Isn't it true that they were simply placed into a highly eliptical Earth orbit that in fact brought it within the affects of Moon's gravity, at which time it slowed down enough to be captured in a lunar orbit?

Yes, essentially.

Of course to be accurate, a spacecraft is within the effects of the moon's gravity while it's sitting on the launch pad. Those effects are just overshadowed by other effects such as the gravity of more massive, nearer objects.

The translunar trajectory was, in essence, a highly eccentric orbit which brought the spacecraft into a velocity state where the moon's gravity, at a certain point, became more powerful than the earth's gravity, and therefore had a more profound effect on the spacecraft's trajectory than the earth's.

This was done for mission planning purposes. The Saturn V had enough capacity to achieve escape velocity with the Apollo payload. It was just safer to stick with the trajectory that offered the most opportunities to recover from failure.

The fact that they remain in Earth orbit (albeit, a highly eliptical one)explains why they experience weightlessness during the whole journey.

They experience weightlessness because they and their spacecraft follow identical trajectories. It doesn't matter whether you characterize that trajectory as orbital or interplanetary. Ask an orbital mechanics expert and he'll say everything's an orbit. They would have been weightless the whole time even had they reached escape velocity.

Weightlessness is something of an illusion. On earth the gravity pulls you down against the floor, so you feel pressure there. It pulls the contents of your stomach downward, but your stomach structurally prevents it from going where gravity wants it to go. Hence you feel pressure there. Without your stomach there, your lunch would pursue a different trajectory than that imposed on it.

When everything's gone ballistic, gravity is still acting on everything the same as it was. There's no such thing as "zero gravity". But because your stomach and its contents are following identical ballistic trajectories and are being accelerated equally by gravity, the net force between your stomach and its contents doesn't exist.

About half of all new astronauts find their stomachs and the contents thereof trying to pursue different trajectories for reasons having more to do with physiology than with gravity and ballistics.

I think you're correct on the first item, that the Apollo spacecraft didn't reach true escape velocity but just close enough to make it to the moon on a timely basis. (Apollo 11's "escape" velocity was 35,579 feet per second, while Mars Global Surveyor's escape velocity - an actual escape velocity - was 37,563 fps.)

You are wrong about weightlessness, however. Weightlessness occurs wherever both the astronaut and the spacecraft are subject only to gravititational forces. If the astronauts were going to Mars (and not under acceleration), they'd still be weightless.

"wrong" is such an ugly term! [img]/phpBB/images/smiles/icon_wink.gif[/img] Actually, I think I just understated my point. . . that being that the craft (and anyone inside for that matter) is always under the gravitational influence of something, regardless of where it's at, and therefore can be considered in orbit around whichever mass has the most influence at the time. As JayUtah aply stated. . . "everything's an orbit" in the eyes of orbital mechanics. Thanks guys!

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. . . My moustache is touching my brain!!!!

(Crappy software just deleted this a second time.)

"Weightlessness" and "zero gravity" are misnomers. The conventional definition of "weight" is the pull of gravity. Astronauts experience practically as much pull of gravity as people on the surface of the earth.

The difference is that the astronaut's evironment falls with them.

What we feel as gravity, is really all the tensions of our body resisting the pull. The ground pushes up on our feet, which holds the skeleton erect, and the organs all hang from the skeleton by tendons or by the skin enclosing the whole body or by the muscles connected to the frame. When a person is in free fall (i.e. skydiving - neglecting wind resistance), they do not experience the reaction force of all those tensions between the tendons and muscles and skin on the organs.

The reason astronauts are said to be weighless is because (a) they do not experience those resistance forces (i.e. the feeling of weight); and (b) they do not observe the visual behavior of weight, falling with respect to their environment. But that is an illusion. As astronaut on the space station is falling every bit as much as a skydiver falls after stepping out of the plane. The only difference is that the astronaut has a significant sideways velocity, fast enough that they fly past the edge of the Earth before they fall down to the surface, so to speak.

Here's a visual of what I mean. Project the Earth as a flat disk. Assume gravity is a uniform field pulling down from under the disk, such that it pulls above the disk and also beside the disk to some referent below the disk. Now drop a skydiver from above the center of the disk. With negligible sideways velocity (and neglecting air resistance), he falls straight onto the disk. Until he opens his parachute and increases drag. Now take an astronaut from above the skydiver and drop her, but throw her sideways really hard. As she falls, she translates to the side until she falls past the edge of the Earth. That is exactly what happens with an orbit. Except the disk is a sphere, and the gravity pulls toward the center of the sphere. The velocity still is the reason the astronaut does not bounce off the ground.

I've always preferred the "super duper cannon on top of the really tall mountain" analogy. Shoot the ball parallel to the ground with enough force to get it a quarter of the way around the earth, and you begin to see how it's ballistic path almost matches the curve of the Earth. Increase the charge so the next shot travels half way around the Earth, and it becomes more evident. Now, use a full charge, and the ball's sideways velocity causes the curved decent tragetory to exactly match the curve of Earth. Voila! the ball's in orbit.

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. . . My moustache is touching my brain!!!!

Actually, it wouldn't it even take less than 1/100th as much fuel if the LM were 1/100th as massive? Rather, I don't think fuel and payload scale linearly with respect to each other as increasing payload, increases the amount of fuel required, which adds extra payload and so on. Perhaps a square relationship?

Not sure, but just a guess [img]/phpBB/images/smiles/icon_smile.gif[/img]

Mark

I edited this to get quote formatted properly--tBA

<font size=-1>[ This Message was edited by: The Bad Astronomer on 2001-11-23 15:24 ]</font>

Granted, I simplified the problem quite a bit. Only if the LM had to put out as much thrust (i.e. opposing force) as the Saturn booster would it require 1/100th the fuel if it was 1/100th as massive. Suffices to say it most certainly does not - the poor thing would have been broken apart accelerating that fast.

You are missing the point. Smart people should be able to figure these things out on their own. That is why it is on an "exam," not a "FAQ."

My impression was that these were serious questions being asked by people who honestly did not know the answer or thought that they were evidence of a hoax.

Jay: My favorite quote relating to Mensa comes from Will Rogers: "We're all ignorant. We're just ignorant about different things."

"<u>Be humble</u>, we're all ignorant. We're just ignorant about different things."

Except for the Bad Astronomer himself, of course. [img]/phpBB/images/smiles/icon_wink.gif[/img]


<font size=-1>[ This Message was edited by: ToSeek on 2001-12-05 10:35 ]</font>

Are you saying that the BA is ignorant in all things? [img]/phpBB/images/smiles/icon_confused.gif[/img]

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Any day you wake up on "the right side of the dirt" is a good day.

T. Anderson

Maybe he's saying the BA isn't humble... [img]/phpBB/images/smiles/icon_smile.gif[/img]

I think I'll stay out of this and let you hash this out!

I was of course acknowledging that the BA is all-knowing but manages to remain charmingly humble nonetheless. [img]/phpBB/images/smiles/icon_wink.gif[/img]

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Everything I need to know I learned through Googling.

And wise too!

[Hands out tissues for purposes of nose wiping...] [img]/phpBB/images/smiles/icon_smile.gif[/img]

Richard Feynman (considered to be the greatest American physicist) had a reported I.Q. of 123 (Stanford-Binet, since that was the I.Q. test given in high schools at that time). He would never have been admitted to Mensa, but he was truly brilliant.

That said, however, there are many knowledgeable people in Mensa. They do not stand out, because a high score on an I.Q. test does not qualify as great knowledge. A high I.Q. merely is an aptitude and not a *given*. People with brains which never are used, or which are used foolishly, remain ignorant. What you folks were discussing, in fact, was that the people with the high I.Q.s who showed ignorance, were not properly educated. They still had good mental capacities, but those mental capacities were never used and/or were misdirected in the direction of baloney. What a waste...

There are a great number of knowledgeable people in Mensa. As in any group of people, there are bound to be various abilities. The single criterion for being a Mensa member is a high I.Q. score (in the top 2%) on one of many possible tests. I.Q. tests taken in the past (such as some earlier S.A.T., G.R.E., etc.) were really I.Q. tests (before they became performance exams [probably superior to I.Q. tests in the sense of measuring knowledge]) can be, and are, regularly used for admittance into Mensa.

There are very many interesting people in Mensa. The most vocally foolish ones may sound or behave like imbeciles, but the test does not measure anything other than what it measures.

I.Q. is a measurement of potential of some kind or another. Obviously it did not measure Richard Feynman's superior abilities, so the test is flawed in that it did not measure his superior level of brilliance.

I happen to belong to a local Mensa group where there are a number of intelligent and knowledgeable people. I also belong to many other organizations where I.Q. is not a question, but where there are equally knowledgeable people. In my local group, the emphasis is directed away from pseudoscience. Most of the silly ones stay home from meetings.

I personally believe that perfection is a state of growth.

Of course, now I am going to get it for admitting to Mensa membership. I just wanted to set the record somewhat straight. I go to Mensa meetings in my area because many of the members are so very interesting AND KNOWLEDGEABLE. They treat women very well, also. Females in Mensa are able to have great discussions on any topic without any male chauvinistic baloney being mixed into the discussions.

ljbrs [img]/phpBB/images/smiles/icon_smile.gif[/img] [img]/phpBB/images/smiles/icon_biggrin.gif[/img]

"I.Q. is a measurement of potential of some kind or another. Obviously it did not measure Richard Feynman's superior abilities, so the test is flawed in that it did not measure his superior level of brilliance."

As somebody once said (I paraphrase): "Your IQ score is nothing more than a measure of how good you are at IQ tests, and nothing else."

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Up the Imps!

Radiation Shielding...

Something occurred to me, that would give an 'accurate' estimate of the amount of material it would take to shield the astronaughts from any radiation from the van allen belts.

I still am as a civilian, but when in the USArmy i worked for a time in germany, (83-86) where our computer system was contained inside two 10 ton trailers (the long single trailers mac trucks haul around) that were attached by an umbilical.

The specifications of these trailers, and the umbilical between them were rather intresting. The outer skin of the trailers were a compite of metals and ceramics, that was semi-rigid. it could be dented, but barely, it tended to push back to it's shape. If the specs were right the composite is stroger by an order of 4 then titanium. The insulation and frame of the trailers was also intresting. The frame was composed of the composite also, with a thin coating of lead. The insulation, was a lead coated fiberous compound, (not fiber glass).

The umbilical was made of the same material used in the N.B.C. suits, (i have no information on what that is), but 1/4 of it is all thats needed to block 99% of radiation in a contaminated area.

Total lead in one van? less then 1/2 ton.

With the umbilical dedatched quickly, the doors sealed, and the AC's turned on to not exaust air, and the internal oxegen tanks turned on, each van could protect about 5 people inside, from a 10 kton tactical nuke landing as close as a 1000 yards away. The trailers might roll from the forch if the blast hit side on, but could sustatian that force, and the rolling. The trailers had extract straps on them that people could use to lash themselfs against the walls, as well as lash lose equipment down.

The Trailers were also rated as survivable from a 100 megton blast from 2 miles+ distance from ground zero. The dose of radiation recived from each cenerio by people inside the trailers was the equivielent of about 6 medical x-rays, as long as they got the trailers sealed.

Comparing the Van allen belts to the radiation of a 100meg ton bomb at 2 miles, is like comparing the hover dam to the sun.

In it's simplest terms the amount of lead needed to shield the astronaughts is negligible. A coat of leaded paint would of been suffient, not to mention that most metals have some radiation shielding qualities, and that leaded paint would of been unneeded.