Launched roller coaster

The launched roller coaster is a modern form of roller coaster. A launched coaster initiates a ride with high amounts of acceleration via one or a series of linear induction motors (LIM), linear synchronous motors (LSM), catapults, tires, chains, or other mechanisms employing hydraulic or pneumatic power. This mode of acceleration powers many of the fastest rollercoasters in the world. 
Launched coasters mainly feature improved speed and acceleration when compared to traditional chain or cable lift coasters. They can be less reliable, however, and require increased maintenance. 
Electromagnetic.
LIM / LSM.
Linear induction motor (LIM) and linear synchronous motor (LSM) coasters use propulsion via electromagnets, which utilize large amounts of electricity to propel the coaster train along its track into the ride elements (e.g. inversions, twists, turns and short drops). Ten design companies managing these types of rides are Vekoma, Intamin, Gerstlauer, Premier Rides, Maurer, Zierer, Mack Rides, Bolliger & Mabillard, Rocky Mountain Construction and S&S Worldwide. Both Rocky Mountain Construction and Bolliger & Mabillard established their first LSM launched coasters recently with the RMC Topper Track Coaster, Lightning Rod, at Dollywood, and B&M's wingrider, Thunderbird, at HolidayWorld.
An example of an LSM launched roller coaster is Maverick at Cedar Point in Sandusky, Ohio.
These launch systems transfer electricity through a motor on the roller coaster's track so that it controls the speed at which it will urge the cars and train either forward or backward on a segment. LIMs are mainly used in Premier Rides roller coasters and Intamin impulse and blitz coasters. However, LIMs can also be used for general transport, such as the Tomorrowland Transit Authority PeopleMover in Magic Kingdom or monorail and maglev trains.
Fluid pressure.
Hydraulic Fluid.
Hydraulic-launched roller coasters give the riders high acceleration, yet with improved smoothness, over the electromagnetic and catapult launch mechanisms. The Swiss manufacturer Intamin pioneered this new style.
The heart of the system is several (usually eight) powerful hydraulic pumps, each capable of producing around 500 horsepower (373 kW). Hydraulic fluid is pumped into several different hydraulic accumulators (energy storing devices) containing two compartments separated by a piston. As the incompressible hydraulic fluid is pumped into one compartment, nitrogen in the other compartment is compressed.
At launch, the fluid under pressure from the accumulators is used to drive a number (typically 16 or 32) of hydraulic motors, which spin a large winch drum that rewinds a cable attached to a catch-car under the train in a matter of seconds. The catch-car moves in a groove in the center of the launch track with the motor at one end, and the waiting train at the other.
While the train inches forward, the pusher moves back from the motor towards the train. Once the pusher connects, the anti-rollback braking system drops beneath the track, giving the train the green light to be launched. In the "Kingda Ka" roller coaster, the system as a whole can produce a peak power of up to 20,800 hp (15.5 MW) for each launch.
These launches are considered capable of giving a far greater and smoother acceleration than the LIM/LSM styles. The acceleration from a LIM/LSM launch is greatest at the beginning and dies off rapidly towards the end of the launch, but the acceleration from a hydraulic launch remains nearly constant throughout the launch.
The first hydraulic launch coaster was "Xcelerator" reaching in 2.3 seconds. The world's current tallest and 2nd fastest coaster "Kingda Ka" at Six Flags Great Adventure, which opened in the spring of 2005 is capable of reaching 128 mph (206 km/h) in 3.5 seconds. The fastest roller coaster in the world Formula Rossa, which reaches in 4 seconds, is also launched using this method.
Hydraulic launched rides usually have a tower after the launch, with differing layouts afterwards depending on the park's financial resources. "Top Thrill Dragster" brakes after the tower and "Kingda Ka" features a single hill after the tower, while "Storm Runner" at Hersheypark offers a series of overbanked turns and inversions after its 180 foot (55 m) tower drop. "Rita" at Alton Towers does not have a tower, only airtime hills and banked turns. "Stealth" at Thorpe Park has a large tower that travels to the left over the top hat, and then slows on an airtime hill with magnetic brakes. "Xcelerator" at Knotts Berry Farm offers two overbanked turns after the tower. Along with the height and speed, these coasters, named "Rocket Coasters" in the industry, are considered more comfortable because of a smoother launch than LIM-style launches.
A recent newcomer to the hydraulic launch industry is Vekoma, who opened a coaster in 2004 called "Booster Bike" at Toverland in the Netherlands, said to give riders a sensation of racing on high performance motorcycles over a low twisted layout, at speeds up to 47 mph (75 km/h). The cars imitate real motorcycles, and the riders sit in the same posture as real bikers.
Pneumatic (Compressed Air).
Using the same type of system as a Hydraulic launch, a pneumatic launch uses compressed air to launch the vehicle. The technology was developed by S&S as the "Thrust Air 2000" model. The first coaster of this type was the "Hypersonic XLC", opened at Kings Dominion in Doswell, Virginia, USA in 2001. This coaster closed in 2007. Another incarnation, the Ring Racer was open for only 4 days. Compressed air launches are able to provide more acceleration than traditional pneumatic launches, with Do-Dodonpa at Fuji-Q Highland in Japan holding the acceleration record since it opened as Dodonpa in 2001, launching passengers from 0 to 112 mph (180 km/h) in 1.56 seconds.
Other styles.
Eddy current launcher (LEM).
Magnets are placed under the cars and a series of flywheels coupled to aluminum discs is in the launch zone: there is no contact between the two. The system can be used also for speed up intermediate launchers, and for braking, with static aluminum blades, at the end of the ride. Thanks to the energy stored in the flywheels, the power demand for launching is flat. Two operating examples of this technique are the "Drifter" at Sochi Park in the Sochi Olimpic Park and at FunWorks, Abu Dhabi (manufacturer I.E.Park)
Catapult.
In the catapult launch, a dropped weight winds a cable to pull the train until it accelerates to its full speed. Dropped weights were used in early installations of Shuttle Loop.
These rides are often not very tall, and usually achieve speeds of 60 mph (96 km/h).
Flywheel.
Flywheel launches are used on some Anton Schwarzkopf designed shuttle loop coasters and Zamperla Motocoasters. A large flywheel is spun at high speeds and is attached to a cable that propels the train forward.
Electric motor and spring tension.
Arrow Dynamics' Launched Loop coasters, which were popular in the 1970s and 1980s, use a powerful electric motor and tensioned springs to propel a launch car forward. The launch car pushes the train outward to a drop, and then returns to its position. After the train reaches the opposite platform, another catch car works the same way. An example of this is Irn Bru Revolution.
Friction wheels.
Another type of launch is by friction wheels. The launch track consists of a series of horizontal tires that pinch the brake fins on the underside of the train. One example of this is the "Incredible Hulk Coaster" at Universal's Islands of Adventure.