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From: karn@petrus.UUCP (Phil R. Karn)
Newsgroups: net.space
Subject: Re: Errors 1202 and 1201 on Eagle
Message-ID: <652@petrus.UUCP>
Date: Thu, 17-Oct-85 12:54:08 EDT
Article-I.D.: petrus.652
Posted: Thu Oct 17 12:54:08 1985
Date-Received: Sat, 19-Oct-85 03:43:24 EDT
References: <851016152712.630861@MIT-MULTICS.ARPA>
Organization: Bell Communications Research, Inc
Lines: 17

> It
> turned out that Eagle landed around 4 miles farther downrange than
> intended--I also don't know if this error had anything to do with that.

This error was due to an incomplete model of the moons very complex
gravitational field. The moon has a very irregular shape, and unless it
is modeled exactly in the programs that simulate an orbit, errors will
accumulate. When Eagle was given its final "state vector" (position and
velocity) before powered descent initiation, it was actually 6800 meters
further downrange and 1400 meters further south. Therefore, the entire
descent was shifted downrange and Eagle landed 7km downrange from the
original target spot.

The desire to demonstrate a pinpoint landing capability was the reason
the next flight, Apollo 12, was landed next to Surveyor III.

Phil