An atom consists of protons which hold a positive charge and electrons which hold a negative charge. If an electron is removed from an atom or molecule (a collection of atoms bound together), the resulting ion would hold a positive charge. Likewise, if a proton is removed, the ion would hold a negative charge. The future prospects for propelling space rockets over millions of miles hinges on these tiny differences.
Chemical fuels
Presently, space rockets are powered by chemical fuels such as liquid hydrogen and oxygen, which can propel a spacecraft to 14,000 feet per second but are limited by the amount of bulky fuel needed and by the very high temperatures (Carnot’s theorem). 14,000 feet per second might seem quick, but ion-propelled craft could go more than 10 times that speed. Imagine what this could mean for the future of space travel.
Ion propulsion
Ion propulsion hinges on the use of a noble gas such as Xenon. This is used as a plasma, an electrically neutral gas, designated as the fourth state of matter. Plasma can be found all over the universe, so re-fueling might be relatively straightforward. The noble gas is ionised and both positive and negative ions are ejected by electrostatic forces to give the required thrust.
Many man-made satellites utilise ion propulsion for minor applications such as keeping geostatic orbit, but why therefore not use it for rocket propulsion?
The drawback
The drawback is that, unlike chemical power, ions do not supply their own energy. Electrical energy has to be supplied. In satellites, this energy is produced from solar cells, but, away from the sun, another means of supply is necessary. Deep Space 1 was NASA’s first attempt at an ion-powered rocket, using NSTAR electrostatic ion thrusters. Although the engines failed after 4.5 minutes and there were many other teething problems, the engines were restarted and the mission was declared a success.
SMART 1 (Small Missions for Advanced Research and Technology) was a European craft launched in September 2003, with 181 pounds of Xenon fuel on board. It currently circles the Earth.
Today, thrusters are said to be capable of reaching speeds of 200,000 mph. Compare this with the space shuttle’s top speed of 18,000mph. But all of these require energy from the sun. The future prospects for ion-propelled space rockets lie in finding an alternative power source.
Nuclear power on board
The obvious solution is to use nuclear power. A small nuclear reactor would be used to produce electricity for years and this, coupled with the possibility of stocking or even producing fuel stations at strategic points, means extended travel throughout the cosmos. However, with the re-entry and crash landing of the Russian spacecraft M-17M, feelings against space rockets carrying nuclear fuel run high.
The future
NASA’s successful Dawn mission uses massive solar panels to power its ion-propelled space rocket (currently) from Vesta on its epic journey to Ceres. This is a valuable exercise, and more and more countries are now investing in the technology for space travel.
NASA planned a mission to study the moons of Jupiter, but this mission lost funding in 2005. The main reason given at the time was that it was too ambitious, but like all large spending projects, politics had a major hand in its demise. JIMO (Jupiter Icy Moons Orbiter) was set to use nuclear fusion (much more efficient than nuclear fission which is used in nuclear power stations) as an electrical producer.
Then NASA and ESA planned a joint venture to Jupiter’s moons which NASA unfortunately pulled out of in 2011. The ESA continued, however, and it plans to launch the Jupiter icy moon explorer in 2022.
There are many developments to improve ion-propulsion technology, and much is being learnt from past and current missions.
It does seem that the power source has to be a nuclear fusion reactor, and developing new safety methods for using this fuel is paramount. We know that the technology of ion-propulsion works, so all that is needed now is the funding and the desire to explore further reaches of space. This will happen, but when is up to citizens.
