Talk:Geosynchronous orbit

From Wikipedia, the free encyclopedia

WikiProject Physics This article is within the scope of WikiProject Physics, which collaborates on articles related to physics.
Start This article has been rated as start-Class on the assessment scale.
??? This article has not yet received an importance rating within physics.

Help with this template This article has been rated but has no comments. If appropriate, please review the article and leave comments here to identify the strengths and weaknesses of the article and what work it will need.
WikiProject Space
Space Portal
This article is within the scope of WikiProject Space.
Start This article has been rated as Start-Class on the assessment scale.
Related projects:
WikiProject Spaceflight WikiProject Spaceflight Importance to Spaceflight: Top

This article has been rated but has no comments. If appropriate, please review the article and leave comments here to identify the strengths and weaknesses of the article and what work it will need.



Contents

[edit] Previous discussions without headers

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)

[edit] 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)

[edit] 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)

[edit] 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.

[edit] 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)

[edit] 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)