57 years ago in July 1969,
the world stood still, staring a go at
grainy, flickering televisions as Buzz
Aldrin and Neil Armstrong descended from
the Eagle Luna module towards the moon.
>> Looking back, it feels almost like a
fever dream of ambition. This was only
66 years after the first airplane took
flight. But against all odds, we broke
free from Earth's gravity and touched
another world.
>> Base here. The Eagle has landed.
>> This frontier busting feat was presented
as absolutely effortless. A triumph of
US might. But was it really all plain
sailing? What the 600 million or so TV
viewers had no idea about was that this
mission nearly failed. Behind the
scenes, approximately 400,000
engineers, scientists, and experts
worked tirelessly around the clock from
incredibly detailed plans years in the
making to keep it all on track. The
slightest deviation could end not just
in human tragedy, but also have huge
global political consequences.
So, how did this scientific army plan
for every eventuality and stop disaster
in its tracks?
I'm Alex Mccoan and you're watching
Astram Extra.
Join me today as we uncover the
incredible science that made the Apollo
11 mission possible. We'll explore the
launch, journey through space, and
descent onto the moon, digging into the
meticulous maths, maneuvers, and
materials that kept the Apollo 11 team
alive that most people don't even know
existed.
The next time you go out at night, look
up, find the moon. Hopefully, you can't
really miss it. And now imagine going
there, traveling more than 384,000
km away from everything and anyone any
human being has ever known and actually
landing on the moon. It blows my mind to
think about, but nearly 60 years ago,
three humans did just that.
On Wednesday the 16th of July 1969, an
estimated half a million people
descended on the roads and beaches
around Cape Canaveral. They were here to
witness the launch of Apollo 11,
humanity's first attempt at a manned
moon landing. A 110 m Saturn 5 rocket
shimmerred in the distance. The
excitement was palpable.
But what none of these lawn chair
lounging enthusiasts knew was that a
problem was about to unfold that could
stop the mission before it even got off
the launch pad. Just as the crew arrived
on site, a leaking hydrogen replenish
valve was discovered 60 m up in the
third stage of the Saturn 5. Not
something you want to see just before
you're set to take off. Because liquid
hydrogen is kept at a bone chilling
minus252°
C, it constantly boils off into gas as
the rocket sits on the pad. So, the
replenish valve allowed the tank to be
constantly topped up, keeping it at 100%
capacity. This was vital. Without a
completely full tank, the rocket would
not be able to complete its trans lunar
injection, the burn that would take the
craft out of Earth's orbit and towards
the moon. The leak was so severe it
could have caused an explosion. So fuel
loading was immediately stopped and the
lines were quickly drained. It was only
just over 2 years since the tragic
Apollo 1 fire where three crew members
had died. So there was no room for error
and certainly no appetite for risk. If
the leak remained unressed, the mission
would be over before it even left the
pad.
So, a brave crew consisting of three
technicians was dispatched to try and
tighten the valve. But with a little
more than 2 hours to launch, time was
running out. The crew were working on
the valve, manually tightening each
bolt, even as the astronauts were
starting to board the craft just 30 m
above them. But when they still failed
to stop the leak, the crew took the
extreme measure of pouring water from an
eyewash station over the valve where it
froze. While the resulting ice
successfully isolated and sealed the
leak, it rendered the valve completely
inoperable. They needed another way to
keep the tanks topped up. Engineers
decided to try using the large main fill
valve to keep fuel in the tank,
something it was never intended for. For
the final hours of the countdown, two
engineers worked to keep the rocket
flight ready. One monitored fuel levels
whilst the other turned the fill valve
on and off, topping up the tanks to
compensate for boiloff.
>> Oxidizer tanks in the second and third
stages now have pressurized. Meanwhile,
Buzz Aldrin, Michael Collins, and Neil
Armstrong sat in the command module in
eerie silence, preparing themselves for
launch. Now sealed off from Earth's
atmosphere entirely, they were concerned
with a different gas, one that was just
as critical to their survival as the
integrity of the rocket itself.
During the planning stages, it had been
decided that the Apollo spacecraft
needed to be as light as possible. To
make that happen, a decision was taken
to fill the astronauts module with pure
oxygen.
Normal air is 78% nitrogen. So only
taking oxygen meant that they didn't
need heavy tanks of nitrogen and allowed
for the use of a lower pressure within
the craft. combined this made for a
lighter weight spacecraft. Win-win,
right? Well, not really. Oxygen is very
flammable. And this was a contributing
factor in the Apollo 1 fire I mentioned
before. After that fire, the gas makeup
NASA used was tweaked to a mix of 60%
oxygen, 40% nitrogen to make it less
flammable. They also pressurized it at a
much higher 16 psi. So if any leaks
occurred, the air would flow out and not
let the humid Florida air in.
Once they were safely in orbit, the
composition would then gradually be
changed to pure oxygen at a lower
pressure of 5 psi. But even this amended
launch mix caused problems. As I
mentioned, normal air is around 78%
nitrogen and 21% oxygen. This mix meant
that humans have a significant amount of
nitrogen dissolved in our blood. Early
testing showed that if astronauts took
off like this, when the cabin pressure
dropped, the nitrogen formed bubbles in
their blood and joints, causing a
potentially lethal condition. It was
therefore mandatory for all the
astronauts to change their internal
makeup before they even set foot on a
rocket. They did this by breathing pure
oxygen for roughly 2 hours beforehand to
flush out the nitrogen from their blood,
which is why you see them attached to
what looks like suitcases as they walk
to the rocket. That's the oxygen. Having
successfully purged the nitrogen from
their veins to survive the launch, the
crew was ready to go.
10 9 ignition sequence start. 6 5 4 3 2
1 zero. All engine running.
Heat. Heat.
But this was just the beginning of their
journey. Now they actually had to get to
the moon. The astronauts started to
prepare themselves for trans lunar
injection, the engine burn that would
send them out of low Earth orbit towards
the mysterious moon. This was a
particularly dangerous part of the
journey as it required some exacting
maths to ensure the correct trajectory.
Get it wrong and they risked being lost
to deep space. And they still had to
make it out of the lethal radiation
field that blankets the Earth, the Van
Allen radiation belts.
The Van Allen radiation belts are
essentially two concentric donuts of
radiation held in place by Earth's
magnetic field. Normally, they act as a
shield protecting our planet and us on
it from the solar wind. But for a
spacecraft passing through them, they
are a high energy gauntlet. And in the
1960s, the lethality of these belts was
a terrifying unknown. Scientists were so
concerned that they even conducted high
alitude nuclear tests, including a
mission called Starfish Prime, to see if
they could physically blow a hole in the
belts to create a safe passage for
astronauts. Needless to say, this was
less than effective and actually added
radiation to the belts. So instead,
NASA's trajectory experts found a
solution in geometry. A team of
so-called human computers, mainly poorly
paid women who would go on to become
NASA's first computer programmers. They
tweaked the mass of the trans lunar
injection to exploit a loophole in the
Earth's magnetic architecture. It was
much safer to go directly out at the
North or South Pole where there wasn't
much radiation, but doing so would have
used up too much fuel. The compromise
was a slant trajectory. NASA precisely
angled and timed the launch and the
burn. So, the spacecraft would bypass
the high density horns of the inner Van
Allen belt entirely and head through the
weaker fringes of the outer belt. But
even after making it through the
radiation belts, the navigational
problems didn't stop. In fact, the
chances of things going wrong only got
higher.
When people think of Apollo 11 flying to
the moon, many imagine its engines were
burning the whole time. But to do that
would have required too much fuel. It
would have made Saturn 5 so heavy, it
wouldn't have made it off the ground.
Instead, for most of its trip through
space, engineers used physics to coast
Apollo 11 to the moon. Well,
specifically where the moon would be in
3 days time. It followed a figure of
eight geometry that used the moon's mass
as a gravitational anchor and free
accelerator.
This was called a free return
trajectory, a mathematical fail safe to
ensure that if the spacecraft's engines
failed, the moon's gravity would
naturally sling the craft back towards
the Earth's Pacific Ocean. Once the
Saturn 5's third stage had provided the
initial shove, the spacecraft became a
ballistic projectile. It was essentially
falling away from Earth, gradually
slowing down until it reached the
equiere,
the invisible tugof-war point where the
moon's gravity finally become stronger
than the Earth's. From that point, the
moon's gravity took over, accelerating
the craft towards its destination for
free. But this required terrifying
precision. If the craft were too slow,
it would fail to reach the moon's
hillphere, the zone where the lunar
gravity takes over, too fast, and they
would overshoot the target entirely,
hurtling into a permanent solar orbit
with no hope of return. To hit the right
window, the Saturn 5's third stage had
to ignite for exactly 5 minutes and 48
seconds. But it wasn't just about time.
Velocity was also key. The engine needed
to add precisely 3.05 km/s to the
rocket's orbital speed. A deviation of
just 1 second in burn time could mean
the difference between a historic
landing and a drift into the cosmic
dark.
Thankfully, it went exactly as planned,
taking the Apollo astronauts from around
28 12,000 km/h to more than 39,000 kmh.
But as they hurdled ever closer to the
moon, the astronauts needed to decouple
from the Saturn 5 rocket, they were
currently encased in one of its top
sections, which was far too heavy to
make it all the way to the moon.
The Apollo spacecraft was not a single
cohesive vessel, but a modular stack
composed of three distinct sections, all
housed within Saturn 5's third stage.
There was the service module, a
windowless powerhouse containing the
fuel cells and the primary propulsion,
the command module where the astronauts
were for takeoff, and the lunar module,
the fragile two-stage craft designed for
the lunar descent.
While we often imagine this trio flying
as a single unit, in fact, it required a
complex piece of inflight assembly known
as transposition, docking, and
extraction.
During launch, the Luna module was
stored beneath the command and service
module, tucked safely inside the
spacecraft lunar module adapter,
essentially a protective garage on the
upper neck of the Saturn 5's third
stage. This was necessary because the
lunar module was far too fragile to be
directly exposed to the forces needed to
climb through Earth's atmosphere.
Once trans Luna injection was complete
and the crew were coasting towards the
moon, they had to build their new ship.
Pyrochnic bolts fired, jettisoning four
protective panels and exposing the lunar
module. The command and service module
or CSM then detached.
To avoid damaging the delicate lunar
module with the massive heat of the main
engine, the astronauts used only the
small reaction control system thrusters
positioned in the top of the CSM's cone
to drift a short distance away. At just
3 and 1/2 hours into the mission with
surgical precision, pilot Mike Collins
turned the CSM 180°, facing it back
towards the spent third stage.
He then moved in for a nose ton-nose
docking, connecting the lunar module to
the top of the CSM, essentially wearing
it like a hat for the remainder of the
3-day journey to the moon. Only with
this mechanical connection complete,
could they now begin what NASA termed
the trans lunar coast towards the moon,
trusting their navigation to a computer
with less processing power than a modern
calculator? But how did they know they
were on course with no real landmarks,
only an empty vacuum?
While Project Gemini, the space program
before Apollo, had experimented with
basic digital maths to aid navigation,
the Apollo program represented a
paradigm shift. It was the first time
human lives were entrusted to a computer
for the entirety of a voyage into space.
The Apollo guidance computer or AGC
developed at MIT's instrumentation lab
was a marvel of miniaturization.
At a time when most computers filled
entire rooms, the AGC was roughly the
size of a briefcase. It was also the
first of its kind to utilize silicon
integrated circuits, the ancestors of
the chips in your smartphone today. By
today's standards, its specs were pretty
humble. Just 4 kilob of erasable RAM and
about 72 kilob of rope memory software
that had literally been woven into the
copper wire by hand.
To know where it was in the featureless
void, the AGC relied on the inertial
measurement unit. This was the
spacecraft's inner ear, a stabilized
platform of three gimbal gyroscopes and
ultra sensitive accelerometers that
allowed the computer to track every
nudge of the thrusters and every shift
in orientation, maintaining a fixed
reference in space without ever looking
out a window.
But even the most advanced sensors in
the 1960s were prone to drift. Over
time, tiny mechanical errors in the
gyroscopes would accumulate, causing the
computer's internal map to slowly lose
its alignment with reality. To fix this,
NASA turned to the oldest trick in the
navigator's book, the stars. From the
cockpit of the command module, Mike
Collins used a sextant just like the
18th century sailors did. He would peer
through the optics to find two specific
guide stars from a catalog of 37 stored
in the computer's memory.
>> Houston, we'd like you to press on to.
>> Then use the sex to measure the exact
angle between these stars and the Earth
or Moon's horizon.
Finally, he fed this data back into the
computer, detailed as a P23 sighting,
which allowed it to reset its internal
gyroscopes.
The crew were now on a straight path to
the moon. And you might think this meant
things got easier, but in reality, it
created a lethal thermal nightmare. One
extreme enough to rip their ship apart.
In the vacuum of space, there is no
atmosphere to circulate heat, which
creates a world of thermal extremes. The
side of the spacecraft facing the sun
can bake in temperatures as high as 121°
C, while the side shrouded in shadow
plunges to a staggering - 157°.
Without intervention, these massive
temperature gradients would have caused
the metal skin of the service module to
expand and contract unevenly,
potentially warping the structure,
freezing fuel lines, or frying the
delicate electronics nestled just inches
away. So NASA used a maneuver called
passive thermal control, more colloally
known to the engineers and astronauts as
the barbecue roll. Just like a
rotisserie chicken over a fire, the
spacecraft was set into a slow rhythmic
spin of exactly three revolutions per
hour, or roughly 0.3°/s.
This constant motion ensured that no
single part of the hull was exposed to
the sun or the cold of deep space for
too long. The internal systems and the
astronauts inside remained at a steady
room temperature of approximately 21° C.
It was a low tech solution to a high
stakes problem. But whilst the
temperature was stable, the astronaut
safety was a different story because out
in space there is one other big threat.
Radiation.
As I mentioned earlier, Earth is
protected by a thick atmosphere and the
invisible magnetic donuts of the Van
Allen belts. But once the spacecraft
leaves these protective shields, it
enters a shooting gallery of high energy
particles.
High doses of these particles could
cause acute radiation sickness, nausea,
and disorientation, which would lead to
fatal errors during a complex lunar
landing. Not to mention the risk of
developing cancer later in life.
Solar particle events caused by solar
flares or chronal mass ejections could
flood the spacecraft with a sudden
deadly burst of protons. These solar
storms are powerful enough to not only
irradiate human tissue, but to scramble
the delicate silicon of the Apollo
guidance computer. Since a leadline ship
would be too heavy to ever leave the
ground, NASA had to rely on intelligence
and timing.
First, they established the Solar
Particle Alert Network.
This was a global ring of observatories
that monitored the sun 24 hours a day.
If a major flare was spotted, a warning
would be sent to Houston, giving the
astronauts time to take cover in the
most shielded part of the command
module. Counterintuitively, NASA had
actually timed the Apollo program to
coincide with the solar maximum, the
period in the sun's 11-year cycle where
it is most active. While this increased
the chance of a solar flare, it also
strengthened the heliosphere, a
bubble-like region of space around the
sun and planets caused by the solar
wind. During solar maximum, the sun's
intensified solar winds acts like a
magnetic umbrella, pushing away much
more powerful and harder to block
galactic cosmic rays. By accepting the
risk of a storm they could monitor, NASA
shielded the astronauts from the
constant drizzle of deep space
radiation.
But this constant monitoring required a
communication line to be open between
the astronauts and Earth the whole time.
And that's not easy given the 300,000 km
distance and the fact that the world had
not yet invented fiber optics, a global
satellite network or the internet.
In the vacuum of space, there is
absolute silence. So instead, to bridge
the nearly 384,633
km gap between Earth and the Moon, every
word, every command, and every shot of
grainy television footage had to be
converted into electromagnetic radio
waves.
Despite traveling at the speed of light,
these signals still face the difficulty
of distance, which created a small lag,
a delay of about 1.3 seconds each way,
meaning an astronaut had to wait nearly
3 seconds for an answer to any question
sent to Houston. To handle the massive
amount of data needed to be sent back
and forth, NASA developed the unified
Sband or USB system. Operating in the
1.5 to 5.2 2 GHz range. This was a
masterpiece of integration. Rather than
having separate radios for voice, video,
and spacecraft health data, the USB
combined them into a single
highfrequency stream. Managing the
stream was the manned space flight
network coordinated by the Goddard Space
Flight Center. Because the Earth is a
rotating sphere, NASA couldn't rely on
just one antenna. They deployed a global
safety net to ensure messages got
through. This net consisted of 17 ground
stations scattered from Madrid to
Canberra, four tracking ships positioned
in the vast stretches of the Atlantic
and Pacific, and a fleet of eight Apollo
range instrumentation aircraft designed
to catch signals where ships couldn't
reach. and all these signals needed to
be able to be received by the spacecraft
which had its own specialized
technology. The command module used four
omnidirectional antennas for close range
but once in deep space it relied on a
steerable high gain antenna, a cluster
of four 31in parabolic dishes. The Luna
module carried its own 26-in steerable
dish. And for the historic broadcast
from the lunar surface, the astronauts
even deployed a 10 ft collapsible
umbrella antenna to ensure the world
could see their first steps. But even
with all of this, there was a hole. For
roughly 48 minutes of every 2hour lunar
orbit, the craft would pass behind the
far side of the moon and the signal
would be lost. In this window, the
astronauts were truly alone, cut off
from all human contact until they
rounded the corner and Earth rose over
the horizon. This meant that huge
sections of one of the most important
moments in the mission occurred in radio
silence. The descent.
In the decade leading up to the Apollo
11 landing, the lunar surface was a
scientific enigma that invited
terrifying speculation. Without direct
physical samples, NASA's planners had to
account for a myriad of potential
theories. The most prominent of these
was the fairy castle theory proposed by
Cornell astrophysicist Thomas Gold in
1956.
He argued that billions of years of
micrometeorite bombardment had ground
the lunar surface into a fine
electrostatic dust in the moon's vacuum.
He said these grains would cling
together in loose porous structures like
fairy castles that would have the
structural integrity of a spiderweb.
Gold warned NASA that even though on the
moon it would be 2.5 tons thanks to
lower gravity, a 15tonon lunar module
wouldn't be able to land on this
surface. It would sink like a stone into
water, burying the astronauts in a miles
deep sea of dust. Other researchers such
as JD Bennell feared a different kind of
instability. They theorized that the
lunar regalith might be pyrooric,
chemically hungry, and highly reactive.
He worried that the moment the hot
exhaust touched the pristine lunar soil,
it would trigger a violent explosive
chain reaction.
Even the craters themselves were a
source of dread. Some geologists
believed that the lips of the lunar
craters were so fragile the mere weight
of a spacecraft would cause a
catastrophic collapse, tipping the lunar
module and leaving the crew stranded on
their sides, unable to launch back to
orbit. NASA's engineers couldn't
disprove these theories, so they did the
only thing they could. They
overengineered for every possible
nightmare.
The Luna module was designed with a wide
spled stance. Its four landing legs
contained honeycomb aluminium structures
designed to compress upon impact,
absorbing the shock of a hard landing
and preventing the craft from tipping.
At the end of these legs sat 37in
circular foot pads, large discshaped
snowshoes designed to spread the LM's
weight across the dust, ensuring it
stayed on the surface rather than
sinking into it. Dangling beneath three
of these foot pads were 68in long blue
probes. They were the spacecraft's cat
whiskers. The moment the probe touched
the lunar soil, a lunar contact light
would glow blue in the cockpit. This was
the signal for the astronauts to shut
down the engine immediately. A critical
move to prevent the engine pressure from
building up against the ground and
potentially causing an explosion or
blowing out a massive unstable crater
beneath them. If the ground began to
give way or if the quicksand proved
real, the astronauts had a panic button.
The abort guidance system allowed for
multiple abort modes with a single
command. The bottom half of the LM
called the descent stage would be
jettisoned and the other half named the
ascent stage would fire, kicking the
crew back into the safety of orbit. This
ability for the LM to split into two
halves was the ultimate fail safe. The
ascent stage was an entirely independent
spacecraft designed to fly even if the
descent stage was tilted, sinking, or
physically damaged. Inside the Luna
module cabin, the paranoia of the
unknown continued. Every inch of the
interior was stripped of flammable
materials backed by dual redundant
oxygen tanks and extra power reserves.
Because on the moon, there was no such
thing as a minor complication.
The Apollo 11 team was ready for any
eventuality. And at 1:44 p.m. ET on the
20th of July, 1969,
Neil Armstrong and Buzz Uldren left my
Collins in the CSM and began their
descent to the lunar surface.
But
it was far from a smooth ride.
12 minutes. That was the time it took
for Apollo 11 to fall from orbit to
history. And it was a descent defined by
chaos. It began with a positional error.
As the LM Eagle emerged from behind the
moon, Neil Armstrong realized that they
were passing landmarks 3 seconds ahead
of schedule. A tiny bit of residual
pressure in the docking tunnel had given
them an extra shove, meaning they were
drifting towards a boulder strewn crater
instead of a flat plane they were
initially aiming for. Then the silence
was shattered by the 1202 program alarm.
Inside the cramped cabin, a yellow
caution light flickered. The primary
guidance computer, a machine with less
memory than a modern car key, was being
overwhelmed by cycle steals. In other
words, a faulty radar switch was
flooding the processor with useless
data, forcing it to reboot mid descent.
And while you were dropping to a
completely unknown surface at more than
100 kmh is possibly the worst time I can
think of to have it issues. Down in
mission control, 26-year-old Steve Bales
had seconds to decide, abort or land.
Trusting the software's ability to
prioritize critical tasks, he gave the
go. But the drama wasn't over. As Eagle
dropped below 150 m, Armstrong looked
out the window and saw a crater filled
with jagged rocks. If they landed here,
the mission would end in a tip over or a
ruptured hull. With nerves of steel,
Armstrong took manual control. He tilted
the craft forward, skittering over the
boulders, searching for a clear patch of
dust. In the background, Buzz Uldren
called out altitudes and descent rates
while a new crisis emerged. The fuel
light. Because they had hunted for a
landing spot for so long, 2 to 3
minutes, the fuel was splashing around,
triggering a lowle sensor. Houston
called out 60 seconds, then 30 seconds.
If they didn't touch down before the
clock hits zero, they would have to
abort the landing and ignite the ascent
engine or crash.
Dust kicked up by the engine obscured
the ground, robbing Armstrong of his
depth perception. He relied on the
contact light probes dangling from the
landing gear.
At 4:17 p.m. ET, the blue light flashed.
Armstrong throttled down and the Eagle
settled into the sea of tranquility with
barely 25 seconds of fuel remaining.
The troubleshooting was complete. The
impossible had been done.
>> Uh, Tranquility Base here. The Eagle has
landed.
>> Roger, TW Tranquility, we copy you on
the ground. You got a bunch of guys
about to turn blue. We're breathing
again. Thanks a lot.
>> Very smooth touchdown.
>> Man had landed on the moon.
But this wasn't merely a triumph of
three men.
>> Behind every maneuver and step taken on
this journey to the moon was a
masterpiece of collective human
intelligence spanning countless
specialtities.
The mission was a tapestry woven from a
million strokes of genius, solves, fail
safes, checklists, and foresight. the
physical manifestation of hundreds of
thousands of minds working together to
push humanity forward in one great leap.
It was proof that when focused on a
singular impossible goal, the quiet
expertise of many could carry the few
safely to a world unknown. But this
isn't the end of the Apollo 11 saga.
Join me again soon for part two where we
continue to uncover the scientific
fingerprints that coat this mission.
We're stripping back the layers of the
most iconic armor in history to reveal
the scientific secrets of the lunar
space suit. We'll dive into the high
stakes orbital ballet required to
reunite the astronauts in the silence of
the void. And finally, we'll face the
ultimate trial by fire. The vital
physics of re-entry, where a thin shield
was all that stood between the crew and
a 3,000 degree inferno. The journey home
has only just begun.