A Conversation for Apollo, The Intermediate Missions

Apollo 11's Landing

Post 1

OPAL_ideas

Just for the sake of historical accuracy, Apollo 11 did not "miss" its landing site by several miles. The actual events were quite dramatic - Armstrong and Aldrin had to deal with a series of system malfunctions and inadequacies. Alarms sounded while they were on approach to the computer-designated landing point, almost distracting their attention. Then, with about half a minute to go, they determined that the computer was going to set them into a hundred yard wide crater surrounded by car-sized boulders. They took over manual control and skimmed the surface for a few miles until they found a clear landing area. After landing successfully, it was determined that they had only 20 seconds of fuel left. Actually, for experienced test pilots, this was considered lots.

Their joint efforts have been highly praised by all pilots. Currently available computer capability is, still, proving to be barely sufficient for such off-world shenanigans – witness the troubles that Mars have been giving to scientists.


Apollo 11's Landing

Post 2

Deke

Hi there and thanks for your comments.

I don't recall that I related that Apollo 11 'missed its target by several miles' as that would have been disingenuous. The landing sites were carefully chosen within the limitations of the photographic evidence available, and within those constraints any safe landing would have been regarded as acceptable. The mare sites were chosen with the possibility of an under or overshoot in mind.

Nevertheless, Apollo 11 did overshoot its landing target ellipse by some 4 to 5 miles and was about a mile off its intended track. In fact Tranquillity Base ended up outside the area of the Orbiter photographs that had been used to certify the landing site.

Armstrong was already aware that he was going to land 'long' at about three minutes into the powered descent when he found Eagle was passing checkpoints about three seconds early, with each second equating to about a mile. His later problems with the overloading computer distracted his attention from picking out a safe spot to land early, but they were not the main cause of the overshoot. Over-flying West Crater accounted for only about a half mile of the overshoot as Eagle was already past the designated landing point by some three to four miles.

It was certainly regarded as a 'miss' by the mission planners though. They went to some lengths to improve their accuracy on later flights and indeed, one of the reasons for the choice of Apollo 12's landing site was to demonstrate techniques for a point landing capability to open up the possibilities for the more restricted terra sites.

Still, it was indeed an incredible feat of flying.
A.M.


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