Description

Surveyor 6 was the fourth of the Surveyor series to successfully achieve a soft landing on the Moon. The primary objectives of the Surveyor program, a series of seven robotic lunar softlanding flights, were to support the coming crewed Apollo landings by: (1) developing and validating the technology for landing softly on the Moon; (2) providing data on the compatibility of the Apollo design with conditions encountered on the lunar surface; and (3) adding to the scientific knowledge of the Moon. The specific primary objectives for this mission were to perform a soft landing on the Moon in the Sinus Medii region and obtain postlanding television pictures of the lunar surface. The secondary objectives were to determine the relative abundance of the chemical elements in the lunar soil by operation of the alpha-scattering instrument, obtain touchdown dynamics data, obtain thermal and radar reflectivity data, and conduct a vernier-engine erosion experiment.

Spacecraft and Subsytems

The basic Surveyor spacecraft structure consisted of a tripod of thin-walled aluminum tubing and interconnecting braces providing mounting surfaces and attachments for the power, communications, propulsion, flight control, and payload systems. A central mast extended about one meter above the apex of the tripod. Three hinged landing legs were attached to the lower corners of the structure. The legs held shock absorbers, crushable, honeycomb aluminum blocks, and the deployment locking mechanism and terminated in footpads with crushable bottoms. The three footpads extended out 4.3 meters from the center of the Surveyor. The spacecraft was about 3 meters tall. The legs folded to fit into a nose shroud for launch.

A 0.855 square meter array of 792 solar cells was mounted on a positioner on top of the mast and generated up to 85 Watts of power which was stored in rechargeable silver-zinc batteries. Communications were achieved via a movable large planar array high gain antenna mounted near the top of the central mast to transmit television images, two omnidirectional conical antennas mounted on the ends of folding booms for uplink and downlink, two receivers and two transmitters. Thermal control was achieved by a combination of white paint, high IR-emittance thermal finish, polished aluminum underside. Two thermally controlled compartments, equipped with superinsulating blankets, conductive heat paths, thermal switches and small electric heaters, were mounted on the spacecraft structure. One compartment, held at 5 - 50 degrees C, housed communications and power supply electronics. The other, held between -20 and 50 degrees C, housed the command and signal processing components. The TV survey camera was mounted near the top of the tripod and strain gauges, temperature sensors, and other engineering instruments are incorporated throughout the spacecraft. One photometric targets was mounted near the end of a landing leg and one on a short boom extending from the bottom of the structure. Other payload packages, which differed from mission to mission, were mounted on various parts of the structure depending on their function.

A Sun sensor, Canopus tracker and rate gyros on three axes provided attitude knowledge. Propulsion and attitude control were provided by cold-gas (nitrogen) attitude control jets during cruise phases, three throttlable vernier rocket engines during powered phases, including the landing, and the solid-propellant retrorocket engine during terminal descent. The retrorocket was a spherical steel case mounted in the bottom center of the spacecraft. The vernier engines used monomethyl hydrazine hydrate fuel and MON-10 (90% N2O2, 10% NO) oxidizer. Each thrust chamber could produce 130 N to 460 N of thrust on cammand, one engine could swivel for roll control. The fuel was stored in spherical tanks mounted to the tripod structure. For the landing sequence, an altitude marking radar initiated the firing of the main retrorocket for primary braking. After firing was complete, the retrorocket and radar were jettisoned and the doppler and altimeter radars were activated. These provided information to the autopilot which controlled the vernier propulsion system to touchdown.

With a payload virtually identical to that of Surveyor 5, this spacecraft carried a television survey camera, a small bar magnet attached to one footpad to detect magnetic material, an alpha-scattering instrument to study surface composition, and convex auxilliary mirrors mounted on the frame to view the surface under the spacecraft, as well as the necessary engineering equipment. The main differences were that Surveyor 6 had polarizing filters on the TV camera, a different type of glare hood, and had 3 auxilliary mirrors instead of 2. Surveyor 6 had a mass of 1006 kg at launch and 299.6 kg on landing.

Instruments

Television

The alpha-scattering surface analyzer was designed to measure directly the abundances of the major elements of the lunar surface. The instrumentation consisted of an alpha source (curium 242) collimated to irradiate a 10-cm-diameter opening in the bottom of the instrument where the sample was located and two parallel but independent charged particle detector systems. One system, containing two sensors, detected the energy spectra of the alpha particles scattered from the lunar surface, and the other, containing four sensors, detected energy spectra of the protons produced via reactions (alpha and protons) in the surface material. Each detector assembly was connected to a pulse height analyzer. A digital electronics package, located in a compartment on the spacecraft, continuously telemetered signals to earth whenever the experiment was operating. The spectra contained quantitative information on all major elements in the samples except for hydrogen, helium, and lithium. Curium collected on the collimator films and was scattered by the gold plating on the inside bottom of the sensor head. This resulted in a gradually increasing background and reduction of the sensitivity technique for heavy elements. One proton detector was turned off during the second day of operation because of noise. A total of 43 hr of data was obtained from November 11 to November 24, 1967. The final data were obtained 4 hr after local sunset. However, after the spacecraft 'hopping' maneuver on November 17, 1967, the sensor head was upside down. Measurements were continued in order to obtain information on solar protons and cosmic rays. Therefore, data for the purpose of the chemical analysis of lunar surface material were obtained only during the first 30 hr of operation. During this period, 27 hr and 44 min of data were known to be noise free.

Alpha-Scattering Surface Analyzer

The TV camera consisted of a vidicon tube, 25- and 100-mm focal length lenses, shutters, polarizing filters (as opposed to color filters used on the previous Surveyer cameras), and iris mounted nearly vertically and surmounted by a mirror that could be adjusted by stepping motors to move in both azimuth and elevation. The polarizing filters served as analyzers for the detection of measurement of the linearly polarized component of light scattered from the lunar surface. An auxiliary mirror was used for viewing the lunar surface beneath the spacecraft. The frame-by-frame coverage of the lunar surface provided a 360-deg azimuth view and an elevation view from approximately +90 deg above the plane normal to the camera z axis to -60 deg below this same plane. Both 600-line and 200-line modes of operation were used. The 200-line mode transmitted over an omnidirectional antenna and scanned one frame each 61.8 sec. A complete video transmission of each 200-line picture required 20 sec and utilized a bandwidth of 1.2 KHz. Most transmissions consisted of the 600-line pictures, which were telemetered by a directional antenna. The frames were scanned each 3.6 sec. Each frame required nominally 1 sec to be read from the vidicon and utilized a 220-KHz bandwidth for transmission. The optical surfaces were the cleanest of any mission because of a redesigned mirror hood. The television images were displayed on a slow scan monitor coated with a long persistency phosphor. The persistency was selected to optimally match the nominal maximum frame rate. One frame of TV identification was received for each incoming TV frame and was displayed in real time at a rate compatible with that of the incoming image. These data were recorded on a video magnetic tape recorder and on 70-mm film. The camera performance was excellent in terms of both the quantity and quality of pictures. Between lunar landing, lunar 'second' landing, and the lunar first day sunset on November 24, 1967, 29,914 pictures were taken and transmitted.

Hardness and Bearing Strength of Lunar Surface

The objective of this experiment was to determine the hardness and bearing strength of the lunar surface by the use of strain gages, accelerometers, and rate gyros.

 

Launch-Orbit Information

Launch Information

Launch Date: 1967-11-07 at 07:39:00 UTC
Launch Vehicle: Atlas-Centaur
Launch Site: Cape Canaveral, United States
Decay Date: 1967-11-10
Mass: 299.6 kg

Orbital Parameters

Type Lander
Central Body: Moon
Epoch start: 1967-11-10 01:01:06 UTC

Lander Coordinates
Latitude: 0.49°
Longitude: 358.6°

Regions Traversed
Lithosphere
Planet
The Moon

Surveyor 6 launched on 7 November 1967 at 7:39:00 UT (2:39 a.m. EST) from launch complex 36B of the Eastern Test range at Cape Kennedy. The Atlas-Centaur booster put the spacecraft into an initial Earth parking orbit from which it was injected into a lunar-transfer trajectory at 8:03:30 UT. A midcourse correction manuever was performed at 2:20:00 UT on 8 November 1967. Surveyor 6 touched down on the lunar surface on 10 November 1967 at 01:01:06 UT (8:01:06 EST 9 November) in Sinus Medii, a flat, heavily cratered mare region, at 0.49 N, 358.60 E (selenographic), the center of the Moon's visible hemisphere.

On 17 November at 10:32 UT the vernier engines were fired for 2.5 seconds, causing Surveyor to lift off the lunar surface 3 to 4 meters and land about 2.4 meters west of its original position. This lunar "hop" represented the first powered takeoff from the lunar surface and furnished new information on the effects of firing rocket engines on the Moon, allowed viewing of the original landing site, and provided a baseline for stereoscopic viewing and photogrammetric mapping of the surrounding terrain. The mission transmitted images until a few hours after sunset on 24 November, returning a total of 29,952 images. The alpha-scattering experiment acquired 30 hours of data on the surface material.

The spacecraft was placed into hibernation for the lunar night on 26 November. Contact with the spacecraft was resumed on 14 December for a short period, but no useful data were returned and the last transmission was received at 19:14 UT on 14 December 1967. The results of the experiments showed that the surface had a basaltic composition, similar to that found at the Surveyor 5 landing site. Engineering and soil mechanics data indicated the bearing strength of the surface was more than adequate to support human landings. This spacecraft accomplished all planned objectives. The successful completion of this mission satisfied the Surveyor program's obligation to the Apollo project. The Surveyor program involved building and launching 7 Surveyor spacecraft to the Moon at a total cost of $469 million.

Summary