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From Why was the 100m Green Bank dish needed together with DSN's 70m Goldstone dish to detect Chandrayaan-1 in lunar orbit?

above: "This computer-generated image depicts the Chandrayaan-1's location at time it was detected by the Goldstone Solar System radar on July 2, 2016. The 120-mile (200-kilometer) wide purple circle represents the width of the Goldstone radar beam at lunar distance. The white box in the upper-right corner of the animation depicts the strength of echo. Inside the radar beam (purple circle), the echo from the spacecraft alternated between being very strong and very weak, as the radar beam scattered from the flat metal surfaces." Credit: NASA/JPL-Caltech. From here

From Why was the 100m Green Bank dish needed together with DSN's 70m Goldstone dish to detect Chandrayaan-1 in lunar orbit?

above: "This computer-generated image depicts the Chandrayaan-1's location at time it was detected by the Goldstone Solar System radar on July 2, 2016. The 120-mile (200-kilometer) wide purple circle represents the width of the Goldstone radar beam at lunar distance. The white box in the upper-right corner of the animation depicts the strength of echo. Inside the radar beam (purple circle), the echo from the spacecraft alternated between being very strong and very weak, as the radar beam scattered from the flat metal surfaces." Credit: NASA/JPL-Caltech. From here

Note that for optical tracking, a "passive reflector" would be a corner-cube retroreflector, or array thereof. There are several old ones on the Moon for tracking the Moon itself left by Soviet and US missions, and Beresheet had one as well though it is probably not operational.

It's possible future lunar satellites will cary retroreflectors as well. A solar sail put in LEO had one, as do some large communications satellites

• Could Beresheet's retroreflector array (still) be used?
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• How will the corner cube retroreflector array be used on Sentinel 3B?
• What exactly is a "Next Generation Lunar Reflector"? Difference in design and performance?
• How will The Planetary Society's LightSail 2 Spacecraft's retroreflectors be used?
• Planetary Society's LightSail Spacecraft's corner cube reflectors; how large, and corrected for aberration?

VLBI will be used to measure the location of the JWST in its halo orbit 1.5 million kilometers from Earth down to centimeters of accuracy. This is absolutely necessary to drive its delta-v budget for station keeping in its orbit to just a few meters per second per year. Part of the trick is also to use the solar shield as a solar sail (the Sun's photon pressure helps hold it in place just to one side of it's most stable halo orbit distance), but there's not much flexibility since it can't be steered completely independently from the telescope. (There is one axis of rotation possible; for some observations the telescope doesn't care how it is rotated around its optical axis).

VLBI tracking in cis-lunar space was tested and refined using lunar rovers and the ALSEP telemetry radio transmitters left on Moon by Apollo lander missions.

• Were the Apollo lunar ALSEP transmitter signals ever analyzed or used after the experiments were shut down?
• Were there any policies or technical reasons for powering down all Apollo ALSEPs in 1977?
• Why were the "perfectly functioning" seismometers placed by Apollo 12, 14, 15 and 16 astronauts all shut off in 1977?

VLBI will be used to measure the location of the JWST in its halo orbit 1.5 million kilometers from Earth down to centimeters of accuracy. This is absolutely necessary to drive its delta-v budget for station keeping in its orbit to just a few meters per second per year. Part of the trick is also to use the solar shield as a solar sail (the Sun's photon pressure helps hold it in place just to one side of it's most stable halo orbit distance), but there's not much flexibility since it can't be steered completely independently from the telescope. (There is one axis of rotation possible; for some observations the telescope doesn't care how it is rotated around its optical axis).

...Is the problem of tracking lunar satellites still an unresolved one?...

tl;dr: On July 2, 2016 the location of the at-the-time-dead Chandrayaan-1 spacecraft orbiting the Moon was determined by transmitting radar pulses from the Goldstone radar dish and receiving reflections with the Green Bank observatory.

This demonstration shows that it's possible, and that it is non-trivial to do radar detection and tracking of small spacecraft at the distance of the Moon.

There are now proposals both in China and the West to build dedicated deep-space radar networks.

• Does transmitting from a few dishes significantly improve the performance of radar surveillance from Earth at GEO and beyond? If so, how exactly?
• this answer to How can we install a radar on radio telescopes like FAST or GMRT?
• What would be a "big picture" understanding of how the orbits of Earth satellites are monitored?
• What will China's new "space station" in Argentinian Patagonia be used for?
• How did Argentina, Namibia, and Pakistan help China monitor and communicate with Chang'e 5?

Tracking is much, much easier and more accurate if the spacecraft is "not quite dead" and has at least a functioning coherent transponder.