What is the furthest Earth orbiting satellite?
What is its speed and purpose?
I don't have a list to find the highest, but I suspect that Spektr-R RadioAstron (used for long baseline radio interferometry) is one of the highest altitudes that isn't associated with a Lagrange orbit.
The Moon interacts with its orbit, so the apogee changes over time. According to the User Handbook
the apogee distance will vary from 286,938 to 371,233 km
It has a very high eccentricity, so I believe there are others with a greater semi-major axis. I'm not sure which measure the question might want for "farthest out"
I found the following "far out" spacecraft:
- TESS (Transiting Exoplanet Survey Satellite) recently launched, not in final orbit yet
- IBEX or Interstellar Boundary Explorer
Here are their IDs:
TESS 43435 2018-038A Spektr-R 37755 2011-037A IBEX 33401 2008-051A Geotail 22049 1992-044A
The problem is that for such high orbits, the gravity of the Sun and the Moon can push them around significantly so their orbits change over time, sometimes by quite a bit!
The all-time winner (of the four that I found) seems to be Geotail. Using historical TLEs shows Geotail's maximum semi-major axis of about 280,000 km or about 44 Earth radii, and a maximum apoapsis of over 500,000 km or about 81 Earth radii. However, according to the Japanese space agency's website (see also Wikipedia), the orbit is designed to cover the magnetotail over a wide range of distances: 8 Re to 210 Re from the earth. This is over 1,300,000 km from the Earth! In fact, some sections of that site and those of NASA/ESA suggest the maximum apogee may have been an even higher 220 Re, over 1,400,000 km distant!
This would not likely have been long term stable, and so after sampling the tail of the magnetosphere out there it was ramped down closer to Earth.
I have two plots for TESS, both current data from TLEs and future data (the big DOT) after it will use a close swing-by maneuver with the Moon and then another propulsive maneuver in order to reach its half lunar month orbit. Once that happens, TESS will be the longest period artificial satellite around the Earth, at least one with a fairly stable orbit and whose information is available publicly.
TESS has this orbit in order to spend most of its time staring at nearby stars looking for exoplanets, then it makes a close pass by Earth to download data, once every two weeks.
You can read more about how TESS' orbit works in this answer to the question TESS orbit and moon resonance.
I've put a plot of TESS' calculated orbit from Horizons below. The green, tightly repeating orbit is the Moon's. The red orbit, inclined, evolving, changing orbit is for TESS only for a few years currently in the Horizon's simulation. It's almost a miracle that it can remain so close to its orbit. Well, it's "just F=ma" (roughly), but it's still beautiful!
TESS might represent the highest non-Lagrangian Geocentric orbit that is stable over decades. It was carefully designed to have half the period of the Moon in order to cancel out perturbing effects. It is called a 2:1 resonant orbit. For orbits higher than that, lunar perturbations may become problematic.
Earth-Moon Lagrange orbits are Geocentric orbits that are in 1:1 resonance with the Moon (they are not lunar orbits). They will have their own stability issues and require station keeping. A particularly stable Geocentric orbit which is associated with the Earth-Moon Lagrange points is the Near Rectilinear Halo Orbit. Read more about it in the questions and their answers:
The Halo orbit associated with the Earth-Moon Lagrange L1 and L2 points are probably the highest Geocentric orbits that are also usefully stable. Instead of being perturbed by the Moon's gravity, they remain in resonance with it and use it to provide additional stability. However, they still require station keeping.
- Why is a near rectilinear halo orbit proposed for LOP-G (formerly known as Deep Space Gateway?)
- What is a near rectilinear halo orbit?
- LOPG/Deep Space Gateway - What is a cislunar orbit?
below: I've put a plot of TESS' calculated orbit from Horizons below. The green, tightly repeating orbit is the Moon's. The red orbit, inclined, evolving, changing orbit is for TESS only for a few years currently in the Horizon's simulation.
A late reply here, but perhaps it'll be of interest to those finding this post as I did. Space-Track is not especially helpful for tracking the really high-flying junk (it's not very important to them). Current record-holder for height is XL8D89E, an unidentified object in a roughly three-month orbit found by the Catalina Sky Survey in 2015. It's probably a recovery of an object found in 2006, though I can't say that I've actually linked the orbits. Information about several objects with orbital periods of a month or so, such as 2010-050B (Chang'e 2 booster), 2013-070B (Chang'3 booster), and some others, is available here.
It’s a bit of a cheat, but a satellite at L4 or L5 is roughly 100 million miles from Earth, quite stable, and has a one year period to its motion around Earth. That’s seems to be the farthest stable & orbit-like setup.
Whether one considers L4 and L5 “orbiting the Earth” is a question for another day...
It all depends on how you define "earth orbiting", and if the spacecraft still needs to be functional.
STEREO-Behind got out to more than 2AU, and it's on its way back now. As it orbits the sun at slightly more than 1AU, it will go "around" the Earth. Unfortunately, we're currently out of communications with it, and they don't know if they'll be able to recover it. (Although the closer it gets to Earth, the easier it should be... assuming it's not rolling so fast that communications would be impossible, or if it's rolling such that the solar panels aren't getting any power)
STEREO-Ahead is less than 1AU from the sun, so doesn't "orbit" the Earth.