There are some way to make the reusable launch system significant. In rocket launch many stage are used. A reusable launch may use multi stage. According to the stage configuration mainly two stage are used.
There are two ideas to Single Stage to Orbit(SSTO). According to the rocket equation a SSTO need high mass ratio.
Mass ratio is defined as the ratio of mass of fully fueled vehicle to mass of empty vehicle.
One way to increase the mass ratio is reduce the mass of empty vehicle by using lightweight structure and high efficiency engines. This may tend to more maintenance as reliability of components can be impaired. So reuse will more expensive to achieve.
Reducing the oxidant weight is another idea. This can be done by burning the fuel in air during the atmospheric flight stage. A dual-cycle power-plant such as liquid air cycle engine can be used for this.
Margins are very small so there are many uncertainty that a vehicle could carry the payload to the orbit.
Two stages to orbit uses two vehicles, combined together at launch. Normally the second stage orbiter is 5-10 times smaller than first stage launcher.
Cost of developing two independent vehicle much but there is one thing is also seriously caring, the complexity of interaction of two independent vehicle as an unit and separation of them.
First stage needs to be returned to launch site for reuse. A reasonable trajectory is given that keeps first stage above the launch site at all time, or by using small air-breathing engine to fly the vehicle back.
The second stage usually returned after flying one or more orbits and re-entering.
Biamese &Triamese
Two or three similar stage are combined side by
side and burned in parallel. Fuel tank of orbital stage are kept full by using crossfeed. Tank are used to run the engine during booster and orbital stage. When boosters run out, they are ejected and glide back to landing.
All the orbital vehicle have vertical launching till the date as rockets have high thrust to wieght ratio.
Every component of reusable launch system should land back safely.
Horizontal landing system requires wings and undercarriage for landing.
Some of the system uses parachute for landing of the reusable component.
Small rockets are also used to decelerate and soft landing on the ground of the vehicle.
Reusable launch system are the future of launching. Hope that one day there will be much effecient and reliable reusable launch system.
@irrahul