progress in technology, electronics and materials, but rocketry is still based on
the mathematical laws of a little-known genius who dreamed of space travels in
the solitude of his home in the country.
Rockets were later rapidly developed by the Nazis in the 1940’s to bomb
London and the UK. The Germans succeeded in building the devastating V2 missiles thanks to the work of a group of engineers led by the genius Werner von
Braun. He and his team unscrupulously surrendered in 1945 and were transferred
to the US, where they contributed significantly to the success of the Apollo lunar
missions.
Regardless of these less than noble origins of modern rocketry, they continue to
evoke enthusiasm among the public and are the only means of transportation into
space. Their basic working principle is the third law of physics elaborated by Sir
Isaac Newton: “for every action (force) in nature there is an equal and opposite
reaction”.
In rocketry, the action is given by the explosion of a propellant inside the combustion chamber of the engine, and the reaction is given by the expulsion of the
exhaust gases generated by the explosion. The vapours are so hot and fast that they
cause the rocket to lift off and progressively accelerate. In practice, the flight of a
launcher is made by continuous explosions generating hot gases jettisoned at
supersonic speed from the exhaust nozzle. At lift-off, the exhaust gases of the
giant Saturn V rocket reached the amazing speed of 1.8 miles per second.
To make it easier to understand, we can present a paradox. Let’s imagine taking
a rifle, pointing it downwards – maybe not right to your feet – and shooting so fast
to the point that the weapon’s recoil lifts you off the ground. It may sound absurd,
but that is basically how rockets work. That is why they are so dangerous and why
rocket science is so difficult. You have to be able to handle continuous explosions
at unthinkably high temperatures and pressures inside engines made of titanium
and ceramic materials.
But there is another aspect, generally unknown, which makes rockets quite
expensive and ineffective to go into space. Since they globally weigh much more
than the mass of gas ejected from the engine, the speed they acquire at each instant
of flight is much lower than the speed of the exhausted gases. This means that you
have to use a huge amount of fuel to reach the orbital velocity even for a twopound microsatellite.
To overcome this inefficiency, engineers designed multiple-stage rockets. Once
the first fraction of propellant has been used up, a part of the rocket (the stage) is
abandoned in flight; as a result, the total weight decreases and the acceleration
increases. However, you cannot go beyond a certain limit of the launch and payload mass ratio, due to current structural limits of the material. The giant Saturn V,
which weighed 6.6 million lbs, transported the 11,000-lbs Apollo capsule, the
only piece of the entire contraption that was supposed to reach the Moon. The
Fundamentals of Astronautics 7
the mathematical laws of a little-known genius who dreamed of space travels in
the solitude of his home in the country.
Rockets were later rapidly developed by the Nazis in the 1940’s to bomb
London and the UK. The Germans succeeded in building the devastating V2 missiles thanks to the work of a group of engineers led by the genius Werner von
Braun. He and his team unscrupulously surrendered in 1945 and were transferred
to the US, where they contributed significantly to the success of the Apollo lunar
missions.
Regardless of these less than noble origins of modern rocketry, they continue to
evoke enthusiasm among the public and are the only means of transportation into
space. Their basic working principle is the third law of physics elaborated by Sir
Isaac Newton: “for every action (force) in nature there is an equal and opposite
reaction”.
In rocketry, the action is given by the explosion of a propellant inside the combustion chamber of the engine, and the reaction is given by the expulsion of the
exhaust gases generated by the explosion. The vapours are so hot and fast that they
cause the rocket to lift off and progressively accelerate. In practice, the flight of a
launcher is made by continuous explosions generating hot gases jettisoned at
supersonic speed from the exhaust nozzle. At lift-off, the exhaust gases of the
giant Saturn V rocket reached the amazing speed of 1.8 miles per second.
To make it easier to understand, we can present a paradox. Let’s imagine taking
a rifle, pointing it downwards – maybe not right to your feet – and shooting so fast
to the point that the weapon’s recoil lifts you off the ground. It may sound absurd,
but that is basically how rockets work. That is why they are so dangerous and why
rocket science is so difficult. You have to be able to handle continuous explosions
at unthinkably high temperatures and pressures inside engines made of titanium
and ceramic materials.
But there is another aspect, generally unknown, which makes rockets quite
expensive and ineffective to go into space. Since they globally weigh much more
than the mass of gas ejected from the engine, the speed they acquire at each instant
of flight is much lower than the speed of the exhausted gases. This means that you
have to use a huge amount of fuel to reach the orbital velocity even for a twopound microsatellite.
To overcome this inefficiency, engineers designed multiple-stage rockets. Once
the first fraction of propellant has been used up, a part of the rocket (the stage) is
abandoned in flight; as a result, the total weight decreases and the acceleration
increases. However, you cannot go beyond a certain limit of the launch and payload mass ratio, due to current structural limits of the material. The giant Saturn V,
which weighed 6.6 million lbs, transported the 11,000-lbs Apollo capsule, the
only piece of the entire contraption that was supposed to reach the Moon. The
Fundamentals of Astronautics 7