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Forum:	Mercury - Gemini - Apollo
Topic:	Lunar Gravity on Apollo Landing Crews

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<table border=0 cellpadding=0 cellspacing=0 width="600"><TR><td bgcolor="#000000"><TABLE BORDER=0 cellpadding=4 border=0 cellspacing=1 WIDTH="100%"><TR bgcolor="#660000"><TD COLSPAN=2><CENTER>T O P I C     R E V I E W</CENTER></TD></TR><TR bgcolor="#494949"><TD valign=top>ejectr</TD><TD>I was just wondering, at what point in their descent to the surface did the Apollo crews first start to feel the effects of lunar gravity.</TD></TR><TR bgcolor="#333333"><TD valign=top>Scott</TD><TD>They first felt "G" forces when they fired the LM's descent engine to begin the powered descent. Stable 1/6 gravity would have been felt after landing.</TD></TR><TR bgcolor="#494949"><TD valign=top>FordPrefect</TD><TD>The average deceleration during the Lunar Module's braking and approach phase was about 3 m/s/s, which equals to about 0.3 g's</TD></TR><TR bgcolor="#333333"><TD valign=top>Obviousman</TD><TD>Has anyone done the sums to confirm this? The answers gel with what I expected to happen, but I have a feeling we are missing something somewhere.Also, I am wondering if the point "...where they first start to feel the effects of lunar gravity..." might actually be at pitchover? Technically, prior to this they were feeling the effect of the DPS....</TD></TR><TR bgcolor="#494949"><TD valign=top>Saturn V</TD><TD>From interviews that I have listened to on the SpaceCraft Films DVDs, the astronauts reported that they did not "feel" the gravity because they were strapped down to the floor during decent to the surface or at least there was a downward force being applied by the straps. This being strapped down to the floor was in effect an artificial gravity. Richard</TD></TR><TR bgcolor="#333333"><TD valign=top>John Charles</TD><TD> <BLOCKQUOTE>quote:<HR>Originally posted by ejectr: I was just wondering, at what point in their descent to the surface did the Apollo crews first start to feel the effects of lunar gravity.<HR></BLOCKQUOTE>As the previous answers indicate, this is a tricky question. If you mean, "when do they feel 1/6-g" then that would be shortly before landing, when the descent engine had decelerated their velocity to be essentialy zero relative to the moon and they were near the surface.During powered descent from lunar orbit down to the moon's surface, their flight path was constantly affected by the moon's gravity, but they couldn't "feel" it separate from the deceleration provided by the descent engine. (Einstein noted that the acceleration due to a rocket engine is indistinguishable from the acceleration due to gravity--they don't "feel" different, and all one "feels" is the vector sum of them both.)But the astronauts were subject to the effects of lunar gravity while in orbit around the moon, and while falling toward the moon from the Earth-Moon Equigravisphere, and even while standing on Earth (think: tides).------------------ John Charles Houston, Texas</TD></TR></TABLE></td></tr></table>

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