Space probes: The evolution and future of astronautics

The aerospace industry is playing a leading role in exploring the limits of human knowledge and its evolution may give rise to mankind’s greatest discoveries. Our surroundings within the immensity of the universe are being studied by robotic explorers, more commonly known as space probes.

The aerospace industry will continue growing to delight us with new possibilities, technologies and knowledge, particularly astronautics.

These artificial devices are designed to withstand radiation, pressure and high speeds in extreme environments by using the latest, most advanced and feasible technology. This involves huge investments to manufacture them, launch them into space, use them and maintain them. Space probes allow us to take samples, measure, photograph and analyse the dust and gases of other worlds.

Space probes are highly useful tools for mankind and have a wide variety of functions. For instance, the Hubble space telescope, which was named after the astronomer Edwin Hubble — considered as the founder of observational cosmology —, floats comfortably in a terrestrial orbit while the Deep Impact probe was sent on a suicide mission to crash into the Tempel 1 comet in order to study the composition of its interior. Other probes are sent far form the Earth to planets like Mars, Jupiter, Saturn or its moons to capture images and analyse them from their orbits. Some probes even land on their surfaces in search of samples and to study their composition, geological processes and analyse their similarities to and differences with our planet.

The aerospace industry, and more specifically the aeronautical industry, holds responsibility for implementing programmes on behalf of space agencies like NASA in the USA or INTA in Spain.

In December 2009, a Delta 2 rocket placed WISE (Wide-field Infrared Survey Explorer) into orbit, a probe equipped with a 4 million pixel telescope that observes the sky at four infrared longitudes and which is taking the most detailed infrared photograph of the universe to date.

Throughout the history of mankind, there was never any clear proof of liquid water existing anywhere else in the universe other than the Earth until a sophisticated space probe reached Saturn on a mission in 1997. The Cassini spacecraft travelled almost 645 million kilometres in four years to start a spying mission aimed at uncovering Saturn’s secrets. This probe not only studied the planet and all its moons, it also managed to observe its rings in detail and discovered Enceladus in Ring E, one of Saturn’s moons, where geysers erupting liquid water were observed. This water freezes when it comes into contact with cold space, creating ice particles that form Saturn’s ring.

Cassini’s discoveries, however, did not end there. It had to make use of its best, most sensitive instruments to study Titan, another of Saturn’s moons despite being larger than Mercury. Titan has a highly dense atmosphere that had already been observed in 1980 by the Voyager space probe on it way to the outer Solar System. Titan was photographed and it was shown that this moon’s dense atmosphere is made up of hydrocarbons like methane and ethane, which create a dense photochemical fog, making it difficult to peer through it. Twenty-five years later, Cassini launched its Huygens probe, which penetrated the dense atmosphere and landed on Titan’s surface, discovering large hydrocarbon lakes fed by liquid methane storms, where simple life forms similar to the single-cell organisms that inhabit the depths of the Earth’s oceans could survive.

Most of the Earth’s methane is gaseous. We call it natural gas and it comes from decomposing bodies.

The aerospace industry has taken giant strides in the area of space probes. The Ranger Programme was carried out in 1960. It launched the first American space probes whose mission it was to photograph the moon and its surface with a view to developing the Surveyor and Apollo programmes. Just two years later, the American Mariner 2 probe flew over Venus. Nonetheless, the first probe to land on Venus was not an American probe but rather a Soviet probe called Venera, which landed in 1970. It revealed that our neighbouring planet is very different from Earth. It is too hot (around 460 degrees centigrade at its surface) and its conditions are too extreme to support any kind of life form.

However, there are even worse conditions at the outer planets or exoplanets. More than just a large rocked is needed to reach them. The main problem facing probes is the fuel needed to get to their destination. A rocket burns a lot of fuel and, if it were to run out, the probe would become useless. There is, however, a solution which is inherent to the cosmos’ structure: gravity. At the beginning of the 1960s, it was discovered that we can use planets’ gravity to help propel spaceships, by launching them further into the Solar System. This technique is called “gravity assist” and works like a virtual thruster which takes advantage of planetary bodies’ immense gravity to propel a spacecraft along a foreseen trajectory. Cassini, for example, used these gravitational slingshots to reach Saturn’s moons.

Space exploration in the 21st century is ready to send probes beyond the Solar System’s external planets to reach distant stars. “Gravity assist”, however, does not allow us to get that far. Travelling into deep space requires another propulsion method which seems more like science fiction; namely, the ionic thruster.

An ion thruster is like a “mini-lineal accelerator”.

An ion thruster replaces chemical fuel with an inert gas like xenon and this gas receives an electric charge which ionizes it and generates an electric field that accelerates the ions in a specific direction, thereby causing propulsion. These thrusters produce very slight thrusts but can be operated during several consecutive months to make the spacecraft travel quicker and quicker. They had already been tested on the Deep Space I probe at the end of the 1990s and have recently propelled the Hayabusa probe belonging to the Japan Aerospace Exploration Agency and helped it hover above an asteroid. It could be said that ion thrusters have revolutionised deep space exploration.

But this is just the beginning, since the VASIMR (VAriable Specific Impulse Magnetoplasma Rocket) is under development. This evolved ion thruster is equipped with an additional radio wave generator and a second phase. It functions by applying electromagnetic energy to plasma, creating a very powerful magnetic field that accelerates the plasma at very high speeds. It is thought that a probe could be sent way beyond our Solar System by using this technology, thereby opening up the way for deep space exploration.

For the moment, we can observe extrasolar planets, especially ones whose size is similar to that of the Earth which are in the habitable zone of their star. This is one of the aims of the Kepler probe, which is fitted with a telescope equipped with a camera having a resolution of 95 million pixels to observe transiting planets (a technique used to search for exoplanets consisting of measuring the variation in a star’s brightness to determine whether there is a planet orbiting in front of it, which causes an attenuation in its brightness).

It seems we will soon have the technology needed to analyse exoplanets’ chemical composition, whether or not they have atmospheres, continents and oceans, whether there is water on their surface, etc. This will be possible thanks to the James Webb space telescope, which has an optical capacity four times greater than the Hubble telescope. This telescope will allow scientists to observe small molecules in the atmosphere of a planet similar to ours, which could be thousands of light years from the Earth.

Space exploration is still in its infancy. Everything seems to suggest that mankind will witness highly significant and surprising discoveries in this century. The aerospace industry will continue growing to delight us with new possibilities, technologies and knowledge, particularly astronautics, through very large projects having ambitious goals that were unthinkable just a few years ago, which will never cease to amaze us.

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