PASADENA, CALIFORNIA--Surveyor VII will both dig and analyze the Moon's surface if all goes well next month in the last and probably most difficult of the United States' series of lunar surface probes.
This Surveyor is scheduled to land in the rough southwest highlands, 18 miles north of Tycho Crater. The four successful Surveyors all have descended in the relatively smooth equatorial belt designated likely for later Apollo astronaut landings.
Scientific investigators of the National Aeronautics and Space Administrations and Caltech's Jet Propulsion Laboratory hope to satisfy their curiosity about this more formidable area of the Moon and add to the increasing knowledge of the composition of the Moon's soil.
Surveyor III last April utilized a claw-type digger to probe the hardness of the lunar surface. Dr. Ronald F. Scott, Caltech civil engineering professor and experimenter on the sampling device, said the digging showed the surface material was granular and slightly cohesive, not unlike some Earth soil.
The ASI readings from Surveyors V and VI indicate that the lunar material analyzed is similar to terrestrial basalts and basaltic achrondite, Dr. Anthony L. Turkevich, University of Chicago, principal chemical investigator, reports. The ASI gold box enables scientists to correlate Moon components with the chemical elements as well as Earth and meteoritic rock types.
Basaltic achrondites form a small percentage of all meteorites that have been found on Earth. It seems possible to scientists that they could be fragments of lunar rock, ejected by the impact of a meteorites on the Moon, Dr. Scott says.
Surveyor's digger, or surface sampler, operated by Floyd Robertson, JPL engineer, and Dr. Scott, will scoop up soil from below the Moon's surface and spread it for the ASI to analyze. The plan calls for the claw to dig as deeply as possible--18 inches is the maximum--as well as scrape surface material.
The claw, on the end of a five-foot aluminum flexing arm, also will be capable of picking up the analyzer box and putting it down on excavated dirt anywhere within an area of a few square feet. On signal from JPL's Goldstone Station, the claw will grasp a small knob above the box. The box is attached to the spacecraft by a nylon cord.
The digger arm can be swung out in a 112-degree sweep, nearly one-third of a circle. It can be lifted as high as 40 inches, and dropped to break up clods or rocks. The falling scoop can exert a pressure of three pounds per square inch. Surveyor III tests, however, found lunar rocks that withstood up to several hundred pounds per square inch when squeezed by the door of the motor-driven digger.
Dr. Scott's conclusion about the surface where Surveyor III landed was that it was mostly fine-grained, slightly cohesive soil much like damp sand found on Earth, with some increase in firmness and density with depth. However, Surveyor III's digger got down only seven inches.
By digging deeper trenches, Dr. Scott believes it will be possible to obtain more data on the bearing strength of the lunar soil. This is done by computing the difference in electrical motor current required to move the scoop in various phases of the digging.
The bearing strength of the Moon in the four Apollo belt areas has been measured at 3 to 8 pounds per square inch at a depth of one to two inches. It is suspected to be stronger further down. At any rate, NASA and JPL scientists now feel there is no need to worry about the ability of any of the four sites tested thus far to support astronauts.
The digger's five-inch claw will have two small U-shaped magnets at its base. With the aid of the television camera aboard, investigators will see whether anything sticks to the magnets. Previous Surveyor magnet tests indicate only about 1/4 of one per cent of the Apollo belt soil is magnetic, perhaps meteoritic iron.
The January mission is the most sophisticated in the Surveyor series. The camera, digger and ASI all are operated via the same radio channel, hence they cannot be commanded simultaneously. Any station in the JPL Deep Space Network can give command signals to the camera and the ASI, but only Goldstone will control the digger. This limits its operation to about five hours daily, with a like period allowed for taking pictures of the excavating.
The first post-landing day will be occupied with photosurveying the landing area near Tycho and warming up the alpha scattering box for its first 20-hour analysis. The digger will be deployed on the second day and start scraping and scooping.
With luck, the scientists hope to make at least two thorough analyses of moon soil--at the surface and in depth--in the first two weeks after the arrival of Surveyor VII.
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