Getting Around in Space: Drives

Maneuver Drive:

In system maneuvering is via VASIMR (Variable Specific Impulse Magnetoplasma Rocket) which can provide a wide range of thrust/efficiency profiles. In emergencies, the drive is capable of generating several gravities of acceleration, but only for limited durations and at the sacrifice of a great deal of propellant. Propellant is normally simple hydrogen, although any reasonable low molecular weight material can be used. The propellant feeds have been specifically designed to use water in lieu of hydrogen to accommodate primitive refueling facilities. The Pournelle carries sufficient power plant fuel (He3) to run the MIGMA reactor at 80% power for 3 years. Delta V is limited by the quantity and characteristics of the working fluid used for propellant.

The VASIMR maneuver drive is shown here. Plasma is tapped from the main fusion reactor and is used to heat the propellant working fluid. Additional heating is provided the helical and ICRH antenna. The plasma is then accelerated via magnetic fields. For high thrust applications, additional propellant can be introduced at the exhaust stream, where thermal expansion increases total effective thrust at the expense of Isp.

Interstellar Drive:

The single item of technology which has made human colonization of the stars possible is the Miller-Weisman hyperdrive. It is, to date, the only known means of travelling between the stars in acceptable periods of time.

The M-W hyperdrive skirts the problem of the C-barrier by actually not moving the ship at all. The rotating masses of the hyperdrive unit create a field which encompasses the entire starship. It is then capable of "tunneling" all the mass within the field instantaneously a few hundred meters away (actual distance depends on the technology and efficiency of the drive - a hundred meters is about average). This effect is cycled at thousands of times per second, equaly to the rotational velocity of the hyperdrive armature. The ship is in essence getting from point to point faster than light would make the same distance, but the ship is not physically moving in excess of C. A hyperdrive ship has a pseudo-velocity which is greater than that of light, hereinafter referred to as "velocity." Individuals crewing hyperdrive craft feel no loss of temporal continuity as they exist for mere nanoseconds along a vector determined by their hyperdrive's alignment. In a sense, it's like viewing a film, only with thousands and thousands of frames per second - it all seems quite natural and continuous. In fact, as far as the effects of time are concerned, the hyperdrive does not suffer the effects of time dilation that would be experienced in craft travelling at relativistic speeds. Another problem avoided by cheating the barrier with hyperdrive is that of red and blue shifting - the compression or expansion of wave motion radialtion as an object approaches or recedes at relativistic speeds - since the ship is not actually in motion.

Of course, to say that ships travelling using hyperdrive are completely motionless is a fallacy. Stutterwarp-equipped craft are usually also fitted with a reaction drive for maneuvering about planets and other large celestial objects, as the efficiency of hyperdrive's "tunnel-distance" decreases by many orders of magnitude when used in a gravity field of any more than 0.01 G. The fact that objects resist inducement into hyperdrive as the gravitational field increases was the chief stumbling block to the technology's discovery and application on Earth.

When a vessel activates its hyperdrive, any inertial velocity the craft had before the drive's activation is conserved through the hyperdrive transition. Therefore, if a ship is cruising at 1,000 kps using a chemical reaction drive when the hyperdrive is activated, the ship would retain this speed relative to the star system of origin when the hyperdrive is deactivated. The "velocity" of a hyperdrive is determining by controlling the "tunnel distance" rather than the cycle rate (which is only tunable within certain parameters). The true limits of "velocity" are determined by the G-field present.

The field effect which the drives generate is termed "stupid" - it will carry along anything which is in the field as if it were part of the ship. Ships often drag along particles of interstellar dust within their fields, but this is not considered a problem since the quantities are usually negligible.

Stutterwarp drives act upon a linear directional field effect. In order to steer a hyperdrive propelled ship, the ship itself must be turned in physical space. This is accompished by using the ship's reaction thrusters to change the heading, a maneuver which can be executed while the hyperdrive is engaged (and often is). Though it may take only a few seconds to change heading by 30 degrees, the distance travelled to accomplish this feat has been hundreds of thousands of kilometers. An alternative for "tighter" maneuvering is to disengage the hyperdrive (known as "all stop"), change heading, then reactivate the drive. Such considerations can play an important role in starship military activities.

Dangers and Problems

The nature of hyperdrive travel - existing discontinuously along a vector - presents a number of problems, most having to do with the utilization of electromagnetic radiations. Of primary concern is the inability of a ship to navigate with active radar at C+ "velocities." Radar becomes quite useless simply because the ship outruns its radar pulse, arriving at a hazard before the radar pulse has had a chance to warn against it. Before a radio beam can get to a stray asteroid and bounce off, the ship would have already collided with it. It is for this reason that ships usually pull their "velocity" below C when entering or passing through a system's cometary halo, asteroid belt, or other area of high debris concentration. The ship is still using its hyperdrive drive, but will bring its tunneling distance down below C for safety. For this reason, however, space hazards must be reported upon contact to authorities. In explored space, zones of higher than normal densities are marked with radio beacons to warn spacers to skirt the area or lower their drive rates. Unexplored space, however, has no such beacons emplaced and collissions with undetectable objects are a constant threat to the explorer.

By the same token, laser and particle weapons are extremely limited at C+ "velocities" since one could "tunnel" into one's own beam. Even if one were to fire a weapon laterally at "velocities" below C, the weapon's beam would be sliced up very badly by the cycling drive. The resultant beam would pulse and might cause damage, but would have great trouble maintaining a continuous burn on the target.

Micrometeorites cannot be attended to by simply erecting a shield on the front of the ship. A craft could tunnel to a spot where a meteorite was already beyond the shield; it would not necessarily have to pass through the shield. It is possible for micrometeorites to temporarily exists within the confines of the ship, or crew for that matter. However, the precautions taken by starship pilots in avoiding "high" density zones make significantly damaging occurrences of such events astronomically small.

Communication

The aspect of hyperdrive which has proven the most annoying is the inherent problem of radio communication. While a drive is activated, any incoming or outgoing radio signal would be chopped to ribbons and distorted beyond the capacity of the ship's crew or computer to decipher it. Two solutions to this problem have been adopted.

The easiest solution to the communications problem is to simply deactivate the drive system for transmission or reception of messages. This method is foolproof and cheap.

Navigating

The inertial reference point chosen in human space is the brilliant A-class star Sirius. Its brightness makes it an unmistakable beacon from all corners of man's domain. Because of the nature of the stutterwarp drive, navigation is actually quite stright forward, in that the navigator selects a specific start and points the ship at it. Navigation relies on detailed spectral star charts, as well as maps of interstellar hazards.

Visual Effects

The nature of the hyperdrive itself, that of defying the laws of physics effectively and travelling at multi-light speeds, creates many spectacular visual effects. These effects have distinct characteristics and have necessitated a unique terminology for the common spacefarer.

The View from the Ship: As discussed earlier, there is no red or blue shift effect observable by the occupants of a hyperdrive driven spaceship. Remember that the ship is not moving near or faster than light in real space. Therefore, instead of "seeing" all the light waves between the two endpoints of a cycle, the observers only see the waves at the first point and at the second point. Those waves in-between never touch the spacecraft and never can be viewed by occupants.

An observer looking in the direction of motion on a hyperdrive powered starship will see light from all the stars and objects in the foreground, as if he were moving at multi-light speeds toward these objects, only without any kind of relativistic doppler shift. For instance, if the ship is moving fast enough past a star, that star might actually appear to be moving with respect to the ship, which, in fact, it is.

Similarly, an observer looking in the opposite direction, that is, where the ship has been, will see the stars and objects in that direction in the same manner, as if the ship were moving at tremendous speeds. However, should the ship suddenly come out of stutter warp, the aft observer will get a real treat known as a "termination image" or "chaser".

Since the ship has been moving effectively faster than light, all the light from previous positions of the ship will "catch up" to the stopped ship. First, the light of the ship from the last cycle point will catch up, then the light from the point before that. What results is an image of the ship moving away, along the vector the ship originally took, but in the opposite direction. Commonly, a termination image is lost rather quickly, but with telescopic enhancements, the image might be maintained for upwards of a few seconds. This effect also comes on gradually as a ship slowly drops below C+ velocities - this is the effect referred to as a "chaser." A chaser image recedes at a slower rate.

It should be noted that pre collapse hyperdrives are far superior to those now manufactured. This makes recovered pre ruin vessels quite valuable.