The illogical travel of the Lem to the moon

[echnaton]

Nov 3, 2010 14:43:10 GMT -4 inquisitivemind said:

And I'm still waiting from a serious article backing up your claims to show me wrong.
I insist for having it.

Your claim, your proof.

[gillianren]

Nov 3, 2010 12:28:11 GMT -4 inquisitivemind said:

Thanks for the acronyms; may be the ones I use are not the good ones, but I'm used to using them, and I think that everybody understands them, even though they may not be the exact terms I should use.

And again, this proves to me that you are not a scientist of any fashion. Not a scholar. Not someone with any kind of understanding of how proper research works. What if I decided that your name was Gargleplatz? Now, that's not your name. It's not what anyone else calls you. But I've gotten used to it, and I think everyone knows who I mean, so that's what I'm going to call you from now on.

Gargleplatz, have you not understood that, among the rocket scientists who think you are wrong are several members of this board? There are people who post here who know you're wrong, because if you were right, the thing they do for a living wouldn't work if they operated the way they're telling you they should.

[inquisitivemind]

What you are showing me is a game.

[Apollo Gnomon]

Gargleplatz, have you not understood that, among the rocket scientists who think you are wrong are several members of this board? There are people who post here who know you're wrong, because if you were right, the thing they do for a living wouldn't work if they operated the way they're telling you they should.

More to the point, several of the people on this forum who disagree with you are rocket scientists.

[inquisitivemind]

Nov 3, 2010 14:46:26 GMT -4 echnaton said:

Nov 3, 2010 14:43:10 GMT -4 inquisitivemind said:

And I'm still waiting from a serious article backing up your claims to show me wrong.
I insist for having it.

Your claim, your proof.

I have given my proof:
I have shown an article which explicitly that the satellite has a natural tendency to go into a flat spin; this means that without an attitude control, it would show its flat side to the earth (which probably is quipped with solar cells); but the antenna is not mounted on the flat side, and that's why it needs an attitude control.
And there are nanosatellites which don't need an attitude control to keep the same attitude toward the earth (although they are not very precise).

[inquisitivemind]

I have not said that the lem could not have various trajectories, and move in very various ways.
What I have said is that there is an optimal trajectory to save as much fuel as possible, and it was the interest of the astronauts to save fuel.

[chew]

The part of the article you cited gave an example for one method of satellite stabilization. And you continue to misunderstand "flat spin".

Read this:
en.wikipedia.org/wiki/Attitude_dynamics_and_control

[Apollo Gnomon]

Nov 3, 2010 14:56:56 GMT -4 inquisitivemind said:

I have not said that the lem could not have various trajectories, and move in very various ways.
What I have said is that there is an optimal trajectory to save as much fuel as possible, and it was the interest of the astronauts to save fuel.

Implicit in your thesis is the assumption that the maneuvers described were not included in the fuel budget.

[chew]

This is an example of a gravity-gradient stabilized satellite:



After launch it took two weeks for it to become stabilized. I ask again, show me your math on how long it would take the CSM to become gravity-gradient stabilized.

[inquisitivemind]

Nov 3, 2010 15:01:05 GMT -4 chew said:

The part of the article you cited gave an example for one method of satellite stabilization. And you continue to misunderstand "flat spin".

Read this:
en.wikipedia.org/wiki/Attitude_dynamics_and_control

It does not disprove what I said.
Some satellites need an attitude control because their natural attitude does not allow them to point exactly to a given point on the earth.
Furthermore they are subjected to external inteferences (like solar ones), which make their attitude vary a little; they are not precise enough for some applications, and they do need an attitude control.
Now, the CMS was much closer to the moon than a satellite would be, so to avoid a too long travel of the Lem to the moon, and it was not stationary toward the moon, it had a relative speed of 6000 km.h relatively to it; that was giving it more stability in its orbital trajectory than a stationary satellite which is farther from the planet and orbits with a greater radius.

[Apollo Gnomon]

I've just re read this portion of the OP:

Now you might ask: Why is it necessary to start countering the horizontal speed as soon as the LEM leaves the LCM (green trajectory) , why couldn't the LEM start to descend vertically, and start countering the horizontal speed when it is closer to the moon (red trajectory)?

Well, if the LEM starts descending vertically, and starts countering the horizontal speed when it is closer to the lunar ground, then the lem will have lost its reserve of height, and will not be allowed to lose as much height as he could if it starts earlier to counter the horizontal speed; as a result, the LEM will have to counter more the lunar attraction than with the first trajectory, not to lose too much height.

and realized that it's completely nonsense.

There is no way for an orbiting body to simply lose altitude without affecting horizontal velocity. It's not a helicopter.

[Ian Pearse]

Inquisitivemind, how about a different approach? Imagine the CSM orientated so that the SPS engine bell is pointed at the Moon and, with the LM still docked, the DPS engine bell pointed away from te Moon. Now, calculate the Centrifigal Force Differential across the length of the complete spacecraft, as per your original post. Now calculate the resultant torque and show us how tat would force the complete stack to assume the "horizontal" attitude you talk about. Some figures to start with - CM height 3.23m, SM height 7.41m, LM height 6.98m. CM mass 5900kg, SM mass 24500kg, LM mass 15440kg (Apollo 11 LM would have been a bit less than this). Radius of the Moon 1737.1km (Mean), orbital heigt 96.6km (circularised). Go to it.

[inquisitivemind]

Nov 3, 2010 15:20:12 GMT -4 Apollo Gnomon said:

I've just re read this portion of the OP:

Now you might ask: Why is it necessary to start countering the horizontal speed as soon as the LEM leaves the LCM (green trajectory) , why couldn't the LEM start to descend vertically, and start countering the horizontal speed when it is closer to the moon (red trajectory)?

Well, if the LEM starts descending vertically, and starts countering the horizontal speed when it is closer to the lunar ground, then the lem will have lost its reserve of height, and will not be allowed to lose as much height as he could if it starts earlier to counter the horizontal speed; as a result, the LEM will have to counter more the lunar attraction than with the first trajectory, not to lose too much height.

and realized that it's completely nonsense.

There is no way for an orbiting body to simply lose altitude without affecting horizontal velocity. It's not a helicopter.

That would be true for a plane, but not in space.
Of course, the orbital body can lose altitude without losing its horizontal velocity; the attraction will slightly increase, so there will be a little vertical acceleration if the horizontal speed remains the same.

Of course, it's not an helicopter; it doesn't behave as such, but still for the helicopter too there is an optimal trajectory for landing.
I have used this analogy, knowing it was not exact, because the lem does not behave like an helicopter, but to help people to understand.

[inquisitivemind]

Nov 3, 2010 15:14:54 GMT -4 chew said:

This is an example of a gravity-gradient stabilized satellite:



After launch it took two weeks for it to become stabilized. I ask again, show me your math on how long it would take the CSM to become gravity-gradient stabilized.

I have never said that the satellites don't need an attitude control.
Some have to have a very precise orientation, and they can also be shaped that they will be more sensitive to interferences.

[chew]

Nov 3, 2010 15:18:29 GMT -4 inquisitivemind said:

Nov 3, 2010 15:01:05 GMT -4 chew said:

The part of the article you cited gave an example for one method of satellite stabilization. And you continue to misunderstand "flat spin".

Read this:
en.wikipedia.org/wiki/Attitude_dynamics_and_control

It does not disprove what I said.
Some satellites need an attitude control because their natural attitude does not allow them to point exactly to a given point on the earth.
Furthermore they are subjected to external inteferences (like solar ones), which make their attitude vary a little; they are not precise enough for some applications, and they do need an attitude control.
Now, the CMS was much closer to the moon than a satellite would be, so to avoid a too long travel of the Lem to the moon, and it was not stationary toward the moon, it had a relative speed of 6000 km.h relatively to it; that was giving it more stability in its orbital trajectory than a stationary satellite which is farther from the planet and orbits with a greater radius.

It disproves everything you have claimed! No where in there does it talk about a satellite's natural tendency to point at the orbited body.

Your "stability in its orbital trajectory" remark is complete nonsense. You confused the centrifugal force demonstration of a weight on a string with centripetal force in orbit. You saw the weight on the end of the string become stable and somehow translated that to spacecraft.