One of the first things a human instinctively does when seeing something interesting is to take a closer look and touch it. While this may seem to be pretty straightforward, doing so with a robotic spacecraft hundreds of thousands of kilometers (and more!) away might not always be possible. While the first Soviet and American spacecraft to land successfully on the Moon during 1966 provided us with our first tantalizing views of the lunar surface using what were then state-of-the-art electronic cameras, we had no means of reaching out and touching anything that was seen. This changed with NASA’s Surveyor 3 mission launched on April 17, 1967. For the first time in the history of space exploration, a spacecraft would land on another world and use a remote controlled robotic arm to touch and investigate another world.
The Surveyor Spacecraft
Work began on NASA’s Surveyor program in May 1960 under the responsibility of Caltech’s Jet Propulsion Laboratory (JPL) in Pasadena, California (for details on the early history and development of Surveyor, see “Surveyor 1: America’s First Lunar Landing”). Built by Hughes Aircraft Company (whose space division is now part of Boeing), Surveyor was arguably the most advanced lunar spacecraft of its day. The basic 2.4-meter tall structure consisted of a simple 27-kilogram tetrahedral frame made of tubular aluminum alloy members. In each of the three lower corners was a landing leg equipped with an aircraft-style shock absorber and a footpad of crushable honeycomb aluminum. The total span of the legs, once deployed, was 4.3 meters. Rising from the apex of the frame was a mast upon which was mounted a gimballed planar high-gain antenna and a solar panel supplying up to 85 watts of electrical power to the lander’s rechargeable silver-zinc batteries. From the footpads to the top of its mast, Surveyor stood three meters tall.
Buried inside the spacecraft’s frame was a Morton Thiokol-built 91-centimeter diameter TE-M-364 solid propellant rocket motor that would provide between 35.5 to 44.5 kilonewtons of thrust, depending on the motor’s temperature at ignition. This 656-kilogram motor, which would later be used as the third stage in various Delta launch vehicles models flown in the 1970s and as the final “kick stage” for the Pioneer and Voyager missions to the outer planets, would be used to negate most of Surveyor’s motion towards the Moon as the lander approached the lunar surface.
Surveyor also carried a second propulsion system for midcourse corrections and attitude control during the main retrorocket burn as well as for the final descent. This system consisted of three vernier engines fueled by monomethylhydrazine hydrate with MON-10 (a mixture of 90% nitrogen tetroxide and 10% nitric acid) serving as the oxidizer. These engines could be throttled by command of the spacecraft’s flight control subsystem producing between 130 and 460 newtons of thrust each. Yaw, pitch, and descent rate were controlled by selective throttling of the engines while roll was controlled by swiveling a single gimballed vernier. During the trans-lunar coast, Surveyor’s attitude was controlled by a set of six nitrogen gas jets, each providing 270 millinewtons of thrust.
All the temperature sensitive electronics were carried in two thermal boxes mounted to the frame. These compartments were covered with 75 layers of aluminized Mylar insulation and the tops were covered by mirrored glass thermal regulators. Compartment A, which maintained it internal temperature between +4° and +52° C, carried a redundant set of receivers and ten-watt radio transmitters, the batteries, their charge regulators, and some auxiliary equipment. The second box, Compartment B, was designed to maintain the temperature between -15° and +52° C. This compartment carried the computer “brains” of the spacecraft which controlled all aspects of the lander’s operation using a total of just 256 commands. Mounted elsewhere on the frame were star sensors, a pair of radar systems for landing, low-gain antennas, propellant, and helium pressurization tanks.
A total of 30 kilograms of instrumentation were carried by the first Surveyors which were considered “engineering models”. Most were engineering sensors such as strain gauges, accelerometers, rate gyros, temperature sensors, and so on to be used to make more than two hundred measurements of the spacecraft’s performance and condition. While not specifically designed for investigating the lunar environment, many of these measurements could be used to determine some of its basic properties including surface mechanical properties and its temperature.
The only true scientific instrument carried by the initial batch of what would be seven “Block I” Surveyors was a slow-scan television camera. The camera was mounted in a 1.65-meter tall mast attached to the spacecraft’s framework. The camera pointed up into a movable mirror that allowed the camera to view 360° of azimuth and from 60° below to 50° above the normal plane of the camera. The 7.6-kilogram camera package was canted at a 16° angle to offer a clear view of the surface between two of the footpads out to the lunar horizon 2½ kilometers away. The camera was fitted with a 25 to 100 mm zoom lens that offered a field of view of between 25.3° and 6.4°. The aperture could be set between f/4 and f/22 and the lens could be focused from 1.2 meters to infinity. A shutter was also included so that various integration times could be used to obtain the ideal exposure. While the nominal exposure time was 150 milliseconds, exposures as long as about thirty minutes could be accommodated. The typical resolution of the camera was one millimeter at a distance of four meters. By combining a series of images taken in a stepwise fashion at various azimuth and elevation angles, panoramic mosaics of the spacecraft and the surrounding terrain could be created.
The camera was also fitted with a filter wheel containing clear and three color filters. With the aid of calibration targets mounted at various points of the spacecraft, pictures taken through red, green, and blue spectral filters could be reconstructed back on Earth to yield full-color views of the lunar surface. The camera could only operate in real time via remote control from Earth using a total of 25 commands. The primary means of transmitting images was through the high-gain antenna. Using this powerful antenna, an image would be broken up into 600 scan lines and transmitted back to Earth in 3.6 seconds. The use of the less powerful low-gain antennas, which served as a backup, would permit an image to be broken up into 200 lines and would require 61.8 seconds to transmit.
A second television camera was included in the original Block I Surveyor design which was pointed downwards to provide a view of the lunar surface and a footpad. These images were to be transmitted during Surveyor’s final approach starting at an altitude of 1,600 kilometer to allow the landing site to be pinpointed, along with providing information on the surrounding terrain. As it turned out, however, this camera was never used on the first two flights in order to simplify the already complex landing sequence. Later, the requirement was deleted and the camera was removed altogether since NASA’s Lunar Orbiter missions were providing the needed detailed images to help interpret the Surveyor findings and place them into a regional context (see “Lunar Orbiter 3: Preparing for Apollo”). Originally it was planned that a series of “Block II” Surveyor spacecraft would carry a much wider array of scientific instruments to perform more detailed studies of the lunar surface.
Surveyor’s launch vehicle was one of NASA’s most advanced rockets called the Atlas-Centaur. The Centaur upper stage used liquid hydrogen and liquid oxygen (LOX) as propellants – the first rocket stage to do so. This combination provided up to half again as much thrust than a like mass of conventional propellants then in use. The Atlas booster used with the Centaur was a modified version of the Atlas D ICBM. The forward propellant tank was altered to accept the wider and heavier upper stage and a new MA-5 engine assembly providing ten percent more liftoff thrust than when the baseline MA-2 system was used.
In order to maximize its payload and launch widow flexibility, the Atlas-Centaur was designed to first place its payload into a low parking orbit. The pair of RL-10 engines powering the Centaur would then reignite at the proper injection point to send the Surveyor lander on its way to the Moon. Due to problems with the development of the Centaur and its in-orbit restart capability, the initial two Surveyor missions were forced to use direct ascent trajectories to the Moon which required only a single burn of the RL-10 engines. With the successful test flight of Atlas-Centaur 9 on October 26, 1966 where the Centaur finally demonstrated its in-orbit restart capability by sending a dynamic model of a Surveyor lander, designated SD-4, into a simulated lunar trajectory, the way was finally clear for the technique to be used in future Surveyor missions.
Unlike the later Apollo lunar landing missions, Surveyor was designed to make a direct descent to the lunar surface from its translunar trajectory about 65 hours after launch with no intermediate stop in lunar orbit. Since Surveyor was designed with the capability of landing on the Moon with an approach trajectory substantially off of the local vertical, most of the lunar hemisphere facing Earth was accessible to Surveyor. Early flights, however, were limited to the equatorial mare regions of what was called the “Apollo landing zone” which appeared to be the safest landing sites based on orbital photography. It was intended that the initial Surveyor missions would provide ground truth data on these proposed sites to support the upcoming Apollo lunar landing missions.
Preparing for the Third Mission
As preparations were being made for the third Surveyor mission, designated “Surveyor C” before launch, the Surveyor program got some bad news. On December 13, 1966 the Block II Surveyor missions were cancelled and along with them, the opportunity to study the lunar surface with a much wider array of scientific instruments. As a result, Surveyor program managers decided to incorporate some of the Block II science payloads already completing development on the remaining five approved engineering flights of the more limited Block I spacecraft.
The first piece of experiment hardware selected for flight was a remote controlled mechanical arm. Formally known as the Soil Mechanics Surface Sampler (SMSS), this arm consisted of a simple tubular aluminum pantograph with a 13-centimeter long, five-centimeter wide scoop attached to the end. One electric motor on the SMSS allowed the pantograph to extend outwards from 58 to 150 centimeters while another opened and closed the door on the scoop. A third motor allowed movement through 112° of azimuth while a fourth provided 42° of motion in elevation. Used in conjunction with Surveyor’s slow-scan television camera, the SMSS would be operated remotely in near-real time by an operator on the Earth to provide information on the mechanical properties of the lunar soil up to a depth of half a meter. The SMSS would give scientists their first chance to touch the surface of the Moon.
The SMSS was attached using the mount which originally held Surveyor’s recently deleted descent camera. The SMSS had to be modified to use the existing camera wiring harness to supply power and commands from the ground to operate the device. Since only a single telemetry channel was available, the original mix of sensors on the SMSS to measure strain, acceleration and position at various points were removed. Instead, only a measurement of the current being drawn by the individual SMSS electric motor in use at any time would be sent back to the ground to allow engineers to roughly estimate the force being applied by the arm. The SMSS would be capable of reaching anywhere from 0.6 to 1.6 meters from the lander in a three meter arc starting from Footpad #2 and from one meter above the surface to as much as 0.45 meters below. All together, the SMSS hardware had a mass of 3.8 kilograms while its separate electronics compartment came in at 2.9 kilograms.
As a result of the loss of Surveyor 2 due to an unexplained malfunction of one of its three vernier engines during the mission’s midcourse correction (see “Surveyor 2: Things Don’t Always Go As Planned”), changes were made to the propulsion system testing procedures of Surveyor C and subsequent spacecraft to avoid a repeat of the failure. Surveyor C also included a pair of flat beryllium mirrors on one of the landing legs. A 25 by 23 centimeter mirror and a smaller 24 by 9 centimeter mirror would provide views of the underside of the Surveyor lander allowing an assessment of how the lander’s vernier engines disturbed the lunar soil. The total launch mass of Surveyor C was 1,036 kilograms – the heaviest so far in the series.
The objectives of the Surveyor C mission were chosen to support the upcoming Apollo lunar landings. The primary objectives were to land in the equatorial Apollo landing zone east of Surveyor 1 (so that a landing out of the local vertical could be demonstrated) and then return television images of the surface. The secondary objectives included obtaining information on the bearing strength, radar reflectivity and thermal properties of the lunar surface as well as observe the effects of the SMSS on the lunar surface material using the television camera.
Several landing sites for the Surveyor C mission were available for a planned launch in April 1967. A landing on some comparatively rugged terrain in Sinus Medii was considered with a launch on April 15 or 16 but, after the loss of Surveyor 2, project management did not want to take the risk. Instead, a smoother site to the west at 3.33° South, 23.17° West in Oceanus Procellarum was chosen. The area had been imaged by NASA’s Lunar Orbiter 1 and 3 missions (see “Lunar Orbiter 1: America’s First Lunar Satellite“) and was eventually designated as “Site 7” for a future Apollo landing. The 60-kilometer wide target area could be reached with a launch as early April 16 but Surveyor C would arrive in the dark an hour before local sunrise violating the requirement that Surveyor land no earlier than one hour after sunrise. Given the restrictions, the first possible launch window extended from 1:24 to 4:09 AM EST on April 17 and would allow a landing 26° off the local vertical on the evening of April 19/20 after a transit of under 66 hours. Launch windows up to about 2½ hours long were available about 1¾ hours later on each successive day until April 21.
The Surveyor 3 Mission
Atlas-Centaur 12 successfully lifted off from Cape Kennedy’s Launch Complex 36B at 3:05:01 AM EST (7:05:01 GMT) on April 17, 1967. After a nominal performance by Atlas 292D, the Centaur separated from its booster six minutes after launch. Ten seconds later, the Centaur’s pair of RL-10 engines were started for their 340-second burn needed to place the stage and its Moon-bound payload into a temporary 163 by 174 kilometer parking orbit inclined 30.0° to the equator. After coasting for 22 minutes and nine seconds, Centaur’s main engines ignited for a second burn of 111 seconds to head towards the Moon.
With the Centaur’s primary task completed, what was now called Surveyor 3 separated from its spent upper stage at 07:39:54 GMT. Tracking showed that Surveyor 3 was now in a 169 by 497,393 kilometer geocentric orbit while the spent Centaur, which had turned and used the venting of its residual propellants to move a safe distance away, was in a 167 by 353,419 kilometer orbit. At 21 hours and 41 minutes after injection, Surveyor 3 performed a midcourse correction with a delta-v of 4.2 meters per second to reach a slightly altered target point at 2.92° South, 23.25° West after a transit time just one second shy of 65 hours.
With about 45 minutes to go before landing, Surveyor 3 began to turn from its cruise attitude and align its retrorocket for landing. At 00:01:16 GMT on April 20, Surveyor 3 automatically ignited its engines 76 kilometers above the lunar surface while travelling at 2,626 meters per second. When the solid retrorocket motor burned out and was jettisoned 40 seconds later, Surveyor 3 was descending at 137 meters per second with the three vernier engines throttling as needed to maintain the descent profile based on data from its radar. Just seconds before landing, however, Surveyor 3 lost radar lock with the surface and switched to an inertial guidance mode where the vernier engines continued to fire instead of cutting off 4.3 meters above the surface as planned.
Surveyor 3 landed with a speed of just 2.1 meters per second at 2.94° South, 23.34° West at 00:04:16 GMT just 2.8 kilometers off its post-midcourse correction target but the spacecraft had still not settled onto the surface. With the engines still firing, Surveyor 3 bounced off the lunar surface and came down again 24 seconds later some 20 meters from its initial point of contact due to the slope of the terrain and the spacecraft’s 0.8 meter per second sideways motion. This was followed by a second hop of about 11 meters and a final 0.3 meter rebound before the vernier engines were finally shutdown by ground command 34 seconds after initial contact with the lunar surface and after 6.8 kilograms of additional propellant had been consumed. Surveyor 3 was now safely down on the lunar surface.
About 58 minutes after landing, Surveyor 3 returned its first images of the lunar surface with the Sun just 11° above the horizon. The quality of the images were somewhat degraded possibly because the camera’s pointing mirror had been dusted by some soil kicked up by the bouncy landing. There were also some difficulties moving the camera’s pointing mirror suggesting that some lunar soil had worked its way into the mechanism. These images revealed that Surveyor 3 had come down on the inner slope of an old 200-meter crater which was quickly spotted in high resolution photographs already returned by Lunar Orbiter 3. The subdued crater had rocks in a range of sizes present with blocks up to four meters long. Reflections from these larger blocks along with the slope may have affected Surveyor’s radar during landing. While Surveyor’s view was limited by the crater rim, images of the footpad impressions left by the multiple bounces combined with engineering telemetry during landing provided more information about the lunar surface. At very least, it confirmed that the lunar surface could safely support the Apollo Lunar Module (LM).
The day after landing, a pyrotechnic locking pin was fired freeing the SMSS to begin its first movements as it was observed via Surveyor’s slow-scan television camera. On April 22 at 05:07:01 GMT, Surveyor’s arm started the first bearing test on the lunar surface penetrating about 2.5 centimeters applying 50 newtons of force. Over the next ten days, the SMSS would perform a total of eight bearing tests, dig four small trenches and conduct 14 impact tests where the arm was dropped onto the surface from some predetermined height. With much effort, the SMSS was used to pick up a small rock and unsuccessfully attempted to break it in the scoop’s jaw in order to test its strength. The arm was also used to pick up and deposit a small amount of lunar soil on Surveyor’s landing pad so that it could be imaged through multiple filters.
All together, the SMSS responded to 5,879 commands during just over 18 hours of operation. Although some information was lost because of the poor quality of telemetry from the arm’s azimuth and elevation motors (possibly the result of soil kicked up and into the mechanism during the triple landing), the lunar soil was found to behave like a fine-grained terrestrial counterpart. The presence of a crust of brittle material 2.5 to 5 centimeters thick was also noted. Humanity’s first attempt to touch the face of another world with a mechanical arm was a success.
During the course of the long lunar day, Surveyor 3 continued to image and study its surroundings. On April 26 between 11:24 and 12:01 GMT, Surveyor 3 witnessed an eclipse from the lunar surface for the first time as the Earth passed between the Moon and the Sun (from the Earth’s perspective, this was a “lunar eclipse”). Surveyor took 20 images of the event through color filters and engineering data were used to determine how the lunar surface temperatures changed over time providing more data on its thermal properties. Four days later, Surveyor 3 took an additional series of 25 wide-angle images to create a crude color photo of the crescent Earth in the lunar sky – another first in the history of space exploration that was only possible because of the 14° tilt of the lander allowed it to see the Earth high above the horizon. In total, Surveyor 3 sent back 6,326 television images during its first lunar day.
Shortly after local sunset on May 1, 1967, Surveyor 3 was placed into hibernation. Unlike Surveyor 1, ground controllers never regained contact with the lander after local sunrise two weeks later to attempt operations during a second lunar day. Surveyor 3 would turn out to be the only successful lander of the series to last only a single lunar day. Despite the lost opportunity to gather some more data from unplanned extended operations, Surveyor 3 had met all of its objectives and easily exceeded expectations. Surveyor was turning into a useful tool for the exploration of the lunar surface.
While the stories of most spacecraft which have landed on other worlds normally ends with last contact, Surveyor 3 would have an interesting postscript. Since Apollo 11 had come down 6.9 kilometers from the center of its landing ellipse during humanity’s first crewed lunar landing on July 20, 1969, one of the tasks for Apollo 12 was to demonstrate a precision lunar landing. Proving such a capability would be required for future missions to more interesting sites where more precise targeting was essential. After much debate, Site 7 was chosen because of the presence of Surveyor 3 (which presented an obvious target) and despite the roughness of the area compared to other sites being considered.
At 06:54:45 GMT on November 19, 1969, the LM Intrepid with astronauts Charles “Pete” Conrad and Alan Bean aboard landed on the lunar surface only 163 meters northwest of Surveyor 3. One of the first things Conrad saw as he was descending the LM’s ladder during the beginning of the mission’s first lunar EVA almost five hours later was the long-silent spacecraft sitting inside what became known as Surveyor Crater. Conrad and Bean approached Surveyor 3 from the southwest during the mission’s second EVA on November 20. After photographing the lander and its surroundings, the astronauts removed the scoop from the SMSS, Surveyor’s television camera and some cable samples. These items were returned to Earth to see how 31 months of exposure to the lunar environment had affected them. To date, Surveyor 3 remains the only automated spacecraft to land on another world to be visited by a later crewed flight. Given the uncertain plans for future crewed lunar landings as well as recent moves to protect such historical sites, it might be the only one for quite some time to come.
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Here is some silent newsreel footage of the Surveyor 3 mission.
Here is some silent television video of Surveyor 3 using its SMSS to test the mechanical properties of the lunar surface (followed by footage of the SMSS being used in later Surveyor 7 mission).
And here is an excellent NASA documentary on the Apollo 12 mission which visited Surveyor 3, Pinpoint for Science.
“Surveyor 1: America’s First Lunar Landing”, Drew Ex Machina, May 30, 2016 [Post]
“Surveyor 2: Things Don’t Always Go As Planned”, Drew Ex Machina, March 13, 2017 [Post]
J. Jason Wentworth, “A Survey of Surveyor”, Quest, Vol. 2, No. 4, pp 4-16, Winter 1993
Third Surveyor Launch Slated at Cape Kennedy, NASA Press Release 67-85, April 14, 1967
Surveyor III Preliminary Science Results, PD-125, JPL, May 15, 1967
Surveyor III: A Preliminary Report, SP-146, NASA, June 1967
Atlas-Centaur AC-12 Flight Performance for Surveyor III, TM X-1678, NASA Lewis Research Center, November 1968