2
$\begingroup$

With the technology available today, 01-01-2023, what is the lowest altitude at which we can orbit a satellite around earth?

$\endgroup$
8
  • 2
    $\begingroup$ Orbit for how many orbits? One? a year? forever? $\endgroup$ Dec 31, 2022 at 19:08
  • 2
    $\begingroup$ Define "orbit". Does it count as an orbit if there's a thruster firing continuously to counteract drag? Does it count as an orbit if the ending point is considerably lower than the starting point? Define "lowest": are you measuring the highest point on the orbit, the lowest point, the average altitude, or something else? $\endgroup$
    – Mark
    Dec 31, 2022 at 20:36
  • 2
    $\begingroup$ The lowest long-time satellite was GOCE. esa.int/Enabling_Support/Operations/GOCE It has orbited on 254 km for about 3 years and then on 229 kn for half of year. It has used xenon thrusters to maintain altitude. $\endgroup$
    – Heopps
    Dec 31, 2022 at 22:35
  • $\begingroup$ As other people mentioned, you could have thrusters cancelling the drag and reaching orbits even lower than GOCE's. $\endgroup$ Jan 1, 2023 at 23:46
  • $\begingroup$ @mhoran: number of orbits? at least >1. The higher the angular velocity, the lower the altitude can be. The ISS, which is orbiting at an average altitude of 400 km, travels at a speed of 8 Km/sec. But that was some years back. I expect today we might have technology with which we might be able to travel faster. In a way, the indirect question was how fast can we go today, and at that speed, what would be the altitude? $\endgroup$
    – Niranjan
    Jan 2, 2023 at 5:59

2 Answers 2

8
$\begingroup$

About 180 kilometers. Give or take 20 or 30 km.

This is actually one of those questions that lacks an unambiguous answer, because even the ISS, at around 400 km, requires periodic boosts to remain in orbit. So you have to specify what counts as "being in orbit". Does it count if you have to do a boost once every orbit? How about a steady small ion drive boost?

If you accept the latter, JAXA (the Japanese space agency) had a satellite meant specifically to address this question. It was called SLATS and nicknamed Tsubame, and the lowest it orbited without using chemical thrusters was 181.1 km. It's been recognized in Guinness World Records as the lowest-orbiting earth observation satellite. It orbited for a week at a little over 167 km using chemical thrusters for additional boosts.

I can't find a source for this, but I suspect a dense, solid projectile could orbit for at least a handful of orbits, without boosts, at similar altitudes.

$\endgroup$
3
$\begingroup$

Astronomer and Astrophysicist Jonathan McDowell (Homepage; Twitter), who in his spare time maintains the General Catalog of Artificial Space Objects (GCAT) and publishes Jonathan's Space Report (JSR) published a paper in Acta Astronautica issue 151 (October 2018), pages 668–677 titled The Edge of Space: Revisiting the Kármán Line.

In this article, McDowell argues that the boundary of space should be defined as 80 km instead of 100 km or 50 mi which are the two common definitions. He presents multiple arguments for why this should be the case, most of which are not relevant to this question.

However, there is one argument made in the article which is relevant to this question: McDowell examines historical satellite data for 43000 satellites and finds that satellites in elliptical orbits which briefly "dip down" to a perigee as low as 80 km are still stable for at least two more orbits whereas satellites that dip down to a perigee below 80 km tend to re-enter in less than 2 orbits.

While this does not directly answer the hypothetical question posed by the OP what the lowest altitude is that we could accomplish, it gives a datapoint on what the lowest altitude is that we have managed to accomplish so far, which is a 80 km perigee for a short time in an elliptical orbit, i.e. in an orbit which spends most of its time above 80 km and only a short amount of time near 80 km.

McDowell also argues in the same paper that at altitudes below 80 km, atmospheric effects dominate orbital effects. This would imply that any object which does "orbit" below 80 km is not really "orbiting" but rather "flying" and thus should not be called a "satellite" or "spacecraft" but rather an airplane, rocket, missile, or some other kind of aircraft. This is the same argument also made by Theodore von Kármán and Andrew H. Haley in the definition of the von Kármán Line.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.