TechMemo:Maneuvering
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Star Fleet Engineering
Bureau of Starship and Starcraft Technology
Star Fleet Engineering
Technical Memorandum
Stardate: 170321 (21 March 2005)
RE: Sublight Maneuvering: Frequently Asked Questions
Why is it important for a starship to maneuver at sublight speeds? A Starship spends most of its time at warp.
This is not entirely true. Faster-than-light drives (warp drive and dimensional-warp drive) are gravitic systems, and are inoperable when in close proximity to a gravity well. This is called a Warp Limit. As such a starship cannot simply warp into and out of a planet's orbit.
Class M planets have a relatively small warp limit, but gas giants and especially stars can have large warp limits, and class M planets are often found within their star's warp limit. Dimension warp is much more sensitive than Warp drive and as such has a correspondingly larger limit, or d-warp limit.
Can a Starship in vacuum maneuver like an aircraft in atmosphere?
No. Aircraft behave and maneuver as they do because the medium they fly within (an atmosphere) provides friction. A vacuum is essentially frictionless. This means that a starship cannot use friction like an aircraft does to change its heading. Sublight maneuvering for a starship has changed little since the first ventures into space in the 20th Century.
Maneuvering in a vacuum is governed by Newton's Laws of Motion, the first of which is:
| An object at rest tends to stay at rest and an object in motion tends to stay in motion with the same speed and in the same direction unless acted upon by an unbalanced force. |
Force is provided by a starship's sublight engines. This force is not needed to maintain a starship's sublight speed and direction, only to change it. For example, a Starship is traveling 'north' at 20% of light speed, and wants to travel 'south' at 20% of light speed, essentially a 180° turn. To perform this maneuver a Starship would first turn to the desired heading (south) using maneuvering thrusters, then activate its engines to provide a force to slow its flight north (braking) until it came to a complete stop, then it would begin moving south. The most common way to measure the force a starship's engines can provide is by reporting the maximum "acceleration."
What is acceleration?
Acceleration is a measurement of how quickly a starship can change its speed and/or direction. The common unit used to measure acceleration is km/sec², or kilometers per second squared (or kilometers per second per second). With modern sublight engines, a Galaxy-class starship's engines can provide a maximum acceleration of 20.65 km/sec². This means that by running at maximum, a Galaxy-class starship can change its speed by 20.65 kilometers per second for every second that passes.
Say a Galaxy-class starship was performing the above maneuver traveling north at 20% of the speed of light and wants to move south at 20% the speed of light). Running its engines flat out, it would take a Galaxy-class starship 48.39 minutes to 'brake' its flight north, then another 48.39 minutes to reach 20% of light speed traveling 'south'.
Thus the faster a Starship can accelerate, the more maneuverable it is.
What kind of sublight engines are there?
The most common sublight engines are impulse drives. An impulse drive is essentially a large-scale reaction drive, which expels mass in a direction opposite of the desired heading, creating a force. As of 2417 Star Fleet is reaching the performance limits of impulse drives.
Another type is the inertia reduction drive, which include Daystrom Spaceframe Industries Distortion Kinetic drive systems. These drives generally operate by effectively reducing the mass of an object. With less mass to push, a reaction drive can achieve higher accelerations by Newton's Second Law which states that acceleration is directly proportional to the net force and inversely proportional to the mass of the object. Star Fleet began using distortion kinetics to enhance impulse drive performance since the Ambassador-class was introduced in the 2330's.
A third common drive type is the gravity planing drive. These drives are "reactionless," meaning that to operate this class of drives do not need to expel mass to operate. Instead they manipulate gravity in order to provide the force to move a Starship. As of 2417 Star Fleet is experimenting with these drives.
What is an inertial compensator and why does a starship need one?
An inertial compensator cancels acceleration effects within a starship. A Galaxy-class starship is capable of accelerating at 20.65 km/sec². At sea level on Earth gravity exerts a force on all objects toward the center of the planet which amounts to an acceleration of 9.806 meters per second squared. This is the level of force a human body as evolved to handle and operate within.
At 20.65 km/sec², a Galaxy-class starship can exert a force upon itself 2106 times that of gravity. Without an inertial compensator to counter acceleration effects upon a starship's crew, they would be a thin layer of paste upon the starship's aft bulkheads.
The level of acceleration an inertial compensator can negate is dependent upon the size of the Starship it is mounted in: The more volume contained within the hull of the starship, the less acceleration the inertial compensator can handle. Thus large starships are 'slower' and less maneuverable.
As of 2417, inertial compensator technology has become more efficient than impulse drive technology, which means that the inertial compensator can handle slightly more acceleration than modern impulse drives can generate.
Is there a sublight "speed limit?"
Yes, that of the speed of light. Sublight engines cannot attain or exceed the speed of light, which is why starships have faster-than-light drives. Effectively, modern Starships cannot exceed 85% of the speed of light for extended periods due to the limits of shielding technology. Above 85% of light speed, a Starship's shielding cannot effectively deflect particles in a starships path, nor counter radiation effects upon the crew.
Star Fleet in general limits its starships to 25% of the speed of light in order to minimize the effects of relativity.
Is "Full Impulse" a speed?
No. Full Impulse is a power setting. Star Fleet limits the performance of its sublight drives to that of 80% to avoid overstressing impulse drives and inertial compensators. Full Impulse is considered to be the 80% performance limit. A Galaxy-class starship can accelerate at 20.65 km/sec² at maximum impulse. At full impulse this starship would accelerate at 16.52 km/sec². Half impulse is 40% of maximum and one quarter impulse is 20% of maximum.
Why not accelerate as fast as possible?
While failure of inertial compensators is rare, it is possible. The more stress placed upon the compensator, the more likely failure becomes. So, under normal circumstances, the 20% safety margin of "full impulse" power greatly reduces the chance of compensator failure. However, during combat situations, it is common to use "maximum military power" which means running the compensator without a safety margin.
If an inertial compensator fails while a starship is accelerating, the results for the crew are invariably fatal.
-Scott Freligh
