Era of moonwalks

APOLLO 15 ANNIVERSARY

On July 26, 1971, exactly forty years ago, Apollo 15, a landmark lunar manned mission (with many firsts) was launched.

It carried the first lunar rover vehicle that traversed extensively for several kilometres on the rugged lunar terrain. It carried about two tons of extra payload to provide enough supplies for a full three-day stay on the lunar surface.

Earlier missions only stayed a little more than a day. The first lunar roving vehicle (LRV) was folded to a side of the lunar module Falcon and provided the first “sightseeing” trips on the moon.

The spacesuits were redesigned to allow the astronauts to sit in the rover for many eight-hour durations, called Extra Vehicular Activities (EVAs).

Although the Russians did not send manned missions to the moon, they achieved firsts, like returning lunar soil in unmanned lunar probes like Luna 16 (they took off automated from the moon back to earth carrying lunar rocks) and more importantly in their unmanned Lunokhod I rover which in 1970 traversed extensively over the lunar surface.

This was part of the motivation for Apollo 15 to carry a (manned) lunar roving vehicle to explore the lunar surface for a few kilometres around the landing point.  They had to prove the point that manned lunar missions were still worth the cost (in spite of the unmanned Russian achievements). Besides, Apollo 14 had radar malfunction which almost spoilt its lunar landing, while Apollo 13 was a flop, returning without a lunar landing.

Landing at Hadley Rille
The site for the Apollo 15 landing was chosen to be Hadley Rille, a half kilometre-deep valley carved out along the foothills of the lunar Apennine Mountains by ancient magma streams (when the moon was in a molten state, soon after the formation). This site, at 26 degrees north, was the most northerly of all Apollo landing spots on the moon.

All earlier landing sites were flat plains clustering around the lunar equator. Moreover, while landing, the lunar module had to clear five-kilometre-high mountain peaks which meant that its trajectory had to approach at a steep 25 degrees as compared to the standard 15 degrees. In turn, this required more fuel than in earlier missions.

The actual lunar touchdown on July 30 was hard with the lunar module Falcon tilting ten degrees with one leg in a crater. This tilt affected their life support packs, with lunar module pilot James Irwin having no access to drinking water.

Again, as compared to previous lunar destinations, this site was only roughly studied with previous best satellite images indicating features only larger than twenty metres. However, on landing, the astronauts found the sun-drenched Apennine Mountains remarkable, with summits (not jagged as earlier thought) smoothly rounded by innumerable micro meteorite falls on the airless terrain.

The orbiting Command module, Endeavour, was also fitted with better imagers which enabled the orbiting astronaut Alfred Worden to spot the lunar module Falcon on the surface. The first rover ride started off, about 15 hours after lunar touchdown, when the lunar module pilots James Irwin and mission commander David Scott had a bumpy drive at a speed of about 12 km per hour to the ten kilometre distant St. George crater.

The following day, the second EVA, involved following the “high road” to the foothills of the Apennine Mountain, hunting for rocks thrown up when a catastrophic impact formed the Mare Imbrium. The highlight was finding the four-billion-year-old Genesis Rock. They also drilled a core sample.

The EVA on the final day’s stay on the moon (about sixty hours after touchdown) involved a trip to the edge of the Rille, the core sample being retrieved. Although satellite images had indicted steep cliffs, the Rille turned out to have gentle slopes making the ride easier. About 80 kilograms of lunar rocks were brought back including the two-metre-deep core sample with about forty different layers of (lunar) material some dating back half a billion years. Falcon took off to dock with Endeavour with this load.

A hard splashdown
Finally at the end of a nearly thirteen-day mission, the astronauts’ return to earth was marked by a hard splashdown with one parachute malfunctioning! Again the lunar module pilot James Irwin suffered serious heart problems on his return, which led to his death in 1991. With his religious bent of mind, he made many expeditions to Mt. Ararat (on earth this time!) to search for Noah’s ark.

The final two Apollo missions were in April 1972 (Apollo 16) and December 1972 (Apollo 17). They each brought back about hundred kilograms of lunar soil and also had EVAs lasting more than twenty hours each. With this the Apollo programme came to an end in December 1972.