While NASA struggled to address issues with the Apollo program to land men on the Moon, its automated missions to the Moon during 1966 and 1967 had made spectacular progress. The Lunar Orbiter series had flown five largely successful missions in five attempts. Not only did the program meet its objectives to map potential landing sites for early Apollo missions, it also managed to map almost the entire lunar surface as well as provide high-resolution images of other sites of more scientific interest that could be visited by later missions (see the Lunar Orbiter page for descriptions of these missions). Likewise, the Surveyor landing missions had scored four successes in six attempts during this time providing the Apollo program with ground-truth data on the relatively smooth mare which would host the first manned lunar landings. With its objectives to support Apollo met, the final Surveyor mission, designated “Surveyor G” before launch, was free to pursue more science-oriented goals. Ultimately it was decided to target Surveyor G for a site in the lunar highlands adjacent to the prominent young crater called Tycho.
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 the 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.
The first “Block I” Surveyors were considered “engineering models” for the more advanced “Block II” versions of the lander which had been proposed. Most of the Block I instrumentation 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.
Originally, the Surveyor camera was also fitted with a filter wheel containing clear and three color filters so that color images of the lunar surface could be reconstructed back on Earth with the aid of calibration targets mounted on key points on the spacecraft. For the Surveyor 6 and G missions, the color filters were replaced with polarization filters with angles of 0°, 45° and 90°. Combined with information on the lighting and viewing geometry, these polarization measurements could be used to help characterize the properties of the lunar surface. As with the cameras used on the earlier Surveyor missions, 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.
The Surveyor G Experiments
With the cancellation of the more advanced Block II Surveyor missions on December 13, 1966 which would have explored the lunar surface with a wider array of instruments, program officials 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 third and fourth Block I Surveyor flights were selected to carry a remote controlled mechanical arm formally known as the Soil Mechanics Surface Sampler or SMSS (see “Surveyor 3: Touching the Face of the Moon”). The fifth and sixth Surveyor missions instead carried a new instrument known as the Alpha Scattering Experiment designed to measure the concentration of various elements in the lunar soil (see “Surveyor 5: Pulling Success from the Jaws of Failure”). For the final flight of the series, both instruments would be carried by the spacecraft for the Surveyor G mission, SC-7, in order to maximize the science return.
The Soil Mechanics Surface Sampler (SMSS) 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 deleted descent camera, which had been carried during the first two missions but never used. 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 was capable of reaching anywhere from 0.6 to 1.6 meters from the lander in a three meter arc 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.
The 13-kilogram Alpha Scattering Experiment carried by SC-7 consisted of three major components: a sensor head, a deployment mechanism and a thermally controlled electronics compartment. The sensor head consisted of a 17.1 by 16.5 by 13.3 centimeter high box on a plate with a diameter of 30.5 centimeters which would sit on the lunar surface once deployed. The sensor head was mounted on the spacecraft during flight and would be lowered to the lunar surface upon ground command by a nylon cord wrapped around a geared cylinder which would unwind under the action of lunar gravity in a series of controlled steps.
Once deployed on the lunar surface, a set of six small radiation sources composed of the artificial element, curium-242 with a half life of just 160 days, would bombard a small part of the lunar surface with alpha particles (essentially nuclei of helium-4 consisting of a pair of each of protons and neutrons) that would penetrate only about 25 micrometers into the lunar surface. A pair of alpha particle detectors located adjacent to the curium-242 sources would be used to detect the energy and number of alpha particles scattered by the lunar surface allowing the concentrations of elements heavier than lithium to be determined.
Four other detectors included inside of the sensor head would measure the energy and number of protons that were emitted by the lunar surface as a result of interactions with the alpha particles. These sensors would allow the concentration of boron, nitrogen, fluorine, sodium, magnesium, aluminum, silicon, phosphorus, sulfur, chlorine and potassium to be assessed. While stowed on the lander, the alpha particle and proton detectors in the sensor head were calibrated using small amounts of einsteinium-252 on the mounting platform. By measuring the concentration of elements present in the lunar surface, scientists could estimate what types of rocks made up the lunar surface. For the Surveyor G mission, the orientation of the SMSS was shifted 30° towards Footpad #3 compared to the way the arm was mounted on Surveyor 3 and 4. This allowed the SMSS to reach the sensor head of the Alpha Scattering Experiment so that it could be picked up and moved to sample multiple sites during the surface operations.
The SC-7 spacecraft also included a pair of metal bars (one magnetic and the other nonmagnetic) attached to one of the footpads just like the previous three missions. Observations of these 5.1 by 1.3 by 0.3 centimeter thick bars by the television camera would allow scientists to determine the magnetic properties of the lunar soil. For this mission, a pair of U-shaped magnets were also mounted on the bucket of the SMSS where they could be brought into contact with lunar surface material in a controlled manner.
As in earlier missions, SC-7 included a pair of small beryllium mirrors mounted on one of the landing legs. Both mirrors had convex surfaces (to provide a wide angle reflection) with the larger one measuring 25 by 23 centimeters and the smaller one being 9 by 24 centimeters. The purpose of these mirrors was to provide a clear view of the underside of the Surveyor lander allowing an assessment of how the lander’s vernier engines disturbed the lunar soil. For this mission, a flat 9 by 24 centimeter mirror was also mounted to the spacecraft’s mast to provide a view of the SMSS during surface operations from a different angle. An additional seven one-centimeter mirrors in view of the camera were mounted at various heights above the surface to monitor the accumulation of lunar dust.
The launch mass of SC-7 for the Surveyor G mission was 1,040 kilograms – the most massive of the series. After it had jettisoned its spent retrorocket and consumed its propellants during descent, the spacecraft would have a mass of at least 289 kilograms upon landing plus however much vernier engine and attitude control propellant were left after touchdown.
The Surveyor G Mission Plan
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 more conventional propellants then in use. Unlike the earlier versions of the Atlas-Centaur used to launch the first four Surveyor missions which employed a modified Atlas D ICBM for its first stage, Atlas-Centaur 15 (AC-15) to be used to launch the Surveyor G mission would sport the improved SLV-3C model of the Atlas. In this version of the Atlas, the propellant tanks were stretched by 1.3 meters to increase the propellant load by 8% to 123 metric tons and lengthen the burn time by ten seconds. The thrust of the improved MA-5 propulsion system was also increased by about 2% to provide a total liftoff thrust of 1,756 kilonewtons. With a total height of 35.7 meters and a liftoff mass of 146 metric tons, the new Atlas-Centaur was now capable of launching up to about 1,135 kilograms towards the Moon on a Surveyor-type mission or about 68 kilograms more than the earlier Atlas-Centaur models. The first of these improved Atlas-Centaurs, AC-13, had flown successfully on September 8, 1967 to send Surveyor 5 to the Moon.
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 AC-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. While Surveyor 4 used the last direct-ascent variant of the Atlas-Centaur still left in NASA’s inventory, Surveyor 3, 5 and 6 successfully used the parking orbit technique to reach the Moon.
Unlike the later Apollo lunar landing missions, Surveyor was designed to make a direct descent to the lunar surface from its translunar trajectory around 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.
Since all of the Apollo-related support objectives had been met with the successful flight of Surveyor 6 (see “Surveyor 6: The Third Time is the Charm”), program managers were free to target Surveyor G for a much more interesting target preferably in the lunar highlands away from the previously explored mare. A science review board ultimately picked the region near Tycho crater. Tycho is a young highland crater with a diameter of 86 kilometers and a prominent ray system which stretches for hundreds of kilometers across the lunar surface. High resolution images returned by the Lunar Orbiter 5 mission (see “Lunar Orbiter 5: Filling in the Gaps in the Maps”) showed a comparatively smooth area covered with material excavated by the crater’s formation just north of the crater allowing relatively pristine highland material to be sampled. The 20-kilometer wide target area was centered at 40.87° S, 11.37° W about 30 kilometers from the northern crater rim. The terrain was too rugged to the south and there were no high resolution images much further north necessitating the smaller than usual target circle.
In order to reach this far southern site, SC-7 would need to perform a gravity turn of 36° from the vertical during its descent on Tycho. With such a small target area, everything would need to go right during launch and two midcourse maneuvers were now included in the schedule 17 and 48 hours after liftoff. If problems prevented Surveyor from landing near Tycho, an alternate landing site with a larger 60-kilometer target circle was chosen in Fra Mauro. The alternate site at 3.75° S, 17.5° W (which was about 3 kilometers south of the eventual landing site of Apollo 14) was covered with ejecta from the formation of the Imbrium Basin. Both landing sites consisted rolling hills which were rougher than any of the mare landing sites. This last Surveyor flight would allow the safety of such highland sites to be assessed for future exploration missions.
Getting Surveyor G to the Moon
In order to meet the mission’s requirements at both the Tycho and Fra Mauro landing sites as well as satisfy launch constraints, the Surveyor G mission had a six-day launch period running from January 7 to 12, 1968. Based on an initial analysis, the launch window on January 7 ran from 12:45 AM to 3:12 AM EST. Daily launch windows of about one to almost two hours in length started later on each successive day. Landing was scheduled to occur about 66 hours after liftoff with the exact transit time dictated by the date and time of launch.
The first piece of Surveyor G mission hardware to be shipped to Cape Kennedy (which reverted to its original name Cape Canaveral in 1973) was Atlas 5903C on October 17, 1967. This was followed by the nose fairing and interstage adapter on October 19 and the Centaur two days later. On October 23 the Atlas SLV-3C booster was erected on Pad A at Launch Complex 36 (LC-36A) as final preparations were being made in parallel for the November 7 launch of Surveyor 6 at LC-36B. The addition of the Centaur on October 24 completed the stacking of AC-15 allowing prelaunch testing to start.
Spacecraft SC-7 arrived at the Cape on November 6, 1967 with inspection, reassembly and initial checkout starting six days later. SC-7 was temporarily fitted with a dummy retrorocket as well as test instrumentation and mated to its adapter on November 24. Encapsulated in its nose fairing, SC-7 was mated to AC-15 on November 29 for the beginning of integrated prelaunch testing. Following the completion of the AC-15/SC-7 Joint Flight Acceptance Composite Test on December 1, the spacecraft was removed from the launch vehicle to start final preparations for its flight. The encapsulated SC-7 was mated to AC-15 for the final time on January 3, 1968 after the Composite Readiness Test for AC-15 was completed.
The final spacecraft readiness test began at 12:25 PM EST on January 6, 1968 with the countdown commencing at the T-680 minute mark. In order to optimize tracking coverage from the downrange stations, a new revised launch window was adopted which now opened at 1:30 AM EST on January 7. The previously scheduled one-hour hold which started at 10:15 PM on January 6 at the T-90 minute mark was lengthened by 35 minutes to align the countdown with the updated launch window. The countdown proceeded smoothly until launch took place at 1:30:00.625 AM EST (06:30:00.625 GMT) in the early morning hours of January 7.
A near nominal performance from the Atlas 5903C rocket and the first 333-second burn of the Centaur placed the upper stage and its payload into a temporary 164.8 by 172.2 kilometer parking orbit with an inclination of 30.7°. After coasting in this orbit for 22 minutes and 26 seconds, the Centaur’s pair of RL-10 engines reignited for a second burn which lasted 115.6 seconds. One minute later, the payload, now officially designated Surveyor 7, separated from the spent Centaur to begin its independent flight in a geocentric 170.4 by 710,184 kilometer orbit with an inclination of 30.7° which would set the lander on an intercept course to the Moon. About five seconds later, the Centaur started turning to begin a retromaneuver first using its own hydrogen peroxide thrusters and by venting its residual cryogenic propellants. The maneuver placed the spent stage into its own 168.5 by 447,757 kilometer geocentric orbit that would safely move it away from Surveyor 7. The Centaur would pass an estimated 19,635 kilometers from the Moon at 13:19 GMT on January 10.
After separating from its spent Centaur upper stage at 07:05:16 GMT on January 7, Surveyor 7 dutifully deployed its various appendages and started searching for its first attitude reference, the Sun, which it located by 07:14:30 GMT. About 12 minutes later, Surveyor made two-way contact with Earth-bound tracking stations allowing the first post-launch telemetry to be received directly from the spacecraft. Surveyor 7 locked its star sensor onto Canopus at 14:47:32 GMT finally settling into its proper cruise attitude. Checkout of the spacecraft systems indicated all was going well.
Tracking of the receding Surveyor 7 showed that it would miss its intended target point on the Moon by only 77 kilometers. The spacecraft was commanded from the ground to turn and, at 23:30:10 GMT, it fired its trio of vernier engines for 11.35 seconds to change its velocity by 11.08 meters per second to set it on the desired trajectory. Tracking after this maneuver indicated that Surveyor 7 would touchdown only 1.7 kilometers from the aim point for its primary landing site north of Tycho. With less than a 10% chance that Surveyor 7 would come down on potentially dangerous terrain, the second midcourse maneuver scheduled for about 06:30 GMT on January 9 was cancelled. The Fra Mauro backup site would have to wait over three years before it would be explored for the first time by the crew of the Apollo 14 mission.
At 00:35:50 GMT on January 10, ground controllers began to reorient Surveyor for its terminal maneuver and final descent to the lunar surface. At 01:02:10.6 GMT, Surveyor’s radar detected that the quickly descending lander had hit the 96.5 kilometer altitude mark triggering the automatic sequence of events to follow. At 01:02:13.4 GMT the vernier engines were started followed 1.1 seconds later by the ignition of the Thiokol TE-M-364 retrorocket. After retrorocket burnout, the vernier engines were throttled to full thrust and the spent motor case was ejected at 01:03:09.7 GMT. The on board computer system started using data from the radar to guide the final descent at 01:03:11.8 GMT with Surveyor falling at a speed of 138 meters per second at an altitude of 12.6 kilometers.
Using data from its descent radar system, Surveyor’s computer guided the spacecraft to a soft landing at 01:05:36.3 GMT at a velocity of 3.8 meters per second with just a brief 20 to 30 centimeter bounce after initial contact. Surveyor 7 had come down at 40.92° S, 11.45° W only a couple of kilometers from its predicted landing point some 35 hours after local sunrise. This marked the fifth successful landing of the Surveyor program out of seven attempts – an excellent record after so many bitter failures (see “NASA’s First Moon Lander” and “NASA’s Forgotten Lunar Program”).
An analysis of the spacecraft’s telemetry following landing showed that it was in excellent health after its voyage. About 41 minutes after touchdown, the first of a set of fifteen 200-line television images were returned to the Earth. Within an hour, the solar panel and high gain antenna had been configured to start transmitting higher resolution 600-line images back home. The images revealed that Surveyor 7 had come down on a relatively level surface of gently rolling, low hills with few craters larger than about eight meters visible suggesting the landscape was much younger than the mare sites visited earlier. Despite the presence of blocks of rock scattered across the surface, it was found that highland sites like this would be safe for future missions.
The Alpha Scattering Experiment was powered up at 09:27:31 GMT on landing day to begin its operations. The intent was to deploy the sensor head on undisturbed soil before the SMSS began work on the lunar surface. After being partially deployed, the sensor head gathered about 4.8 hours of background data before being commanded to be lowered the rest of the way to the surface at 22:09:00 GMT. Unfortunately the deployment mechanism jammed before the sensor head reached the surface. While ground controllers diagnosed the problem, another 7.2 hours of background radiation data were gathered.
Engineers eventually decided to use the SMSS to help free the stuck sensor head. The SMSS was powered up at 01:00:28 GMT on January 11 and was initially used to conduct the first bearing test on the lunar soil. Afterwards, ground controllers, using images from the television camera for guidance, twice bumped the dangling sensor head in an unsuccessful attempt to free it. The procedure was stopped at about 09:30 GMT as the Goldstone tracking station went out of range.
Ground testing of the deployment hardware eventually found that debris kicked up into the deployment mechanism by the landing had caused the problem and they devised a solution. New instructions were sent to the SMSS starting at about 16:00 GMT on January 12 to push the sensor head sideways against the propulsion system’s helium tank then push it downwards with about four newtons of force to free the mechanism. The fix worked and the Alpha Scattering Experiment sensor head was finally lowered with the help of one last push by the SMSS to make contact with the surface.
With its sensor head finally deployed, the Alpha Scattering Experiment started taking data at 16:42:25 GMT on January 12 on an undisturbed site. Unfortunately, the sensor head temperatures continued to rise during the lunar day and hit 50° C forcing a shutdown at 08:21:27 GMT the following day. During the next five days, the SMSS was positioned to help shade the sensor head from the lunar noontime Sun allowing a total of 27.4 hours of data to be accumulated by 07:20:50 GMT on January 21 during intermittent use at this first sample site.
These and subsequent measurements showed that the highland surface material contained less iron and titanium than the basalt-covered mare sites examined by Surveyor 5 and 6 but more aluminum and calcium. Combined with the slightly lower density of the rocks (based on mass estimates from the SMSS), this finding suggested that the highland rocks are a feldspar-rich anorthositic gabbro suggesting the Moon was a thermally differentiated and chemically evolved body – not a cold, unevolved primordial object as some scientists had predicted.
During the course of the lunar day, the television camera made numerous panoramas of Surveyor’s surroundings as well as monitored operations of the SMSS as it made a total of seven trenches, performed numerous bearing test as well as manipulated rocks and other surface materials. Star images allowed the orientation of the lander to be determined precisely as well as confirm the camera’s pointing. Because of the far southern location of the landing site, the Earth was low enough in the sky to allow easy observations by Surveyor 7. On January 20, the camera was used in an attempt to detect lasers directed at Surveyor from a half dozen sites scattered across the continental US as part of a laser communications test. Only two sites located well into the night side of the Earth were eventually detected as a pair of magnitude -3 point sources in images first acquired at about 09:06 GMT – a two-watt laser on the 1.52-meter telescope at Table Mountain in California and a four-watt laser on the 0.6-meter telescope at Kitt Peak in Arizona. The experiment not only proved that lasers could be used for space communications but increased confidence in the proposed use of retroflectors to be left on the Moon by future Apollo missions to measure lunar distances accurately.
With local sunset fast approaching, ground controllers used the SMSS to pick up and redeploy the Alpha Scattering Experiment’s sensor head to a new location at 07:25:50 GMT on January 21. This second site was a 5 by 7 centimeter rock where data were taken for 10.3 hours. At about 11:50 GMT the following day, the SMSS was used to redeploy the sensor head to a third site inside of a trench that the SMSS had prepared earlier so that the composition of the subsurface soil could be characterized.
With local sunset occurring at 06:06 GMT on January 23, Surveyor began its planned period of early nighttime operations. These included more television observations of the Earth and stars as well as a sequence of 100 images of the solar corona out to an apparent distance of 50 solar radii. The Alpha Scattering experiment was shutdown at 15:36:07 GMT after taking data for 6.7 hours at its third sample site. Following the completion of its planned post-sunset operations by about 21:00 GMT, Surveyor 7 was finally placed into hibernation at 14:12 GMT on January 26 as its temperatures began to fall too low for its battery to operate effectively. During its first lunar day, Surveyor 7 had transmitted 20,993 television images back to Earth along with 66 hours of data from the Alpha Scattering Experiment and performed 36 hours and 21 minutes of SMSS operations.
In hopes of gathering more data during the second lunar day, commands were sent at 19:01 GMT on February 12, 1968 with Surveyor 7 responding almost immediately. Unfortunately, initial telemetry indicated that the spacecraft’s battery had been damaged by the long, cold lunar night limiting the amount of power available. Despite the problems, Surveyor 7 managed to transmit another 45 200-line images of the lunar surface and gather another 34 hours of useful measurements from the Alpha Scattering Experiment which had been left at the third sample site at the end of the first lunar day. On February 14, the SMSS responded to commands proving that it had survived the lunar night as well. One last set of commands to move the sampler arm were sent on February 20 but any further SMSS operations were not possible due to the power system issues. With the condition of its battery worsening as the Sun climbed high into the sky, Surveyor 7 was finally shutdown at 12:24 GMT on February 21 ending NASA’s last Surveyor mission.
Surveyor 7 was a resounding success providing scientists with important information about the lunar highlands and demonstrating that such sites could be visited by future Apollo missions. With the prospects that Tycho would be visited by a crewed mission dashed with the cancellation of the Apollo program, Surveyor 7 remains the southern-most landing on the lunar surface to this day.
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Here is a brief contemporary video about the Surveyor 7 mission:
Here is some silent video footage of the SMSS in action during the Surveyor 7 mission:
For more articles on NASA’s Surveyor program, check out Drew Ex Machina’s Surveyor Program page.
Raymond N. Watts, “Surveyor 7 on the Moon”, Sky & Telescope, Vol. 35, No. 4, pp. 223-225, April 1968
Last Surveyor Series Mission, NASA Press Release 67-316, January 4, 1968
Surveyor VII A Preliminary Report, SP-173, NASA, May 1968
Surveyor VII Mission Report Part I. Mission Description and Performance, Technical Report 32-1264, JPL, February 15, 1969
Flight Performance of Atlas-Centaur AC-13, AC-14, AC-15 in Support of the Surveyor Lunar Landing Program, TM X-1844, NASA Lewis Research Center, February 1970