Realistic Space Maneuvering or,
"Hey, it doesn`t move like an aircraft!":


It should be understood that for a spacecraft traveling and maneuvering in space, it is far different from the way an aircraft maneuvers in an atmosphere. This is simply because the forces that apply to both are very different. In space there is no atmospheric friction to affect travel, no wing lift is needed, and the forces of gravity are both lighter, and acts upon the craft in a different way. In many science fiction stories, starships quickly get up to a top speed and then travel at that speed continuously even though thrust is still applied. This is incorrect.


In space there is theoretically no limit to the top speed of a spacecraft other than the limits caused by fuel constraints, and the speed of light. Movement in space is, as a general rule, not determined by a top speed but in terms of how much acceleration a craft has.


In a very general way, a reaction drive (thrusters) type starship uses particles that are accelerated to give the starship thrust. If the starship does not have some form of hydrogen catcher field, then the ship needs to retain enough reaction mass from acceleration to be able to slow down or will need to be able to be caught and refueled. In many cases, most starships will use thrust to get up to a desired speed and will then continue unpowered at the speed achieved by the acceleration for months and will travel until they get near their destination before decelerating. A similar method of space travel can be seen today. Space probes are launched, and while often they use a slingshot around celestial objects to further increase speed, they will travel unpowered for years to get to their destination. Good examples of this are the Pioneer space probe and the Voyager space probes which took pictures of many of the outer planets.


In actuality, the speed of light itself is impossible to reach, because as Einstein`s Theory of Relativity points out, that the closer you get to lightspeed, the larger an objects apparent mass becomes. At lightspeed an object would have infinite mass, and since the energy expended in the acceleration of the object to any given speed is directly proportional to that objects mass, it follows that to accelerate a object to lightspeed would also require infinite energy.


Another limit is that as a object travels closer to the speed of light, the flow of time around the object would be distorted, so that it would appear to the rest of the universe as if the time in the object would be slowed down. (Follow the links at the bottom of the page for a MUCH better and expanded explanation of Relativity)


In game terms, the author has added the factor that particle shielding will not allow speeds beyond a certain level, effectively circumventing the problems posed by Relativity.


In here, the author will for the most part will discuss thrusters, but much of this can also be applied to anti-gravity systems which will mostly work in similar ways. They are reaction less and do not require any sort of mass to create acceleration and as such as much less limited by fuel constrains. They can likely also pull much higher accelerations.


In most situations, a vehicle in space can simply continuously accelerate by applying force/thrust in the opposite vector as the direction of travel. If the vehicle stops applying force, it will simply continue to travel in the same vector without slowing down or speeding up. In an atmosphere an aircraft slows down due to friction. This means that devices such as air flaps cannot be used to slow down a starship. Instead, a vehicle in space must apply force in a vector directly opposite the course it is going in to slow down. This can be done by forward maneuvering thrusters but can be done most effectively by flipping the entire ship 180 degrees and applying the main thrusters directly against the vector of travel. It will require the same amount of applied force that was used to reaching the speed the ship is traveling at decelerate to a stop.


In the same respect, wing flaps and a rudder cannot be used for side maneuvering. Instead, force must be applied to push the ship into the desired course. Like forward and reverse maneuvers, force can come from either maneuvering thrusters or the main thrusters.


Unless it is negated, all of the force of the original vector is retained. This original vector of travel can only be negated by applying force against the course of travel. This means any application of force in a vector of greater than 90 degrees from the previous vector of travel will apply some force to slow down the object. Slowing down or completely changing direction of travel is not as simple as it is in an atmosphere, although small vector changes to make the ship less easy to hit are relatively easy. For these reasons maneuvers like banking are not done in space (sorry Warsies and Trekkies) because an aircraft uses atmospheric friction on its wings to make a course change.


One of the most useful side effects of space maneuvering is that a vehicle in space may spin around its center of gravity freely without changing the vector of travel although in many cases these maneuvers will reduce the ability to apply forward force. This spinning is in reality far easier to perform than it is to change the vector of the vehicle's travel. A relatively small amount force is simply applied to cause the ship to spin. If the vehicle wishes to stop the spin, the same amount force must be applied to stop the spin or it will continue spinning. It is far easier to spin a vehicle in space than it is to actually change the vector of travel significantly because there is no need to defeat forward momentum. Such spinning of the ship would not cause undue stress on the ships structure (not if it is designed right anyway), and performing such a spin would be a trivial matter. The force applied to make a ship spin will cause tiny vector changes but for all intents and purposes these changes will be insignificant. Some of the force of a vehicles main engines may still be applied in order to make vector changes or accelerations, but can only be applied when the vehicle's thrusters are in the direction desired. A good example of this might be for a vehicle which is spinning to only apply force when the front of the vehicle is facing in the desired direction of travel to continue forward acceleration.


There are many reasons why spinning a vehicle could be desired. One is simply to bring the ships forward main battery to face a target that is to the side or rear, a second is to protect a damaged side, and a third is to have a starship spin continuously so that it may bring weapon systems from multiple sides to bear on the same target vector. Good examples of this kind of maneuvering can be found in the series Babylon 5, where fighters turn on their own axis to fire at targets behind them, and starships spin 180 degrees to perform radical braking maneuvers.


Ultimately such maneuvering will be very common in space, and the ability to perform it should be assumed to be included in all relevant piloting skills, and no penalties to perform such maneuvers should apply.


Since these moves are so common, there is also no reason to assume that a starship should suffer any kind of negative effects during such a maneuver. After all, the energy required to spin the ship around is negligible compared to full power acceleration or deceleration of the ship, and the ship`s structure should be able to handle the stress easily.


http://math.ucr.edu/home/baez/physics/relativity.html
http://www.math.washington.edu/~hillman/relativity.html
http://www.dmoz.org/Science/Physics/Relativity/



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Writeup Mischa (E-Mail Mischa) and by Kitsune (E-Mail Kitsune).


Copyright © 2000, Mischa & Kitsune. All rights reserved.



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