Mission Log

With the engineering questions answered, the last Surveyor was released to do science. Every previous mission had been sent to a flat, dull, equatorial site because those were the places Apollo might land; Surveyor 7 was aimed instead at the rugged ejecta blanket north of the crater Tycho, a young and geologically dramatic highland region no crewed mission would ever attempt.

It landed in January 1968 among boulders and rubble, and its alpha-scattering instrument immediately produced a result that mattered: the highland soil was chemically different from the maria, much lower in iron and richer in aluminium and calcium. The Moon was not one rock type but at least two, implying a differentiated body with a genuine geological history.

The instrument nearly failed to work at all. Its deployment mechanism stalled, leaving the sensor hanging above the surface, and controllers used the spacecraft's own surface-sampling scoop — improvising well beyond its design purpose — to push the instrument down into position, then to lift it and move it to fresh spots for further measurements.

The scoop went on to dig trenches, break rocks and conduct bearing tests, and the mission returned more than 21,000 images of a landscape utterly unlike the smooth plains the earlier spacecraft had photographed. It also detected laser beams aimed at it from two observatories on Earth, an early test of laser ranging.

It survived one lunar night and fell silent in February 1968. The programme it closed had cost about $469 million, landed five times out of seven attempts, and removed every remaining doubt about whether the surface would hold a spacecraft — eighteen months before Apollo 11 put the question beyond argument.