A single-stage space system (from the English A single-stage-to-orbit or SSTO - One step to the orbit) is a single-stage spacecraft capable of achieving orbital speed, starting from the surface of the planet, without using separating parts. This term is usually, but not exclusively, used to describe reusable space systems. At the moment, this concept has not yet been translated into reality and all launches were carried out and are carried out by multi-stage single-use or partially reusable missiles.
Launching a payload into low Earth orbit today costs between $ 10,000 and $ 19,000 per kilogram. The use of single-stage reusable devices is likely to significantly reduce this cost by optimizing the cost of manufacturing components and increasing their service life. Nevertheless, the costs of basic research and design of single-stage reusable space systems significantly exceed the similar costs of creating single-use systems due to a number of objective factors of a fundamental and technological nature.
The launch of single-stage spacecraft from the Earth’s surface is theoretically possible, but has a number of serious technological difficulties for practical implementation in reality. The principal factors are: the magnitude of the speed that the spacecraft needs to gain in order to enter the orbit of an artificial satellite - approximately 7.9 km / s (28,440 km / h); the need to overcome the gravitational attraction of the Earth, which has the most noticeable effect in the early stages of flight); flight through dense layers of the atmosphere, which imposes restrictions on the speed of flight due to the influence of the atmosphere on the temperature and strength loads of the structure and engine operating modes.
The systems differ in launch and landing systems: Vertical takeoff and landing ( eng.VTVL ), Vertical takeoff and horizontal landing ( eng.Vertical takeoff, horizontal landing abbreviated VTHL ), Horizontal takeoff and horizontal landing ( eng horizontal takeoff and horizontal landing abbreviated HTHL ).
The most famous single-stage space systems:
VTVL: USA: Delta Clipper (DC-X), Roton SSTO ; Russia: Crown ; Japan: Kankoh-maru ,
HTHL: Skylon ,
VTHL: USA Lockheed Martin X-33 .
Despite the promising prospects, none of these projects have yet been brought to the stage of orbital testing, mainly due to the difficulties in finding the optimal design of the propulsion system.
As part of the research, VTVL flight tests were conducted: DC-X USA, 1991-1996, RVT Japan, 1998- ...
The scheme of a single-stage launch from the surface is much easier to implement on other planets devoid of a strong gravitational field and dense atmosphere, such as the Moon and Mars , which was demonstrated by Soviet automatic lunar stations and the American Apollo program.