For those who follow the world’s space programs, it is well known that things do not always go as planned. A mission can go very wrong with no warning leaving engineers and scientists scrambling to figure out what has happened and, if possible, correct the problem. While the history of space exploration is filled with instances where the brilliant efforts of ground controllers pay off and they are able to salvage a mission from the jaws of failure, sometimes that does not prove to be possible. One little-known and unfortunate example of the latter is NASA’s Surveyor 2 mission which was suppose to soft land on the Moon in September 1966 after its predecessor managed to do the same thing in the program’s first try less than four months earlier.

The Surveyor Spacecraft

Work began on the 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 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 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 on a direct descent trajectory towards 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. Roll was controlled by 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. 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. 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 instruments carried by the first Surveyors were a pair of slow-scan television cameras. One was pointed downwards to provide a view of the lunar surface and a footpad. These images would 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.

The second 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 7.3-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 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.

Surveyor’s launch vehicle was 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 to be a modified version of the Atlas D ICBM. The forward propellant tank was modified 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. Unfortunately, delays in the development of the Centaur forced NASA to adopt a direct ascent profile for the first Surveyor missions that required only a single burn of the Centaur with no stop in low orbit (see “50 Years Ago: The Launch of Atlas-Centaur 5”).

Unlike the later Apollo lunar landing missions, Surveyor was designed to make a direct descent to the lunar surface from its translunar trajectory 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, would be limited to the equatorial mare regions which had been initially selected based on photography from Ranger’s successful impact missions of 1964 and 1965 (see “50 Years Ago Today: The Launch of Ranger 7” and “50 Years Ago Today: The Launch of Ranger 8”) and appeared to be the safest landing sites for the early Apollo missions.

The Surveyor 2 Mission

The primary objectives of the first Surveyor mission were fairly straightforward: demonstrate that Surveyor could be launched, communicate as well as be controlled from the Earth and successfully land on the surface of the Moon via a simple, nearly vertical descent profile. Surveyor 1, launched on May 30, 1966, accomplished these minimal objectives as well as most of its “low priority” objectives of returning images and a wealth of engineering data from the lunar surface (see “Surveyor 1: America’s First Lunar Landing”).

The objectives of the program’s second mission, designated “Surveyor B” before its launch, would build on the success of Surveyor 1. The primary objectives of the Surveyor B mission were to soft land on the Moon at a site east of Surveyor 1 in order to demonstrate an oblique approach and landing up to 25° out of the local vertical. Once on the surface, Surveyor B would return post-landing television imagery and other engineering data like its predecessor.

With its objectives similar to its predecessor’s, the SC-2 spacecraft for the Surveyor 2 mission carried the same complement of instruments as Surveyor 1 but had a slightly increased launch mass of 1,000 kilograms due to a number of modifications made to key spacecraft systems based on flight experience. The landing site chosen for the mission was located near the center of the visible face of the Moon at 0.05° S, 0.67° W in Sinus Medii. The landing site, which had been photographed during the Lunar Orbiter 1 mission (see “Lunar Orbiter 1: America’s First Lunar Satellite”), would allow an approach that was 23° to the local vertical and provide a close up inspection of yet another potential Apollo landing site.

The launch vehicle assigned to the Surveyor B mission was the second “operational” Atlas-Centaur designated AC-7. The first launch window for the Surveyor B mission extended from about 5:51 to 7:33 AM EST on September 20, 1966 with an arrival on September 22 after a 63-hour transit. If this window were missed, shorter launch windows were available during each of the following three days with later launch times on each successive day. The last chance for launch on this month was provided by a 14-minute window starting at 7:35 AM EST on September 23.

The Atlas first stage of AC-7 was erected on the pad at Cape Kennedy’s Launch Complex 36A on June 22, 1966 only three weeks after the launch of Surveyor 1. This was followed a week later with the mating of the Centaur upper stage and the beginning of almost six weeks of testing. Meanwhile, the Surveyor SC-2 spacecraft arrived at the Cape on July 19 for the start of its preparations for launch. After SC-2 was encapsulated in its fairing, it was mated to AC-7 on August 9 for a series of integrated tests. Following the completion of these initial tests, SC-2 was demated a week later for the removal of test items and final preparations for launch. SC-2 was mated with AC-7 for a final time on September 16 for its September 20 launch.

After dealing with a series of minor issues during the countdown, 137-metric ton AC-7 finally lifted off from pad 36A at 7:31:59.8 EST (12:31:59.8 GMT) on September 20, 1966 only 8.5 seconds before the close of the first day’s launch window. With a nominal performance of both stages of the Atlas-Centaur, the Centaur’s pair of RL-10 engines were shutdown after a total of 686.2 seconds of powered flight with the stage and what was now called Surveyor 2 travelling at a velocity of 10.53 kilometers per second. After coasting for 66 seconds, Surveyor 2 separated from the spent Centaur and started aligning itself into its cruise attitude. Surveyor 2 was now in a 165.0 by 784,170 kilometer geocentric orbit with an inclination of 33.4°. After turning and performing a retro maneuver by expelling its 118 kilograms of residual cryogenic propellants to distance itself from Surveyor 2, the spent Centaur was in a 168 by 588,992 kilometer orbit which placed it a safe 730 kilometers from the spacecraft five hour after separation. In its new trajectory, the spent Centaur would miss the Moon by 5,675 kilometers.

Tracking of the receding Surveyor 2 showed that it had been injected into an almost perfect trajectory to hit its target. It was calculated that only a minor 1.20 meter per second course correction burn would be required 16½ hours after launch to adjust the aim point and arrival time of the spacecraft. At 5:00:02 GMT on September 21, Surveyor 2 began its midcourse maneuver. Unfortunately, Surveyor’s Vernier Engine 3 failed to ignite during the planned 9.8-second burn sending the spacecraft into a tumble. Initially it was hoped that the nitrogen gas jets could be used to regain control, but at 5:14:29 GMT ground controllers commanded the attitude control system off after half of the gas supply had been consumed leaving just under a kilogram of nitrogen left and the spacecraft tumbling at a rate of about 58 RPM.

Ground controllers quickly determined that Vernier Engine 3 had failed to ignite and attempted to get it started. At 7:28:20 GMT, the engines were commanded on for a two-second burn but again only two verniers actually fired. Next, the verniers were commanded on five times in succession for 0.2 seconds for five minutes followed by a two-second thrust period. After the fifth such sequence of burns, a 2.5 second burst was made at high thrust. Following another sequence of five 0.2-second firings starting at 7:44:56 GMT, a final attempt was made to open the fuel pressure regulator valve using high thrust for 20 seconds. None of the 39 attempts to get Vernier Engine 3 started worked leaving Surveyor 2 tumbling at a rate of about 136 RPM. While the exact cause of the engine failure was never determined, it seemed that the flow of MON-10 oxidizer to the engine had been affected preventing it from igniting.

With a landing now completely out of the question, it was decided to use Surveyor 2 for a series of engineering tests during the time it had left before its inevitable lunar impact and destruction. The spacecraft was commanded to erect its solar mast to get mechanical data on the system. But since Surveyor 2 was unable to lock onto the Sun, it would continue on battery power alone. The propulsion system’s helium gas was also purposely vented to provide information on the reliability of the system’s pressure sensor. The spacecraft landing radar was activated at 9:13 GMT on September 22 as it approached the lunar surface in a test of a weakened battery’s ability to power this power hungry system.

With the spacecraft tumbling at 146 RPM, Surveyor 2 was commanded to ignite its retrorocket at 9:34:29 GMT on September 22. Contact with Surveyor 2 was maintained for about 30 seconds with the tumble rate dropping to 111 RPM as the retrorocket fired. The now silent spacecraft hit the lunar surface at 2.7 kilometers per second at 5.5° N, 12° W southeast of the crater Copernicus. While a subsequently formed failure review board failed to pinpoint the cause of the vernier engine failure, it did recommend a series of changes to the propulsion system to prevent a number of possible causes from affecting a future Surveyor mission. In the mean time, preparations for the Surveyor C mission continued with the hope of launching in the spring of 1967.

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Related Video

Here is a collection of film footage showing the preparation and launch of Atlas-Centaur 7 carrying NASA’s Surveyor 2 spacecraft.

Related Reading

“Surveyor 1: America’s First Lunar Landing”, Drew Ex Machina, May 30, 2016 [Post]

“50 Years Ago: The Launch of Atlas-Centaur 5”, Drew Ex Machina, March 2, 2015 [Post]

General References

J. Jason Wentworth, “A Survey of Surveyor”, Quest, Vol. 2, No. 4, pp 4-16, Winter 1993

Second Surveyor Launch Set for September 20, NASA Press Release 66-248, September 14, 1966

Surveyor II Mission Report: Mission Description and Performance, JPL Technical Report 32-1086, April 1, 1967

Atlas-Centaur Flight Performance for Surveyor Mission B, NASA Technical Memorandum TM X-1616, April 1968