KGSS: Minmus-stationary orbits

[togfox]

The Kerbin Geographic and Science Society (KGSS) is a casual and open society of volunteers that like to inject a little bit of real life science into the Kerbal Space Program. Exploding rockets and designing bizarre planes is fun but once you learn basic rocket design and orbital mechanics you may feel the urge to do something more purposeful. For those looking for a mission with a reason, or a reason to do a mission, the KGSS invites you to attempt the below hypothetical mission:

Insert a satellite in Minus-stationary orbit

The KGSS needs to place a satellite in a geostationary orbit above Minmus to measure night/day surface temperatures over a five Minmus day period. It is how unknown what the correct geostationary altitude is or if Minmus can maintain craft in this orbit. Your mission is to:

- determine the correct geostationary orbit for Minmus

- determine if a craft can remain stable in this orbit

- to orbit Minmus for five Minmus days so surface temperature readings can be collected (hypothetical).

Variations: Kerbin/Mun geostationary orbit

Mods: Any

Restrictions: None

Rewards: Fun

Tips: You will need to calculate or google the appropriate orbital altitude. Mechjeb mod can also help you calculate orbital periods.

The KGSS tries to inject real (or hypothetical) science into your space missions. If you decide to attempt this mission then please share your findings in SPOILER tags so the rest of us can enjoy the same fun you had in discover the result. More information on the KGSS can be found here: http://kerbalspaceprogram.com/forum/index.php?topic=11388.0

[maltesh]

Minmus\' stationary orbit radius is significantly larger than Minmus\' SOI.

[SunJumper]

A geostationary object going around Minmus would be a telescope on Kerbin. As Minmus is tidally locked, it\'s geostationary height is some 40,000km.

[aphazael]

As Minmus is tidally locked, it\'s geostationary height is some 40,000km.

Your number may be correct, but your reasoning is not. Whether a body is tidally locked has no effect on it\'s geostationary radius/speed. This is determined solely by the body\'s mass

[Tim_Barrett]

It\'s impossible since Kerbin\'s gravity would affect it, and from any angle from minmus it would be spinning too slowly.

[maltesh]

The challenge is not completely insoluble, however.

In the KSP physics simulation, there are points where you can be A) In an unpowered orbit, and stationary relative to a point on Minmus\' equator, for the requisite time period.

Where these points are, I leave as an exercise for the player.

[Alchemist]

It\'s just how celestial mechanics work: for a tidally locked body the theoretical stationary orbit is always higher than the Lagrange points that are on the SOI border (we don\'t have the L-points, but the SOI radius is approximately the same).

IRL the only stationary points are the Lagrange points. In KSP we don\'t have them, but we can get on the same orbit around Kerbin just outside the SOI

[ggPeti]

If you think again carefully, you\'ll find that

In the KSP physics simulation, there are points where you can be A) In an unpowered orbit, and stationary relative to a point on Minmus\' equator, for the requisite time period.

is true.

[PakledHostage]

The challenge is not completely insoluble, however.

In the KSP physics simulation, there are points where you can be A) In an unpowered orbit, and stationary relative to a point on Minmus\' equator, for the requisite time period.

Good idea! The range of available sub-points are limited to a range of longitudes roughly 173° wide on the Kerbin-ward side of Minmus, but it is still better than a telescope on Kerbin\'s surface.

[ggPeti]

Which, by the way, would only work on one of the poles anyway.

[MaverickSawyer]

what about matching the orbit of Minmus, but be either ahead or behind it enough to be outisde its SOI, but close enough to still take detailed observations?

[SunJumper]

The geostationary orbit is at the altitude of the object where the planet\'s rotational speed is equal to the orbital period.

[MaverickSawyer]

Right, so if Minmus is tidally locked, placing something at the same altitude should produce the same results. After all, for such a long 'day', the orbit would be inside the SOI of Kerbin...

[togfox]

It\'s certainly fun to try. Getting the precise orbit will be nigh impossible with the current controls/engine but the principle can be tested. Of course, only two \'spots\' can be done like this - immediately before and immediately after the celestial body. I shall try.

[NovaSilisko]

Minmus being tidally locked was actually a mistake. Not sure if it will be resolved in 0.16 or not, but it most likely will be resolved at some point.

[SunJumper]

Another thing I thought of, Minmus needs a minimum diameter of some 200 - 400km to be spherical, yet it seems to be some 50km across, so maybe its shape is not too realistic.

[togfox]

Hmmm. I\'m not sure what you\'re saying. The diameter of minmus from pole to pole should be the same as equator to equator - you\'re suggesting it\'s not? There will be terrain variance of course. Are you suggesting something else?

[SunJumper]

No, bodies need to have a sufficient gravitational pull to have them relax into spheres. Either Minmus gets bigger, or it should be irregular.

[ggPeti]

But it is very irregular, its almost spherical shape is due to ice filling up the deep parts. And whatever kind of ice it is, it\'s very amorphous so it relaxes into a sphere easily.

[PakledHostage]

No, bodies need to have a sufficient gravitational pull to have them relax into spheres. Either Minmus gets bigger, or it should be irregular.

Like so many things in the Kerbol system, Minmus is extremely dense. (So are our beloved Kerbals... Coincidence?) This too would affect the radius at which it becomes spherical. I found an article that derives the potato radius of a celestial object. It shows that the radius at which a body can be expected to be spherical is a function of the body\'s density and the properties of the materials that it is composed of.

Minmus has a reference radius of 60 km (i.e. the radius that the altimeter is referenced to). It has a mass of about 4.23x10^19 kg. That gives it an average density of roughly 46700 kg/m^3. That\'s 9 times greater than the density of Earth! I think we need to just suspend our disbelief and accept that Minmus is mostly spherical.

[SunJumper]

Do these values agree with Minmus\'s gravitational force?

[sal_vager]

Sciency stuff

Oh well, there goes my theory in a puff of science

Density of mint icecream.

Density of the Earth.

[Divaglio3578]

The exact geostationary orbit around Minmus is 4303 1/2 kilometers. Much larger than its SoI