# Talk:Geosynchronous orbit

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geosynchronous orbit != geostationary orbit

    a geostationary orbit must be:
1. geosynchronous
2. circular
3. equatorial (zero inclination)


GEOSYNCHRONOUS LAG The main article says: "Every satellite in geosynchronous orbit has an average altitude of about 35,780 km (about 22,233 miles).." Let us think. For a non-zero inclination, the 35,786 km radius will always produce the 24-hour period of circling around the Earth, but of the circling on a plane different from that of the equator. Therefore for an external (extratrrestial) observer, the longitudinal rotation will be lagging behind the Earth's rotation, and for the terrestrial observer the longitude of that satellite will be constantly increasing (i.e. apparently travelling westward). Therefore, the 24-hour period of rotation of any non-zero-inclination satellite can only be achieved by multiplying its orbital velocity by the tangent of the inclination; that will mean a lower orbit. Am I wrong? OldtimerUS (talk) 21:46, 13 March 2008 (UTC)

Science fiction writer and scientist Arthur C. Clarke wrote about this belt in 1945, hence the name. Clarke's and Herman Potočnik's visions of geostationary communications satellites were made a reality in 1962 with the launch of Telstar.

Hang on, this gives the wrong impression that Telstar was a geostationary satellite - it wasn't, the first one was Intelsat 1 in 1965. -- Arwel 09:46 Apr 15, 2003 (UTC)

Removed: Free Body Diagram section/:insert diagram here/:insert Text or other math here.Mat-C 18:09, 30 Apr 2004 (UTC)

The empty Free Body Diagram section still served a purpose in that it would be useful if it was not blank. Leaving it there may motivate someone to add a diagram, without it, it is far less likely. { MB | マイカル } 18:20, Apr 30, 2004 (UTC)

That is why it is here, "todo" lists don't belong in articles. What exactly is this diagram? I might be able to draw it.Mat-C 18:48, 30 Apr 2004 (UTC)

(I've saved my changed, but a bit more to do at some point)Mat-C 18:48, 30 Apr 2004 (UTC)

Free body diagram. I suggest you check out the free body diagram on page 2 of this pdf since it is esentially what we need mionus the whole tower thing. Although since I am not a physicist I can not be sure if this is all that is needed, it seems to me that this is a pretty sparse diagram. { MB | マイカル } 21:15, Apr 30, 2004 (UTC)
Here is another great place for inspiration.
• I removed Clarke's and Herman Poto&#269nik's visions of geostationary communications satellites were made a reality in 1962 with the launch of Telstar as it looks plain wrong to me (not a geo-synch orbit)
• I stated that "geostationary" can be applied to other non-earth bodies, feel free to separate that bit out of the first paragraph if thats not the case.Mat-C 18:51, 30 Apr 2004 (UTC)

I agree with moving a lot of the geostationary orbit stuff to that page, however I believe there may be a case for the Derivation of orbital period stuff to be here as well - it shows how to calculate the orbital period for all non-active circular geosync orbits. Only problem now is we have two geostationary links Mat-C 20:20, 1 May 2004 (UTC)

Are there uses for circular geosynchronous orbits that aren't geostationary, i.e. geosync orbits that are circular but not at the equator? If there is such a use then I agree that it would make sense to put your derivation here as well.
I previously considered merging geosynchronous orbit and geostationary orbit, but it seems like there is plenty to write about each separately. Wmahan. 20:41, 2004 May 1 (UTC)

The section on history of geosynchronous comm satellites indicated that they are no longer used for telephone communications. I edited this because it is no longer so - in fact, I am employed by a telephone company that must use satellites to reach over 35 of its communites, since there is no practical or affordable way to extend either fibre optic or microwave to those locations. Doubtless, places in Alaska and Greenland are in the same situation, and as Russia's telecom infrastructure improves, it will have to do the same. gcapp@praize.ca

Ships at sea also use satellite phones, so I added that. Would it be useful to link to Inmarsat?

Might it be useful to include a derivation of the height of geosynchronous orbits, and maybe also the height of the orbit in the case of the Earth? I've just had to do it for an essay and it's pretty easy. I've just started using Wikipedia though so I'm all fingers and thumbs with the equation writing system.--Kimonokraken 18:00, 23 April 2006 (UTC)

the size of the orbit is already there: "A circular geosynchronous orbit in the plane of the Earth's equator has a radius of approximately 42,164 km (from the centre of the Earth) or approximately 35,786 km (22,236 statute miles) above mean sea level."
The derivation is at Geostationary orbit#Derivation of geostationary altitude.
—wwoods 21:31, 23 April 2006 (UTC)

It seems like there is no consensus to merge, so I am removing the merge tag. — Swpb talk contribs 23:09, 21 February 2007 (UTC)

## synchronous/sidereal period

what about an orbital period that has half the sidereal rotation period of the Earth so that it appears above the same spot exactly twice in one day or integer multiples of the rotation period. Couldn't these be considered geosynchronos orbits, after all they are synchronised with the earth rotation period? I don't know whether they're useful though...

The Molniya satellites are in 12-hour orbits. They're (roughly) over the same area every other orbit.
However, while the orbital period is intentionally a fraction of the Earth's rotational period, calling it "synchronous" is more likely to cause confusion than clarification.
—wwoods 17:39, 11 Apr 2005 (UTC)
The term for the orbit of a satellite with a 12 hour period is semi-synchronous. So yes, you are right that it is snychronised in some manner. GPS satellites are also in this category as they have 12-hour periods. --Owlmaster08 (talk) 11:43, 6 February 2008 (UTC)

## Geostationary orbit

Hello! Can someone please add a section on Geostationary orbits? Avraham 02:40, 15 December 2006 (UTC)

Perhaps we should merge Geostationary orbits into Geosynchronous orbits? On WikiProject Rocketry, these two pages were listed as "needing attention" under the merge/split section. Seeing as they are quite similar, I was wondering what everyone else thought about such a merge. --Matthew Desjardins (14:23, 3 February 2008 (UTC))
Keep Separate These subjects are related but their practical implications are different. Geostationary particularly references objects above the equator where there are specific applications and limited "real eastate" available. Geosynchronous is a much broader concept and deserves a separate treatment. The question starting this thread is unclear - it looks to me as though this article has clearly referenced the Geostationary orbit article for quite some time. Both articles could use improvement but they should each evolve separately. As I am a layman, insert haha's below if I've misinterpreted anything :) Franamax (talk) 02:35, 3 February 2008 (UTC)
Ok, thanks. I will remove the suggestion on the Rocketry page --Matthew Desjardins (14:23, 3 February 2008 (UTC))
Keep Separate Whilst a Geostationary orbit is a special case of a Geosynchronous orbit, that would be a poor reason to subsume Geostationary orbit into Geosynchronous orbit. If this merge were to happen, then by similar logic Geostationary transfer orbit would have to be merged into Geosynchronous orbit. What is the point of the proposed merge? Geostationary orbits deserve an exclusive article, as is currently the case. BlueOrb (talk) 07:39, 4 February 2008 (UTC)
I agree that they should be kept separate. Also, I dislike the change where it says that a geostationary orbit with null eccentricity and inclination is sometimes called geostationary. I would definitely say that it is usually or customarily called geostationary. I do not know about spacecraft design, but in the field of telecommunication satellites, the word geostationary is much more common than geosynchronous. This is true in Europe but I think it is true elsewhere, too. So I advocate for changing the sometimes with usually, normally or the like. Fpoto (talk) 14:51, 13 July 2008 (UTC)

## Synchronous orbits around objects other than the Earth

Article reads: Synchronous orbits exist around all moons, planets, stars and black holes — unless they rotate so slowly that the orbit would be outside their Hill sphere or so fast such an orbit would be inside the body.

There are two problems with this statement. 1. Talking about syncronous orbit around a black hole is not entirely meaningful. A black hole does not have a surface and the rotational period is somthing that can only be deduced indirectly. Also gas gigants don't have a surface and it is hard to decide their rotational period (for a recent example see: http://www.space.com/scienceastronomy/060503_saturn_day.html). Also one would have to take into account relativistic effects such as frame draging in the case of a fast rotating black hole, which is not mentioned in the article.

2. The statement that syncronous orbits don't exist for very fast rotating bodies is theoretically true, but can in practise only happen for small objects such as astroids and very small moons. Large objects and black holes are held together by gravity and the centrifugal accelration exactly maches the gravitational force at the geosyncronous orbit, thus, an object rotating so fast that a geosyncronous orbit would only exist inside the object must be held together by another force than gravity and the object has to be small.

Fixed Lessthanideal (talk) 01:35, 2 December 2012 (UTC)

## Reason for change from semi-major axis to altitude

To quote in detail more the reference from Vallado... "This book defines several categories of orbits by the forces, including gravity, which influences their motions: low-Earth orbits (LEO-to about 800 km altitude, a<7178 km); mid-Earth orbits (MEO-from about 800 km to 30,000 km altitude, a=7178 km to 36,378 km), and geosynchronous orbits (GEO-at about 35780 km altitude, a about equal to 42158 km)."

If the Geosynchronous orbit is not Geostationary, then the altitude will vary slightly as it orbits. The altitude (commonly the variable h) is easily confused with the semi major axis (commonly the variable a). The altitude is the height above the surface of the earth. The semi-major axis is a basic parameter of an ellipse, which for circular orbits is equal to the radius of the orbit (center of the Earth to the satellite). Semi-major axises are fixed, assuming no perturbations. Altitudes change throughout the orbit but often times a single number may be given as an average altitude.

I am not an expert, but will earn a BS in Astronautical Engineering in about 3.5 months. --Owlmaster08 (talk) 08:56, 6 February 2008 (UTC)

I've been uncomfortable about this change since it happened. I think the original change to "altitude" was prompted by confusion over the difference between altitude - distance above the average radius of the Earth - and orbital distance - distance from the centre of gravity (I know, I know, there's a barycentre in there somewhere).
The unresolved problem here is that the article currently says that a GSO has "an average altitude of about 35,780 km". If I understand the orbital equation correctly, that is the maximum altitude at zero eccentricity, a geostationary orbit is a special case where this is the constant altitude, and the general case GSO is an ellipse whose semi-major axis is equal to (35,780 + big-E/small-R). Am I right so far?
If I'm still on track, consider the special case of an elliptical orbit with zero eccentricity (I think that's right - the Earth is the centre of the ellipse). Now 35,780 is the maximum altitude, so it simply can't be the average altitude.
Now extend this to eccentric orbits - "maximum" doesn't work either. I don't see any alternative to returning to describing the orbit in terms of semi-major axis distance, and correcting the axis length to the correct figure. Unlike Homer Simpson, I've never been to space, so I'm putting this out for comment. Please feel free to correct my ignorance! :) Franamax (talk) 01:06, 8 July 2008 (UTC)
Unfortunately the change was in fact wrong. The third Keplero's law states that the major axis of an orbit is linked to the orbital period. This means that all geosynchronous orbits share the same major axis, which is what is correctly written in the formula at Geosynchronous_orbit#Orbital_characteristics. This contrasts with the first two lines, where it speaks about average altitude while, in fact, it should speak about maximum altitude. I am going to correct this problem... All right, while correcting I realised that it should not speak of maximum altitude either, because that depends on eccentricity. I could easily find the max and min altitudes using the ellipse equations, but average is a more subtle concept, because average in space and average in time would give different results, so I do not know how useful that would be.
In summary, I edited in order for it to be correct, now I ask: should we add max and min altitudes? Should we delete the reference to the book, while all that is needed is the major axis, which is clearly treated in the relevant page and is already linked? Fpoto (talk) 09:36, 11 July 2008 (UTC)
Do you mean max and min altitudes for an eccentric orbit? Wouldn't the minimum altitude then technically be zero, i.e. just above the Earth's surface?
Well, no, why ever? That depends on eccentricity. If it is zero, we have a geostationary orbit, if you increase it just a little you begin to detach from circularity, so the minimum altitude will be lower. Fpoto (talk) 15:24, 13 July 2008 (UTC)
One problem with citing a single figure for any altitude, if I understand correctly, is that altitude is measured above mean sea level. Since the Earth is an oblate spheroid, this figure will be different for an equatorial orbit vs. a polar orbit.
That is still another issue, but it is not important in this context, as we are speaking about altitude above mean sea level, meaning that we take the Earth as a sphere. The fact is, mean altitude is different depending what you are averaging on, as described in Semi-major_axis#Average_distance. Fpoto (talk) 15:24, 13 July 2008 (UTC)
One possibility is to just discuss altitude for a zero-eccentricity orbit, as in "For an orbit with zero eccentricity, the maximum orbital altitude is xx,000 km above the Equator and yy,000 km above the poles." I'm not sure whether that makes things better or worse :) Franamax (talk) 00:41, 12 July 2008 (UTC)
As I wrote above, I think this is not very important. I am not even sure that average altitude is important at all. Is it? Does the Vallado book cited by Owlmaster08 share any light on this? The quote reported above only says that sometimes average altitudes are given, and nothing more. Fpoto (talk) 15:24, 13 July 2008 (UTC)

## terrestrial

It says "terrestrial communications facilities (microwave, fiber-optic), even undersea" - terrestrial isn't through a cable such as fiber-optic, is it? Not according to the Wikipedia page on terrestrial. —Preceding unsigned comment added by 85.211.159.225 (talk) 19:59, 24 February 2008 (UTC)

Actually, the Wikipedia page on terrestrial right now (and on 24Feb) is a disambiguation link that begins with "Terrestrial refers to things having to do with the land". Fibre-optic cables are laid on, under, or very close to the ground. "Land" can also refer to ground under water - when a ship sinks, we talk about it "landing" on the bottom; and I can own a piece of "land", even if part of it is underwater; so I think terrestrial does survive the narrow definition. Think "land" as opposed to "space". Maybe that sentence in terrestrial needs to be firmed up a bit though... Franamax (talk) 00:42, 8 July 2008 (UTC)
In telecommunications, terrestrial is usually contrasted with satellite and deep space. For example, you have terrestrial wireless communications (usually abbreviated to wireless comm), satellite wireless communications (usually satellite comm) and so on. Fpoto (talk) 15:30, 13 July 2008 (UTC)

## Definition of GEO

GEO actually stands for Geosynchronous Equatorial Orbit (Earth is given by "Geo" in "Geosynchronous") I know I read this in a booster manual and will look for a citation. I haven't changed it because I'm new to Wikipedia as an editor. Featherwinglove (talk) 15:18, 27 July 2013 (UTC)

More reliable sources with alternate definitions are welcome, but unless you can argue that the NASA reference already in the article is somehow not reliable, the existing definition with the reference should stay.  Thanks, Unscintillating (talk) 15:57, 27 July 2013 (UTC)
(head->wall) I thought I read it in the glossary of the Delta II or Delta IV User's Guide, but the latest edition gives it as Geosynchronous Earth Orbit. Of course, definitions change and this might have happened; it might be a symptom of how our Space Age has waned and become more Earth-centric since the 1960s. For "LEO", I prefer to think of it as "Low Energy Orbit" instead of "Low Earth Orbit" because low altitude circular orbits have similar purposes over every body: taking advantage of Hohmann and Oberth effects for transfers to higher orbits or escape trajectories, reduced synodic periods with both launch sites and destinations, close observation of the body you're orbiting, ease of access from and communications with the surface, etc.. I know I'm the exception in using LEO that way. Featherwinglove (talk) 18:55, 27 July 2013 (UTC)
Got it: Ariane 5 User's Manual Issue 5 Revision 1, 2011 July pp. 0.11 at http://www.arianespace.com/launch-services-ariane5/Ariane-5-User%27s-Manual.asp The Proton Launch System Mission Planner's Guide 2009 July edition has GEO standing for just "Geosynchronous Orbit" (no Earth, no Equatorial.) Atlas V Launch Services Mission Planner's Guide 2010 March edition doesn't have any occurrence of "GEO" and uses GSO instead (it doesn't even have a "GEOMETRIC" or "GEOGRAPHIC" to distract Ctrl-F on a case-sensitive search!) As for the NASA reference you're referring to, um... is that the "For Students > Grades 5-8" reference? (Argument that this reference might not be reliable is the same as the argument that this beautiful cutaway of the Saturn V rocket might not be the one to go to for authorative information: https://xkcd.com/1133/) Featherwinglove (talk) 23:02, 27 July 2013 (UTC)
Alright, ref confirms so I've added it to the page and the geostationary orbit page. — Reatlas (talk) 05:33, 28 July 2013 (UTC)
I think it's important to convey that there isn't a consensus in the industry about what the Clarke Orbit should be called (despite being named that by the IAU itself, which is hard to beat in terms of "official", I have never once seen it referred to as "Clarke Orbit" in technical literature.) I'll never stop laughing if the industry winds up inheriting whatever consensus the community of Kerbal Space Program (the game) reaches regarding KEO, or KSO, or GKO, or Klarke Orbit ...if they ever reach a consensus, that is. Featherwinglove (talk) 11:53, 30 July 2013 (UTC)