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The sign accompanying the radar antenna. It reads

Apollo Rendezvous Radar Antenna

One of the most critical guidance and navigation systems developed for the space program was the Rendezvous Radar installed in the Apollo Lunar Module (LM). This system made it feasible for the LM to detach from the Command Module (CM), descend to the lunar surface, and then return to lunar orbit and search out and redock with the CM "mothership." A successful redocking between the two spacecraft was the only way that the two astronauts who had descended to the lunar surface could get back home safely, as the LM was not equipped with a heat shield for Earth reentry.

The unit on display to the right is an actual LM Rendezvous Radar Antenna. This system was the first solid-state electronic radar system to be used in space. The radar was used by the astronauts in the Lunar Module to search out and detected special guidance signals being sent out by the Command Module, waiting overhead in lunar orbit.

The LM's Rendezvous Radar System had the capability of detecting the Command Module from more than 400 miles away. The received signal was then used by the astronauts as a homing beacon to begin closing in on one another in a complex rendezvous and docking procedure.

When both spacecraft had redocked, the two lunar astronauts transferred all necessary hardware and stowed items, including film and moon rocks, back into the Command Module for the return home. The abandoned LM was then sent crashing back into the lunar surface to create artificial "moon quakes" for the seismic instruments left behind on the surface by the astronauts.

The Rendezvous Radar System was first tested in an Earth-orbit flight during Apollo 9. But, tis first true test in lunar orbit, more than 240,000 miles from the safety of Earth, was conducted by Tom Stafford and his Apollo 10 LM crew mate Gene Cernan, during their historic mission to the moon in May, 1969.

The photo below shows the Rendezvous Radar Antenna being tested in Earth-orbit by the Apollo 9 Lunar Module. The radar antenna, identical to the unit on display to the right, can be seen in the bottom center of the photo, attached to the Ascent Stage of the spacecraft. Tom Stafford and his Apollo 10 crew were the first to use this system in lunar orbit during their December, 1969 mission.

Note that Apollo 10 actually flew in May 1969; there was no Apollo mission in December 1969.

Also note that I only photographed the text of the sign, and not the Apollo 9 photograph to which the sign refers. The LM Rendezvous Radar Antenna is visible in numerous Apollo 9 photos, including AS09-20-3060, AS09-21-3185, and AS09-19-2973.