MISSION ACCOMPLISHED

The three successful Rangers satisfied the objective set for the Block III series in terms of supporting Apollo. The maria proved to be cratered on all scales, but with a smoothly undulating surface of generally shallow slopes. And the presence of large blocks of rock lying on the surface suggested sufficient bearing strength to support a lander. In addition, radio tracking had enabled the estimate of the mass of the Moon to be much improved. It also established the axis that is aligned towards Earth to be about 1 km longer, with the centre of mass being offset several kilometres from the geometric centre in a direction away from Earth.

When some 200 scientists gathered at the Goddard Space Flight Center in April 1965 to discuss the combined results of the Ranger project, Harold Urey and Gerard Kuiper still disagreed about whether the Moon was thermally differentiated. Thomas Gold insightfully noted that the pictures represented a mirror in which each person saw evidence to support his own hypothesis.

One lesson of Ranger was that lunar geological units were so severely blurred by impact ‘tilling’ at the fine scale that in undertaking photogeological mapping it was better to use a medium scale of 1:1,000,000, as was used by the Air Force Chart and Information Center in St Louis for its Lunar Astronautical Chart series.

Ranger had provided a close look at several sites, but what was required next was for an orbiter to provide a broader view at better-than-telescopic resolution and for a soft-lander to provide ‘ground truth’.