Friday, June 29, 2018

Psi-Wars Propulsion Technology

Psi-Wars features vehicles of all sorts, from hover cars for high speed chases to starfighters zipping around great and mighty capital ships in battles that look surprisingly reminiscent of WW2 battles.  This post takes a look at what technologies the Psi-Wars setting uses to traverse its planets and the galaxy, including:

  • Hyperspace drives
  • Hyperdynamic technology and aerospace engines including plasma thrusters, impulse drives and the grav drive
  • Ground-based propulsion technology including repulsorlift technology, legged vehicles and tracks.
  • Aquatic propulsion technology and why it is slowly becoming obsolete.
For those who want additional details about the design process, including the specifications (compatible with the design process of GURPS Vehicles 3e, and with the previous power post!), $3+ patrons can find the design notes here.

Aerospace Propulsion

For the Psi-Wars galaxy, the discovery and mastery of hyperspace, and its hyperdynamic nature, meant that air and space travel merged into the same technologies. While occasionally one can find primitive aliens making uses of gasbag technologies or turbofans or space rockets, the rest of the galaxy uses hyperdynamic engines to drive both its spacecraft and aircraft.


The Hyperdrive “shunts” a ship from “normal” space to four-dimensional “hyperspace,” which allows the ship to travel at far greater speeds. A typical hyperdrive engine reaches speeds of 30 light years (10 parsecs) per hour, through more powerful drives can reach speeds two or three times as fast! While in hyperspace, a ship cannot see or interact with “real space” matter, though strong gravity fields, like those found on planets or around stars, or for light years around black holes, can distort the medium of hyperspace, making travel difficult, throwing the ship off course, or even pulling the ship out of hyperspace entirely. Thus, the spacefarer must carefully choose his course before activating his hyperdrive. Generally, a hyperdrive is activated once a ship has left a planet’s orbit, and the ship travels a course that takes it to just outside the orbit of their target world.

The act of shunting a ship into hyperspace takes far more energy than the act of traveling through space. This energy can be through the use of energy banks, which generally take 24 hours to recharge on an inactive ship, or by actively burning hyperium fuel. The latter requires a hyperium fusion reactor, but the amount of hyperium required is a fraction of the mass of an energy bank, and has become the preferred means of paying the high costs of hypershunting. In principle, once a ship is in hyperspace, it can remain there for as long as the traveler wishes (and “exit” for free, like “falling” into real space), but in practice, the farther one must travel without interacting with real-space, the more likely one is to go wildly off-course. In practice, most hyperspatial journeys are “hops” of 100-200 light years at most.

The medium of hyperspace is not a perfect vacuum, but a sort of hyperfluid through which the ship can travel and, with a hyperdynamic field, can “push” off of. This medium distorts and changes over time, and can interact with the ship, making passage more difficult, disrupting the ships travel, or driving it off course. Some regions have placid, easily traversable hyperspace between their systems. The most well-known of such regions is the galactic center, where travel between worlds is relatively easy. The easiest and most well-charted courses tend to become major trade routes and avenues along which major empires project their power. These tend to be called “hyperlanes” or “hyperstraits.” Other regions have much “denser” or more “difficult” hyperspatial medium: most travelers avoid these, but especially daring navigators might give them a shot, and may well know a “pass” through such a dense region. The space between the galactic arms or between galaxies tend to be notoriously tricky to traverse. Finally, the hyperspace medium has “weather,” and hyperstorms can kick up, throwing ships out of hyperspace or making travel difficult. The death of the homeworld of Styx when its star suddenly collapsed into black hole threw their entire region of the galaxy into a chaotic storm that raged for centuries and makes travel in that region treacherous to this day.

Charting a hyperspace route takes 30 minutes and requires a Navigation (Hyperspace) skill roll. A successful roll means the jump will occur without incident. A failure means the ship is “off course,” typically ten parsecs times the margin of failure, while a critical failure can put the ship nearly anywhere, ruin the hyperdrive or crash the ship into a star or planet (though not a recommended choice for pcs!).

Modifiers: The GM may assign a difficulty between -0 and -10 to a particular route, depending on how “dense” or “easy” the region is to traverse. A well-charted hyperlane adds +4. Every 30 light years (or 10 parsecs) after the first 100 light years (or 30 parsecs) applies a -2 to your navigation rolls; and, of course, if your route takes you over multiple “regions” of hyperspace with different difficulties, the GM should apply the penalty for the roughest region of hyperspace. Finally, “hyperspace weather” can apply between -1 to -10, with a typical hyperstorm applying a -4 to the roll, and typical “bad weather” applying a -2.

Shunting into hyperspace requires the drive charging for 5 minutes, though it can be charged faster with a Mechanic (Hyperdrive) roll with a time modifier applied.

Hyperdynamic Drives

Hyperspace contains a “medium” through which a ship must travel, and off of which a ship may push. Ships equipped with hyperdynamic fields may this medium to accelerate and to maneuver. Depending on what drive has been equipped, this may allow a ship to maneuver through space as though it were a jet aircraft, or it may grant it contragravity-like properties, or allow it to float serenely through the sky like an airship. Ships with hyperdynamic fields maneuver through atmosphere exactly as they do through space.

Outside of a gravity field, hyperdynamic drives allow a hyperdynamic ship’s relativistic frame of reference to accelerate to light speed. This happens naturally: once a ship exits the orbit of a planet, its frame simply accelerates without additional cost to the ship. As the frame accelerates, this is a form of psuedovelocity: if the ship collides with another ship, the collision occurs at the ship’s “real” speed (typically measured in miles per hour, rather than thousands of miles per second!). Furthermore, when ships enter another ships frame of reference, while an outsider will see both traveling in the same direction at the speed of light, in their own reference, they seem to be traveling at their own, natural speeds. In practice, this “frame dragging” simply means that ships that wish to travel to other worlds may do so very quickly (typically in minutes or hours) while still engaging one another at their own “normal” speeds.

Hyperdynamic Plasma Thrusters

A plasma thruster is a form of “fast” reactionless drive that produces extremely fast thrust, and interacts with hyperspatial medium as though it was as diffuse as air. This gives the plasma thruster performance similar to a jet engine. Ships equipped with plasma thrusters travel at supersonic speeds and might have “afterburners” to allow them to reach even higher speeds, but must maintain high speeds in both atmosphere or space or risk “losing grip” on the hyperspatial medium and losing control. They maneuver similar to aircraft with wings. Unlike other hyperdynamic drives, plasma thrusters require no direct power input, but do consume hyperium fuel.

A plasma thruster has a bright, highly visible and hot signature that resembles rightly focused blue or red “flame.” They require extensive hyperdynamic structures, and often have a great deal of surface area dedicated to either aerodynamics like wings, or hyperdynamic control structures (which may or may not resemble wings, but still take up a considerable volume of the craft’s volume).

Plasma thrusters tend to be used on starfighters and starbombers; occassionally, it sees use on craft intended only for aerial travel. It can also operate as a jetpack, though such engines need decent heat dissipation.

Hyperdynamic Grav Drives

A grav drive was the first of the three hyperdynamic propulsion systems and was believed, at first, to interact with gravity itself; only later was it discovered that it interacts with the hyperspatial medium, but the name stuck.

A grav drive provides both a motive thrust and “lift,” allowing it to move at very high speeds (up to 600 miles per hour), or to float perfectly in place, granting it high maneuverability. Such a drive must at a minimum, provide enough lift to counteract the vehicle’s mass, but requires no “minimum” speed like a plasma thruster, and is less efficient at extreme masses than the impulse drive, which tends to limit it to medium-class starships, such as corvettes, or smaller craft like gunships where the ability to hover is more important than the ability to maximize speed. It consumes only energy to produce both thrust and lift.

A hyperdynamic grav drive produces an intense blue or red glow from its engines, but no visible flames.

Hyperdynamic Impulse Drive

A hyperdynamic impulse drive is a large, heavy thing engine that interacts with the hyperspatial medium as though it was “dense,” similar to water. This greatly slows its speed, which cannot exceed 300 miles per hour and is typically below 100 miles per hour, but “pins” it against the hyperspatial medium, so that it does not interact with gravity at all. Even at perfect rest and consuming no energy at all, an impulse drive allows a ship to float perfectly above a planet or even above the ground.

An impulse drive is very heavy, requiring at least 5 tons of mass, but is more efficient at large scales than the grav drive, and is by far the cheapest of hyperdynamic drives. This makes it the preferred choice for extremely large vessels, such as interstellar capital ships and transport vessels. It sees much use on planets, often replacing sea travel with slow-moving-but-cheap aerial transport.

An impulse drive produces a faint and streaky blue, white or red glow, often appearing like diffuse, escaping gas; it resembles the ancient “ion drive” in appearance, and is sometimes (mistakenly) referred to as an ion drive.

Ground Propulsion

Repulsorlift Drivetrains

A repulsorlift utilizes the opposite of a tractor beam, a pressor beam, to both lift a vehicle off the ground and to provide directional thrust by pushing off the ground. The result resembles a low-flying grav-drive, but works with a completely different technology. Vehicles equipped with a repulsorlift seems to hover or skim across the ground with about a foot of clearance. It moves swiftly, slightly faster than a wheeled vehicle under ideal conditions, but does not require a road.

Repulsorlifts tend to see use most often on the equivalent of cars or motorcycles, but also sees use in high-speed military vehicles. Because it must expend energy to both lift and push the vehicle, it tends to be less efficient for very heavy vehicles, unless built around a rail that interacts with efficiently with the repulsorlift: hover-trains tend to be common on highly industrialized worlds, or on worlds with intense mining.

While repulsorlifts don’t require roads, they do (marginally) benefit from them and, of course, a hover vehicles can still crash into a tree or a spike of rock, so many municipalities that can afford to do so still pave their roads, as it provides a convenient path for pedestrians, makes life a little easier for hover-cars, and provides clear routes for traffic.

Legged Drivetrains

Legs provide vehicles with greater mobility, but less speed and higher costs than a hover-vehicle. Thus, legged drivetrains tend to be used only for highly specialized vehicles, though the Cybernetic Union makes extensive use of them. They don’t require a “lifting energy” when resting, and which makes them slightly more useful for heavier vehicles such as tanks, but their high cost limits such vehicles unless the vehicle needs to be highly agile (such as scuttling side to side to dodge shots, or stepping over broken and rugged terrain). Most legged drivetrains have four or more legs, as this provides more stability than two-legged designs.

Tracked Drivetrains

Vehicles with tank-style treads do exist in the Psi-Wars setting. These tend to be limited to older vehicles and has largely been superceded by the repulsorlift, except where the vehicle is exceptionally heavy. Giant, industrial crawlers use tracks, as do super-tanks. Older vehicles may as well, like the Gristian track-cycle. Vehicles with tracks tend to be the slowest of the three sorts of ground vehicles and the least agile, but they’re cheaper and more rugged than their counterparts.

Animal Propulsion

On remote or primitive worlds that lack a major industrial base, locals often use indigenous species as transportation. One might see an alien raider riding a multi-legged, feral-looking creature into battle, or see aliens who have hooked up wagons to great behemoths to draw their vehicles through great salt deserts. This tends to be rare in the “civilized” galactic center, however.

Aquatic Propulsion

Aquatic propulsion has largely been overtaken by the Hyperdynamic Impulse Drive, as it provides similar performance but can travel to space. So one is more likely to see serenely floating skyships over the oceans of a world than to see ships plying the seas. That said, starships make poor submersibles, and a Magneto-Hydrodynamic Turbine is slightly more efficient than an Impulse Drive if one only wants to travel by sea, or beneath the sea.

On more primitive or poor worlds, aliens still make use of sails, paddle wheels and animal transportation when traveling on water.

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