Rendezvous radar

The lunar module carried two important radar systems that were tested prior to landing. The first checkout was for the rendezvous radar while the CSM was still nearby. This radar worked in conjunction with a transponder on the CSM to give the crew’ and the LM computer information about how far away the CSM was, how fast it was approaching and in what direction it was located. Although there were backup methods for the spacecraft to rendezvous, this radar was an important primary component for bringing the two spacecraft together. Its dish antenna wras attached to a 2-axis mount that permitted pan and tilt movement. When it started operating, it sw ept the view in front of the LM, looking for the CSM until a return signal from the transponder was found. The receiving horn was split into four so that if the dish were not exactly borcsighied on the CSM, the received signal would be stronger in one of the horns. The electronics could then operate to aim the antenna until all four horns received an equal strength signal. The angle of the dish then represented the direction to the CSM. The information from the radar wras factored in along with knowledge of the LM’s state vector and orbit to derive all the necessary information needed by the crew to make appropriate rendezvous manoeuvres.