Launch rails are familiar to just about any model rocket enthusiast. Launch rails are also used in some military missile launchers as well as on aircraft carriers. They help the missile/aircraft stay on-target until it achieves a large enough velocity (about 100 ft/sec) that aerodynamic forces will keep its flight steady. Military launch rails often also use "cradles" to hold the launching missile, which are accelerated independently along the length of the rail to give the rocket an extra velocity oomph.
Scaling lainch rails up for use in an actual space launch is an old idea from the dawn of the space age, usually taking the form of a length of elevated track that uses various means to accelerate a rocket-carrying cradle. The concept was abandoned for space travel as they turned out to be more expensive and more trouble to engineer than they were deemed worth.
Its possible that emerging nations or private interests without the resources to obtain more advanced technologies may use launch rails to help their fledgling space efforts. Also, while orbital launch rails are somewhat impractical on Earth, on other terrestial worlds such as the Moon and Mars, which have greatly reduced gravity and no or very little atmospheric pressure, they could prove to be a practical and economically-viable option for future settlers.
DEADFALL LAUNCH RAIL
Tech Level: 9
A deadfall is the simplest kind of launch rail. One positions the rocket intended for launch on a specially-built wheeled cradle at the top of an incline, and lets it zoom down along a reinforced track. At the bottom, the track curves up again to launch the vehicle into the air. Think of a huge oversized ski-jump, except the "jumper" here is a large multi-ton rocket. The rocketís engines may be ignited at the the top of the deadfall in order to boost the velocity gained, but the exhaust may damage the rail. A more practical method would be to ignite the engines the moment the rocket is clear of the rails and is starting its ascent.
The gain in velocity from such an arrangement would most likely be a pittance compared to the overall velocity needed to gain orbit (around 25,000 mph), but in cases where every drop of fuel is precious it could prove invaluable. Such was the case in the classic sci-fi movie When Worlds Collide, where the rocket ark used a deadfall launch rail to begin its Hail-Mary flight for survival.
PRESSURIZED LAUNCH RAIL
Tech Level: 9
The cradle carrying the rocket is propelled forward by channeled pressurized gasses behind it, either from a huge build up of steam (as is used on modern aircraft carriers) or from an explosive chemical reaction, similar to the way bullets are propelled down a rifle barrel. These types of powered rail-guided systems are also called launch catapults.
While a marked improvement in velocity gained over a deadfall launch rail, a pressurized launch rail still only adds a negligible amount of velocity to the overall speed needed to achieve orbit, approximately several hundred miles per hour at most. Pressurized launch rails need not be curved like deadfall launch rails, but instead can be angle up in straight lines, even almost completely vertical, depending on the exact design.
ELECTROMAGNETIC LAUNCH RAIL
Tech Level: 10
Magnetic levitation technology is used to propel a launch cradle along a specially-constructed track. This is the same technology used in electromagnetic monorail trains, such as those found in Japan.
Because the launch cadle and its track do not actually touch, just "levitate" close to each other thanks to magnetic repulsion, friction is reduced to near zero, allowing impressive accelerations. Advanced electromagnetic launch rails could give an initial boost of close to the speed of sound to its payload.
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