The descent engine
should have dug a huge crater in the lunar surface.
This question is covered in depth here.
We should hear the lunar
module's descent engine firing in the radio transmissions during the
When firing in a vacuum most rocket engines are silent. Even the
large SPS engine on the service module was not audible from the
command module. This is because the noise from a rocket engine is not
really coming from the engine, but from the effect of the exhaust on
the surrounding atmosphere. It's the shock wave of the supersonic
exhaust gases colliding with the air near the engine nozzle. If
there's no atmosphere, you shouldn't expect to hear a loud sustained
But you can expect to hear an ignition transient. The space
shuttle astronauts report hearing bangs and pops as the steering jets
work. This is a noise produced when the rockets first ignite. When
they're running smoothly, they run silently.
Astronauts report feeling gentle vibrations through the structure
of their spacecraft as the engines fire. The rush of exhaust products
through the throat of the engine would produce some flow noise that
would be transmitted through the engine mounts to the frame of the
spacecraft. But this doesn't necessarily produce audible sounds in
Consider also that the microphones used in aerospace for pilots and
crew are built to operate in a noisy environment. You have to speak
very close to the microphone in order for the sound to be picked up.
The microphone helps cut cabin noise in aircraft. So even if the
engines were to make a sound, it's very unlikely that the microphones
would pick them up. Astronaut Bill Anders called his microphone a
"tonsil mike" because he quipped that you had to practically shove it
down your throat to make it work.
You will never see a
photograph of any Apollo spacecraft showing its engines
There is lots of footage of the Saturn launchers with their engines
You don't see footage of the SPS engine firing because how could
such pictures have been taken? The SPS engine and the DPS engine are
used when the command and lunar modules are separated, but because of
the orbital mechanics necessary to accomplish the landing and
rendezvous, the spacecraft are many miles apart when these maneuvers
You can see the lunar module's ascent engine firing on the later
Apollo missions when the television camera was placed to record the
The photo below (left) and
descriptions of the space shuttle's RCS operation shows we should see
a visible flame from the lunar module ascent stage. Both these
engines burn hypergolic
fuels. [David Wozney]
This argument is based on the assumption that all hypergolic
engines behave the same way. The lunar module ascent engine and the
space shuttle RCS systems use different fuel. The space shuttle's RCS
jets use monomethyl hydrazine (MMH). The lunar lander's ascent engine
used Aerozine 50, a trade name for
a half-and-half mixture of hydrazine and unsymmetric
dimethylhydrazine (UDMH) developed for the Titan 2. The photograph
above (right) shows a Titan 2 booster with its Aerozine 50 engines firing. In
fact, once in operation the Aerozine 50 exhaust plume is essentially
colorless and transparent.
At left are two photographs of rocket engine tests in the U.S. Air
Force's AEDC rocket propulsion laboratories were engines are tested in
simulated high altitude environments.
The photo on the far left is a rocket burning Aerozine 50 and
nitrogen tetroxide, the exact mixture of propellants used on the lunar
module's ascent and descent stages. The exhaust plume is nearly
In comparison the photo on the near left is a solid fueled rocket
motor burning in the same test chamber, photographed from a slightly
greater distance away. The plume is bright and opaque. Someone
accustomed to the smoky, bright plumes of the Saturn V or the space
shuttle is likely to be surprised by the clean pale plume of the
Aerozine 50 engines.
Because the word "hydrazine" appears in the names of several fuels and
also appears alone as a third type of fuel it's understandable that
lay persons will confuse them, or assume they're largely the same
substance. They aren't. Hydrazine, MMH, UDMH are significantly
different in chemical formulation. The substances are related, of
course, but not in visible combustion characteristics. We might draw
a parallel between gasoline, kerosene, and diesel fuel. These are all
hydrocarbons and share many chemical properties. But each has a
unique combustion characteristic.
The visibility of the flame from hydrazine-type propellants depends
on factors that include the precise form of hydrazine used, the design
of the rocket motor, and the prevailing lighting conditions. The
photograph of the shuttle's RCS plume was apparently taken with long
exposure (note the visible stars in the background) and so may appear
brighter in that photograph than if it were seen directly. The
photographer intended to capture the RCS plume as the subject of his
photograph and so adjusted his camera accordingly.
Some conspiracists point out that the film of the lunar module
ascending from the lunar surface to meet the command module doesn't
show any visible exhaust products. That's because by the time it
comes into view of the command module the engine has stopped firing.
Just as a baseball thrown upward will continue to rise after it has
left the propulsive effect of your hand, the lunar module continues to
rise after its engine stops firing. Unlike space ships in the movies,
real spacecraft don't have to fire their engines continuously in order
to make headway.
The flames from the steering jets don't generally show up on film
because their plumes are too small, and also because the motion
picture camera is not running at normal speed during the rendezvous.
It's shooting only a few frames per second rather than the typical 24
fps in order to conserve film. Since the bursts from the lunar module
with its RCS system in pulse mode would last only a few tenths of a
second, it's likely that they'll happen between film frames if they
were visible at all.
We should see thick
smoke from the hypergolic engine of the lunar module ascent stage, as
in the above photograph of the Titan 2 launch.
Liquid-fueled rocket engines, including the hypergolic engines we
are considering, often smoke during ignition and then burn very
cleanly after liftoff. This is because the engines run roughly during
the ignition process and then settle down into a steady state of
operation. During this ignition transient unburnt propellants can be
ejected from the nozzle as smoke. Similar "smoky" ignition transients
can be observed in commercial jet engines and even some cars.
The duration of the ignition transient increases with the size and
complexity of the engine. Large engines like the space shuttle main
engines, with many internal pumps and turbines, take almost six
seconds to reach steady-state operation. Small engines like the LM
ascent engine with few moving parts reach steady-state operation in a
fraction of a second and thus produce little if any smoke. Above is a
Titan 3B rocket being launched, producing comparatively little smoke.
The conspiracist examples of hypergolic engine ignition and
operation are always tests conducted in an atmosphere. For Aerozine
50 and nitrogen tetroxide this presents a special additional concern,
since each of these chemicals reacts spontaneously with air. Nitrogen
tetroxide produces an opaque orange vapor cloud on contact with air,
and Aerozine 50 produces a white vapor cloud.
To ignite an Aerozine 50 engine, you typically first begin injecting
nitrogen tetroxide into the combustion chamber, followed a split
second later by the fuel. In an atmosphere, the nitrogen tetroxide
will immediately begin to react with the atmosphere and produce a
cloud. In a vacuum this does not happen.
NASA: MARS ODYSSEY LAUNCH
The video frames at right show the ignition of a Boeing Delta-II
second stage, powered by an Aerojet AJ10-118K engine burning Aerozine
50 and nitrogen tetroxide. The engine shown is virtually identical in
size and operation to the engine used as the descent stage motor on
the Apollo lunar module.
The numbers in the upper right corner of each frame are the
elapsed time in seconds between each video frame. From ignition to
steady-state operation requires less than one second, produces no
significant smoke, and the steady-state plume is invisible. This is
how an Aerozine 50 engine normally behaves in a vacuum, and it is
entirely consistent with the video footage of the lunar module
The complete six-minute Real Video footage of this launch sequence
from the Kennedy Space Center.
The American flag was
planted very close to the spacecraft. Shouldn't the blast from the
ascent engine have burned it or knocked it down?
The flag planted by the Apollo 11 crew was in fact knocked down as
the ascent engine fired. This was not immediately reported to the
public for sentimental reasons. NASA had not anticipated the
difficulty of driving the flag pole deeply enough into the hard
packed lunar soil.
The heat from the rocket exhaust would not ignite or scorch the
flag. The lack of oxygen would keep it from burning. The exhaust
gases from a rocket engine disperse rapidly in a vacuum, losing
temperature and pressure in the process. By the time the exhaust gas
reached the flag it would likely be too cold to cause visible damage.
The spectacular film
footage of the Saturn rocket staging had to have been produced in a
studio. How else could you get such footage?
Engineers have been putting motion picture cameras in rockets for
almost as long as they've been building rockets. When a rocket
malfunctions, that footage is often the best means of determining what
went wrong. It's an invaluable diagnostic tool.
Filming rocket operations is little different from filming events
under other adverse conditions. The motion picture camera is enclosed
in a housing which prevents it from being damaged. The camera is
ejected as the spent rocket stage enters the atmosphere, and it falls
back to earth either shielded by its housing or slowed by parachutes
where it is recovered.
NASA tested the Mercury
space capsules with animals. Why were no animals used to test the
The animal tests undertaken as part of the Mercury project were not
intended to test the spacecraft so much as to test the behavior of
complex organisms in space. At that time it was not known whether
human beings could survive in zero gravity, or could survive the
stresses of launch and landing. The animal tests proved that complex
organisms like chimpanzees could survive launch and landing and
happily work in space in the meantime, and so no further animal tests
The spacecraft hardware could be tested without having any live
passengers. The telemetry technology was very limited during the
Mercury project. By the Apollo era, lots of information was available
to controllers on the ground via onboard sensors and telemetry, and so
they could verify that the spacecraft was suitable for human use
without needing to send biological specimens.
The Soviets sent live specimens into lunar orbit. This again was
not so much to see if the spacecraft worked but to test the effects of
radiation on living tissue. The United States also sent biological
specimens into high earth orbit aboard smaller spacecraft in order to
learn how the Van Allen belts and solar radiation would affect them.