There are three basic types of modern starship drives:
Impulse drive is the standard motive system for slower-than-light
manoeuvering for all star vehicles.
The hopper drive is used to explore uncharted regions of space.
The jump drive is used for instantaneous travel along pre-charted interstellar
-- From "Every Citizen's Guide to Practical Science",
Practical Science, 1st Edtion, Terra, 2651.
Impulse, or fusion, drives are literally powered by the stars. Using simple
hydrogen isotopes, impulse drives maintain a "hot fusion"
reaction, similar to the fusion reaction in stars, that provides the energy needed
to accelerate a spacecraft across interplanetary distances. While "cold fusion"
and "hot fusion" technology had been around since the late 20th Century, it was
not until the mid-21st Century that practical fusion engines were developed,
culminating in the first fusion craft in 2032. Commissioned by the United Nations
Solar Trust, and built by McDonnell-Douglas Engineering, the Sagan was launched
from the L3 station in 2041, and flew a regular shuttle route between Luna, Mars,
and Titan for the next 75 years before it was decommissioned. The Sagan is
currently on display at the Spacefarer's Museum complex on Deimos. "Cold fusion"
has conversely seen a different use, in the energy cells that power nearly all
While the power that fusion drives can generate is certainly a necessity for
space travel, what really makes the fusion drive practical is the fuel that
it requires. The hydrogen isotopes hydrogen, deuterium, and tritium are clean
(helium is the end product of the fusion reaction), abundant, and easy to obtain
in space, being the primary component of the solar winds of stars. Thus in
order to refuel, a ship need only sweep up hydrogen as it travels through
space. And the impulse drive is designed to do just that.
The impulse drive consists of two basic elements: the engine itself, and the
ramscoop. The engine section consists of electromagnetic field generators,
usually mounted at the stern of the ship. Hydrogen is released into the
electromagnetic field created by these generators, where it is compressed with
near-star force to create the "hot fusion" process. The energy released is then
used to propel the ship, as well as provide power for the ship's systems,
including life support, communications, weapons, and shields. In case of emergency,
most ships also back up these critical systems with an array of standard
cold-impulse cells. Large freighters and capital ships usually operate under a
thrust of around one or two standard gravities, while light fighters and couriers
can sustain thrusts of up to eight gravities.
The ramscoop section of the impulse drive is also composed of electromagnetic
field generators -- on small ships, these are in fact the same generators as
those used for the engine section. The generators project a ramscoop field, up
to several kilometres around and ahead of the ship, which sweeps hydrogen gas
into large intakes in the bow of the ship, where it is filtered and stored in
the ship's fuel tanks. Because the amount of hydrogen swept into the tank
is proportional to a ship's speed, a ship moving at high enough speeds can
collect enough fuel to maintain its engines indefinitely. Thus a ship must use
tanked fuel for acceleration, but once at speed it can rely on ramscoop intake
for operation. Larger ships moving at moderate speeds actually sweep up more
fuel than necessary, and so are able to refuel its tanks as it flies. On the
other hand, smaller vessels usually run at a slight deficit, and must refuel
periodically from a carrier or tanker.
One side effect of the ramscoop is drag, caused by the hydrogen collection
itself. Because the amount of drag a ship experiences is also proportional to
its speed, the drag in fact places a maximum on the speed at which a ship can
travel, based on its thrust and size. For capital ships and bulky freighters,
this maximum is around 150 kps; For fighters, it is around 500 kps or so. If
a ship were to shut of its engines, it will slowly lose velocity, and will
eventually come to a complete stop.
Because of the similarities in their basic design with impulse engines,
ramscoops are able to offer an additional benefit in the form of "afterburners".
This is especially good news for small crafts like fighters and racers, for
which speed is a premium. In this mode of operation, the opening of the ramscoop
field is reduced to decrease drag, and the hydrogen collected is routed past
the ship rather than into the tanks. At the ship's stern, the ramscoop field
captures and compresses the gas to fusion, acting like a second set of engines.
The result is 50% more thrust and a nearly doubled top speed. However, because
no fuel is being collected into the tanks, the ship will quickly run out of
fuel if it runs with afterburners for too long. Of course, a ship can simply
reduce the ramscoop field while maintaining normal thrust, thereby decreasing
drag and increasing its top speed. However this comes at the cost of
manoeuvrability. Because ships manoeuvre by manipulating the engines' fields
to redirect the exhaust, a higher thrust requires a higher manoeuvering thrust.
Thus ships only use reduced-scoop speeds when they do not expect to
manoeuvre, such as when travelling between worlds.
Monopoles are used to generate the complex electromagnetic fields used by both
impulse engines and ramscoops. Unlike regular magnets which have both north and
south poles, monopoles only have one pole, which can be either north or south.
Most monopoles are quite weak, and are mainly used like amplifiers to control
and direct much larger fields created by standard electromagnets. The complexity
of a ship dictates how many monopoles a ship needs, while its mass and size
determines how powerful each monopole must be. Thus starfighters usually
require thirty microgauss monopoles, cruisers or free traders require twelve
milligauss monopoles, and large passenger liners require four centigauss
monopoles. Because monopoles are an artifact left over from the Big Bang, they
can no longer be created in the normal universe, making them a very valuable
commodity, and the focus of much exploration outside of normal space routes.
Since the ramscoop is useful for powering ships at sublight speeds, a different
kind of drive is needed for spacecrafts to traverse the huge distances involved
in interstellar travel. Currently there are two types of drive in existence:
the Hopper Drive and the Akwende Drive. Commonly mislabeled as "faster-than-light"
drives -- since relativity does ensure that nothing can in fact travel faster
than light -- these devices nevertheless achieve something just as incredible:
the instantaneous transportation of a spacecraft from one point in space to
another, more distant point. While the operation of these two drives differ
in some respects, they both depend on knowledge of Gravitic Warp Theory.
Gravitic Warp Theory
The basis for Gravitic Warp was in fact discovered in 2214 by accident, during
an attempt to solve the antigravity problem. During that time, antigravity
vehicles worked not by diverting and channeling gravity, as modern devices do
now, but by cancelling gravity, which had the unfortunate side-effect of causing
sensations of weightlesness in antigrav vehicles. Since the Grand Unified Theory
implies the existence of antigravitons -- counterpart particles to gravitons
that carry repellant antigravitic forces, instead of attractive gravitic forces
-- it was theorised that if enough antigravitons could be produced, one could
generate a sufficiently large antigraviton flux that such antigrav vehicles
would retain their weight, while possessing all the advantages of regular
It was during one such effort to create an antigraviton flux that "Antigraviton
Flow" was discovered. By this time it had been conclusively shown that antigravitons
could be produced by colliding matter and antimatter in a suppressed gravity
field. During the course of the experiment, it was discovered that the
generated antigravitons showed a very slight tendency to move in a single
direction. That direction changed within the course of a year, and when
correlated with the position of the Earth, seemed to point in the rough
direction of Alpha Centauri. Further study revealed that the exact position
that the antigravitons were attracted to was a small patch of space between
the orbits of Pluto and Neptune. However it would be several decades before
the implications of Antigraviton Flow was fully understood and harnessed.
Currently much of Gravitic Warp Theory is still clouded in speculation, with
three competing theories to explain the observed effects, each of which incidentally
requires the suspension of a different fundamental law. But enough empirical
research has been compiled that the effects can at least be described.
According to regular physics, all objects of appreciable mass exerts gravity
on other objects. This gravitational field also happens to cause warps in
space-time. Gravitic Warp Theory postulates the existence of an "antigraviton
potential field", which a body of sufficient mass can generate. Such an antigraviton
field is generated only if the body manages to exceed the "Olivarez Equilibrium
Boundary", a theoretical threshold that determines if a body would actually
possess an antigraviton potential at all. Below the Olivarez Equilibrium, a body
will not be able to warp space sufficiently to have any antigraviton potential
regardless of its mass; conversely once a body has surpassed the boundary point,
it will generate an antigraviton field proportionate to the amount that its
mass bends space-time. Antigraviton Tropic Anomalies or "Jump points", of which
the patch of space between Neptune and Pluto is one example, exist at the very
edge of the antigraviton field of an object, at a point between the centres of
two antigraviton fields. If two bodies in space are close enough together that
their antigraviton fields overlap, no jump point would exist between them. Masses
with larger antigraviton potentials also exhibit more jump points than other
less massive bodies.
Thus far the situation is fairly simplistic. What complicates the picture (and
interstellar gravitic calculations) is the fact that the antigraviton potential
of a particular body is influenced by the gravitic influence of all other bodies
surrounding it. To put things in perspective, even the field of a star is affected
to varying extents by such trivial masses as planets, comets, asteroids, even
dust particles and gas molecules. Such influence depends both on the position
of these bodies relative to the star, and their mass at each point in time.
These bodies also influence the "path" of a jump line, often causing it to
curve within space, so that a jump point would not necessarily lie strictly
between the centres of two antigraviton fields. In addition, there also exists
universal (or at least semi-universal) variations in the antigraviton fields
of all bodies. All these factors affect both the size and shape of a star's
antigraviton potential field, which in turn affect the size, location, and even
the very existence, of all jump points. This is why jump buoys are necessary
to both mark and continually track the existence and position of jump points,
if only to expedite the jump process for a ship.
All this has a bearing on interstellar jumps. While the jump itself is instantaneous,
ships need to spend time travelling between jump points, and getting to the
exact location of a jump point. In addition, on occasion a phenomenon known
as "equipotential eclipsing" can occur, where a third body interposes itself
between two others, attracting a jump line to itself, and thereby creating a
separate node along the jump line. Planetary bodies as small as Luna could
cause just such an effect, causing a ship to revert to realspace prematurely.
The ship will then have to realign itself to its new location, search for the
second jump point to its original destination, and then jump again. Very rarely
such eclipsing could be close enough or large enough to obliterate the jump
line all together, so that a ship has no choice but to wait until the eclipsing
Finally, a ship's journey along a jump line also causes its own gravitic effects
on the jump line, thus affecting the jump conditions for ships following it;
it's own jump conditions remain unperturbed. There have also been instances
where a jump line has vanished during a ship's jump, causing the ship to
completely disappear from realspace, into some as yet unknown dimension of
space. Thus contrary to popular belief, jump travel is not safe, is in fact
quite dangerous, even insanely so. It is only because jump pilots are extremely
careful with jumps, that jump travel is even feasible at all.
Hopper Drives, more formally known as Morvan Drives (after Dr. Andre Morvan)
or antigrviton pulse generators, are the first working "Faster-Than-Light"
engines created by humanity. Invented in 2304, it gave humanity the means
to finally engage in some practical form of interstellar travel and colonisation.
Hopper Drives take advantage of the space-time warping effect produced by large
concentrations of gravitons and antigravitons. While large gravity wells abound
in space, concentrations of antigraviton particles occur more rarely in nature.
However, they can be created artificially with an appropriately large
matter/antimatter reaction, taking place far from any significant source of
gravity. A large enough concentration of antigraviton particles is capable
of creating a local and very temporary "space warp" in its immediate area. If
space-time is warped to a sufficient extent, a "well" in space-time is formed
that for an instant can close in on itself -- an effect that is thought to be
caused by pressure from "subspace", an as yet highly theoretical concept. A
ship positioned at just the right location on the lip of this well could then
"hop" across it before it opens up again, in effect traversing the distance of
the well in an instant of time.
In order to accomplish this, a Hopper Drive sets off a powerful but tightly
focused matter/antimatter reaction that generates enough antigravitons to create
a temporary "well" in space-time. A ship correctly positioned on the edge of
the well's event horizon would then be able to hop across space as the warp
closes. Of course this in itself is an extremely dangerous manoeuvre. If the
ship is positioned even a tiny fraction too close to the space-time well, it
will be sucked in when the warp closes, and annihilated down to the subatomic
level (This same principle is the basis for gravitic mines). In addition, the
warp must be done far from other gravity sources, or else the gravity space-time
well will never close, and the ship will again be exposed to the gravitational
forces of the well. Note that the safe distance for a hop in the Sol system
is around 1.25 times the aphelion of Pluto's orbit, assuming that Pluto, Uranus,
and Neptune were far away from that point.
Since the Hopper Drive's space-time warp is quite localised, the distance
actually traversed by the ship is typically around 0.2 to 0.35 of a light
year. As a result, many hops are still required to travel between stars.
However, an efficient hopper ship can maintain hopper rates of up to the
equivalent 10 times the speed of light. Nevertheless, hopper travel is
still quite slow as compared to jump travel, which is why hopper-ships have
earned the nickname of "sloships". It does not help that one must allow at
least 18 hours (some starship captains might even prefer a standard day) between
consecutive hops, or even longer, depending on local gravitic conditions. Since
a Hopper Drive causes warps in space-time itself, sufficient time and distance
must be allowed to pass before space-time is stable enough to allow another warp.
Besides which it also takes time to place a reactionary charge in the matter/antimatter
reactor, calculate the event horizon, and collect enough ram scoop energy to
fuel the hop.
During the early days of space travel, the Hopper Drive was the only practical
means of traversing interstellar distances. Today most spacecraft use the safer
and more economical Jump Drive, while the Hopper Drive is mainly used by explorer
and deep-space patrol craft.
Gravitic Warp Theory forms the basis for modern-day Jump Drives. Utilising the
jump points of stars to instantaneously travel between them, jump drives are
considered safer and more powerful than hopper drives despite the risks involved.
Since jump drives rely on natural, more stable jump points relatively near stars,
rather than creating dangerous and temporary local distortions in space-time,
they allow in-system approaches closer to the orbits of habitable planets than
do Hopper Drives, which can only be operated far from other gravity wells. Of
course jump drive travel is restricted only to existing jump lines. Since
heavier objects produce more jump lines, most jump lines run to or between
super-heavy stars, which are incidentally usually too massive to support any
sort of planetary system. They are however useful as transit points for travel
between inhabited star systems.
The Jump Drive is formally known as the Akwende Drive, after Dr. Shari Akwende
who invented it in 2588. The first working Confederation prototype was installed
on the Haile Selassie, which made a successful jump-transit from Sol to Polaris
on 2588.315, returning on 2588.323. Apart from the Akwende Drive itself, a jump
ship must also have a containment vessel of antiprotons, the fuel for the
antigraviton generator. Most large ships also have the equipment to create more
antiprotons to refuel itself, though this is not strictly necessary.
In order to make a successful jump, a ship must first find the exact location
of a jump point. In most explored systems, jump buoys are used to continuously
mark and track the location of jump points. However the ship must still pinpoint
for itself the precise location of the jump point in space. This it accomplishes
by switching on its jump drive at a very low level, producing a slow trickle
of antigravitons. Sensing equipment around the drive then track the drift of
the antigravitons, and slowly discover the jump point's location. Most civilian
craft can only home in on jump points when they're within a few hundred thousand
kilometres of them; conversely, military and exploration vessels can plot jump
points across many millions of kilometres.
Once a jump point has been properly located, the ship starts its fusion engines
and heads toward it. As the ship gets closer to the jump point, the attraction
of the antigravitons toward the point becomes stronger. At around 500 metres
from the jump point, the ship is close enough that the antigravitons can actually
arrive at the point itself before decaying, and the jump drive finally begins
to produce real thrust from the antigraviton flow, albeit a very small amount
(the 500-metre distance is more or less constant, based on the half-life of the
antigravitons). At this point, the ship stops at the edge of the jump area to
get a precise bearing on the jump point, including its drift rate. It then
kicks in its engines to get as close as possible to the jump point, and activates
the jump drive at full power. The high thrust provided by the jump drive drags
the ship to the exact jump point. Once the source of antigravitons coincides
with the jump point, an antigraviton field is created. If the intensity of the
field is sufficient based on the mass contained within the field and the speed
at which the mass is moving, then everything in the field vanishes at the point
of departure and arrives at the point of arrival, keeping all its original
It should be noted that all parts of the jump-ship must be subjected to roughly
the same amount of antigraviton flux. If a ship is too big for its antigraviton
flux, then only the parts that are within the field will complete the jump,
while the rest of the ship gets left behind, with disastrous results. Standard
jump drives are capable of projecting an antigraviton field of around 500 metres
in radius, based on the half-life of antigravitons. However, this radius is
not fixed, and is somewhat dependent on the power of the drive itself. Larger
capital ships require much more powerful jump drives. The most powerful drive
every built was able to generate an antigraviton field of some 12000 metres,
and was used in the 22000 metre long Kilrathi Dreadnought.
Since the speed of the ship affects the amount of antigravitons required to
initiate the jump, a ship can reduce the jump's energy needs by carefully
manoeuvering to the exact location of the jump point, and matching vectors with
the jump point's drift, before turning on the drive. While this results in the
minimum-energy jump for a given mass, it nevertheless takes quite some time to
achieve. However, for ships that are almost as large as their antigraviton fields,
this is the safest way to make a jump.
When a ship generates more antigraviton energy than it needs for the jump, the
excess is dissipated in the now-familiar burst of light and neutrinos at both
ends of the jump. Since this jump-burst is easily detectable even at long range,
a ship can make a "stealth" jump by taking the time to calculate the exact amount
of antigraviton energy needed for the jump, provided it is also equipped with
a "variable-flux engine". Under normal conditions, ships seldom bother with
this manoeuvre, and in fact very few civilian ships even possess the necessary
equipment to calculate the antigraviton flux.
While jumps generally maintain a fairly good success record, there are many
inherent risks which constantly remind us of its tenuous nature. Apart from
the dangers of drifting jump lines and equipotential eclipsing, among others,
one must also contend with the fact that each jump draws energy out of the jump
line used. This energy is proportional to the energy required to initiate the
jump. Most of the time the amount of energy reduced in the jump line is negligible,
but in some rare cases it could be enough for the jump line to connect to
a new destination, or even disconnect from realspace entirely. Ships unlucky enough
to be caught in these type of disconnections simply disappear. No one really
knows where those ships disappear to, and they are presumed destroyed.