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How long will interstellar journeys take?


Sky Kerman
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there are probablu many with everyone being a certain distance from kerbol.  so we will set the distance to = x .it will also depend on what tech you have so we set that as = y

that leaves us with a simple equation on how long it will take.

x/y ≈ the time depending on skill and the how much cargo you have

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We don't know exactly yet. There was a lot of speculation that they would be scaling down interstellar distances by a factor of 10 just as the Kerbol system is, but we've also heard the devs say a "mult-lightyear journeys", which sounds like they might be sticking with real-scale for interstellar missions. If the engines we're getting can get us up to 10-20% C that would mean transit times between 20-40 years to the very closest stars. 

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1 hour ago, jastrone said:

there are probablu many with everyone being a certain distance from kerbol.  so we will set the distance to = x .it will also depend on what tech you have so we set that as = y

that leaves us with a simple equation on how long it will take.

x/y ≈ the time depending on skill and the how much cargo you have

This is simply incorrect, or at least a vast oversimplification. Isp, fuel, dry mass, etc. are all factors that need to be considered.

If you want some actual maths...

1 hour ago, Pthigrivi said:

but we've also heard the devs say a "mult-lightyear journeys"

Figures to me that they're simply slowing down KSP's speed of light to match everything else.

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2 hours ago, Pthigrivi said:

If the engines we're getting can get us up to 10-20% C that would mean transit times between 20-40 years to the very closest stars. 

I would like the first interstellar engines to have speeds like that (or maybe even lower) but the most technologically advanced interstellar engines be able to move ships between stars in less than twice the time that it takes for light to travel there (as in, they can reach speeds very close to C and cruise there) so I'm hoping that there is a progression of transit times from several decades to several years

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1 hour ago, t_v said:

(as in, they can reach speeds very close to C and cruise there)

remember, for most of our interstellar journeys, there wont be a "cruise" phase like we're used to in KSP 1. We'll be using very very high isp engines to accellerate for half the journey, then to turn around once and decelerate into an eventual capture once we reach our destinations. 

(can you tell I dont know how to spell "bachristichrome trajectories"?)

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4 hours ago, Turtlegirl1209 said:

remember, for most of our interstellar journeys, there wont be a "cruise" phase like we're used to in KSP 1.

This is somewhat hard to believe; it'd be a bit unrealistic to expect any technology short of antimatter to be able to sustain full thrust for the entirety of an interstellar journey.

There will 100% be a cruise phase unless you somehow managed to pack enough fuel and thrust into one vessel to get there in a single continuous burn, which I deem unlikely.

Edited by Bej Kerman
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9 minutes ago, Bej Kerman said:

This is somewhat hard to believe; it'd be a bit unrealistic to expect any technology short of antimatter to be able to sustain full thrust for the entirety of an interstellar journey.

There will 100% be a cruise phase unless you somehow managed to pack enough fuel and thrust into one vessel to get there in a single continuous burn, which I deem unlikely.

There has been enough talk of brachistochrone trajectories that I would expect them to be the main way of interstellar travel.

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4 hours ago, Turtlegirl1209 said:

remember, for most of our interstellar journeys, there wont be a "cruise" phase like we're used to in KSP 1. We'll be using very very high isp engines to accellerate for half the journey, then to turn around once and decelerate into an eventual capture once we reach our destinations. 

If you don’t have enough delta-v or your engine is good enough, you won’t want to be accelerating the whole time.

First, the actual time that you gain from using a baristochrone trajectory decreases as you accelerate closer to the switching point. What is the purpose of increasing your velocity by 100 m/s when you are only benefitting from that for like 5 minutes, which would gain you next to no distance. Early ships that do long accelerations and decelerations will realistically accelerate to a cruising speed, then coast for a third of the journey, then decelerate. Not only is it more economical, but it affords a higher acceleration due to lower starting mass, so for shorter trips it might actually gain time relative to a heavier ship not using its full potential.
 
Second, if you have an engine that can accelerate you to 0.99C before the halfway point, going any faster would be pointless unless you are really short on LS, which probably isn’t a concern at that tech level. Cruising is just better for dV in general, whether you are cruising at 0.2 C or 0.9. 

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At Warpx1,000,000 a Kerbal decade is 92 secs so say x100,000  15-16mins. 

Given the furthest extents of KSP 1 were a couple of hours at max warp in the earlier times of the game I don't think  4 to 5 decades is out of the question for the dedicated players. This can be done  without increasing time warp max factor but still allowing engine burns at full current timewarp. 

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On 9/19/2022 at 3:23 AM, t_v said:

If you don’t have enough delta-v or your engine is good enough, you won’t want to be accelerating the whole time.

First, the actual time that you gain from using a baristochrone trajectory decreases as you accelerate closer to the switching point. What is the purpose of increasing your velocity by 100 m/s when you are only benefitting from that for like 5 minutes, which would gain you next to no distance. Early ships that do long accelerations and decelerations will realistically accelerate to a cruising speed, then coast for a third of the journey, then decelerate. Not only is it more economical, but it affords a higher acceleration due to lower starting mass, so for shorter trips it might actually gain time relative to a heavier ship not using its full potential.
 
Second, if you have an engine that can accelerate you to 0.99C before the halfway point, going any faster would be pointless unless you are really short on LS, which probably isn’t a concern at that tech level. Cruising is just better for dV in general, whether you are cruising at 0.2 C or 0.9. 

I say  you will burn for 1/3 then cruise and brake for 1/3 in all cases, exception is stuff like an solar sail there you use no fuel or perhaps you want to burn a bit longer if fuel is just an small fraction of your ship mass.
Last is if the ship is g force limited like an ship in the expanse. 

For normal cases the 1/3 -1/3-1/3 split should work best. 
Now one thing who might upset this is that you will have way higher TWR at the end as you have burned all your fuel.  This might even be true if you use an ship with side boosters, think falcon heavy with crossfeed. 
Here acceleration will increase until you burned the two side boosters dry, you now drop them and brake with the core. 
 

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4 hours ago, CyanAstro said:

Has there been any talk on how kerbals will survive space travel for this long?

I know it’s going to be hard-science but you could suggest that Kerbals have biology which allows for some sort of stasis for long periods of time.

We don't know yet. A lot of us are really hoping for some kind simple but interesting life-support mechanic, but we don't really know if Kerbals age or die over time. I think stasis is unlikely because as you say the devs seem pretty committed to 'hard science' solutions. And with transit times of 30-50 years its certainly plausible that those journeys are within a Kerbal lifetime (however long that is?). 

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On 9/23/2022 at 4:02 PM, Pthigrivi said:

We don't know yet. A lot of us are really hoping for some kind simple but interesting life-support mechanic, but we don't really know if Kerbals age or die over time. I think stasis is unlikely because as you say the devs seem pretty committed to 'hard science' solutions. And with transit times of 30-50 years its certainly plausible that those journeys are within a Kerbal lifetime (however long that is?). 

Having kerbals going into stasis if life support run out is one way to deal with this without killing them. You now need to send an rescue mission as they will not get out of it simply by sending an packet of life support resources.

Now I have an problem with very long travel times. In KSP 1 I tend to do stuff near Kerbin, I train new kerbals, I set up and launch crew rotation and resupply missions to planetary bases then recover them.  In short time don't move that fast, its not often I time warp more than a week before I have to do another step. 
At this point the game tend to stop working reliable but that is KSP 1 with tons of mods. 
 

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1 hour ago, magnemoe said:

Having kerbals going into stasis if life support run out is one way to deal with this without killing them. You now need to send an rescue mission as they will not get out of it simply by sending an packet of life support resources.

I think this is the best compromise idea I've seen yet

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