Launched on January 7, 1968, the Surveyor 7 was a lunar unmanned Lander that successfully landed on the lunar surface on January 10. The last of the original series of Surveyor moon Landers of the 1960s. Surveyor 7 was the only spacecraft of the series that landed in the lunar highland region. A.S. Ganesh takes a look at Surveyor 7-the only purely scientific mission in the series.
With the objective of landing human beings on the moon, NASA worked on various issues through the 1960s. The decade saw spectacular progress being made as we understood our natural satellite better than ever before.
First, the Lunar Orbiter series had flown five successful missions in five attempts meeting its objective of mapping potential landing sites for the early Apollo missions and in fact mapping almost the entire lunar surface. The Surveyor landing missions, meanwhile, enjoyed four successes (1, 3, 5, and 6) in the first six attempts providing the Apollo programme with ground-truth data.
Freed up for science
With most of its objectives met, NASA opted to use the last of the Surveyor missions for a purely scientific purpose, targeting a landing site in the lunar highlands – outside of potential landing sites of the early Apollo missions.
Even though the Surveyor missions had initially been planned as a series of seven spacecraft, three more missions had been added in 1963 to take the total to 10. But with the Success of other missions, the later Surveyors were cancelled in December 1966.
Officials, however, decided on incorporating some of the science payload planned for these later Surveyors on the remaining approved Surveyor spacecrafts. While Surveyor 3 and 4 carried a remote controlled mechanical arm known as the soil Mechanics Surface Sampler (SMSS), Surveyor 5 and 6 carried the Alpha Scattering Experiment designed to measure concentrations of various elements on the lunar soil. It was decided that Surveyor 7 alone would carry both these instruments in order to maximize the science return.
Coasts to the moon
Launched on January 7, 1968, the Surveyor 7 had an uneventful coast to the moon. As initial tracking suggested that the Surveyor 7 would miss its intended target on the moon by just 77 km, the spacecraft was commanded from the ground to place it on the desired trajectory. Tracking after this manoeuvre indicated that Surveyor 7 would touchdown just 1.7 km from the point aimed at a less than 10% chance of coming down on potentially dangerous terrain.
As a result, the second of the planned mid-course corrections on January 9 was cancelled. And as expected the Surveyor 7 successfully landed on January 10 on the ejecta blanket emanating from the bright Tycho crater, a mere 2.4 km from its target.
Ground controllers fired pyrotechnic charges about 21 hours after landing in order to drop the alpha-scattering instrument on the lunar surface. The controllers used the surface sampler robot arm to force down the alpha-scattering instrument when it failed to Move beyond an intermediate position.
Following the alpha-scattering instruments first chemical analysis, the sampler was used to pick up the instrument and move it to two additional locations. The scoop on the samplers arm was employed to pick up soil, dig up trenches and conduct a number of surface-bearing tests.
Plenty of useful data
Nearly 66 hours of alpha-scattering data were obtained on three samples during the first lunar day and over 36 hours of SMSS operations had been performed. Following the local sunset on January 23, Surveyor 7 completed its planned post-sunset operations before being put into hibernation on 26, 80 hours after the local sunset.
Communications, which were paused during the hibernation resumed on February 12 in the hopes of gathering more data during the second lunar day. Even though Surveyor 7 responded immediately to the commands, initial telemetry suggested that the long, cold lunar night had damaged the spacecraft’s battery limiting the amount of power available.
Despite these problems, Surveyor 7 transmitted 45images of the lunar surface on the second lunar day, in addition to the 20.993 it had relayed on the first lunar day. The Alpha Scattering Experiment which had been left at the third sample site at the end of the first lunar day, gathered another 34 hours of useful data on the second lunar day.
Surveyor 7 was finally shut down on February 21, bringing the curtains down on NASA’s highly successful Surveyor series of missions. In addition to providing over 21.000 photos from its missions, Surveyor 7 also served as a target for Earth-based lasers in order to measure the distance between the Earth and the moon more accurately.
The results from the alpha scattering instruments highlighted that the crust of the lunar highlands is poorer in iron than the mare sites that had been analysed by the other Surveyors. The resounding success of Surveyor 7 not only provided scientists with invaluable information about the lunar highlands, but also opened up these sites as well as potential targets for future planned human landings.
Picture Credit : Google
