The Moon's Gravity and its Effects on Apollo Astronauts

[zillax0rz]

I was watching a couple specials on the moon recently and it discussed the Apollo missions and how the moon's gravity is roughly a sixth of the Earth's and it made me wonder... for the crew of Apollo 10, which flew within 10 miles of the surface, did they feel any affect of the moon's gravity? Meaning, did they fall to the bottom of the craft? At what point does an object began to be captured by the moon and gravitate towards?<br /><br />Thank you to any and all responses.

 

[Boris_Badenov]

Welcome to SDC, & that is a great first question!!! The only reference I was able to find was on this page. <br /> And it said;<br /><br /><font color="purple">The computation of the actual orbit elements of LM 4 was done in a three-<br />step process. From technical references about the Apollo program there is <br />enough information to calculate the delta v of the LM. "Snoopy" didn't <br />land on the moon, so most of the propellant of the ascent engine wasn't <br />yet needed when Mission Control fired it at May 23, 1969 at 6:07 UT. The <br />engine ran until burnout. Delta v can be calculated to 1150 m/s.<br />(1) Under the assumption the LM accelerated parallel to the orbital<br /> tangent, the delta v adds to the circular velocity of Apollo around <br /> the moon (note the Apollo orbits were retrograd). By this, an escape <br /> hyperbola and its asymptotic velocity and angle can be calculated. <br /> <font color="yellow"><i>Snoopy left the moon's gravity well at 1336 m/s and an angle of 58.5</i></font><br /> deg against the orbit tangent/moon center.</font><br /><br />From this I'd say yes, the Apollo 10 LM experienced Lunar gravity at it's closest approach to the Lunar surface.<br /> <div class="Discussion_UserSignature"> <font color="#993300"><span class="body"><font size="2" color="#3366ff"><div align="center">. </div><div align="center">Never roll in the mud with a pig. You'll both get dirty & the pig likes it.</div></font></span></font> </div>

 

[CalliArcale]

<blockquote><font class="small">In reply to:</font><hr /><p>No, they were in micro gravity the entire time they were in orbit around the moon.<p><hr /></p></p></blockquote><br /><br />Basically what this means, ZillaxOrz, is that they were most certainly experiencing the Moon's gravity -- that's what was pulling them into orbit. (If the Moon's gravity were not tugging on them, they would gone sailing right on past it!) But because they were drifting in space, they were basically in freefall -- their spacecraft was being tugged exactly the same as they were, so they were not actually aware of the Moon's gravity.<br /><br />Astronauts experience the same thing in Earth orbit, as shuttle_guy said. They are deeply in the influence of Earth's gravity, but they do not actually feel it. This is because you don't feel gravity itself -- you feel changes in acceleration thanks to the way your body senses up and down. If you're in freefall, there is no change to feel. You can experience this yourself the next time you visit an amusement park. Pay close attention during the first big drop on a roller coaster. It's not completely zero gravity, but it's close enough to get the idea. You aren't actually experiencing less gravity, but you still get lighter. This is because the roller coaster is dropping at the same rate that you are.<br /><br />Your body weight is really just the amount of force your body applies to the floor. If the floor isn't dropping, you'll be pressed against the floor by gravity. But if the floor is dropping at the same rate that you are, you won't press against it at all and you will be weightless!<br /><br />And welcome to Uplink! <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>

 

[rumsfeld46]

If I remember correctly the Apollo 10 mission had a lunar lander and decended down twards the moons surface. They had actually left orbit to do this. I believe they would have been feeling more of the affects from the landers thrusters themselves then they would have felt from the gravity of the moon. However, the mooms gravity was acting on the lander to pull them in, it was only their engine that kept them from crashing. http://www.nasm.si.edu/collections/imagery/apollo/AS10/a10.htm

 

[rumsfeld46]

But isn't "Free Fall" actually the affects of lunar gravity?

 

[MeteorWayne]

No and yes. Without the gravity, the craft would go straight into space away from the surface.<br /><br />With the gravity and orbit, the rate of fall matches gravity, so for those within, there is no (or very little) acceleration. <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[rumsfeld46]

Ahhh, understood. <img src="/images/icons/smile.gif" />

 

[jimfromnsf]

Actually Apollo 10 never was going towards the lunar surface. It performed the DOI (descent orbit insertion) burn, which put it from a 60 x 60 nmi to 60x 8 nmi orbit. How it differed from Apollo 11 is that it did not perform the PDI (powered descent initiation) burn at the 8 nmi altitude to start the actual "landing", instead, it performed a posigrade burn that put it in a 8 x 198 nmi orbit. <br />

 

[rumsfeld46]

My mistake. After further investigation into this subject,<br />It does appear that Apollo 10 never actually made a powered decent toward the surface. Only was placed into a lower orbit then the Command Module. Hence, all orbital forms of gravity would apply. The astronauts would only feel weightlessness even at 47,000 ft. above the lunar surface. The moon, having virtually no atmosphere to slow it down very easily could orbit even at this low altitude.

 

[3488]

You are correct. The LEM passed close to the surface, although 47,000 feet is still<br />a long way from the surface & well above the summits of even the tallest lunar<br />peaks.<br /><br />The Apollo 10 LEM was the dress rehearsal for the initial approach, to the point of powered descent,<br />& then the ascent back up to the orbiting CM, exactly as if the LEM had landed on the moon.<br /><br />That was never tested till the famous Apollo 11.<br /><br />Andrew Brown. <div class="Discussion_UserSignature"> <p><font color="#000080">"I suddenly noticed an anomaly to the left of Io, just off the rim of that world. It was extremely large with respect to the overall size of Io and crescent shaped. It seemed unbelievable that something that big had not been visible before".</font> <em><strong><font color="#000000">Linda Morabito </font></strong><font color="#800000">on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.</font></em></p><p><font size="1" color="#000080">http://www.launchphotography.com/</font><br /><br /><font size="1" color="#000080">http://anthmartian.googlepages.com/thisislandearth</font></p><p><font size="1" color="#000080">http://web.me.com/meridianijournal</font></p> </div>

 

[zillax0rz]

Thanks to everyone with the insightful comments. It is appreciated.<br /><br />Just so I got this straight... at no point are the astronauts ever falling to the bottom of the craft until the craft itself is on the surface? Until then, both the craft and the astronauts are falling at the exact same speed, therefore they're always "floating." Even as the moon's gravity pulls them toward the surface, it's pulling both the craft and the astronauts at the same rate.

 

[mithridates]

Well, they would start falling to the bottom of the craft as soon as it start firing its rockets to break its fall in order to land safely. The humans would still be falling and so they would hit the bottom of the ship, and they would feel gravity but I'm not sure how many g's they would feel because it would depend on the force of the rockets firing in reverse. Like an elevator. <div class="Discussion_UserSignature"> <p>----- </p><p>http://mithridates.blogspot.com</p> </div>

 

[zillax0rz]

That makes sense in my head, but please clarify one more thing for me.<br /><br />I would figure that the LEM weighs more than the two astronauts. If you remove the rockets and just have the craft and astronauts falling to the moon, the moon wouldn't pull the heavier craft faster than it does the astronauts? Since it weighs more, wouldn't it fall faster?<br /><br />I'm sure I'm wrong but for some reason, that's how my brain is thinking at the moment.

 

[3488]

Hi Zillax0rz,<br /><br />Actually no.<br /><br />The pull of gravity is the same, no matter how heavy it is.<br /><br />Galileo proved this in the 17th Century by dropping two objects from the Leaning Tower of Pisa<br />(a heavy iron ball & a light weight wooden one, I think).<br /><br />Because the Earth has a dense atmosphere, Air Resistance could slow down less <br />dense objects, but that is not the issue with the moon.<br /><br />On the moon, one could drop an oil supertanker & a feather from a great height & they would hit<br />the lunar regolith together.<br /><br />I hope that helps.<br /><br />Andrew Brown. <div class="Discussion_UserSignature"> <p><font color="#000080">"I suddenly noticed an anomaly to the left of Io, just off the rim of that world. It was extremely large with respect to the overall size of Io and crescent shaped. It seemed unbelievable that something that big had not been visible before".</font> <em><strong><font color="#000000">Linda Morabito </font></strong><font color="#800000">on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.</font></em></p><p><font size="1" color="#000080">http://www.launchphotography.com/</font><br /><br /><font size="1" color="#000080">http://anthmartian.googlepages.com/thisislandearth</font></p><p><font size="1" color="#000080">http://web.me.com/meridianijournal</font></p> </div>

 

[Boris_Badenov]

And then there was this this experiment . <div class="Discussion_UserSignature"> <font color="#993300"><span class="body"><font size="2" color="#3366ff"><div align="center">. </div><div align="center">Never roll in the mud with a pig. You'll both get dirty & the pig likes it.</div></font></span></font> </div>

 

[robnissen]

Very cool. I had completely forgotten about that. Its funny, growing up as a kid in the 60s, I had no idea that I was living in the glory age of manned spacecraft. I would never have believed that 35 years after the Apollo era, astronauts would be reduced to glorified truck drivers, ferrying supplies 200 miles to the ISS.

 

[MeteorWayne]

The amount af mass falling to the surface makes no difference.<br /><br />A heavy object and and a light object fall at the smae speed.<br /><br />This is the famous experiment preformed by Galilleo at the tower of Pisa, and repeated on the moon by astronauts.<br /><br />If there is no air (which provides resistance) a feather and a car will fall at the same rate, controlled by the gravity of the larger object. <br /><br />Edit: I should have known this would have been answered before I checked in, Thanx guys.<br /><br />BTW, who was the astronaut that conducted the experiment on the moon? <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[jimfromnsf]

All objects accelerate at the same rate in the same gravity field. Remember Galileo's experiment off the Leaning Tower of Pisa? The Apollo 15 astronaut replicated it with a drill and a feather on the moon. Both hit the ground at the same time <br /><br />Dave Scott