# What's the lowest (practical) altitude an object can be and still be considered in a stable orbit. **URL:** \ **Category:** Factual Questions\ **Created:** [September 1, 2017, 4:22am UTC](https://boards.straightdope.com/t/whats-the-lowest-practical-altitude-an-object-can-be-and-still-be-considered-in-a-stable-orbit/795227 "2017-09-01T04:22:51Z")\ **Posts on this page:** 9\ **Page:** 2
**Author:** ![watchwolf49](https://avatars.discourse-cdn.com/v4/letter/w/e9c0ed/32.png) [@watchwolf49](https://boards.straightdope.com/u/watchwolf49)\ **Post date:** [September 1, 2017, 10:27pm UTC](https://boards.straightdope.com/t/whats-the-lowest-practical-altitude-an-object-can-be-and-still-be-considered-in-a-stable-orbit/795227/21 "2017-09-01T22:27:30Z")
> [@Riemann](#): > > But obviously standing on the equator is not remotely similar to being in orbit anyway. As discussed, there’s a unique geostationary distance of 42km, or 36km above the surface. > > Theoretical orbital speed at the equatorial surface is 8km/s, or 17 times faster than the speed of the earth’s rotation. > [Orbital speed - Wikipedia](https://en.wikipedia.org/wiki/Orbital_speed#Tangential_velocities_at_altitude) The comparison was to the centripetal force … since we’re holding doubt that’s technically true for orbits … ---
**Author:** ![DPRK](https://avatars.discourse-cdn.com/v4/letter/d/4491bb/32.png) [@DPRK](https://boards.straightdope.com/u/DPRK)\ **Post date:** [September 1, 2017, 11:30pm UTC](https://boards.straightdope.com/t/whats-the-lowest-practical-altitude-an-object-can-be-and-still-be-considered-in-a-stable-orbit/795227/22 "2017-09-01T23:30:14Z")
> [@Riemann](#): > > But obviously standing on the equator is not remotely similar to being in orbit anyway. As discussed, there’s a unique geostationary distance of 42km, or 36km above the surface. ?? Surely this is a typo and should be 42 Mm / 36 Mm. Orbital speed approximately 3 km/s. ---
**Author:** ![Francis\_Vaughan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/francis_vaughan/32/3093_2.png) [@Francis\_Vaughan](https://boards.straightdope.com/u/Francis_Vaughan)\ **Post date:** [September 1, 2017, 11:45pm UTC](https://boards.straightdope.com/t/whats-the-lowest-practical-altitude-an-object-can-be-and-still-be-considered-in-a-stable-orbit/795227/23 "2017-09-01T23:45:26Z")
> [@Chronos](#): > > It’s also possible to have a mission that calls for an orbit somewhere in between LEO and GEO, or for one out beyond GEO, but those are fairly rare. The best example of an intermediate orbit is the constellation of GPS satellites. The combination of a need for efficient coverage of the globe and the need to have a spread of satellite positions over the sky as seen from Earth pretty much demands such an intermediate orbit. ---
**Author:** ![joema](https://avatars.discourse-cdn.com/v4/letter/j/a9adbd/32.png) [@joema](https://boards.straightdope.com/u/joema)\ **Post date:** [September 2, 2017, 4:19am UTC](https://boards.straightdope.com/t/whats-the-lowest-practical-altitude-an-object-can-be-and-still-be-considered-in-a-stable-orbit/795227/24 "2017-09-02T04:19:03Z")
> [@Francis\_Vaughan](#): > > The best example of an intermediate orbit is the constellation of GPS satellites. The combination of a need for efficient coverage of the globe and the need to have a spread of satellite positions over the sky as seen from Earth pretty much demands such an intermediate orbit. Besides GPS there are many satellites in medium earth orbits. This is a real-time graphical depiction of all known satellites and larger debris objects in earth’s vicinity. > **[Stuff in Space | stuffin.space](https://stuffin.space/)** > > Stuff in Space is a realtime 3D map of objects in Earth orbit, visualized using WebGL. - Click and drag to move it - Scroll mouse wheel to zoom in/out (or use +/- buttons at bottom right) - Position cursor over any object to see name and orbit - Click on object to see details The ring abound earth is geostationary satellites at 22,500 miles. ---
**Author:** ![eburacum45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eburacum45/32/8690_2.png) [@eburacum45](https://boards.straightdope.com/u/eburacum45)\ **Post date:** [September 2, 2017, 8:36am UTC](https://boards.straightdope.com/t/whats-the-lowest-practical-altitude-an-object-can-be-and-still-be-considered-in-a-stable-orbit/795227/25 "2017-09-02T08:36:09Z")
> [@Darren\_Garrison](#): > > I not too long ago read a SF novel with another especially low orbiting satellite (can’t remember which one, possibly a Neil Asher book?) One scene in the book takes place at an atmosphere-free, geologically dead planet where some past ancient civilization had carved a miles deep and wide trench around the circumference of the planet. A large city/satellite had been built (by a modern civilization) that orbited in that trench below the surface of the planet. _The Hydrogen Sonata_, by Iain M Banks. The city-habitat of Fzan-Juym orbits in an artificial canyon around Eshri. Bank’s last SF novel, unfortunately. ---
**Author:** ![MichaelEmouse](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/michaelemouse/32/101_2.png) [@MichaelEmouse](https://boards.straightdope.com/u/MichaelEmouse)\ **Post date:** [September 2, 2017, 10:45am UTC](https://boards.straightdope.com/t/whats-the-lowest-practical-altitude-an-object-can-be-and-still-be-considered-in-a-stable-orbit/795227/26 "2017-09-02T10:45:39Z")
Some informative graphs: [https://www.google.ca/search?q=orbital+decay+altitude&num=20&tbm=isch&source=lnms&sa=X&ved=0ahUKEwi226SYqIbWAhWESSYKHW-vDW8Q\_AUIfCgB&biw=1644&bih=883#imgrc=03O60X2nJkEzRM:](https://www.google.ca/search?q=orbital+decay+altitude&num=20&tbm=isch&source=lnms&sa=X&ved=0ahUKEwi226SYqIbWAhWESSYKHW-vDW8Q_AUIfCgB&biw=1644&bih=883#imgrc=03O60X2nJkEzRM:) As others have said, it’s nigh impossible to be 100% stable because of the atmosphere reaches far away. I think about 200km altitude (at both perigee and apogee) should give you a few days or weeks, though. A major consideration for ISS orbit altitude is likely to be the energy cost of getting people up there and back. Without that, the ISS could be higher and require less stationkeeping. ---
**Author:** ![Lucas\_Jackson](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lucas_jackson/32/303_2.png) [@Lucas\_Jackson](https://boards.straightdope.com/u/Lucas_Jackson)\ **Post date:** [September 2, 2017, 2:37pm UTC](https://boards.straightdope.com/t/whats-the-lowest-practical-altitude-an-object-can-be-and-still-be-considered-in-a-stable-orbit/795227/27 "2017-09-02T14:37:19Z")
> [@joema](#): > > Besides GPS there are many satellites in medium earth orbits. This is a real-time graphical depiction of all known satellites and larger debris objects in earth’s vicinity. > > [http://stuffin.space/](http://stuffin.space/) > > - Click and drag to move it > - Scroll mouse wheel to zoom in/out (or use +/- buttons at bottom right) > - Position cursor over any object to see name and orbit > - Click on object to see details > > The ring abound earth is geostationary satellites at 22,500 miles. Wow, thanks for that cool link. It’s getting crowded up there! ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [September 2, 2017, 4:05pm UTC](https://boards.straightdope.com/t/whats-the-lowest-practical-altitude-an-object-can-be-and-still-be-considered-in-a-stable-orbit/795227/28 "2017-09-02T16:05:09Z")
> [@DPRK](#): > > ?? Surely this is a typo and should be 42 Mm / 36 Mm. Orbital speed approximately 3 km/s. Yes, of course you are right on the order of magnitude error - thanks for that. The geostationary orbital speed is 3 km/s. The 8 km/s figure that I gave is the theoretical orbital speed at the earth’s surface. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [September 2, 2017, 4:26pm UTC](https://boards.straightdope.com/t/whats-the-lowest-practical-altitude-an-object-can-be-and-still-be-considered-in-a-stable-orbit/795227/29 "2017-09-02T16:26:04Z")
> [@](#): > > The ring abound earth is geostationary satellites at 22,500 miles. More specifically, the sharp ring is true geostationary satellites (geosynchronous in circular orbits above the equator), while the broad ring around that is geosynchronous satellites in inclined orbits. From the inclination, it looks like most of those were Florida launches. With an orbit like that, the satellite won’t be perfectly stationary relative to the Earth, but will trace out a figure 8 relative to the surface, which is sometimes good enough (and a bit cheaper). There are also some geosynchronous satellites in elliptical orbits, which at any given time includes most of the satellites above geostationary height. This allows you to spend most (but not all) of your time almost (but not quite) directly above a point on the Earth that isn’t above the equator, but the drawback is that while you’re over that point, you’re about twice as far away. You’d expect this, for instance, for spy satellites watching Russia. At any given moment, there will also be some of these satellites below GEO, but they’re harder to spot on that diagram since there’s a lot of other stuff there. [Previous page](https://boards.straightdope.com/t/whats-the-lowest-practical-altitude-an-object-can-be-and-still-be-considered-in-a-stable-orbit/795227.md?page=1)