Exposing PseudoAstronomy

July 14, 2009

The Apollo Moon Hoax: Why Is There No Blast Crater Under the Lunar Module?


Introduction

For my continuing series in the Apollo Moon Hoax, I am going to address a claim that anyone who has taken physics could explain: Why there is no “blast crater” underneath the lunar module’s rocket engine on the moon’s surface.

All posts in this series:

The Claim

The basic claim goes as follows: Before the Apollo landings, real NASA scientists and real artists (as opposed to fake ones) thought that the engine firing may create a blast crater underneath the lunar module. Pictures of the real site, however, showed no such crater, not even a big depression in the surface, as though the module was just “placed there.”

Obviously, the NASA people who didn’t create the crater on the soundstage/set/Area51/whatever were trying to tell future generations that this was a faked event, leaking this information out so no NASA higher-ups would realize.

Let’s Talk About Pressure

In physics, I think almost everyone knows that much discussion is given to studying “forces.” What is a force? A force has units of mass * length / time2. In other words, a force can be thought of as “what it takes” to accelerate a certain mass over a certain distance in a given amount of time. Gravity is a force. A human stepping exerts a force. A rocket engine exerts a force.

Moving one step further in complexity, we get pressure. Pressure is force / area (mass / (length * time2) ). So while a human stepping exerts a force, when you divide that force into the area of a human footstep, you get a pressure exerted.

The concept of force is actually shown in a neat magic trick that my parents would never let me do as a child: Take a coin, such as a dime. Take a nail and a hammer. Try to hammer the nail into the dime. You probably won’t be able to. Now take a pin and try to hammer the pin into the dime. It will likely go in. Why? Because while you are exerting the same force through the hammer, it is concentrated over a much smaller area with the pin, and hence you are exerting a greater pressure.

Another way to think about that is to take your finger and push on your forehead. All you may get is a white mark for a bit before the blood returns. Now, think (don’t do!!) about what would happen if you took a pin and tried the same thing. You would puncture the skin because while you exert the same force, you are exerting a much greater pressure through the pin.

How Is Pressure Relevant? — The Crux of Debunking This Claim

First, some numbers: The lunar module (LM) descent stage engine had a maximum thrust of 9870 ft-lb, but this was throttleable back to a minimum of 1050 ft-lb. Sounds like a lot. But, the diameter of the nozzle was 63 inches, which is an area of about 3120 in2. Dividing this into the force (thrust) and you have a pressure range of 0.4-3.2 ft-lb/in2, otherwise known as psi. This is equivalent to the metric 2760-22,100 N/m2. But let’s stick with psi.

Anyone who owns a car probably knows that this is already significantly less than your tire pressure … by a factor of 10-100. When Apollo 11 landed, the thrust was down to about 1/3 of max, so down to around 1 psi.

Now let’s look at the average adult footstep: The average non-American weighs around 150 lbs. The average human footprint is around 50 in2 (don’t believe me? do the math yourself!). Divide the first into the second and you have the average human footstep exerting a simple 3 psi.

This is 3x larger than Apollo’s engines!!

The very fact that the astronauts walking on the moon did not create “blast craters” underneath them should be explanation enough as to why the engine did not create a blast crater under it — the pressure was simply too low.

Then Why Did They Think It Would Before?

Good question. The best explanation that I could find is that when the hoax believers say, “NASA scientists,” it implies all NASA scientists. But it could just as well mean 2 NASA scientists as 2000. Hence, I would hypothesize that this was a possibility that was raised by a few people, but the majority in the review board said it would not happen and so the missions went ahead.

As for the artist renderings, well, many of the pictures painted at the time also show a big yellow-red flame coming out of the rocket engine as the LM touches down. But – as was known by all NASA engineers who knew about the fuel system – the fuel used would create no visible exhaust “flame” while in the lunar environment. Hence, an artist rendering should be taken as just that – an artist rendering and not as a scientific gospel.

Final Thoughts

Well, this is actually one of my shorter posts, but I’m trying to be less verbose these days as some feedback I’ve gotten is that I type too much. Regardless of that, though, I think that I’ve covered this claim reasonably well. All because some people thought one thing prior to Apollo landing does not mean that Apollo finding something else is evidence of a hoax. That’s what scientific exploration is.

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