Surveyor Program

The Surveyor programme was an early series of American robotic lunar landers developed to demonstrate the practicality of soft landings on the Moon in preparation for the Apollo crewed missions. Operated by the National Aeronautics and Space Administration (NASA) and managed by the Jet Propulsion Laboratory (JPL), the programme provided foundational engineering data, direct imagery, and scientific measurements during a pivotal phase of the space race. Seven Surveyor spacecraft were launched between June 1966 and January 1968, of which five successfully achieved soft landings, becoming the first United States probes to do so on any astronomical body. The programme’s success established the technological confidence required for human exploration of the lunar surface.

Background and Development

The Surveyor programme began in 1960 as NASA sought to acquire essential knowledge for future crewed landings, particularly concerning the lunar surface environment and the engineering systems required for safe descent. In 1961, Hughes Aircraft Company was selected to design and construct the spacecraft. The programme’s total cost was reported as 469 million USD, reflecting its strategic importance during a period of rapidly advancing space technology.
At the time, little was known about the mechanical properties of lunar soil. Before the Soviet Luna 9 mission in early 1966, there were significant uncertainties about the depth and consistency of the Moon’s dust regolith. Concerns persisted that a lander might sink into deep deposits, rendering a human landing attempt hazardous. Surveyor vehicles were therefore equipped with instruments such as robotic soil scoops, alpha particle scattering sensors, and magnets to study the soil’s chemical and mechanical characteristics.
The programme also served to test midcourse trajectory correction systems and advanced descent technologies including throttleable vernier engines, closed-loop terminal guidance computers, and radar altimeters. Demonstrating these systems in the hostile thermal and radiation environment near the Moon was a crucial step toward enabling the Apollo landings.

Mission Architecture and Flight Profile

Each Surveyor spacecraft was launched individually aboard an Atlas–Centaur vehicle, which injected the lander directly into a translunar trajectory without entering Earth orbit. The flight to the Moon typically lasted 63 to 65 hours. Upon arrival, the spacecraft executed a direct deceleration from a high-speed impact trajectory of approximately 2.6 km/s.
The initial reduction in speed was performed by a solid-fuel retrorocket that fired for roughly 40 seconds from an altitude of around 75 km. After this burn, the retrorocket and radar unit were jettisoned at about 11 km above the surface. The remaining descent phase was managed by three liquid-fuel vernier engines using Doppler radar guidance. In several missions, including Surveyor 5, operational anomalies such as helium leaks led to adjusted descent sequences.
To minimise contamination of the surface by exhaust plumes, the vernier engines were shut down approximately 3–4 metres above the lunar surface, allowing the craft to drop in free fall and land at a speed of roughly 3 m/s. Upon touchdown, engineering telemetry, temperature data, and video imagery were transmitted to Earth, with operations typically limited during the two-week periods of lunar night when solar power was unavailable.

Scientific and Engineering Contributions

Across the programme, Surveyor spacecraft transmitted tens of thousands of images revealing surface morphology, boulder distributions, horizon characteristics, and the texture of the regolith. The presence of firm load-bearing soil was verified through trenching experiments conducted by landers equipped with digging arms. These activities demonstrated that the lunar surface could safely support both robotic and crewed landers of the type planned for Apollo.
The missions also supplied data on the Moon’s physical environment, including surface temperature variations, reflectivity, chemical composition, and the behaviour of dust under mechanical disturbance. Additionally, Surveyor 7 contributed to early laser-illumination experiments, detecting beams projected from Earth-based observatories.
One of the most notable outcomes of the programme was the retrieval of parts from Surveyor 3 by the Apollo 12 astronauts in 1969. These components, including its television camera, were returned to Earth and examined to assess the long-term effects of lunar exposure on spacecraft hardware.

Overview of the Missions

Surveyor 1 (1966)Surveyor 1, the first of the series, was launched on 30 May 1966 and achieved a successful soft landing on 2 June in Oceanus Procellarum within the Flamsteed P ring structure. The spacecraft transmitted more than a month of imagery and engineering data, resuming activity after lunar night cycles and continuing to provide telemetry until January 1967. Its observations contributed to refining measurements of the Moon’s motion and orbit.
Surveyor 2 (1966)Surveyor 2, launched on 20 September 1966, experienced a malfunction during its midcourse correction burn. The resulting loss of control caused the spacecraft to impact the Moon at high speed on 22 September, making it one of the two unsuccessful missions in the programme.
Surveyor 3 (1967)Launched on 17 April 1967, Surveyor 3 landed in the Mare Cognitum region on 20 April. It transmitted 6,315 images, including early views of Earth from the lunar surface. An anomaly in its landing radar caused its vernier engines to continue firing after touchdown, leading to two unintended “hops” that damaged its systems. In 1969, Apollo 12 astronauts visited the site, retrieving hardware for analysis—the only time humans have examined an unmanned probe on another celestial body.
Surveyor 4 (1967)Surveyor 4 was launched on 14 July 1967 but lost communication 25 minutes before its expected landing in Sinus Medii. Evidence suggested a possible explosion of the retrorocket during its terminal descent.
Surveyor 5 (1967)Surveyor 5 launched on 8 September 1967 and landed in Mare Tranquillitatis on 11 September. Despite a helium leak affecting descent propulsion, it executed a successful landing. It transmitted 19,118 images and extensive scientific data until December 1967.
Surveyor 6 (1967)Launched on 7 November 1967 and landing three days later in Sinus Medii, Surveyor 6 became the first spacecraft to lift off from the lunar surface deliberately. On 17 November it performed a 25-second vernier burn that carried it several metres laterally before relanding, demonstrating controlled lunar ascent and manoeuvre capability.
Surveyor 7 (1968)Surveyor 7, the final mission, launched on 7 January 1968 and landed on the outer rim of Tycho crater on 10 January. It conducted extensive imaging and soil analysis and uniquely recorded laser beams directed at it from observatories on Earth. The mission objectives were fully completed before contact ceased.