Kerbin's Radius

[Candre]

I recently came across a reddit post that makes the bold claim that Kerbin\'s radius is not actually 600km but rather 540km. But when I modify my persistence file to have a semi-major axis of 605km, I get an orbit at an altitude of 5km. That indicates that the radius is 600km. Can somebody elaborate on the error?

[Guest]

That man is very false. The lead game dev should know too. Harv?

[Talisman]

Why are you trusting reddit?

[Radion]

The author of the post later says that the diameter of Kerbin is, in fact, 600 KM, after being pointed to a link proving it so. Worry not, the developers know exactly how big the planet they made is.

[UmbralRaptor]

That person was thrown by the map view giving altitudes instead of semi-major axes.

[VincentMcConnell]

They are wrong, wrong, wrong, wrong WRONG!

Don\'t believe me?

Try this:

Radius of Kerbin is 600KM. Orbiting at 100KM is an orbital radius of 50KM. Add 600 to 100.

Semi Major Axis is 700KM.

Now do the orbital period calculations based on that Semi Major Axis and get a stop watch to verify your figure. The guy on reddit doesn\'t know what he\'s talking about.

[NovaSilisko]

I can confirm that the radius of Kerbin is exactly 600,000m, or 600km.

[VincentMcConnell]

The math to do so is extremely easy. I love how that redditor thinks he\'s going to start a space program... Might want to first learn some basic calculations, dude.

[samstarman5]

I can confirm that the radius of Kerbin is exactly 600,000m, or 600km.

Well that spoils some of the fun. May as well have God send us a text telling us 9 angels can sit on the head of a pin.

The math to do so is extremely easy. I love how that redditor thinks he\'s going to start a space program... Might want to first learn some basic calculations, dude.

Don\'t tell him that the circumference of Earth was determined with an error of +/- 100 miles back when the pyramids were being built. Wouldn\'t want him to lose all faith in the internet.

[Tiberion]

I do believe he got confused due to following development too closely in the past; There was an update where Kerbin was changed, and there was an extra 60KM thrown around for some purpose, and then corrected. Something about the atmosphere and the math being used to calculate others. There\'s still a map around that has Kerbin with a radius of 660KM, and I imagine that is where the 60KM in question came from.

I\'d look up the specific patch note for specifics... but I don\'t want to.

[duckunlimited2]

Yep, kerbin\'s radius is 600,000 meters. I shall show you some proof:

Ever wonder why the mun\'s altitude is 11,400,000 meters and mimus\'s altitude is 46,400,000 meters? Why do they need an extra 400,000 meters? why can\'t they round it up to the millions place? Its because if you add kerbin\'s radius (600,000m) to their altitude, their orbital radius is 12,000,000 meters and 47,000,000 meters respectively. A nice, sensible number, that makes sense. If kerbin\'s radius was not 600,000 meters, then we get funky numbers like 12,100,000 meters or 36,900,000 meters, which don\'t make sense.

[StinkyAce]

So it's 600km in diameter?

So 372 miles.

I guess the physics of known celestial bodies are not relavent?

[Vanamonde]

1 hour ago, StinkyAce said:

So it's 600km in diameter?

So 372 miles.

I guess the physics of known celestial bodies are not relavent?

Not diameter: radius. And the physics is the same, except that KSP celestial bodies are fantastically dense and impossible close to each other.  

[DAL59]

That post was from 2012.  

[NSEP]

KSP's planets are small, sure, but whwhwhhoooohholy moly what a necro.

[Vanamonde]

On 11/26/2017 at 6:20 PM, DAL59 said:

That post was from 2012.  

But the question is still relevant and the answer hasn't changed. 

[Piatzin]

Radius of Gilly?

[Delay]

2km? Just a guess.

[NSEP]

Well, the reddit user apparently corrected himself to 600km. Problem solved? After half a decade? Finally?

[WillThe84th]

On 11/28/2017 at 12:44 AM, Delay said:

2km? Just a guess.

Actually it's 13km.

[Gargamel]

On 11/28/2017 at 6:14 AM, NSEP said:

 After half a decade? Finally?

That makes it sound so old.....

[septemberWaves]

Doesn't the information tab in map view contain data like the equatorial radius? I'm pretty sure that kind of stuff is pretty easily available in-game.

[The Aziz]

Maybe it wasn't back then in 2012.

Also, "equatorial radius" it's not that any other radius is different, planets in KSP are perfect spheres.

[Haruspex]

Just now, The Aziz said:

Also, "equatorial radius" it's not that any other radius is different, planets in KSP are perfect spheres.

Tell that to Gilly, please. 

[OhioBob]

1 hour ago, The Aziz said:

Also, "equatorial radius" it's not that any other radius is different, planets in KSP are perfect spheres.

The datum by which elevation is measured is a perfect sphere, but the planet itself can have quite a bit of irregularity.  But I assume it was the datum to which you were referring.  In real life a celestial body's datum is often a spheroid.

 

Edited December 1, 2017 by OhioBob