# Different Approach to Lunar Soft Landing : Feasible?

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#### rogerinnh

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Unpowered Lunar Landing<br /><br />I’ve come up with what I think is a unique approach to landing on the Moon.<br /><br />Comments are welcome.<br /><br />The earliest Lunar touchdowns consisted of simple trajectories from Earth to the Earth-facing surface of the Moon and were not actually touchdowns but rather crash-intos. Subsequent to those early attempts the approach that has always been taken is to first go into Lunar orbit and then to de-orbit to a rocket-powered touchdown.<br /><br />But now consider the fact that the Moon is not a stationary object. It is revolving around the Earth in its orbital trajectory at approximately 3,291 feet per second (if my calculations are correct). Suppose that you had a space craft positioned along the Moon’s orbital trajectory, such that the Moon was moving away from the space craft. Now suppose that the space craft started at “just the right position” away from the Moon, along the Moon’s orbital trajectory, and was “dropped” towards the Moon. The space craft would accelerate towards the Moon (because of the Moon’s gravity), as the Moon was moving away from the spacecraft. If the space craft’s starting position and velocity were “just right” then the point in time and space where the space craft “caught up with” the Moon would be such that the velocity of the space craft would exactly equal the velocity of the Moon along its trajectory (i.e. 3,281 feet per second). The space craft would therefore “touch down” on the Moon’s surface at zero relative velocity, a perfect soft landing without any rocket power required.<br /><br />A similar possibility exists from the opposite direction. If the spacecraft is positioned along the Moon’s orbital trajectory such that the Moon is approaching the spacecraft then, given the appropriate initial velocity of the spacecraft, moving “away from” the Moon, along Moon’s orbital trajectory, the Moon would “catch up” to the space craft at just the right time and position such that the relative velocities b

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#### MeteorWayne

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It doesn't really work that way. Once you are in the gravitational grasp of an Planet or Moon, even if your initial relative velocity is "zero" (note, it must be greater than zero or it will not be captured), the gravitational acceleration will still attract the object to the escape velocity.<br />I don't have the moon's numbers handy, but if an object crawls inside the earth's 1.5 million km earth's Hill sphere( even at 1 millimeter per billion years), by the time it hits the atmosphere, it will be moving 11.2 km/sec (~ 25000 mph). For the earth, depending on it's size, shape, and mass, it will be slowed down by the atmosphere. For the moon, with no atmosphere, the escape velocity (hence impact speed) will be 2.4 km/sec {I looked it up <img src="/images/icons/smile.gif" /> } which equals 5400 MPH. <br /><br />OUCH! <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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#### Leovinus

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As I was reading the original post, I was thinking to myself, "Why does this sound impossible?"<br /><br />My other thought was: "Even if it was possible, would it be more or less fuel-efficient than the tried-and-true method?" <div class="Discussion_UserSignature"> </div>

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#### vogon13

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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 /><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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#### vandivx

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whatever I might sometimes think of scientists I am sure that those who figure these things out like various trajectories of landing crafts have long ago covered all such possible approaches and know damn well what they are doing as this area has been well probed and I would more expect to be impressed to find what is being done than otherwise<br /><br />vanDivX <div class="Discussion_UserSignature"> </div>

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#### MeteorWayne

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If you don't want to splat, you must counter the force of gravity, which requires energy. <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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#### Leovinus

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Here's an idea:<br /><br />Suspend the lunar lander from a parachute. Because there is no air around the moon, we must manually inflate the chute. Thus, we point the rocket engine upward so that we can gently float to the surface. <div class="Discussion_UserSignature"> </div>

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#### vandivx

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LOL and you be the astronaut on board<br /><br />vanDivX <div class="Discussion_UserSignature"> </div>

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#### Leovinus

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Sorry, I'm just the idea man. I leave it to others to implement and carry out my brilliant suggestions. <div class="Discussion_UserSignature"> </div>

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#### bonzelite

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<font color="yellow"><br /><br />Suspend the lunar lander from a parachute. Because there is no air around the moon, we must manually inflate the chute. Thus, we point the rocket engine upward so that we can gently float to the surface.</font><br />that's a cool idea. <br /><br />

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#### bonzelite

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<font color="yellow"><br />Can such a trajectory be designed? <br /></font><br /><br />it sounds like you're suggesting a "Lunar Sychronous" orbit, sort of. you're baiscally sending a craft near the Moon to match it's velocity and relative motion to the Earth. <br /><br />indeed, myriad satellites are in Geosynchronous/geostationary orbit. but can they be made to soft touch down to the Earth? i've never known this to be possible. once the craft lowers beyond a certain threshold, it's orbit destabilizes and it begins to free-fall.

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#### vonster

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<blockquote><font class="small">In reply to:</font><hr /><p>Suspend the lunar lander from a parachute. Because there is no air around the moon, we must manually inflate the chute<p><hr /></p></p></blockquote><br /><br />Of course .. yes!<br /><br />The key to this is that - since we are weightless in space - the astronauts can 'launch' themselves away from the space craft (chute in hand) <br /><br />.... by pulling hard against thier own bootstraps. Can you see this? Or not<br /><br />Ok maybe Im not explaining it very well<br /><br />.<br /><br />.

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#### ldyaidan

##### Guest
Good question. How far off of the moon do we have to get to be out of it's gravity well? I know the first missions will need a lander, but is it feesible to have a "lunar elevator"? This could simply be a structure that has a docking port at the space end, and leads into the lunar infrastructure on the other. Get in, ride the "car" to the end you are needing, and get off... Again, depending on how tall the structure would have to be...(I'm thinking more of a rigid structure than the space elevator concept)<br /><br />Rae

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#### Leovinus

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Here's another idea. If the surface of the moon was smooth enough, you could orbit 1 inch above the ground because of the lack of air. (Ignoring variations in gravity field which throws everything off). But suppose you had the equivalent of a maglev track running across the surface of a really long flat plain. You set up your orbit such that the low point is right over this track. Then instead of the maglev track being used to accellerate the ship, you'd use it to decellerate it. To get it back into orbit, use the maglev track to accellerate it.<br /><br />The power for the track is of course solar power. <div class="Discussion_UserSignature"> </div>

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#### yevaud

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I've heard about that possibility before, but in reference to landing vehicles on Mars. Pretty darned interesting idea, if you ask me. <div class="Discussion_UserSignature"> <p><em>Differential Diagnosis:  </em>"<strong><em>I am both amused and annoyed that you think I should be less stubborn than you are</em></strong>."<br /> </p> </div>

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#### Leovinus

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I can't imagine doing it on Mars since there is an atmosphere. You couldn't take an orbit down to ground level.<br /><br />Can anybody do the math for me and tell me what the orbital speed would be at ground level for an elliptical orbit 60 miles high by 0 miles high? <div class="Discussion_UserSignature"> </div>

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#### yevaud

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No, I meant the Magnetic Capture of approaching aircraft.<br /><br />Low low atmospheric pressure means to airbrake, they'd damn near have to skim the surface a few orbits. The magnetic landing/braking system mentioned would be useful. <div class="Discussion_UserSignature"> <p><em>Differential Diagnosis:  </em>"<strong><em>I am both amused and annoyed that you think I should be less stubborn than you are</em></strong>."<br /> </p> </div>

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#### search

##### Guest
Hello Roger<br /><br />There were no crash intos and what you describe is more or less what they did<br /><br />From:<br />http://history.nasa.gov/afj/loiessay.htm<br />"Lunar Orbit Insertion, on the surface, appears to be a standard orbital mechanics problem, solvable using straightforward, albeit sophisticated tools to calculate a solution. In reality, the message from the computers is, "If you want to get into lunar orbit, well, you can't get there from here." Not easily, that is.<br />Significant constraints are built into, or inherent in the Apollo system, that all conspire together to prevent a LOI burn which satisfies all the mission objectives.<br /><br />Check the plane of trajectory and landing site<br />http://history.nasa.gov/afj/simbaycam/apollozone.jpg<br /><br />From (Apollo 10):<br />http://www.astronautix.com/details/apo27558.htm<br />The crew was impressed by the lunar landscape, although Stafford insisted it looked like a big plaster of Paris cast. The three found it almost incredible that someone back on earth had been smart enough to place them within 110 kilometers of the moon - but there they were. They caught just a glimpse of the surface a minute before they fired the service module engine to go into lunar orbit, an activity that required all their attention. The six-minute retrograde maneuver seemed interminable, just as it had to Borman's group, but the engine kept firing and their confidence in it kept growing. When the engine finally shut down and they were sure that it had done its job, Stafford and Cernan had time to look at the lunar surface. They likened one area to a volcanic site in Arizona. Finally Stafford forced his attention back inside the cabin and told his crewmates that he thought the best thing to say when they got

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#### Leovinus

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<i>Can anyone find a drawing of an apollo orbit and post it?</i><br /><br />O <div class="Discussion_UserSignature"> </div>

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#### search

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Could be.<br />I am stil surprised that I could not find any drawings of orbit trajectories.<br />Further more when I went to the NASA website and tried to open some resources I was redirected to another kennedy page. and when in the Apollo 11 page I found this:<br />http://www-pao.ksc.nasa.gov/kscpao/history/apollo/apollo-11/apollo-11.htm<br /><br />Altitude: 186km x 183km <br />Orbits: 30 revolutions<br />Duration: 08 Days, 03 hours, 18 min, 35 seconds <br />Distance: miles <br />Lunar Location: Sea of Tranquility <br />Lunar Coords: .71 degrees North, 23.63 degrees East<br /> <br /><br />This is the poorest info I have ever seen...<br />Is all the information secret?<br /><br />I think we need some researchers to join this thread...

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#### rogerinnh

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Regarding the posting by SEARCH stating"There were no crash intos and what you describe is more or less what they did".<br /><br />There were indeed "crash-intos". Not manned crash-intos, of course. But the very first missions to the Moon by the US (and I think also by Russia) were spacecraft that simply crashed into the Moon. I remember vividly following the mission on TV and watching the video as it approached the lunar surface. The very last image was less than half a frame's of video because it crashed at mid-frame.<br />

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#### Leovinus

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Just being able to hit the moon back then was a heck of an achievement. <div class="Discussion_UserSignature"> </div>

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#### rogerinnh

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MeteroWayne states:<br /><br />It doesn't really work that way. Once you are in the gravitational grasp of an Planet or Moon, even if your initial relative velocity is "zero" (note, it must be greater than zero or it will not be captured), the gravitational acceleration will still attract the object to the escape velocity. <br />I don't have the moon's numbers handy, but if an object crawls inside the earth's 1.5 million km earth's Hill sphere( even at 1 millimeter per billion years), by the time it hits the atmosphere, it will be moving 11.2 km/sec (~ 25000 mph). For the earth, depending on it's size, shape, and mass, it will be slowed down by the atmosphere. For the moon, with no atmosphere, the escape velocity (hence impact speed) will be 2.4 km/sec {I looked it up } which equals 5400 MPH.<br /><br /><br /><br />That doesn't sound correct. Perhaps if an object starts out at an extremely high altitude from the surface then it will hit at or near "escape velocity". But I'm pretty certain that if I hold a ball a few feet off the ground and drop it, it is NOT travelling at 5,400 miles per hour when it hits the ground.

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#### rogerinnh

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Leovinus writes:<br /><br />"Even if it was possible, would it be more or less fuel-efficient than the tried-and-true method?"<br /><br /><br /><br /><br />It is definitely true that fuel efficiency is a completely separate issue. My gut feeling is that it would definitely be more fuel efficient. Unless the craft needed to subsequently lift off of the surface (think of a supply-delivery craft or a habitation module), it could do away with the landing/liftoff rocket hardware, which at a minimum would make it much lighter.<br /><br />

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#### Leovinus

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I still think you'll drop like a rock when you get close to the moon with your method. <div class="Discussion_UserSignature"> </div>

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