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'Star Trek' - Impulse Engines and Warp Drive

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This entry is for reference purposes only. The Star Trek name, fictional characters and all references to Impulse Engines and Warp Drive remain the copyright of CBS Paramount Television.

When humans first stepped off their home planet of Earth in the Solar System to travel to Earth's nearest space body – its Moon, a distance of merely 400,000km – it took them three days to get there. To travel across the vast distances of interstellar space would require far, far greater propulsion power than that provided by primitive chemical rockets. After a period of experimentation with ion1 drives on the eve of the 21st Century, humankind would have to await the development of a method of controlling fusion power before it was able to seriously consider travelling further afield.

In the 23rd Century science fiction world of Star Trek, where space exploration has come of age, starships of the United Federation of Planets will be equipped with two propulsion systems: Impulse Engines and Warp Drive.

Impulse Engines

Although not the main method of propulsion, the ship's impulse engines are used when travelling at sub-light speeds, within a solar system or in regions of space unsuitable for warp drive. They are also used to provide the ship's power when not travelling at warp speed. Although capable of driving the ship faster, impulse engines are normally only used up to about quarter light speed - above this speed reduced efficiency and other undesirable effects begin to manifest themselves. Even so, at quarter light speed, the distance equivalent to that travelled in three days by the first space pioneers can be covered in only a little over five seconds.

The first stage of the impulse engine is the reaction chamber, in which the deuterium2 fuel undergoes a proton-proton fusion reaction, creating a high energy plasma. If additional power is required for a short period, a little anti-matter can be fed into the impulse reaction chamber to boost power output.

If the ship is stationary and only requires power for the normal operation of its internal systems, the output from the reaction chamber is fed to the electrical generators that provide the ship's working power. If propulsion is required, the plasma is directed into the accelerator/generator and the space-time driver coils. The exhaust from the coils is vented into space via steerable exhaust directors which enable the ship to be steered using motive power.

Although impulse engines enable the outermost planet Neptune to be reached in less than two days, travel to Earth's next-nearest star from the Sun, Proxima Centauri, would still be a 20-year undertaking. Exploration beyond the Solar System needs the benefit of the pioneering research work of Dr Zefram Cochrane3.

Warp Drive

Humans have not yet managed to find a way to exceed the speed of light, so the writers of Star Trek came up with their own technological advances to explain how their starships could cover such immense distances so swiftly.

Cap'n, the engines can't take much more!
– Montgomery ('Scotty') Scott, Chief Engineer USS Enterprise... regularly

Whereas impulse engines depend upon a deuterium-fuelled fusion reaction to generate power, the warp drive utilises a controlled release of the enormous energy available from the interaction of matter with antimatter. More properly called Continuum Distortion Propulsion, the field generated by the engines distorts (or 'warps') the space-time continuum, compressing the space immediately in front of the ship and stretching the space immediately behind the ship. This enables apparent speeds of up to 1,000 times light speed to be achieved.

Two similar, but not exactly equivalent, scales have been used to calibrate 'warp speed'. On both the earlier and later scales, warp speed 1 (or warp factor 1 as it is commonly known) is the same as the speed of light4, while the upper end of the later scale is warp factor 10 – Eugene's Limit, an infinite, and therefore in practical terms, unattainable speed. Lt Thomas Eugene (Tom) Paris of Voyager reached warp factor 10 in a modified shuttle during one of the many attempts by the crew to return home from the Delta Quadrant. Under the influence of the extreme warp field, Paris and his kidnap victim Captain Kathryn Janeway evolved into amphibian lifeforms - although they were de-evolved back to normal by the holographic Doctor. This uncontrollable effect has rendered further attempts at warp factor 10 impractical.

Galaxy-class starships cruise at warp factor 6, which would enable them to cross Earth's Solar System5 in two minutes, and to travel from Earth to Proxima Centauri6 in only five days. The maximum speed is normally warp factor 9.6, a speed which can be maintained for up to 12 hours. Since it was discovered that Warp Drive damages the structure of space permanently, Star Fleet set a maximum speed limit for all further warp travel, but not all alien races abide by the directive.

Central to the operation of a warp engine is the warp core, in which the matter-antimatter reaction occurs, controlled by a dilithium crystal. In Star Trek chemistry, dilithium is the only substance known to science that does not react with antimatter. A slurry of supercooled liquid deuterium provides the reaction medium in which the matter and antimatter are brought into contact. The resulting plasma is directed into the field coils housed in the warp engine nacelles, the large 'fins' that project backwards from the main hull of the ship.

Impressive though the speed of a warp-powered starship is, travel to other galaxies is beyond their capability. Even at warp factor 9.6, the journey to the Andromeda galaxy would last 1,375 years. Future journeys of this magnitude will require the use of Transwarp. The Borg have had some success with this, but as yet only within the galaxy, not between galaxies – at least as far as the Federation is aware.

The Future

People like Gene Roddenberry, Arthur C Clarke and Leonardo Da Vinci had ideas way ahead of their time. Today's flip-top mobile phones look just like the communication device featured in Star Trek: TOS in the flower-power decade. Once upon a time cloning, organ transplantation, babies created outside the womb, man-made satellites or a visit to the Moon were considered impossible. Now they are all science fact. We have only known about the existence of galaxies other than our own for about 90 years. Travelling to the stars in our own galaxy, for the moment, remains bound in the imagination: it may never become a possibility for frail humankind, due to all the social and ecological problems involved. As for travelling at light speed and above, who knows what may be encountered by such pioneers, but no doubt there will be brave men and women willing to volunteer if and when the technology eventually becomes available.

A Trek Across Our Galaxy

If you could travel outside our galaxy and then look back, this is an artist's impression of what you would see: our galaxy the Milky Way is huge, even on a galactic scale. It is a grand barred7  spiral galaxy (type SBb or SBc) containing somewhere between two and four hundred billion stars. Our own Sun is 26,000 light years from the galactic centre - a light year is the distance light travels in one year, roughly 5.88 trillion miles or 9.46 trillion km. If all these big figures make your head spin, then you're not alone.

Other Planets

According to SETI founder Frank Drake's estimation there could be 30 billion rocky worlds like the Earth within the Milky Way. SETI8 has turned up some interesting results – although the 'WOW' signal from August 1977 remains unexplained, people continue to watch and listen.

The first hundred extrasolar planets discovered were all gas giants, like our own Jupiter. Such planets are incapable of supporting life (as we know it). What we are interested in are terrestrial worlds like the Earth. A rocky planet-finder project is underway and astronomers have a list of likely candidate stars within 50 light years that they'd like to check out, including 55 Cancri A, which is home to the most planets9 that we know of at the time of writing.

There are plenty enough stars with planetary systems already detected to go exploring if the technology of Warp Drive is ever realised. Extra-galactic travel, however, may never be a possibility for mortal beings - it will probably always remain a privilege of the gods.

1An electrically-charged atom.2An isotope of the element hydrogen.3ST VIII: First Contact (1996).4186,000 miles (or 299,792km) per second.5Students learn in Star Fleet Academy that warp speed is not allowed within a solar system. It cannot be stressed enough that warp speed isn't allowed within a solar system under any circumstances. Violations are dealt with severely.6A distance of 4.2 light years.7The bar is estimated to be 27,000 light years long.8The Search for Extra-terrestrial Intelligence.9Unfortunately those five planets are all gas giants.

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