But satellites are not up there only to take pictures or broadcast TV channels.
Usually, we look at smartphones to check where we are or set up our car navigators to find the best route to our destination. This practise has become ordinary
only thanks to satellites, and in particular the Global Positioning System (GPS)
satellite fleet, one of the most incredible wonders of the twentieth century.
Most people believe that a navigation device communicates with a satellite to
pinpoint where it is on Earth, but it does not. Smartphones or car navigators simply receive signals coming from satellites in space and do not transmit anything.
The GPS was made by the US armed forces, which did not want to reveal the
position of its troops by emitting radio signals from its devices. When we open
any geolocation application on a smartphone, we should be aware that we are
using a military system that was initially designed to exploit radio signals from
space and guide US nuclear submarines, and only later was granted freely to the
public sector.
One might think that GPS satellites are in a geostationary orbit, allowing them
to send their signals all over the Earth. But this is not the case. From that huge
distance, we would need large antennas on our smartphones to receive radio signals, which would make our device very difficult to handle. In LEO, the situation
would be even worse, because the satellites would be visible only for a couple of
minutes and would remain out of our horizon for most of the time. That is why the
24 GPS satellites fly at an altitude of 12,400 miles, called medium Earth orbit
(MEO), at 2.5 miles per second. The spacecraft fleet is split in some crossed orbits
at that altitude, so that each satellite takes about 24 hours to make a complete tour
around the Earth. In this way, every device on the ground can receive signals from
at least four GPS satellites continuously for at least one hour, and the microprocessor inside the device can calculate its precise geographic position.
To conclude this brief compendium of astronautics, one cannot fail to mention
the discipline that represents its most exciting and iconic side, the so-called “rocket
science”, a term commonly used to indicate something that requires high skills
and an extraordinary intelligence. In the twentieth century, the race to the Moon
between the US and Russia and the building of the huge Saturn V rocket created
in public opinion the idea that space rocketry was something extraordinary.
Rockets are called launchers by experts and engineers, precisely because they
launch satellites, probes or manned spaceships into space. As of today, they are
still the only means that humankind has been able to build to escape the Earth’s
gravity. The man who brilliantly developed the mathematical methods to design
space rockets was an obscure Russian professor, Konstantin Tsiolkovsky. He
lived and worked near Moscow in the early twentieth century. In 1903 he published a study called Exploration of Outer Space by Jet Engines, in which he
described the equations to make rockets fly, which are exactly the same that aerospace engineers use today to design modern launchers. Humankind has made
6 Fundamentals of Astronautics
Usually, we look at smartphones to check where we are or set up our car navigators to find the best route to our destination. This practise has become ordinary
only thanks to satellites, and in particular the Global Positioning System (GPS)
satellite fleet, one of the most incredible wonders of the twentieth century.
Most people believe that a navigation device communicates with a satellite to
pinpoint where it is on Earth, but it does not. Smartphones or car navigators simply receive signals coming from satellites in space and do not transmit anything.
The GPS was made by the US armed forces, which did not want to reveal the
position of its troops by emitting radio signals from its devices. When we open
any geolocation application on a smartphone, we should be aware that we are
using a military system that was initially designed to exploit radio signals from
space and guide US nuclear submarines, and only later was granted freely to the
public sector.
One might think that GPS satellites are in a geostationary orbit, allowing them
to send their signals all over the Earth. But this is not the case. From that huge
distance, we would need large antennas on our smartphones to receive radio signals, which would make our device very difficult to handle. In LEO, the situation
would be even worse, because the satellites would be visible only for a couple of
minutes and would remain out of our horizon for most of the time. That is why the
24 GPS satellites fly at an altitude of 12,400 miles, called medium Earth orbit
(MEO), at 2.5 miles per second. The spacecraft fleet is split in some crossed orbits
at that altitude, so that each satellite takes about 24 hours to make a complete tour
around the Earth. In this way, every device on the ground can receive signals from
at least four GPS satellites continuously for at least one hour, and the microprocessor inside the device can calculate its precise geographic position.
To conclude this brief compendium of astronautics, one cannot fail to mention
the discipline that represents its most exciting and iconic side, the so-called “rocket
science”, a term commonly used to indicate something that requires high skills
and an extraordinary intelligence. In the twentieth century, the race to the Moon
between the US and Russia and the building of the huge Saturn V rocket created
in public opinion the idea that space rocketry was something extraordinary.
Rockets are called launchers by experts and engineers, precisely because they
launch satellites, probes or manned spaceships into space. As of today, they are
still the only means that humankind has been able to build to escape the Earth’s
gravity. The man who brilliantly developed the mathematical methods to design
space rockets was an obscure Russian professor, Konstantin Tsiolkovsky. He
lived and worked near Moscow in the early twentieth century. In 1903 he published a study called Exploration of Outer Space by Jet Engines, in which he
described the equations to make rockets fly, which are exactly the same that aerospace engineers use today to design modern launchers. Humankind has made
6 Fundamentals of Astronautics