Narrowing the Choice

NASA last week narrowed to five the number of lunar landing sites being considered for Apollo astronauts. Two of the three-mile by five-mile elliptical landing zones are in the Ocean of Storms on the west side of the visible face of the moon, one in the appropriately named Central Bay and two in the easterly Sea of Tranquillity. All are relatively smooth and unobstructed, giving the astronauts a good chance of selecting a spot that is free of boulders, ridges or rifts that could endanger the landing of the lunar module (LM).

The sites have more in common: all lie close to the lunar equator--and for good reason. Plans for the lunar mission call for the Apollo command ship to circle the moon in an 80-mile-high equatorial orbit while the LM descends to the surface below. Setting down the LM anywhere but near the equator would require change-of-plane maneuvers--both for landing and returning--that would consume large additional amounts of the craft's precious fuel. Once a launch time has been set, scientists will pick a site where the sun will be at least 7DEG and no more than 20DEG above the horizon in back of the LM crew when they swoop down. From this position, the sun will illuminate the surface in a way that will bring out the most contrast, making it easier for the crew to land safely.

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