KSP Solar System Scale

[Awass]

I read that even the the whole KSP Solar System could fit within the orbit of Venus. I'm just wondering why the devs chose to scale the solar system down from the real one. Is there a practical reason for it, and are they planning to bring everything up to scale later?

[lajoswinkler]

Planets big as real ones would be just too much for today's average personal computers.

[Whackjob]

Not to mention actual realistic travel times. Going to the Mun? Hope you've got six days of free time!

[xclusiv8]

Planets big as real ones would be just too much for today's average personal computers.

That has absolutely no truth to it and is frankly a total lie. A modern day PC could easily simulate our whole solar system. The density of foliage of earths forests and so on is much harder but doable depending on the type of methods used.

[swiftgates24]

I read that even the the whole KSP Solar System could fit within the orbit of Venus. I'm just wondering why the devs chose to scale the solar system down from the real one. Is there a practical reason for it, and are they planning to bring everything up to scale later?

The entire solar system isn't inside the orbit of Venus. Jool alone is the size of Venus.

[doggie015]

If simulating the solar system is too much for a modern PC then how can Orbiter do it just fine?

[chri]

think about planes, to get around kerbin inside the atmosphere (so no time warp!) you would need days

[Ralathon]

The reason the system is scaled down is due to the same reason we don't have multibody physics: Gameplay.

In real life it takes 15 minutes to get from launch to orbit. The majority of that is spend thrusting sideways to get orbital speeds. Since you're likely to do hundreds of launches in KSP that gets really tedious really quickly. The laws of physics only allow 2 solutions:

- Reduce gravity so you attain orbit at slower speeds.

- Reduce planetary radius so the orbit can have a smaller radius and thus is slower.

Option 1 would look unrealistic on the surface (objects falling as if you're on the moon etc), so the devs chose to just scale the planets down a factor 10.

[lajoswinkler]

Not to mention actual realistic travel times. Going to the Mun? Hope you've got six days of free time!

That's what higher time warps are for.

That has absolutely no truth to it and is frankly a total lie. A modern day PC could easily simulate our whole solar system. The density of foliage of earths forests and so on is much harder but doable depending on the type of methods used.

Procedural rendering, yes. I don't think it would be able to actually do the real surface.

The entire solar system isn't inside the orbit of Venus. Jool alone is the size of Venus.

Eeloo's apoapsis is at 113549713200 metres, which is 113549713.2 kilometres, which is 0.11 billion kilometres.

Venus has an aphelion at 108939000000 metres = 108939000 kilometres = 0.1089 billion kilometres.

So yes, Eeloo's orbit would be a bit bigger, but most of it would fit inside Venus orbit. Funny, I've never tought about this. Crap, Solar system is a huge place.

[Awass]

The reason the system is scaled down is due to the same reason we don't have multibody physics: Gameplay.

In real life it takes 15 minutes to get from launch to orbit. The majority of that is spend thrusting sideways to get orbital speeds. Since you're likely to do hundreds of launches in KSP that gets really tedious really quickly. The laws of physics only allow 2 solutions:

- Reduce gravity so you attain orbit at slower speeds.

- Reduce planetary radius so the orbit can have a smaller radius and thus is slower.

Option 1 would look unrealistic on the surface (objects falling as if you're on the moon etc), so the devs chose to just scale the planets down a factor 10.

Good point. I think that just about clears it up.

[Specialist290]

Crap, Solar system is a huge place.

There's the whole reason, right there, distilled into a single pithy phrase

[csanders]

I love what the KSP team has done with this game. The size of the solar system, planets. The closest moon is at 0 inclination. KSC (Kerbal Space Center) is at the equator. This does a lot for getting people playing, because it's not overly difficult. You don't have to worry about the launch site being at a higher latitude than any moon's inclination (which happens with KSC (Kennedy Space Center) some times of the year). You can get to places without spending a lot of time getting there. For instance, it takes about 6 earth years to reach Saturn with a Hohmann transfer.

Without timewarp, one could choose to go to the Mun in a night.

One needs about 3X Dv to orbit Earth, making launches 3 times longer.

[CalculusWarrior]

I love what the KSP team has done with this game. The size of the solar system, planets. The closest moon is at 0 inclination. KSC (Kerbal Space Center) is at the equator. This does a lot for getting people playing, because it's not overly difficult. You don't have to worry about the launch site being at a higher latitude than any moon's inclination (which happens with KSC (Kennedy Space Center) some times of the year). You can get to places without spending a lot of time getting there. For instance, it takes about 6 earth years to reach Saturn with a Hohmann transfer.

Without timewarp, one could choose to go to the Mun in a night.

One needs about 3X Dv to orbit Earth, making launches 3 times longer.

Saying that makes me wonder if the devs will ever implement alternate launch sites for users who want to try harder launches, like what NASA does.

Then again, it might birth a class of KSP players who think less of you if you only use the 'easy' option.

[arq]

Even at 100000x warp, it still takes a decent while for a Kerbin->Eeloo transfer. But higher warps cause further complications with SOI transfers and other aspects, so spacing planets on a Solar scale would be either tricky (make higher warps) or slow.

The other side is the size of celestial bodies. As others have said, getting to orbit would be much more tedious with a larger Kerbin. A convenient side-effect is the dramatically smaller surface area that must be generated and maintained. Also, LKO is a just over 30mins per orbit. LEO is a bit longer.

So generally, KSP would involve a lot more waiting if everything were scaled to Solar sizes.

[csanders]

Saying that makes me wonder if the devs will ever implement alternate launch sites for users who want to try harder launches, like what NASA does.

Then again, it might birth a class of KSP players who think less of you if you only use the 'easy' option.

They might, but I don't think it would add much. By the time you get the skill to do those launches, you should be replicating it with various landing crafts on other bodies as they rendezvous with other ships. This is where I think the game is well balanced with handling orbital mechanics - you don't have to do off-plane launches until you have the skill to put yourself in a situation where you need to do them. For the most part.

But I imagine if they add other launch facilities, they won't put them right at the equator.

FYI: I've been playing Orbiter for nearly 7 years, so I'm familiar with a sim that does our scale solar system, and launching from Kennedy. Also n-body perpetuations, non-spherical gravity, and gravitational torque (Orbiter's timewarp does not kill rotation... or the cut the feed to engines, god help the soul that hits RCS rotation under 1000X timewarp). I actually made an equator base in Orbiter to get the advantages we have in KSP.

[csanders]

Even at 100000x warp, it still takes a decent while for a Kerbin->Eeloo transfer. But higher warps cause further complications with SOI transfers and other aspects, so spacing planets on a Solar scale would be either tricky (make higher warps) or slow.

The other side is the size of celestial bodies. As others have said, getting to orbit would be much more tedious with a larger Kerbin. A convenient side-effect is the dramatically smaller surface area that must be generated and maintained. Also, LKO is a just over 30mins per orbit. LEO is a bit longer.

So generally, KSP would involve a lot more waiting if everything were scaled to Solar sizes.

I think the SOI problem would be mitigated if KSP automatically went to a lower timewarp when one happens. I think they should already. At least on my machine, the game lags when it does an SOI transfer, and that lag caused my first Kerbal death. RIP Jeb hitting the Mun at 10000X.

Anyway, some people may say that the bigger systems won't matter because timewarp solves the problem. Yes and no. Timewarp will make it take about the same amount of player time, but it increases how much timewarp management one has to do to play. It's more button pushing and staring at numbers with very little added "fun."

[Pixel of Life]

- Reduce planetary radius so the orbit can have a smaller radius and thus is slower.

But isn't this against the laws of physics as well? The closer to a planet you are, the faster you need to be moving to stay in orbit.

I'm fairly sure the engines are just really overpowered when compared to the real things.

[Tex_NL]

But isn't this against the laws of physics as well? The closer to a planet you are, the faster you need to be moving to stay in orbit.

...

Not against physics, just counter intuitive. Yes, you will need to move faster but lower orbits require less dV.

[Ralathon]

But isn't this against the laws of physics as well? The closer to a planet you are, the faster you need to be moving to stay in orbit.

I'm fairly sure the engines are just really overpowered when compared to the real things.

You need to go faster if they would have kept the mass the same. However, as they reduced the radius they also reduced the overall mass to keep the surface gravity at 1G.

a = G*M/r^2. r got 10 times smaller. So the lower term got 100 times as small. To keep the acceleration at the surface the same the mass needs to be 100 times as small as well. The volume of the object is 1000 times as small so this means you have to up the density by a factor 10. This is why objects in KSP have ridiculous densities.

In the end, what keeps you in orbit is that the surface is curving away faster than gravity is curving your path. Gravity will be roughly the same at Low Kerbal Orbit as it is in Low Earth Orbit but the curvature of the surface is much higher. So you stay in orbit with a lower velocity.

The engines we have in KSP are actually ridiculously weak compared to real life engines. Just look at some TWR's for real rocket motors. Not to mention our wet/dry ratio for fuel tanks is ridiculously bad.

This is again a bit of balancing. If we got realistic values it would be too easy to get into orbit.

Edited September 29, 2013 by Ralathon

[Eskarina]

Since everything is pocket size, rockets can be pocket sized too.

[-Velocity-]

I love what the KSP team has done with this game. The size of the solar system, planets. The closest moon is at 0 inclination. KSC (Kerbal Space Center) is at the equator. This does a lot for getting people playing, because it's not overly difficult. You don't have to worry about the launch site being at a higher latitude than any moon's inclination (which happens with KSC (Kennedy Space Center) some times of the year). You can get to places without spending a lot of time getting there. For instance, it takes about 6 earth years to reach Saturn with a Hohmann transfer.

You missed two.

1) The devs also made the galactic equator (i.e., the disk of the Milky Way) line up perfectly with the ecliptic (the plane of the solar system). It gives us a great visual reference to shoot for when doing burns- we know if we're thrusting out of plane if our rockets are not pointed into the Milky Way. IRL, the galactic equator is at an angle of something like 45 degrees to the ecliptic, I can't remember exactly.

2) The axial tilt of Kerbin is zero, I think, or damn close to it. So launching strait east puts you on the ecliptic. IRL, the axial tilt of Earth is 23 degrees.

I really hope that the devs actually understood what they were doing with these things, and not that they just *thought* that the Milky Way should line up with the ecliptic. Certain things in this game (like how Duna's atmosphere extends into space for much less distance than Kerbin's- that's wrong, despite the low pressure and mass, Mars' atmosphere extends into space slightly further than Earth's atmosphere, owing to the low gravity) make me wonder if the devs really know their astronomy that well.

Edited September 29, 2013 by |Velocity|

[Werwolf]

Certain things in this game (like how Duna's atmosphere extends into space for much less distance than Kerbin's- that's wrong, despite the low pressure and mass, Mars' atmosphere extends into space slightly further than Earth's atmosphere, owing to the low gravity) make me wonder if the devs really know their astronomy that well.

Erm.... it's not Mars, though. It's Duna. They didn't make everything exact, because then why not just call it Earthling Space Program, and have the same old boring planets? It's a game.... they created it. Let them create what they wish. If you want realistic accuracy, try Orbiter.

[Chrisd857]

I recall that at least one driving factor was there was a time before time warp was implemented. With the Mun where it is, you can get there within a few hours, which is not totally unreasonable for gameplay. Imagine no time warp and a Mun 3 days out...

[Blue]

If the planets were scaled up, surface area would be also scaled up, increasing surface travel time.

When's the last time you travelled 50km across the surface of somewhere? Can you imagine if you had to increase that to 500km simply because that's how the game worked?

[Axder]

Well Kerbal solar system is incredibly big just planets are curently in just small part of it, yes eelo is prety much as far away from sun as venus is, but Suns SOI is much larger I tried tu put space station into furtherest orbit around sun as posible, and it takes more than 70 years to get to apoapsis (Which is around 7 hours in real world on maximal time warp)