GNSS satellites (at least GPS ones) are in Medium Earth Orbit (MEO). LEO satellites can use GNSS for positioning. Is this still possible for satellites in elliptical, such as Molniya, orbits? For geostationary satellites, all GNSS satellites will be in a relatively small solid angle (but still much larger than the earth one), but in principle, it should still be possible to use GNSS. How far up has GNSS-based positioning been used, and how does the precision degrade with distance to Earth, theoretically and in practice?
The furthest satellite that I have seen use GPS is the AO-40, an amateur built satellite. In fact, they did a research paper on the subject. The paper states that it was able to achieve a navigation solution at 60,000 km, which is about 1/6th of the way to the moon, and well beyond the belt of Geosynchronous satellites. I'm sure there are other satellites which have demonstrated this technology even further, but just to receive the signal beyond the GPS constellation is impressive.
It should be stated that this problem is difficult because the GPS antennas are all focused at the Earth, thus, not much radiation extends beyond the GPS constellation. Still, it can be done, if you do it carefully. Furthermore, there are now special receivers for HEO GPS reception, such as can be found here.
There is at least one mission that continues to try to break the record further away, being NASA's MMS mission. They have gone beyond AO-40's record to hit 70,000 km, since I originally wrote this answer.
Since the offer for the answer to be updated wasn't taken up I'll post it as a new answer.
As of August 6, 2021 it's still 70,135 km above Earth from 2015
- NASA.gov's NASA’s MMS Breaks Guinness World Record
- Space.com's High-Flying NASA Mission Sets New GPS World Record
- Science Daily's NASA's MMS breaks Guinness World Record
The Science Daily link contains:
NASA's Magnetospheric Multiscale mission, or MMS, is breaking records. MMS now holds the Guinness World Record for highest altitude fix of a GPS signal. Operating in a highly elliptical orbit around Earth, the MMS satellites set the record at 43,500 miles above the surface. The four MMS spacecraft incorporate GPS measurements into their precise tracking systems, which require extremely sensitive position and orbit calculations to guide tight flying formations.
From GuinessWordRecords.com's Highest altitude GPS fix:
- Who: MMS NAVIGATOR GPS RECEIVER
- What: 70,135 KILOMETRE(S)
- Where: UNITED STATES (GREENBELT)
- When: 13 MARCH 2015
The highest altitude GPS fix is 70,135 km above Earth, detected aboard NASA's (USA) spacecraft MMS Navigator, and relayed to Goddard Space Flight Center, Greenbelt, Maryland, USA, on 19 March 2015.
The GPS signals were captured by a NASA's own GPS receiver, named Navigator.
All records listed on our website are current and up-to-date. For a full list of record titles, please use our Record Application Search. (You will need to register / login for access)
NASA Goddard video MMS Breaks World Record:
LOUD, ANNOYING MUSIC warning!