Surveyor

Surveyor (BDB Landvermesser) demonstrated the feasibility of soft lunar landings and gathered detailed surface data needed for Apollo crewed landings. Surveyor 1-4 were launched on Atlas LV-3C and the subsequent three missions on Atlas SLV-3C. The craft does not orbit but decelerates from impact trajectory using the Star-37 retro motor, which then separates and the Surveyor descends on its three hydrazine engines. Engines cut off 3.5m above the surface to avoid contaminating the landing site. An alpha spectrometer experiment replaced the auxiliary battery used in early missions.

Due to delays in development of the Centaur upper stage, the Surveyor Orbiter mission concept was instead carried out by the smaller Atlas Agena-launched Lunar Orbiter.