2 Questions about Orbits (Trying to Understand KSP Orbits & Real World Orbits)

[Turk_WLF]

I’m trying to understand how to translate Real World Orbits in the KSP Orbits. I know that Low Kerbin Orbit is 80 Km (a good stable orbit) & GSO is 2868 km (I think). I’m just wondering if I want to put a Space Station in the same orbit as the ISS which ranges from 330-435 km or put a Space Telescope in the orbit as the HST which is a LEO 559 Km.

1) How do I go about figuring how to convert the Real World Measurements into KSP Measurements? I know that Kerbin is 10 times smaller than Earth is.

2) I’m just wondering if there are any tips or tricks to equally space Satellites like networks of communication satellites (4/system/orbit).

Thanks,

[Sirine]

A) This is a game, its not flight simulation. This is a game, its not flight simulation.This is a game, its not flight simulation.This is a game, its not flight simulation.This is a game, its not flight simulation.This is a game, its not flight simulation.This is a game, its not flight simulation.This is a game, its not flight simulation.This is a game, its not flight simulation.This is a game, its not flight simulation.This is a game, its not flight simulation.This is a game, its not flight simulation.

The game logic is NOTHING similar to real world.

C) Tips:- Try playing it vanilla. Try enjoy the game for what it made for. Before you install a single mod.

1) RSS mod (Real Solar System)

2) Remote Tech 2 mod.

Edited September 26, 2014 by Sirine

[Claw]

Yes, the Kerbin system is laid out very differently from the "real world" Earth solar system. I would caution against trying to apply real distances and other measures against stock KSP. LEO, MEO, GEO, and all the other Earth type orbits are at completely different altitudes.

Also, KSP is a patched conic simulator, and not an n-body simulator. If that doesn't mean anything to you, it basically means simplified physics. Certain things like Lagrange points do not exist.

There are mods that overhaul the system to provide bigger solar systems, more "real world" representation of the Earth system, and "better" physics. I always encourage users to become engrossed in the stock game first. Once you decide what part interests you, find mods to fill that interest.

If you have reached that point, then I would say Real Solar System (RSS) might also be a good mod to look into.

As for setting up satellites in orbit, many people will set up a resonant orbit when releasing multiple satellites. If you don't know what those are, you can try the wiki or come back here to ask.

Good luck!

~Claw

[Hannu]

How do I go about figuring how to convert the Real World Measurements into KSP Measurements? I know that Kerbin is 10 times smaller than Earth is.

Unique conversion does not exist, because KSP does not have all physical aspects which have had an effect to orbit selection of real spacecrafts. You have to first decide what things you want to.

I’m just wondering if there are any tips or tricks to equally space Satellites like

Real world's trick is very accurate determination of position and velocity, orbit predictions and frequent small corrections. KSP have no such disturbances but it also do not have ways to put satellites to enough accurate orbits. Even if you edit savefile to get perfect orbital parameters, smallest possible errors will increase, because accuracy of floating point numbers and their calculations are limited, and you need finally adjustments.

- - - Updated - - -

How do I go about figuring how to convert the Real World Measurements into KSP Measurements? I know that Kerbin is 10 times smaller than Earth is.

Unique conversion does not exist, because KSP does not have all physical aspects which have had an effect to orbit selection of real spacecrafts. You have to first decide what things you want to.

I’m just wondering if there are any tips or tricks to equally space Satellites like

Real world's trick is very accurate determination of position and velocity, orbit predictions and frequent small corrections. KSP have no such disturbances but it also do not have ways to put satellites to enough accurate orbits. Even if you edit savefile to get perfect orbital parameters, smallest possible errors will increase, because accuracy of floating point numbers and their calculations are limited, and you need finally adjustments.

[KerikBalm]

How do I go about figuring how to convert the Real World Measurements into KSP Measurements? I know that Kerbin is 10 times smaller than Earth is.

Kerbin is not Earth - relative to its radius, the atmosphere is much thicker. A 70km orbit in KSP would be like a 700 km orbit IRL. Whereas a 50km orbit decays pretty fast, a 500km orbit for Earth will last a long time.

You can't convert them, they aren't the same proportions.

[mhoram]

2) have a look here: http://forum.kerbalspaceprogram.com/threads/28829?p=930468&viewfull=1#post930468

[Ippo]

Instead of just replying with irrelevant stuff that is not helping OP in anyway (I'm looking at you, Sirine), let's solve the problem, shall we?

Ok, so we know 3 points for sure:

• Low orbit
  
• Geostationary orbit
  
• Moon orbit: since Kerbin has 2 moons, I'll try using both Mun and Minmus
  

Here are the heights of those orbits, in kilometers:

[TABLE=width: 500, align: center]

[TR]

[TD=align: center][/TD]

[TD=align: center]RSS[/TD]

[TD=align: center]KSP[/TD]

[/TR]

[TR]

[TD=align: center]Low orbit[/TD]

[TD=align: center]~ 200[/TD]

[TD=align: center]~ 80[/TD]

[/TR]

[TR]

[TD=align: center]GSO[/TD]

[TD=align: center]35876[/TD]

[TD=align: center]2868.75[/TD]

[/TR]

[TR]

[TD=align: center]Moon[/TD]

[TD=align: center]384000[/TD]

[TD=align: center]12000 (Mun)

47000 (Minmus)[/TD]

[/TR]

[/TABLE]

Let's plot the 2 series:

The first series (assumin Moon = Mun) looks like a logarithm or a square root. I used MATLAB to fit them: the logarithm is a surprisingly bad fit, but the square root is just sweet (99.2% correlation):

The second series (assuming Moon = Minmus) looks more like an exponential instead: in fact, it's a very, very good fit (99.8% correlation):

So, to recap:

• if you assume that the Mun is the Moon, use 8.613 * sqrt(4.886 * x)
  
• if you assume that Minmus is the Moon, use 1344 * exp( 9.257 * 10^-6 * x )
  

P.S:

A) This is a game, its not flight simulation.

It's =/= its.

The game logic is NOTHING similar to real world.

Except for the simulation of orbital mechanics. I heard it plays a pretty big part in the game.

C) Tips:- Try playing it vanilla. Try enjoy the game for what it made for. Before you install a single mod.

He IS playing vanilla. Pay attention.

Edited September 26, 2014 by Ippo
Typo in a formula

[Sirine]

@Ippo: Your formula is flawed. OP is talking about Earth (not RSS), and KSP (LKO is about 69.something).

[KerikBalm]

I think in there you should have the radius of the planet, ie, surface is 600km vs 6,000 km from the cnter of mass, and then do all your other points from the center of mass

[Ippo]

@Ippo: Your formula is flawed. OP is talking about Earth (not RSS), and KSP (LKO is about 69.something).

RSS stands for Real Solar System: guess what solar system that mod is simulating...

I think in there you should have the radius of the planet, ie, surface is 600km vs 6,000 km from the cnter of mass, and then do all your other points from the center of mass

Mmm, I didn't think of that. I'll try later, now I have to leave for work, c ya!

[Sirine]

Earth is not sphere. RSS is.

It is Not compare-able.

[Red Iron Crown]

How do I go about figuring how to convert the Real World Measurements into KSP Measurements? I know that Kerbin is 10 times smaller than Earth is.

KSP uses real world units, i.e. meters, seconds, kilograms, so no conversion is necessary in that sense. If you are trying to simulate real world orbits, how you go about it depends on which part you wish to simulate closest. If you wish to match orbital periods (time to complete an orbit), you can use Kepler's third law to calculate it:

T = 2*pi*sqrt(a³/(G*M))

If you wish to simulate altitude in the sense of Kerbin looking like Earth from a certain altitude, it is the proportion of diameters that matters. Earth is about 10.5 times larger than Kerbin, so Kerbin from a 100km orbit looks like a lot like Earth from a 1050km orbit.

This is a game, its not flight simulation.

It is both. Squad advertises it as such:

"Fully-fledged, Physics-based Flight Simulation ensures everything will fly (and crash) as it should."

[metaphor]

Even though the orbital mechanics of the game are pretty much the same as real orbital mechanics, the length scales are completely different from the real world, and different from each other.

The Earth is 10.5 times bigger than Kerbin in diameter. But Earth's atmosphere is only about 1.6 times thicker than Kerbin's atmosphere, so as a proportion of diameter, Kerbin's atmosphere extends 6.5 times further out than Earth's atmosphere. The Moon orbits 30 Earth diameters out from Earth, but the Mun only orbits 10 Kerbin diameters out from Kerbin. So all the proportions are off, and you can't really scale Earth orbits to Kerbin orbits and vice versa, something will always be wrong in proportion.

As far as your second question goes, if you want equally spaced satellites in the same orbit you should pay attention to their orbital period and make sure it's the same. And you can use a single delivery vehicle for all the satellites. For example, if you want to put 4 satellites in an orbit with an 8-hour period, you could get your delivery vehicle into a 6-hour period, then deploy each satellite one by one at subsequent apoapses (and circularize each satellite by itself). That way each time you would arrive at apoapsis 2 hours ahead of the previous satellite, or 1/4 of an orbit, resulting in 4 satellites in an 8 hour orbit with 2-hour gaps between them.

[Turk_WLF]

Apparently I didn’t make myself that clear in my questions. Yes I know that is just a game/simulator not really related to the real world, but I just was using the ISS & the HST Orbits as reference points to put similar vehicles into similar Kerbin Orbits.

I just want to know is there a way I can figured out how the orbits would relate to Earth to get similar point Kerbin space/orbit.

Also I’m just looking for tips how to equalizing spacing between the satellites of 4 or more Satellites in the same orbit (like GSO).

I hope this helps to clarifies what I want to know.

[Rhomphaia]

Apparently I didn’t make myself that clear in my questions. Yes I know that is just a game/simulator not really related to the real world, but I just was using the ISS & the HST Orbits as reference points to put similar vehicles into similar Kerbin Orbits.

I just want to know is there a way I can figured out how the orbits would relate to Earth to get similar point Kerbin space/orbit.

Also I’m just looking for tips how to equalizing spacing between the satellites of 4 or more Satellites in the same orbit (like GSO).

I hope this helps to clarifies what I want to know.

For spacing satellites, the easiest way would be to launch all satellites on a carrier in an orbit with 3/4th the desired orbital period and the apoapsis at the desired altitude( or 5/4 orbital period and periapsis at the desired altitude) the circularize each satellite when it hits the apsis.

When comparing orbits, the 2 main metrics you could use are; orbital period vs ratational period of the parent body, and orbital radius vs parent body radius.

Unfortunately, kerbin has a comparatively huge atmosphere and high rotational speed so the radius equivelent of LEO orbits is usually in the atmosphere and the comparible orbital period is usually underground.

[metaphor]

Apparently I didn’t make myself that clear in my questions. Yes I know that is just a game/simulator not really related to the real world, but I just was using the ISS & the HST Orbits as reference points to put similar vehicles into similar Kerbin Orbits.

I just want to know is there a way I can figured out how the orbits would relate to Earth to get similar point Kerbin space/orbit.

Also I’m just looking for tips how to equalizing spacing between the satellites of 4 or more Satellites in the same orbit (like GSO).

I hope this helps to clarifies what I want to know.

You could start out with where the kerbals would put an ISS or Hubble equivalent. In other words, if the solar system looked exactly like the kerbal system, in what orbit would we put the ISS or Hubble? The ISS has the inclination it does since it has to be reachable by ships launched from the Russian space center, and it has the altitude it does so that it can stay above the atmosphere but low enough that debris nearby is deorbited relatively quickly. Since there is only one space center in KSP, and the atmosphere stops at 70 km, by following the same constraints the ISS in KSP would be in an equatorial orbit just above 70 km altitude (unless you had another space center you wanted to launch ships from). Hubble is as close to the Earth as it could be, to allow crewed repairs, but still outside of any significant atmospheric disturbances. So in KSP Hubble would also be right above 70 km in an equatorial circular orbit.

For a communications satellite equivalent, the best orbit would be geostationary, so the KSP equivalent would be keostationary orbit at around 2800 km (whichever altitude has an orbital period exactly equal to the rotation of the planet).

[tater]

Earth is not sphere. RSS is.

It is Not compare-able.

If you are willing to accept a possible ~0.5% error, it's a sphere.

[artwhaley]

The other thing that makes real world flights way different than KSP ones... Neither us nor the Russians have equatorial launch sites... so Hubble and the ISS both have inclined orbits. If you're really trying to model real world orbits, you'll have to take that into consideration too... and that greatly complicates launching to rendezvous - you have to time it right or you may wind up with major plane changes to make....

As another perspective... I wouldn't worry so much about the numbers - think about the mission profiles. Design an orbit for your telescope that puts it above other traffic, at an altitude that whatever you use to transport crew can reach it for service missions. You might incline it slightly so it stays mostly out of the way of future missions headed to deep space?

For your station, pick an orbit that is easily achievable from your launch site - put it where both your crew transports and your fuel lifters can reach it - but you may want it safely above or below your standard parking orbits. Consider how and where you want to land crew return ships.

As a slightly less realistic consideration - if you'll be using your station to park vessels prior to transferring out of Kerbal Orbit... you might pick an orbit high enough to get your desired time warp capability so you don't spend two weeks waiting for a launch window....

In short - have the same sort of conversations with yourself to pick orbits that NASA has for their real vessels... and arrive at orbits that are FUNCTIONALLY the same in the game, and don't worry if they're mathematically accurate.

[TythosEternal]

I think I understand what you are trying to do, in which case you should ignore all the nit-picky whiners and (as usual) just listen to Red.

T = 2*pi*sqrt(a³/(G*M))

This analogy will make the best translation between KSP Kerbin-centric and IRL Earth-centric orbits, but there is one more step: make sure you scale by the rotational periods of the respective planets (i.e., roughly 24 hours for Earth vs. 6 hours for Kerbin). That way, your ground-fixed orbits will line up. Basically, divide the period of the desired Earth-centered orbit by 4 before you plug it into the above equation.

[cantab]

For Earth orbits go like this:

Low Earth orbit: From 160 km to 2000 km.

Medium Earth orbit: From 2000 km to synchronous orbit.

Synchronous orbit: 35,786 km

High Earth orbit: Above synchronous orbit

The 2000 km LEO/MEO orbit is basically arbitrary, while the "bottom" of LEO and the height of the stationary orbit both come from physical situations.

For Kerbin we have those same physical considerations. The lowest stable orbit is just under 70 km, and it's actually sharply defined unlike with Earth where it's a gradual reduction in drag. Synchronous orbit is simply defined and is 3469 km. So it's only the low/medium orbit boundary that needs to be chosen.

And as it happens the game does give us a candidate value: 250 km, the altitude where science experiments switch from being "In space near" to "Space high over".

[arrowhen]

And as it happens the game does give us a candidate value: 250 km, the altitude where science experiments switch from being "In space near" to "Space high over".

Another possibility would be 240 km, the altitude where your minimum time-warp goes up to 1000x. If we assume that time-warp is an actual feature of the Kerbal universe (i.e., Kerbals developed the ability to alter their perception of time in order to counter their natural tendency to make terrible decisions out of boredom), that would likely be a practical consideration in establishing orbit boundaries.

I use 250 km as my standard MKO because it's an easy number to remember and gives me a bit of room to maneuver without getting dropped down into the slower warp zone.