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Questions regarding Low Earth Orbit or LEO, which refers to orbits at an altitude between approximately 160 kilometers / 100 miles and 2,000 kilometers / 1,200 miles.

The very-low-earth-orbit tag has no usage guidance, but it has a tag wiki, can you help us summarize it?

  1. Should we give a numerical value for the bottom end of LEO at 160 km, or some other altitude, or should we leave it unspecified in the tag description, other than perhaps at least one orbit around the Earth should still be possible to qualify?
  2. SpaceX and the FCC agree in official documents that there is such a concept as very-low-Earth orbit. For tagging purposes what usage guidance should we provide?

Some potentially related posts in meta:

and in the main site:

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    $\begingroup$ McDowell implied in "The Non-Kármán Line" that the difference between LEO and MEO was to be based on time: the boundary is where an Earth revolution takes 2 hours, but they rounded it up to 2000 km (1250 mi). Perhaps such a line could be drawn between VLEO and LEO too. One hour perhaps, if that's possible. $\endgroup$
    – user43968
    Sep 18, 2021 at 5:52
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    $\begingroup$ According to this calculator, it takes 1 hour 27 min 30 sec for a revolution at 151 km (94 mi) altitude. A possible boundary to be set. keisan.casio.com/exec/system/1224665242 $\endgroup$
    – user43968
    Sep 18, 2021 at 6:12
  • $\begingroup$ @Giovanni Since SpaceX and the FCC have very-low-Earth orbits at several hundred kilometers, perhaps VLEO can just be a subset of LEO? And for both, the only practical lower limit could be as simple as "likely to make it all the way around the Earth once"? I don't see any benefit to arbitrarily choosing a specific number. The guidelines are just meant to be helpful to users when choosing tags, they aren't meant to be rigid definitions of terms. $\endgroup$
    – uhoh
    Sep 18, 2021 at 6:26
  • $\begingroup$ I don't see why one should distinguish between LEO, MEO et cetera in the first place. Only geostationary/-synchronous orbit is a peculiar type of orbit, all other ones are just lower or higher or intersecting with it. As for tags, one may put/add the "orbit" tag to a tag of the atmospheric altitudes in question: "thermosphere" or "exosphere". This way, the other orbit types become superfluous (except geostationary) and VLEO might be retained as not precisely defined. $\endgroup$
    – user43968
    Sep 18, 2021 at 7:12
  • $\begingroup$ In the diagram you can see an altitude around 180 km (600K ft) between the end of Argon and the beginning of Helium. This altitude could be used for discernment as well. lh3.googleusercontent.com/proxy/… $\endgroup$
    – user43968
    Sep 18, 2021 at 7:15
  • $\begingroup$ @Giovanni this is Stack Exchange. We have the tags. As shown in the question LEO has 300+ questions and it started in 2013. You are welcome to post "Should we merge LEO and MEO tags?" as a new question and see how others feel. It's best to include a discussion of what problem the proposed change solves. $\endgroup$
    – uhoh
    Sep 18, 2021 at 7:18
  • $\begingroup$ Currently the LEO tag is defined as above 160 km (100 mi). Hence anything below is certainly VLEO or a parking orbit. Users may use VLEO if the orbit goes beneath 100 mi at some point. $\endgroup$
    – user43968
    Sep 18, 2021 at 7:40
  • $\begingroup$ Here is another depiction supporting SE's current stance: researchgate.net/profile/Pietro-Carlo-Boldini/publication/… $\endgroup$
    – user43968
    Sep 20, 2021 at 11:03
  • $\begingroup$ @Giovanni there is really no such thing as "SE's current stance" on this. The tag was written and adjusted grammatically back in mid-2013 when the site started and it hasn't received any attention until your edit. $\endgroup$
    – uhoh
    Sep 20, 2021 at 15:31
  • $\begingroup$ I mean the current description, that LEO is 160-2000 km (100-1200 mi), and that VLEO logically is beneath. The 160-2000 km were standing there before my edit, I edited the conversion only. $\endgroup$
    – user43968
    Sep 20, 2021 at 15:42
  • $\begingroup$ @Giovanni ya I got it, the numbers are from 2013, a lot has changed since then! $\endgroup$
    – uhoh
    Sep 20, 2021 at 15:44

2 Answers 2

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There is no point defining lower limits of our LEO or VLEO tags such that they end at some arbitrary number of kilometers. If a question is about an orbit one kilometer less than the lowest number, then someone may think a new tag is needed.

I propose the following tag usage for Space Exploration SE:

The LEO tag : from 2,000 kilometers / 1,200 miles down to the point where the spacecraft can barely make one orbit around the Earth. Below this, use the tag.

The VLEO tag : A subset of LEO orbit. Use this tag only for maintained orbits low enough that regular boots or continuous thrust is used to maintain altitude. Examples include GOCE and the lower Starlink satellites, especially those that orbit substantially below the ISS.

note 1: SpaceX and the FCC agree to refer to them as being in very-low-Earth orbit in official documents.

note 2: I think this is the least obtrusive way to proceed as virtually no retagging would be needed. VLEO is a "specialty concept" and if the specialty tag is missing no harm is done. LEO will continue to be the default tag for all orbits under 2000 km.

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  • $\begingroup$ I agree "VLEO" may be a subset of "LEO", but don't mix that up with orbital vs sub-orbital. Suborbital flights may go to MEO altitudes but still remain suborbital. Mercury-Redstone 2 reached an apogee of 253 km (157 mi). In that case, it's probably proper to use the sub-orbital tag and thermosphere tag. Likewise, if a spacecraft reaches orbital velocity but doesn't complete the orbit, it may use the VLEO tag, or perhaps there should be a parking-orbit tag. $\endgroup$
    – user43968
    Sep 20, 2021 at 15:53
  • $\begingroup$ @Giovanni as I've explained above, we're discussing tags, not definitions. If you think you have a superior set of usage guidance for all of these tags, summarize them in your own answer, explain why the changes improve the site and discuss how many (hundreds of) existing question posts written over the last ten years will have to be retagged. $\endgroup$
    – uhoh
    Sep 20, 2021 at 15:59
  • $\begingroup$ I'm doing the same you are doing here, and I agree with your opinion, except sub-orbital can be used at higher altitudes, and VLEO at lower ones as well. $\endgroup$
    – user43968
    Sep 20, 2021 at 16:01
  • $\begingroup$ @Giovanni so its not the same, so go check how many existing questions will have to be retagged. What is the number? How is your way better? $\endgroup$
    – uhoh
    Sep 20, 2021 at 16:02
  • $\begingroup$ Aren't Mercury-Redstone flights under the tag sub-orbital (if it would matter)? $\endgroup$
    – user43968
    Sep 20, 2021 at 16:03
  • $\begingroup$ @Giovanni I've proposed an answer. If you have a better one, please post it as an new answer post. $\endgroup$
    – uhoh
    Sep 20, 2021 at 16:04
  • $\begingroup$ My number is the same as yours: where a spacecraft can complete one revolution is LEO/VLEO. $\endgroup$
    – user43968
    Sep 20, 2021 at 16:04
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    $\begingroup$ I think you didn't get I'm unregistered. Unregistered users cannot post questions and answers on meta, we can only comment. $\endgroup$
    – user43968
    Sep 20, 2021 at 16:26
  • $\begingroup$ @Giovanni Oh! I didn't realize that. Okay got it. $\endgroup$
    – uhoh
    Sep 21, 2021 at 0:51
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I'm going to propose that for the purposes of our tag's lower altitude limit:

we leave it unspecified in the tag description, other than perhaps at least one orbit around the Earth should still be possible to qualify.

and for the tag we don't specify an upper altitude limit except that it's somewhere below 400 km and requires fairly aggressive station-keeping and altitude maintenance propulsive maneuvers.

The idea being that tag usage guidance is only meant to help question authors choose which tags to add, and should be consistent with the existing body of questions on the site already.

I'll wait a few weeks, and if no objections I'll make the changes.

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