Rocketdyne RS-18 LEM Ascent Engine

[blackparticle]

I've been having an on/off debate for a couple of years now with a friend who is fairly sure that certain aspects of the Apollo missions were 'faked'. I won't bore anyone with the usual arguments but there is one aspect of this that I'm struggling to find an answer for.

From my research it's actually never been discussed as far as I can tell... and that's the ascent engine used in the LEM.

I've analysed the video footage of the Apollo 17 LEM ascent stage -

Checking the given specifications of the engine and the weight of LEM module at lift-off and accounting for 1/6th gravity of the moon, the ascent speed of the module in the video does indeed match the mathematics (a = Dv / Dt).

That's not my stumbling block.. It's the fuel used and the effects of ignition.

The Rocketdyne RS-18 was powered by a hypergolic mixture of Aerozine-50 fuel (N2H4 / C2H8N2 ) and Nitrogen Tetroxide (N2O4).

This fuel was originally developed and used in the Titan II ICBM programme which then was re-developed and used for the Gemini programme. And this is where I can't equate the two and provide a suitable explanation for the discrepancy.

Here are a couple of videos of a Titan II ICBM launch.

Another Titan II Launch

As you can see from those videos, the initial chemical reaction produces a significant amount of what appears to be carbonised 'smoke' whereas the Apollo 17 LEM engine start appears to be a perfectly clean reaction.

While the engine in the Titan II programme was made by Aerojet and designated as LR-87, the principal was very similar to the RS-18 specified for the LEM and the reaction of the fuel, should, therefore, also be similar. Unfortunately, as I'm not a rocket scientist, I can't counter this and can only go by the visual evidence but it's the one part of the argument that I have no answer for.

Are there any chemists out there who can fully work out the reaction of the fuel and oxidiser and what the reaction by-products would be?

What do other people think?

p.s. I've posted this in the science section as I'd like to keep any 'emotional' arguments to a minimum.

[Essex Stargazer]

Well this should be interesting

A conspiracy thread

I thought it was all filmed in area 51

isn't that why the USA don't want anyone near the place

" sits back and awaits the flack "

[Dave R]

This is addressed here (bottom of that post):

[...] the fuel on the LM was also used on the Titan rockets used in the Gemini program. Have a look at their exhausts, and you’ll see they’re virtually invisible, even in the Earth’s atmosphere.

So why do the Gemini launches have big clouds of smoke? Because when the engines are being started, the fuel/oxidiser ratios aren’t perfect, and so either spare fuel or spare oxidiser reacts with the air. This can’t happen on the Moon.

Also here:

That's because nitrogen tetroxide is pre-injected and it reacts chemically with air. That produces smoke. If you watch N204/hydrazine combustion a few seconds after liftoff, you see that there is no smoke and almost no flame -- even in air.

Pre-injected oxidizer creates an initial imbalance in fuel mixture. Incomplete combustion occurs, producing intermediate products that aren't there in steady-state combustion. They incandesce. That's the ignition transient.

Ambient pressure resists plume dispersion. If the plume is kept columnar, it's kept hot and thus incandescent. In a vacuum, the plume disperses too rapidly to retain enough heat to maintain incandescence. Even RP-1 plumes, which are full of particulates and bright yellow-orange, are almost invisible at steady state in a vacuum.

[Zakalwe]

There also were some significant differences in the engine design as well. The LEM motor was designed to be throttleable, and was not started at full power. The engine bell was also not cooled, instead it had an ablative surface (similar to a re-entry heatshield) that was burned away as the motor was being used. This design was selected to provide the simplest possible design. The fact that the ablative surface burned meant that the power delivery characteristics changed as the engine fired, but the LEM computer was programmed to take this into account during descent.

[rocketandroll]

I was going to say...

Giving you my 'rocket scientist' opinion...

The 'smoke' is almost certainly something produced as a reaction of the exhsust plume with air. Thats the ibvious reason it isnt there when used in vaccuum.

Dont get me started on numpties who think the moon landings were faked. The simplest argument that they werent is simply... Given the political situation at the time, if people with no experience or knowledge of aeronautics or astronautics can find reasons why it was clearly faked... Why didnt the Russians find them and tell the World?

Ben

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[acey]

The question has been answered: the missile takes off in Earth's atmosphere and the LEM takes off from the airless moon, hence the difference in appearance.

I think we should maybe have a forum sub-section neutrally named "Unorthodox theories" where Apollo hoaxes, Niburu, astrology etc could be discussed by like-minded souls. And we could have some stickies giving answers to FAQs. Just a thought.

[blackparticle]

Cheers for the input. Even Carl Sagan said, "Extraordinary claims require extraordinary evidence.". I shall add this to the discussion.

[Zakalwe]

I think we should maybe have a forum sub-section neutrally named "Unorthodox theories" where Apollo hoaxes, Niburu, astrology etc could be discussed by like-minded souls. And we could have some stickies giving answers to FAQs. Just a thought.

The rubbish spouted by Apollo "hoax" believers is anything but a theory. A theory is "

1 a coherent group of general propositions used as principles of explanation for a class of phenomena: Einstein's theory of relativity.

2. a proposed explanation whose status is still conjectural, in contrast to well-established propositions that are regarded as reporting matters of actual fact.

3. Mathematics . a body of principles, theorems, or the like, belonging to one subject",

none of which applies, as all of the "evidence" that they spout can usually be debunked in a matter of moments, by anyone with more than 3 working brain cells, an ability to investigate things for themselves, and an enquiring mind.

[acey]

A theory is "

The word comes from Greek "theoria" meaning "contemplation, looking at". Your definition refers to its use within the sciences, and would not cover the way it is widely used e.g. within the humanities.

I said "neutrally named" because, like you, I think the Apollo hoax and similar fringe ideas are rubbish. Whether or not they are "theories" is part of the (to me, pointless) debate that could be conducted within a specially dedicated sub-section.