Ships move through ordinary space using Maneuver Drives.
- See also NAFAL for alternative drives.
Description / Specifications
Power for the drives is provided by the ship's power plant . Tech level requirements for maneuver drives are imposed to cover the grav plates integral to most ship decks, and which allow high-G maneuvers while interior G-fields remain normal.
Maneuver drives can be made up either of grav modules or thruster plates, which both use Gravity control technology to make use of the graviton.
Gravitic drives produce a field which alters the way incoming gravitons react with the ship, allowing them to be used for thrust.
Thrusters are more advanced. A combined spin-off of gravitic and damper technology, thruster technology uses a strong molecular repelling force, reacting with both the strong and weak nuclear forces, to create a reactionless drive. Thrusters do not require the presence of a large gravity field to operate efficiently, thus are usable even outside of a gravity well. They are highly localized with virtually none of the projection ability of anti-grav.
Thruster plates are usually mounted in the aft of a ship, as they tend to build up a slight ionization field around them. This is generally bled off into space.
History & Background / Dossier
Prior to the period when gravitic drives were introduced, a number of systems were used, often for very different purposes.
The earliest and simplest form of propulsion for space vehicles. They are akin to huge teakettles heating quantities of water into high-pressure vapor, which is then released to create thrust. Although simple and inexpensive, they not very inefficient. Miniature resistojets are often used for station keeping and attitude change by much more advanced craft.
Solid Fuel Rocket
Usually associated with the propulsion of unmanned missiles. Solid rockets play an important role in the early stages of spaceflight. They can be dangerous to use since, once ignited, they cannot be turned off. As a result, any failures within solid rocket systems have a high probability of catastrophic results. However, the solid rocket retains the advantage of a very high power-to-weight ratio. One parytial solution was the segmented solid engine, with layers cast in the shell, isolating buffer layers of inert material, and indivigual ignitors. These allowed the semented engine to burn one or more portions on command. However, the design includes details which introduce reduced reliability and several failure modes not present in single burn solid engines, and other technologies in time suplanted the solid segmented rocket; the hybred solid/liquid being a major contender, using a stable oxydizer with a stable solid fuel.
Liquid Fuel Rocket
The basic start-up technology most civilizations use to get off their planet and into space. The high power of these engines makes them good bootstraps, but also makes them voracious fuel eaters. While some energy can be gained from rockets, this is usually ignored or used to charge batteries since rocket operation is usually very short. The rockets most frequently encountered in known space (98% of the time) are cryogenically fueled (liquid hydrogen and liquid oxygen). Others use hydrocarbons, although the costs and environmental disadvantages of using that fuel type generally outweigh any conceivable advantages. One type which works well is the propelyne/hydrogen peroxide engine system, using a hydrocarbon fuel and H2O2 oxidizer fuel; this system tootally bypasses all the cryogenic issues and the attendant expenses, as well as the leakage issues attendant to hydrogen, and gives delta V in excess of the H2O2 system- but requires the fuel to be stored in a pressure vessel, and attention to materials used which come into contact with the high grade peroxide, as some metals can serve as catylists (silver a common example) to trigger it's decomposition into water (reaction mass) and oxygen (oxydizer) with a net energy yield which is quite dramoatic- in fact, rockets using H2O2 alone have been used. As H2)2 tends to decompose all by itself over time, it is not good for missions where it must wait for long periods before use; hydrazine is superiod for that mission profile, and as it is it's own oxydizer, it is often used by emerging races for robot explorer probes or station keeping mini engines on sattelites.
Becomes practical for manned vehicles at TL7. The thrust in this system is created by electrically reducing the fuel to a stream of charged particles (ions) which creates a very low thrust. The ion engine indicated on the chart is actually comprised of more than 100 separate 5O-centimeter thrusters. The primary advantage of this system is its endurance, low power requirements and reliability. However, the low velocities generally relegate vessels of this type to short range runs taking weeks or even months. The fuels used for this are known as "ionizates." This term includes mercury, and a variety of liquefied noble gases (argon, neon, krypton, etc). The values given for this fuel represent an average since some of these substances would be more than indicated and others less. Ionizates are found as trace elements on most Earth-like atmospheres, but are more frequently gathered from certain gas giants and their moons, which occasionally boast large concentrations of noble gases. Note that an ion drive is a mass driver operating with molecules for reaction mass; the techniologies tend to blur into one another.
MDs use electromagnetic repulsion (the principle used by the weapons of the same name) to generate thrust. Just as firing a gun will impart acceleration to the firer in Zero-G, so will the electronic firing of rocks, which in this case are propelled in (and discharged from) an endless treadmill of steel containers. The primary drawback to such systems is that they require tremendous amount of raw mass as propellant. Poor prospectors find this vice to be a virtue, as they can put a pressure dome on a small asteroid (very small), emplace one or two mass drivers and a power source, and begin firing pieces of the rock for propulsion. Another major use of this system is to propel promising asteroids out of a belt and toward mining vessels which can then reduce the asteroids to useable ores. Also not that anything that can fire pebbles at sufficent acceleration to be useful as a propulsion system is also sufficently robust to be interesting as a weapon system- and unlike plasma, pebbles don't spread out or cool off as they travel further away from the launcher, a fact not lost on Navy minds. See further Fusion Rockets.
Nuclear Thermal Rockets
These need a dedicated, on-board nuclear power plant in order to function. They use the heat from the reactor to excite liquefied gases for a high-pressure release. This gives them the nickname “nuclear teakettles.” Nuclear thermal rockets are very efficient, but very expensive, systems; they require the addition of a separate power plant. They are most effective when using liquefied hydrogen, although most non-oxidizing atmospheric gases will do in a pinch. This gives the vehicle an excellent self-refueling capability, which is handy since it is still a fairly voracious consumer of fuel.
Some races have devloped fusion thrusters which either bleed plasma off a reactor and focus it aft for reaction thrust, or flat out build a linear fusion reactor that leacks at the aft end for thrust, with a significant matgnetic focusing and directing assembly aft of everything else to improve efficency and give vectoring ability. This approach is ancestral to more modern thrust systems, used until the reactionless technology revolution; see further MHD.
Magneto-plasma-dynamic drives utilize hydrogen plasma to create thrust. This is, in effect, a crude, very low temperature plasma gun. With this technology, true in system commerce can begin to flourish freely and easily.
Identical to those in COACC, but given the importance of space exploration and utilization, this technology is pressed into intrastellar use long before it becomes common in COACC military craft. Generally, after first being used as an energy source, fusion technology is next employed in spacecraft because of its excellent power-to-thrust ratio and because it produces considerable power to run the ship’s other systems. Even after gravitic drives arrive on the scene, many designers prefer fusion because these drives, unlike gravitics, do not experience decreased performance when they venture more than 100 diameters from a significant gravity source. Of course, this limitation to gravitic drives disappears at TL11, when fusion drives lose their last tangible advantage. Experimental fusion rockets (more properly called plasma rockets) are used at the very end of TL8. With fusion moving just past the break-even stage, they represent the first application of this immature technology in a spaceflight role.
References & Contributors / Sources
- Classic Traveller Book 2: Starships
- Classic Traveller High Guard (Book 5)
- MegaTraveller Referee's Manual
- MegaTraveller Starship Operator's Manual
- MegaTraveller Hard Times