Different Approach to Lunar Soft Landing : Feasible?

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rogerinnh

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Vogon13 write:<br /><br />"In the Newtonian realm of physics, your trajectory should be reversible. <br /><br />So where is the spot on the moon where objects levitate off into space with no input of energy?"<br /><br /><br /><br />It's a state secret as to the exact location of the levitation points on the Moon.<br /><br />But serviously,....<br /><br />You'll have to explain what you mean by reversibility.<br /><br />If I drop a ball here on Earth and it bounces a few times and eventually comes to rest, should I expect that sometimes it will "unbounce" back up to my hand? Personally I've never seen that happen.

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rogerinnh

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OK, let's take a different perspective on this...<br /><br />We've got an International Space Station (ISS) orbiting the Earth. I've got a space ship on the Earth that I want to launch and have it dock with the ISS. If I launch from just the right place on Earth, at just the right time, into just the right orbit (i.e. the oribit of the ISS) then my space craft will arrive in orbit at exactly the same position and velocity of the ISS and it will make a nice, gentle, soft-docking with the ISS. No need to first go in orbit around the ISS and then de-orbit for the docking.<br /><br />Now, instead of aiming for the ISS, suppose my objective is docking with (i.e. landing on) the Moon. The Moon is orbiting the Earth, albeit a lot further out than the ISS. Can I launch my spacecraft from the Earth so that its intended orbit is identical to that of the Moon, and so that it arives in that orbit at the exact same position as the Moon, so that I can touch down on its surface (the "trailing surface") just like I joined up with the ISS? OK, the Moon has a bit more gravity than the ISS. So I guess the question is whether or not a trajectory can be designed that also takes the Moon's gravity into consideration and still allows for the spacecraft to touch down softly, unpowered.

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search

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Sorry Roger<br /><br />There is some confusion here and I think I was the one creating it.<br /><br />I did not realize you were talking about the unmmaned missions.<br /><br />Nevertheless I am still surprised of how little can be found in NASA website.<br /><br />When going to the Apollo History page:<br />http://www.hq.nasa.gov/office/pao/History/apollo.html<br /><br />And then going to the Test flights and Lunar missions:<br />http://www.hq.nasa.gov/office/pao/History/apollo/welcome.html#chart<br /><br />Then you open any Mission and go down the page and try to open the corresponding "Detailed Mission Description (KSC)" I am redirected to:<br /><br />------------------------------------------------------------------------------------------------<br />Page not Found<br /><br /><br />The page you have requested might no longer exist or has had its name changed.<br /><br />Suggestions<br /><br />Go to the Kennedy home page.<br />Go to our FAQ page to search for the information you were looking for or submit a question.<br />Use the "Back" button on your browser to return to the previous page.<br />Use the Search box on the left side of the page to find the information you want.<br />------------------------------------------------------------------------------------------------<br /><br />The fact is that I have been trying to find any Apollo orbit diagram, drawings or plan. <br /><br />NOTHING. ZERO<br /><br />Can anyone assist me on this?

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rogerinnh

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Regarding the lunar orbit trajectory, I found this:<br /><br />http://www.nasa.gov/centers/langley/news/factsheets/Rendezvous.html<br /><br />You have to scroll down a bit to a place wherethere is a photo of a guy in front of a blackboard showing the trajectory. There is another diagram on this page which I think is wrong. It shows the craft aproaching from the wrong side of the Moon. I think the photo shows it correctly, basically a figure-8, approaching the advancing side of the Moon for orbit insertion.<br /><br />And, yes, it's ODD that the NASA site has dead links an dlittle info about the missions.

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search

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Thanks<br /><br />Still it is quite miserable information don't you think?!<br /><br />I know it as been some years but still should deserve a better presentation.<br />After all it was the golden years and the highest achievement ever from NASA.<br /><br />I hope I can find something else somewhere else. I will post if I do.

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spacester

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<font color="yellow">Can such a trajectory be designed?</font><br /><br />No.<br /><br />Just no.<br /><br />I'm self-taught on this subject and the reason I took up the study was that I was sick and tired of knowing when the experts really meant "no" when they said "no". Oftentimes, they will say "no" when what they really mean is that "given the following paradigm of spaceflight, no".<br /><br />In this case, it's a real, actual NO.<br /><br />Here's the deal:<br /><br />OK picture the model of a taut sheet with spheres resting on it as our representation of the cis-lunar gravity field. The Earth causes a bigger "dent" in the sheet than Luna. Our spacecraft has to be in some kind of orbit at all times, spinning around in freefall. If in Earth orbit, it is spinning around like a marble in the dent Earth puts in the sheet.<br /><br />The Moon's dent cannot be compensated for - you have to achieve the 'saddle' where the Earth's dent and the Moon's dent merge. At this point, you're going to fall into the Moon's dent no matter what.<br /><br />The scenario you specify seems to require a magical ability to place a craft in space with a chosen position and velocity and real gravitational fields don't work that way. <div class="Discussion_UserSignature"> </div>

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MeteorWayne

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The point is, how do you get it to a few feet off the ground? That's where all the enrgey would be spent in that case. Once you get it there, no problem <img src="/images/icons/smile.gif" /> If we are talking about an incoming speed close to zero, at the Hill radius, the impact is at 5400, unless you decelerate it.<br />If the velocity is less than zero, it never enter's the moon's gravitational field, so never comes near the moon. If it's greater, the speed is more than 5400.<br />Once it crosses the line, it's 5400 or more unless you stop it. <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>

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MeteorWayne

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In general, the ISS has no gravity (yes there is some, but in any case, when you dock you are adjusting the velocity constantly so you don't hit it.) Without decelerating, if you perfectly match the speed before you enter the ISS's gravitaional field, you might hit at a millemeter per second. But without decelerating, you will hit.<br /><br />The moon has much more gravity, enough that you will hit at the speed mentioned above unless you decelerate.<br /><br />Physics can be your friend or enemy, but it doesn't change <img src="/images/icons/smile.gif" /> <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>

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vogon13

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Ok, instead of having the craft touch the lunar surface at ~0 kph, I will stand there with a small fly swatter and ever so gently pat it exactly backwards along the path it just took down and watch it go all the way back to where it came from.<br /><br /><br />Think about it . . . . <br /><br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

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