When I asked my previous question about love on multi generation ship, I left blank the where are the people going. Simply because I do not know.

Now I am in search of software which would ease some calculations.

Example: Say the ship is travelling to a system which is 35 light years away. The basic math tells me, that if I want to be here in 600 years, I have to travel 0.06c on average for the whole time (hopefully I did not mess even the basics :) )

But the thing is, such ship will probably spend some time accelerating and then braking.

Being lazy person, I am in search of software which would allow me to enter these variables and calculate time to travel:

  • How far (in lightyears) am I travelling
  • What is the fastest speed I want to achieve during travel (fraction of light speed)
  • How heavy the ship is
  • How long do I want to accelerate and brake

Is there such software I could use?

P.S.: As of the engines and/or rockets pushing the ship to movement, I feel like hand-waving this and make them from unobtainium.

  • $\begingroup$ maybe add: what fuel and/or what kind of engines does my ship own at all... it would make a huge difference, if you try to accomplish this using this-day rocket fuel or some future... whatever-engine. If you happen to know this, the math-guys may be happy about the ... the... ips and deltaV of your ships engine. And its mass. Thrust-Weight-Ratio is a huge thing if you ask for acceleration times. Minor impact for "where is the target located relative to start point"; can you do gravi-accelerating at a local gas giant maybe? or use the sun for this purpose? $\endgroup$ Jan 20, 2016 at 9:43
  • $\begingroup$ @ConfusedMerlin added. But the thing is, I plan making the rockets out of unobtainium - I am going to hand wave it. At this time I care about if I am travelling somewhere where I can reasonably get to without breaking laws of physics $\endgroup$ Jan 20, 2016 at 9:48
  • $\begingroup$ I doubt there is software to calculate this. However, the math isn't really that hard, particularly if you are willing to set the ship's accelleration. Have a look at Transit times to Mars and Jupiter on Space Exploration for some helpful hints. $\endgroup$
    – user
    Jan 20, 2016 at 10:11
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    $\begingroup$ You might also add relativity at 0.06c you won't experience a lot of time dilatation, but at 0.1c every "normal", non-relativistic day seems to be one hour shorter for the traveller, so your 600 year travel will only take 594 years for the astronauts. If your ship travelled with 0.5c, it would be 522 "deck years", and at 0.8c it would be 360 "deck years". $\endgroup$
    – mg30rg
    Jan 20, 2016 at 14:05

3 Answers 3


Why there is one. I use this one all the time:

Space Travel Calculator and the source code is at https://github.com/nathangeffen/space-travel

Happy travels!

  • $\begingroup$ This. This is exactly what I wanted! $\endgroup$ Jan 21, 2016 at 7:07

You want to accelerate for half the distance, or half the amount of fuel, and then you simply turn the ship around and decelerate for the same amount of time.

Yes, really... in space where you have no friction to bother you, and where you have engines delivering a set amount of thrust — i.e. applying a force on your vehicle — it is that simple.

Now assuming that your story is set to have this trip to take 600 years and the distance is indeed 35ly, then you have two options:

  1. the engines burn through the fuel quickly, get you up to speed and then you spend most of the journey coasting. Then the coasting speed is 0.06c... you can essentially ignore the acceleration/deceleration phase and the speed is slow enough to be able to ignore relativistic effects. This option is likely if you are using reaction engines where chemical fuels or perhaps something like the proposed Orion spacecraft (i.e. using nuclear explosions) propel you. Reaction engines are very powerful, they get you up to speed quickly, but they use up lots of fuels and are very bulky.

  2. You have enough fuel to keep the engines burning the whole trip. Then you will have your ship accelerate up to 0.12c at the midpoint, and then you will turn the ship around and start slowing down again, otherwise you'll just zoom past your target. This is likely if you are using ion engines and something like a Polywell — or any other fusion design — reactor to provide them with energy. Ion engines are extremely fuel efficient, and they can use electricity to power them, but they do not deliver much thrust.

In either case you do not need any software to calculate this, my numbers are close enough. :)

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    $\begingroup$ +1 for reminding me that maybe I am searching complications in things which actually are not that complicated $\endgroup$ Jan 20, 2016 at 9:56
  • $\begingroup$ This, unless you want to go into mass assists, for which you will need more than just some software, it really is that simple. Take A your acceleration (you can calculate this from thrust and mass of ship) and B your total time frame. You can reach a total distance of A * B * B / 2 calculation: top speed after half the journey accelerating = A * B / 2, average speed of half the journey accelerating = (A * B / 2) / 2, average speed of the whole journey = (A * B / 2) / 2 * 2 = A * B / 2, your total distance traveled = A * B / 2 * B. $\endgroup$
    – Selenog
    Jan 20, 2016 at 10:00
  • $\begingroup$ Yep, it's really not that complicated! The accelerate/decelerate method is what Frederik Pohl theorises in Gateway (well worth a read if you haven't). The advantage of this method is, provided the acceleration is constant, you don't have to worry about gravity generation - incidentally, accelerating constantly at 9.8m/s (earth gravity) will get you to 0.6c in 212 days. A year's worth gets you (theoretically) to the speed of light, but clearly the amount of force required to keep it up increases exponentially as you get closer to $c$. $\endgroup$ Jan 20, 2016 at 11:43
  • $\begingroup$ No it would not require more force to maintain 1G inside the spacecraft I Stanley... the relativity theory means that for you it makes no difference at all whether you are moving at Newtonian or relativistic speeds... you would still have 1G inside the spacecraft for the same amount of force output. $\endgroup$
    – MichaelK
    Jan 20, 2016 at 12:23
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    $\begingroup$ @MichaelKarnerfors Yes, "you will be going like a pinball between the planets for quite some time" but if you can spare yourself a few kilo(if not mega-)tons of fuel which you don't have to accelerate to relativistic speeds and take care of for 600 years, that might worth considering. $\endgroup$
    – mg30rg
    Jan 20, 2016 at 15:38

I'm unaware of anything specifically for this - but if you're proficient with excel, openoffice, or Libreoffice, you can create a nice little calculator for your own uses. It has the advantage of being able to be customized easily.

http://www.wolframalpha.com/ can work pretty well for quick questions, but if you're getting anywhere near the speed of light then special relativity kicks in and things get a lot trickier.


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