Multistage modularised boost rocket

The invention relates to rocket and space engineering, in particular to boost rockets of different classes using modular rocket units. The inventive boost rocket comprises at least two stages connected to each other by a packet mode. The first stage has up to six identical modular rocket units. The second stage is embodied in the form of a monoblock and has a diameter to diameter ratio between the lower and upper parts thereof ranging from 1.25 to 1.35. Liquid fuel cruising rocket engines, preferably identical, are used for all stages. The volume ratio of the fuel tank of each rocket unit to the fuel tank of the second stage ranges from 0.40 to 0.52. The combined power of the engines of each said unit ranges from 0.8 to 1.1 with respect to the combined power of the engines of the second stage. In order to carry out a pitch guidance, yaw steering and lateral control, the cruising engines of the modular unit are of a pivoting type, and the second stage is provided with fixed engines and control engines. The inventive boost rocket makes it possible to put into orbit a wide mass range of payloads with high energy efficiency ( mu pg. > 3%) by changing the number of the modular rocket engines from 0 to 6.