The Lightspeed Challenge

[splatn't™]

Simple. Reach lightspeed with stock parts. Anything else goes (infinite fuel) I can’t wait to see the absurdities that come out of this.

Edited October 23, 2019 by splatn't™

[Pds314]

6 hours ago, splatn't™ said:

Simple. Reach lightspeed with stock parts. Anything else goes (infinite fuel, cfg editing, etc.) I can’t wait to see the absurdities that come out of this.

Let's see.. highest TWR with infinite fuel and no actual fuel is the separatron... if you make a craft almost entirely out of them, and they're empty or nearly empty and leave it running at 4x physics warp for 14 hours or so...

Edited October 23, 2019 by Pds314

[splatn't™]

Just now, Pds314 said:

Let's see.. highest TWR with infinite fuel and no actual fuel is the separatron... if you make a craft almost entirely out of them, and they're empty or nearly empty and leave it running at 4x physics warp for 14 hours or so...

Precisely! I want this kind of absurdity out of this challenge.

[Eriksonn]

Firstly i am abit confused by the sentance:

6 hours ago, splatn't™ said:

Anything else goes (infinite fuel, cfg editing, etc.)

as i dont really know if those things are allowed or disallowed, but assuming that those are not allowed there is a massive problem here:

I think that you are underestimating the speed of light, as 300 million m/s is vastly faster than any normal speed that people are used to(and that includes all of the high speed crashes into the mun that would be considered very fast by non-ksp players)

Just becauce i am that type of person i am going to do the math on how much is needed to get to that speed in the stock game. As much as i like them, i am going to ignore gravity assists, as whatever can be gained from them is completely negligable compared to lightspeed.

I was at first going to write how i got to the final awnser, but that got longer than i expected, and was hard to read as i cant get fancy math notation here...

Therfore i will just tell you about my final results instead.

So if we assume a ship made entirely out of one ion engine and a bunch of the large xenon tanks, and we stage off each individual tank when empty, then the deltav for a ship with N tanks is approximatly 32961*log(N) m/s.

I know that that equation seems kindof small, and it is, but the process to get it was not simple, and i did kindof give up slightly at the end, as the problem actually didnt have a nice mathematical solution, so i approximated abunch and got this, although this is a damn good approximation despite the amounf of guessing and trial and error that went into making it. Anyhow, lets get to the results...

so if we want a ship with 300 000 000 m/s in deltav, we need e^(300000000/ 33785) tanks. This number has 3856 zeroes if written out in decimal form, and this is for the most effective spacecraft physically possible in the stock game. To put that number in context for a bit, filling the entire observable universe with xenon tanks will not even be close to the amount that we need, 10^80 compared to 10^3856. That means that we still have 10^3776 times too few xenon tanks.

Oh and btw, the amount of tanks needed is very sensitive to the weight of the engine and the rest of the spacecraft, as adding an extra 300 kg of stuff to this Engine+tanks spacecraft(like for example a probecore, a few batteries and a few solar panels), increases the tank count by about 10^300

 

Edited October 23, 2019 by Eriksonn

[Pds314]

With infinite fuel a separatron should be able to get there within.. 14.4575838156 hours at 4x physics warp.

 

Edited October 23, 2019 by Pds314

[splatn't™]

Just now, Eriksonn said:

Firstly i am abit confused by the sentance:

as i dont really know if those things are allowed or disallowed, but assuming that those are not allowed there is a massive problem here:

I think that you are underestimating the speed of light, as 300 million m/s is vastly faster than any normal speed that people are used to(and that includes all of the high speed crashes into the mun that would be considered very fast by non-ksp players)

 

I know that lightspeed is fast, and that it would be impossible without infinite fuel. However, infinite fuel is allowed in this challenge, but the rules have changed to ban cfg editing.

[Eriksonn]

I kindof guesses that infinite fuel was allowed, but i enjoyed doing the math regardless, just to give a perspective as to how hard it would be without infinite fuel

[splatn't™]

1 minute ago, Eriksonn said:

I kindof guesses that infinite fuel was allowed, but i enjoyed doing the math regardless, just to give a perspective as to how hard it would be without infinite fuel

just use gravity assists lmao

[Pds314]

Without infinite fuel is much more difficult. Ladder drives and K-drives don't play well with physics warp.

Without reactionless drives, my first instinct is to put and absolutely massive lander leg cannon in space with a tiny projectile. But this may not be enough.

Without cheats or exploits, C is quite unreachable. Ion engine stages need a mass ratio of around 0.5, including payload, to get 30000 m/s of Delta-V. That means we need on the order of 10000 stages, enough would obviously be larger than the universe.

 

Speaking of large craft, on possibility would be to have a vehicle with a 1 kg detachable end spin until the edge speed is the speed of light, then decouple. To do this while remaining under 477 rpm, we would need the boom to be quite large. Circumference of about 50,000 km. Radius of about 8500 km. So a spinner that's bigger than Jool. Still, this is probably not especially difficult. Another thing we can do is put all the rest of the mass much closer to the center. And don't store any fuel or electricity in the spinner itself but in a connected, non-rotating fuel depot.

299792458 m/s is a lot, but 299792458 kg*m/s is not necessarily so. And we can cheat by using jet engines blowing at a relatively large radius. If necessary, at Kerbin's north pole so planetary rotation isn't important.

 

One factor that isn't taken into account here is whether parts can survive this sort of tension. This is because the answer is almost surely yes, since the idea is to use cube struts or similar physics-less parts.

Edited October 23, 2019 by Pds314

[Eriksonn]

Just now, Pds314 said:

That means we need on the order of 10000 stages

in my first post on this topic, my math showed that you need 10^3800 stages, that is a 1 followed by 3800 zeroes, to put that in perspective, that would be like taking all the atoms in the entire sun, and making each one of those atoms into a whole sun, and then replacing all the atoms in each of those suns with xenon tanks, only then would you get somewhat close to the amount of tanks/stages that you will need

[Pds314]

2 minutes ago, Eriksonn said:

in my first post on this topic, my math showed that you need 10^3800 stages, that is a 1 followed by 3800 zeroes, to put that in perspective, that would be like taking all the atoms in the entire sun, and making each one of those atoms into a whole sun, and then replacing all the atoms in each of those suns with xenon tanks, only then would you get somewhat close to the amount of tanks/stages that you will need

You definitely don't need 10^3800 exponentially larger stages. That would mean each stage having 10^-3791 m/s of delta-V or so. You do need around 10^3800 xenon tanks though.

Edited October 23, 2019 by Pds314

[Eriksonn]

17 minutes ago, Pds314 said:

You do need around 10^3800 xenon tanks though.

That was exactly what i ment, that the ship would need 10^3800 tanks, and the same amount of stages, as i assumed that each tank was staged off as it get empty.

17 minutes ago, Pds314 said:

That would mean each stage having 10^-3791 m/s of delta-V or so

That is indeed almost exactly the average deltav per stage

Not sure what you ment by expoentiall larger stages, as each stage is just a single tank, if it was becauce of the sun example, that was just a demostration of the amount of tanks required

Edited October 23, 2019 by Eriksonn

[Kergarin]

Is the Kerbol system large enough to do this acceleration? Doesn't the game crash at some distance or is it working infinite?

[Pds314]

15 hours ago, Kergarin said:

Is the Kerbol system large enough to do this acceleration? Doesn't the game crash at some distance or is it working infinite?

I mean, it might crash or become unplayable at like 10^300 meters, but C should be reachable in just 60 hours with unlimited fuel empty separatrons. So that's 30 light-hours =~3*10^13 meters. Hardly an unfeasible distance, even if it it is a solid 300 times Eeloo's Apoapsis.

Edited October 28, 2019 by Pds314

[PositronLance001]

if you use earlier games u can use o-10s.