Why HB's think the LM is top heavy

[Everett]

First post, and I have a theory of why hoax believers think the LM is top heavy. (NOTE: I don't believe in the hoax)

Essentially, it boils down to the LM being so wide relative to its height. After all, everyone knows that rockets are tall, thin and pointy, and since the LM is so wide, it has to have so much more weight up top, so it's top heavy. Rockets aren't top heavy because they're thin at the top.
It almost kinda sorta makes sense, if you try not to think about it from a scientific or engineering standpoint. Or more likely, if you've never encountered or heard of such exotic concepts as 'center of mass' and 'moment of inertia.'

Ironically, having the center of mass so low actually makes it not top heavy. Still, the non-engineer part in me wants to think having the mass distributed low and wide could cause problems with stability, requires excessive maneuvering, which would be engine gimbaling, if a force is applied at the side, far from the center of mass.

Of course, the answer is that the (ascent) engine is fixed, and in a vacuum, there isn't anything to apply the force. Except for the RCS system, where being so far off to the side actually makes it work better.

Also ironically, the Soviet version of the LM, the LK, apparently actually suffered from the 'moving astronaut' problem they accuse the LM of. Really, the cosmonaut's center of gravity had to stay within 3 cm?

[ka9q]

Our friend hunchbacked still claims that one of the "incoherences" he found are the asymmetric ascent propellant tanks (as though he's the first to ever notice...) The imbalance would quickly exhaust the RCS propellant supply, he says, and the LM would crash or be unable to dock.

He claims this was an "obvious joke" from the honest engineers protesting the wicked CIA's thumbscrews, or something.

Attempts to explain that the different densities and masses of Aerozine-50 and N₂O₄ actually required the tanks be mounted at different positions fell on deaf ears. So were attempts to explain that the RCS could draw propellants from the ascent tanks specifically to keep them from running dry should attitude control maneuvers be much more frequent than planned. If I got any response from him at all, it was that any information from NASA can't be trusted and can therefore be ignored. One wonders why he looks at the same information for his "evidence"...

[Echnaton]

Welcome to the forum, Everett.

The mistakes of hoax believers and the reasons for them are a topic of great discussion around here.  Particularly when actual hoax believers are in short supply, as they are now.  The gangly and intuitively awkward looking LM is a masterpiece of design for those of us in the form follows function crowd, because the function is right there, jutting out in plain view.   I really fail to see how anyone cannot look at the LM and see its beauty.  I often wonder about what hoax believers would see if they applied the same thinking to comparing a modern aerodynamic car and an old car that has an exposed exhaust system with the spare tire mounted in plain view. 

[raven]

It strikes me as particularly insane when they comment on the 'foil' covering. Besides the fact that that is not the structural portion of the body, have they ever even looked at other  satellites and space probes? You see that kind of covering all the dang time!
But yes, the LM was a good ship. She did what she had to do admirably and even did some things she was not designed for.

[ka9q]

This "top heavy" LM claim is a good example of the pitfalls of basing physics on intuition.

Even some of the models used in school are a little misleading. For example,  stabilizing a rocket is sometimes compared to balancing a broomstick, but that's not really true. When a broomstick tilts a little off vertical, the force of gravity still pushes straight up, creating an increasing torque that causes the broomstick to rotate even farther off vertical. When a rocket rotates a little off course, the engine thrust vector rotates with it, leaving any torque around the rocket's c.g. unchanged.

[Everett]

Still strikes me as odd that they used tape to attach the foil. (and I always thought it was actual gold foil - the things you learn on this site.) I would have thought adhesives would have been used, but if tape works better and weighs less, then so be it.

The LM doesn't look odd to me, it looks like any other lander.

It never has looked odd to me, either, but since my first exposure to space travel was watching "Apollo 13" (repeatedly), I guess it wouldn't.

[Glom]

Tape is pretty common in aerospace engineering. Just look at your plane the next time you fly. You'll often see it about.

The real mystery of tape is what is the purpose of the tape that divers sometimes have on them?

[ka9q]

People assume it's the ordinary cellophane tape they have at home, but it ain't. It's Kapton, an orange plastic that can tolerate temperatures basically down to absolute zero and up to a few hundred C. I've got some rolls of the stuff.

Kapton is used in large sheets for thermal blankets, giving them their gold color. Gold is commonly used to plate connectors and other electrical parts but rarely is it exposed to space; its equilibrium temperature in sunlight is among the highest of all aerospace materials. I've even seen it used to cover the central collector of a thermal solar power dish.

The visor used on the Apollo helmets was covered with a very thin layer of gold because it's good at blocking near IR without completely blocking visible light. This reduced the cooling load on the life support system.

[DataCable]

I really fail to see how anyone cannot look at the LM and see its beauty.

"You really think that thing's beautiful?"
"God no.  It looks like a toaster oven with legs, but I'm not gonna tell him that."

Still strikes me as odd that they used tape to attach the foil. [...] I would have thought adhesives would have been used

Err, tape is adhesive... with a substrate attached.

[ka9q]

I've always liked the LM. Something so thoroughly optimized for its function has to be beautiful.

Form follows function, but then again I'm an engineer. Non-engineers may disagree, but they wouldn't have made a working lunar lander either.

[Everett]

Ok, now I'm confused.
The gold/orange wrinkled foil is Kapton, right? But your saying the tape used is also Kapton? I was under the impression that the Kapton was itself taped to the structure using a separate piece of tape. (Like a piece of paper being taped to a wall with a strip of scotch tape on the top, where the paper is the Kapton.) So is there also a tape version of Kapton with adhesive on the back, used like the scotch tape in the example above? Or does all Kapton have adhesive on the back, like completely covering a sheet of cardboard with strips of scotch tape?

(I know the materials are far more advanced then cardboard, paper and scotch tape, but I'm using it as an example to figure out how it's attached.)

[Allan F]

Kapton is the material which carries either the reflective aluminium layer, or an adhesive. Used because it is strong, lightweight and heat resistant.

Edit: It was used in either large sheets as insulation or narrower strips with adhesive.

[ka9q]

Right. The "gold foil" is actually Kapton with a very thin layer of vapor-deposited aluminum on the back. It comes in various thicknesses, which accounts for the different colors. The thicker films look dark orange, the thin ones appear yellow or gold.

This sheeting has an interesting property. It appears much darker at far infared wavelengths than at visible wavelengths. This means it radiates heat much more readily than it will absorb it from the sun. But because of the aluminum on the back, it both absorbs and radiates very poorly in that direction. So by stacking up a bunch of these sheets and leaving a gap between them to avoid heat conduction you make a "thermal blanket" that works something like a thermos bottle (remember the LM is in a vacuum). This insulates the LM from its environment as much as possible.

Notice how crinkly the blankets on the LM look? That's intentional. The layers were crinkled up before joining to reduce the contact area between them.

[Chew]

I've always liked the LM. Something so thoroughly optimized for its function has to be beautiful.

+1

[smartcooky]

I've always liked the LM. Something so thoroughly optimized for its function has to be beautiful.

Form follows function, but then again I'm an engineer. Non-engineers may disagree, but they wouldn't have made a working lunar lander either.

Watching the episode Spider from the television series From Earth to the Moon gave me some real appreciation of what an outstanding feat of engineering the design and construction of the LM really was!