Most realistic way to scale up Kerbin to mimic Earth?

[Northstar1989]

After trying to calculate impact damage from a predicted asteroid impact with Kerbin, and starting a thread about how gigantic Kerbals are; I got to thinking- what would be the most realistic way to scale up Kerbin to mirror Earth?

I can see several (potentially equally valid) lines of thought here:

(1) Scale up Kerbin to the real-world parameters of Earth, like is done in the classic version of the "Real Solar System" mod configs... This sets orbital velocity (which is then much higher, though gravity acting on spacecraft remains the same, due to the greatly reduced curvature of the larger planet) and atmospheric height to the correct values, but leaves the interesting problem that all KSP parts are meant to be at approximately 64% scale of their real-world counterparts, and the Kerbals themselves are approximately 40% the size of humans...

However, this makes it virtually impossible to build rockets that perform on par with their real-world counterparts (without a procedural parts mod), as, in extremely over-simplified terms, the Delta-V of a rocket is essentially determined by its burn-time: which is determined by its height (ignoring variances in ISP for a moment), whereas the height-limit of a rocket is (for structural/stability reasons) essentially determined by its width... Since KSP parts are only to 64% scale, in a real world-sized game, it is impossible to build rockets as large and effective as could be achieved with comparable real-world technology.

(2) Scale up Kerbin by a 1:6.4 scale ratio (as is currently done in a popular alternative config version of "Real Solar System"). This preserves the relationship between the size of KSP parts, and the size of the planetary radius- but sets the Delta-V to orbit as much lower than in the real world, due to the shorter atmosphere and reduced planetary curvature... Still, these values would seem to be best-balanced, and lead to the most similar performance of KSP rockets to the real technologies they are miniatures of- as the performance of a rocket is heavily influenced by the relationship between its burn-time (and thus height) and the Delta-V to orbit..

(3) Scale up Kerbin by an approximately 1:4 scale, so as to preserve the relative size of an individual Kerbal vs. the planetary radius. While it doesn't make a tone of sense from a game-balance perspective, it does from a realism perspective: it might seem more plausible that Kerbals (if they are supposed to emulate humans) simply build relatively larger rockets compared to their body-size than humans, than that Kerbals are smaller compared to their planet than humans (which would be the effect achieved with either of the other scale-ups...)

One thing is clear between all the options. Kerbin DOES need to be made larger in order to create more realistic (and also, coincidentally, harder) game balance. The question is, by how much...

I'd like to hear what you guys all have to say about the issue. I'm guessing you'll all lean towards (1)- simply setting the parameters to real-world values: but as I've stated, that creates major problems with Kerbal rockets only being to 64% scale. With such a re-scaled planet, you are forced either to have unrealistically restrictive limits placed on rocket size (from an engineering perspective- economic/financial costs be darned) that prevent them from performing as well as comparable real-world technology; or you install mods that let you build at a real-world scale (such as Procedural Parts), but then have the opposite problem instead- 6.4 tons of payload in things like electronics and orbital labs can do all the same things that would require 10 tons in real life... (thus meaning Kerbal rockets then essentially out-perform real world rockets with mods allowing 100% scale rocket-construction).

Regards,

Northstar

[Tortoise]

That's a nice point you have there, but I do believe that Kerbin wasn't made to mimic planet earth, but have its own unique attributes, along with the rest of the solar system in ksp.

[Northstar1989]

By the way, I'm afraid some of you may still not end up understanding what I mean by 64% scale rockets under-performing 100% scale rockets- so let me give an example:

Say you have a simple rocket that is a fuel tank 2.5 meters wide and 6.4 meters tall (for a total volume of 125.6 cubic meters) with an engine underneath that consumes 1 cubic meter of fuel per second, producing 1000 kN of thrust (these numbers are arbitrary- to have a standard for comparison). This is the KSP-scale rocket.

Now let's say you have another simple rocket that is a fuel tank 3.90625 meters wide and 10 meters tall (for a total volume of 479.12598 cubic meters) with an engine underneath that consumes 2.441 cubic meters of fuel per second, producing 2441 kN of thrust (this engine has precisely the same thrust per square meter of area on the bottom as the first one).

The first rocket of the two is a precisely 64% scale version of the second. It has the same ration of height to width. The same ratio of thrust to cross-sectional area. And the same ISP. Yet, it will have a shorter burn-time for the engine than the 100% scale rocket (125.6 seconds vs. 196.3 seconds), and thus in vacuum, a reduced Delta-V... It's only advantage is that it would produce more thrust per cubic meter of fuel stored- and thus might have a higher TWR...

It doesn't take a genius to figure out the larger rocket probably has the advantage of the two, at least if both rockets start from orbit...

Lifting off from the surface of Kerbin/Earth, things get a little more complex due to aerodynamics and drag- but since Real Solar System and other re-scales don't change the actual gravity exerted by Kerbin/Earth (only the density of the planet), only the planetary curvature (and thus, speed necessary to achieve orbit) and atmospheric height (which effects the minimum stable orbital height, as well as time spent in-atmosphere, experiencing drag) are actually altered...

But, since the 100% scale rocket is taller relative to its mass, it out-performs its 64% miniature aerodynamically, and will experience less drag relative to its mass in a FAR-like aerodynamics system (I can only assume anyone playing with RSS would play with FAR as well) and thus will ascend through that higher atmosphere with relatively less issue...

The question then remains- which is the more "realistic" re-scale then: a 1:10 re-scale that brings Kerbin up to approximately Earth-size (and atmosphere heights and planetary curvatures), or a 1:6.4 re-scale, which maintains the ratio of the size of equivalent rocket technology to its real-world relationship with planetary radius, but consequently still has a lower atmosphere height and higher planetary curvature (and thus decreased orbital speed) than real-world Earth?

Regards,

Northstar

P.S. At times like these, I just wish Squad had given us an Earth-sized planet and real-world sized rockets to begin with, instead of messing around with a 10% scale planet and 64% scale rockets... (which, in stock game, drastically out-size real rocket technology in size comparison to the planetary radius)

Edited May 18, 2014 by Northstar1989

[Mipe]

1. Why rescale Kerbin when you can just create a new Earth-like planet somewhere in the Kerbol system? Let poor Kerbals keep their grassy home, dagnabbit!

2. Scale around part sizes by redeclaring the units. 64 meters is now 100 (kerbalized) meters.

It's all relative.

[Vaporo]

The whole reason Squad decided on a 1/10th scale planet was entirely so that it would be quicker to get each launch into orbit, thus vastly reducing the time that it takes to test rockets.

So, I would disagree with you. There is a very good reason that the planets are not just perfectly scaled clones of their real world counterparts.

Edited May 18, 2014 by Vaporo

[R0cketC0der]

In my opinion, the best way to do this is using the real size like in RSS + Realism Oberhaul. This gives you a realistic sized earth together with realistic parts.

[cantab]

I think the KSP parts being "scaled down" isn't the problem, given they already span a range of sizes.

[Vanamonde]

The planets are scaled the way they are for the gameplay reason of keeping flights to a reasonable game timeframe, and Squad is against the idea of changing that. Also, the subject has been discussed endlessly, without result, to the point that it has been added to the list of subjects not to suggest on this forum, so this thread will be closed now.