at 10:55

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