Physics Demystified: Revisiting the moon landings.

21st July 1969, 02:56 UTC

“That’s one small step for a man. “

“One giant leap for mankind.”

So go the words, uttered by Astronaut Neil Armstrong as he became the very first human being to set foot onto the lunar surface.

For the very first time, humans wondered.

Was it truly possible, for life to flourish beyond our tiny little planet?

The space race was an immense source of inspiration.

The gaze of the entire world was transfixed upon the efforts of NASA to put a man on the moon.

One of the most famous and inspiring speeches of all, given by President John F. Kennedy in his address to congress.

“First, I believe that this nation should commit itself to achieving the goal, before this decade is out, of landing a man on the moon and returning him safely to the Earth.”

“Magnificent Desolation”

“No single space project in this period will be more impressive to mankind, or more important for the long-range exploration of space; and none will be so difficult or expensive to accomplish.”

You drive a Ferrari? Peasant! Check out my dope-ass Moon Buggy!

“We propose to accelerate the development of the appropriate lunar spacecraft.”

“We propose to develop alternate liquid and solid fuel boosters, much larger than any now being developed, until certain which is superior.”

Marvels in engineering; The Saturn V

Unfortunately, 6 landings later, culminating with Apollo 17, the Apollo program was scuttled by NASA.

An entire generation wandered:

Would we ever return?

Would the time ever come again, that humans possessed the means and will to venture beyond this tiny blue dot?

Will we feel that sense of adventure again, as we ventured into the great unknown.

Will the heavens be once again, within our grasp?

Thankfully, 50 years later, the entire world has seen an almost 180 degree attitude shift toward space exploration.

World governments, are waking up to the strategic value of outer space.

Private entrepreneurs, are seeing the economic value of the resources lie out there.

Once again, there is hope.

We are going back to the stars.

John F Kennedy would be so proud.

In the following section, I shall include snippets of Kennedy’s lesser know second speech, which he delivered at a stadium in Rice University.

The speech stirs the soul.

Many years ago the great British explorer George Mallory, who was to die on Mount Everest, was asked why did he want to climb it. He said, “Because it is there.”

Well, space is there, and we’re going to climb it, and the moon and the planets are there, and new hopes for knowledge and peace are there. And, therefore, as we set sail we ask God’s blessing on the most hazardous and dangerous and greatest adventure on which man has ever embarked.

Houston, your City of Houston, with its Manned Spacecraft Center, will become the heart of a large scientific and engineering community. During the next 5 years the National Aeronautics and Space Administration expects to double the number of scientists and engineers in this area, to increase its outlays for salaries and expenses to $60 million a year; to invest some $200 million in plant and laboratory facilities; and to direct or contract for new space efforts over $1 billion from this Center in this City.

“But if I were to say, my fellow citizens, that we shall send to the moon, 240,000 miles away from the control station in Houston, a giant rocket more than 300 feet tall, the length of this football field…

…made of new metal alloys, some of which have not yet been invented, capable of standing heat and stresses several times more than have ever been experienced, fitted together with a precision better than the finest watch”

“carrying all the equipment needed for propulsion, guidance, control, communications, food and survival, on an untried mission, to an unknown celestial body, and then return it safely to earth”

“re-entering the atmosphere at speeds of over 25,000 miles per hour, causing heat about half that of the temperature of the sun — almost as hot as it is here today — and do all this, and do it right, and do it first before this decade is out — then we must be bold.”

Kennedy would be pleased to know, that we’re not just stopping at returning to the moon, but we have ambitions to go far, far beyond.

A most peculiar ring world

In recognition of the renewed interest and vigor with which the world is embracing space travel, let us take a trip down memory lane, and revisit a few concepts and phenomena relevant to the moon landings and interplanetary spaceflight.

Gravitational slingshot

Gravitational slingshot of Juno, the space probe sent to Jupiter.
Gravitational slingshots plots of Cassini,

The diagrams are pretty intuitive i reckon?

By using the gravitational field of a planet, an approaching spacecraft will utilise an approach vector that increases its velocity to a desired level.

It’s simple to envision.

But I can promise you the calculus required to even begin to understand its intricacies is downright insane.

But why do we do this, you might ask?

The simple reason is that the distance between celestial bodies boggle the mind.

Spacecraft already take an awful length of time getting from one body to the other.

Hence by utilising a gravitational slingshot, it greatly reduces fuel consumption, and by extension, the fuel load, and by extension, the power the spacecraft needs to develop in order to escape the atmosphere.

Oh god, it’s getting confusing isn’t it?

But since the title of this blog is Physics Demystified, we can just leave this as such.

Communications blackout during atmospheric re-entry

When a spaceship returns to Earth, there will be a communications blackout.

No radio communication will be able to go in, nor out.

When an object moves at supersonic velocity within at atmosphere, it creates a pressure cone, or more specifically, a Prandtl–Meyer expansion fan.

Commonly seen when military aircraft go supersonic.

We won’t go into the thermodynamics here, but the white cloud you see here, is due to a pressure drop, and hence a temperature drop, leading to condensation.

At supersonic velocities, the air in front of the moving object gets compressed.

And the pressure cone dissipates as a propagating pressure wave.

Most military aircraft travel at about Mach 2 (Twice the speed of sound), when we hear them roar above our heads.

Now, imagine for a second.

What happens when an object moves at Mach 25.

25 times the speed of sound.

When you have an object moving so fast, try to picture in your mind the level of compression of the air.

test footage of a US Navy Railgun.

That gigantic orange cloud you see, is the air behind the slug of a railgun.

The slug moves at such high velocities, that the air in front of the slug gets compressed so much, the air molecules undergo ionisation.

The air is compressed so hard,

That electrons are being ripped away from the nucleus.

SpaceX’s Falcon 9, over the skies of California.

The condom shaped cloud that you see, is a plasma sheath.

This plasma sheath is so highly electrically charged that it simply prevents radio waves from passing through.

A Faraday cage.

Imagine this.

Both you and a friend are standing about 50m apart from each other, on an open field.

On a quiet night, by raising your voice and speaking loudly, the 2 of you would be able to hear one another.

But say, if there was a rock band jamming at full volume, between the two of you.

Regardless of how loud you shouted, you’d still get drowned out by the din.

And that is a simple explanation of the science behind radio blackouts.

And that concludes yet another episode on Physics Demystified!

The renewed effort to reach the moon, truly is something inspirational.

To me, the pursuit speaks volumes of the human spirit.

It shows us what we can do, when humans work together toward a common goal.

It shows us that with the power of hope, even against such monumental difficulty, we can prevail.

Till next time,

Daryl.

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