Space exploration has always been an intriguing prospect. Back in the 1950s, the obsession with getting to space first fuelled the United States of America and the USSR to take part in the Space Race, a competition against each other to prove their dominance. The USSR gained significant ground over its competitor by landing a one-two punch of sending the first satellite into space (Sputnik 1 in 1957) and the first human in space (Yuri Gagarin in 1961). However, all we can seem to remember

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Figure 1: The Battle Commences

from this time period is the Apollo 11 moon landing in 1969, a feat that was never matched by the USSR (mainly due to mismanagement of resources and a gross lack of quality-control), which then refocused on Earth orbital space stations. After the fall of the USSR, the importance of space travel increased, with true spaceflight cooperation being finally achieved between the US and Russia.

The Space Race’s legacy is an immensely useful one. It left the world thriving with communications and weather satellites, a continuing human presence in the International Space Station and bolstered education and research with increased spending in them, leading to various spin-off technologies. Nowadays, space exploration seems like a thing of the past, at least when it comes to satellite launches and maintaining the ISS. What we are more interested in is space travel, comprising of everything from space tourism to deep space travel in an effort to discover and colonise Earth-like planets. In this endeavour, companies like Virgin Galactic have begun work on the latter, with 2017 being the year for the company to begin orbital test launching.

The Battle of the Billionaires

What’s more interesting is Elon Musk’s SpaceX, which has lately begun collaborating with the USA’s Department of Defence to launch reconnaissance satellites, a major breakthrough for the company as this paves the way to future missions backed by the United States government. With rocket designs which would be the largest in the world, future mission to the moon and even Mars seem to be within our grasp in the near future. With all of this excitement about space travel, it would be apt for us to look into space propulsion, especially with regards to some science fiction, as it seems to be absolutely prophetic as the days go by.

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Figure 2: The Battle of the Billionaires

Though developments driven by the likes of Musk and Branson receive the most attention, when it comes to propulsion technology, they are quite conventional and not very interesting. It is also noted that these developments aim for short-distance travel, with Mars being the furthest destination. While a manned mission to Mars would be monumental, the challenges it brings are more on the survival side rather than transportation. Companies such as Mars One focus almost entirely on astronaut conditioning during transit (covering nutrition and exercise) and planning for colonisation through modular living quarters on the planet itself as interplanetary travel on the propulsion side is just a matter of mass fuel storage.

It is also apparent that any Martian trip would only occur in one direction; that is the astronauts that become a part of the mission would have to live out the rest of their lives there. This suggests that the propulsion technology is quite primitive and unsustainable as there isn’t enough for return trips. The quest for propulsion technology that would solve this issue has been a subject of research for many years. In this regard, we may look to science fiction for some guidance. This seems peculiar in and of itself, but many of today’s technologies that we are wont to take for granted have been predicted by sci-fi writers decades before their conception. Arthur C. Clarke, a legend amongst them, even wrote about geostationary satellite communications, the bedrock of most modern communication methods from cellphones to the World Wide Web, back in 1945. This was before broadcast television was anything resembling a commercial concern!

Ion-estly Am Amazed

And so we have come to the part where we discuss one of the many methods of cutting-edge space propulsion as discussed in science fiction. Leaving behind faster-than-light travel and hyperdrives (both innovative yet still unfounded in real-life science), let’s talk about ionic propulsion. When it comes to deep space travel, this is often touted as the gold-standard of realistic technologies. The operational details are quite simple. To understand them, it is enough to have a basic knowledge of ionisation. Usually in conventional engines, the fuel is a complex chemical substance which is broken down into simpler compounds. The chemical bonds between the atoms of this substance that are broken in the process expel energy which drive the engine either by being converted to rotational kinetic energy in a drive shaft or by directly being expelled from the engine to provide direct thrust.

Ionic propulsion systems work almost like the latter. The fuel (or propellant) used is simpler, though. Usually it is xenon, a stable, relatively heavy gas that is susceptible to ionisation, a process which transforms neutral atoms into charged atoms (or ions) either by stripping or adding electrons, the former producing positive ions and the latter producing negative ions. In this case, the xenon atoms are bombarded by electrons in a compartment called the discharge chamber. This bombardment pushes more electrons off the xenon atoms producing positive xenon ions. Since the xenon is a gas, the ionisation produces plasma, which is just a gaseous form of ions.

This plasma is then directed to a positively charged porous plate, which is configured to increase the discharge plasma’s voltage to a very high degree, sitting opposite a negatively charged electrode.

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Figure 3: Ionic Propulsion Diagram

As the ions pass through the pores (or apertures) of this plate, they are sped to great speeds (about 90,000 miles per hour) due to their high voltage and attraction to the negative electrode. These ions are then expelled as an ion beam out of the spacecraft, exiting with an equivalent amount of electrons to neutralise their positive charge and lessen the negative charge of the spacecraft (which will only lessen the thrust produced by the ionic beam).

Conclusion

Though the beam’s speed is substantially higher than what we are used to, the small mass of the xenon atoms result in a very small forward force. Hence the acceleration produced by this system is immensely weak, in the order of micro Newtons. However, due to the compressibility of the xenon gas and the fact that a very small amount is used up per unit time of operation, the ionic propulsion system can be allowed to run for a very long time (tens of years) at low acceleration. Since there is very little resistance in space, as it is mostly empty, the acceleration builds up the velocity of the spacecraft in such a manner as to achieving speeds at a sizeable fraction of the speed of light along the way.

With minimal assistance in steering using smaller thrusters located around the spacecraft, it is entirely possible to use this technology for intergalactic travel. The only problem to this is the fact that it would take a very long time for the high speeds to be reached. As an interim solution, a marriage of the short-distance acceleration provided by developments pursued by the likes of SpaceX and Virgin Galactic and ionic propulsion could be the future of deep space exploration or even mass voyages to distant galaxies. However, the upkeep of the health of the passengers in the spacecraft has to be researched before any such expedition occurs. As it stands, though, these are exciting times in the chapter of space exploration. Here’s to hoping we can finally unlock the stars.

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