Ion vacuum drive

The Ion Vacuum Drive is the most common type of starship engine throughout the Known Worlds. It is used on every class and scale of ship, from fighters to capital ships, and is widely regarded as the single most versitile engine ever devised.

Development

There is no recorded date for the invention of the Ion-Vacuum drive. Very likely, numerous civilizations developed the technology independently of one another. Earliest recorded use dates back to the Mage Wars though it may have been used in Antiquity.

By the Golden Age it was the standard in starship engine. There are many different designs of Ion-vacuum drives, making the technology as diverse as the internal combustion engine. All operate around the same basic principles.

Operating Principle

The Ion-Vacuum drive employs a ramscoop to suck in fuel from the vacuum of space. Anything will do; trace gasses, dust, whatever matter is in front of the ship gets sucked into the engine and combined with "dry" plasma where it burns intensely. The plasma is then ionized in the primary drive chamber, adding energy to it and causing further expansion as it is expelled out the back of the ship, causing forward motion.

Dry Plasma

Dry Plasma is pure, highly-energetic plasma formed by a matter/anti-matter reaction. This plasma is generally used as a 'spark' to burn materials gathered by the ramscoop, forming "drive" plasma.

Drive Plasma

Drive Plasma is the plasma used to propel the ship before ionization. Drive Plasma is produced when fuel is mixed with dry plasma and burned. In a traditional ion-vacuum design, the fuel source is material gathered by the ramscoop, though anything can be used for fuel.

Fuel

Technology similar to that of Bussard collectors are used in the ram-scoops. The traditional fuel for an ion-vacuum drive is whatever is gathered from these collectors. In larger ships, waste from the vessel is burned for fuel. Deuterium is also a popular fuel source as it is plentiful and highly effective. Once a fusion reaction is sparked in the deuterium, the matter/anti-matter reactor is no longer required. Most large ships will use a system like this as deuterium is plentiful and easy to store while anti-matter refinement and storage is not.

Power Requirements

The Ion Vacuum drive is curious in the high variability of its electric-to-fuel ratio. More available fuel = less electricity. Less fuel = more electricity. Its efficiency then varies according to fuel availability, with highlier-available fuel allowing for greater speeds while retaining greater economy. However, the equation is often more complicated than that.

Aside from energy used in plasma manufacture and containment, the engine requires electrical energy to ionize the plasma in the pre-fire chamber. When more fuel is available, less electricity is required. More fuel being burned results in less-energetic plasma, which produces less thrust. At lower speeds, such as the cruising velocities of large ships, this is no problem, as even with a very high fuel/dry plasma mix, 30-40 PSL can still be reached with little ionization.

However, smaller craft, such as fighters, lack the power generators needed to produce highly-ionized plasma. For thousands of years, the Bussard Ramjet was the preferred solution, as it required relatively low power and no fuel. However, it was slow at changing velocities and useless for maneuvering.

In the late Fifth Age, the technique of "sweetening the mix" allowed the Ion-vacuum drive to dominate as a main engine. This simply involved burning more antimatter fuel to achieve higher velocities, thus resulting in a higher dry plasma/fuel ratio. It significantly decreased fighter range, but allowed for 70PSL+fighters to become a reality.

Self-Powering Variant

A self-powering variation of the Ion Vacuum drive was developed for the Harpy-class of long-range bomber built by the Gudersnipe Foundation. The design simply used the mechanical motion of the expanding dry and drive plasma through the engine to produce electrical energy, which is then used both to ionize the plasma and to power the ship. The problem with this variant is that it requires drastically more anti-matter. In the Harpy, it allows the ship not to have an internal power generator.

Though completely inefficient in a large starship, this design works well for fighters where speed is of higher value than endurance.

Similar Technologies

Some variation of the ion-vacuum drive has been invented by dozens if not hundreds of cultures. The basic principle and operating functions make it one of the most effective N-space designs possible.

Ion Drive

The erroneously-named Ion-Drive is a similar variant to the ion-vacuum engine that essentially works without the "vacuum" part. Instead of a Bussard collector, the ship caries a reservoir of material to "burn" in the engine to produce thrust. The rest of the operating principle is the same.

Typically, some type of gas is used. Xenon is a popular choice, being gaseous and heavy, though hydrogen and helium are not uncommon due to their plentiful nature. Less "clean" fuel sources are also used, such as waste material from the ship, or essentially "whatever we can find".

Ion engines are common in very large-scale operations where precision is important. A engine fueled by a reservoir of a pure substance will have a much more consistent output than one fueled by whatever the collector picks up. Of course, in a pinch, these ships can burn anything. In order to re-fuel en route, they will employ either ram-scoop collectors or bring along an escort of much smaller ships that use standard ion-vacuum drives to gather fuel.

Since the fuel is ultimately being converted to plasma, literally anything works, but when other materials are used it defeats the purpose of the drive.

Deuterium Drive

A further variation used deuterium as the fuel-source. Much like the ion drive: the operating principles are the same, with deuterium being added to dry plasma where it under goes a fusion reaction. The rest of the operation is the same, except that like the ion engine there is no collector. This variant is popular because it requires less power to operate and produces substantially more thrust. Many ion-vacuum drives are even augmented with deuterium fuel injector for increased performance.

Deuterium Drives are popular for small vessels and large high-performance ships. On smaller vessels the increased output and low power requirement make up for the fuel availability and endurance concerns, while the similarity to existing ion-vacuum technology makes them easy to maintain.

Larger applications benefit from higher thrust-to-weight ratios, allowing a smaller fraction of the ship's mass to be made up of "engine". For cargo ships plying a well-established route, this is ideal.

Notable Examples

• The Ion-Vacuum drive on the Saratoga is notable for being under-powered for the ship's size (one of several serious design short-comings of the Glorious Heritage-class). The crew, who had not read the ship's operation's manual, dealt with the issue by running the engine at much higher pressure levels than they were designed for. Every time a component failed, the crew replaced it with a custom-made, over-built version, until the engines could cope with the stresses they were placing on it.

• A.S. Sundew was a privately-owned freighter that gained wide attention when it was found that the ship's ion-vacuum drive had been in continuous operation for one hundred and six years. To quote the captain: "Grand-Pappy said if he ever turned off the engine, he'd never get it started again... so he never did. If it worked then, it otta' work now.".