PURPOSE: To reduce weight of each stage by lessening the ratio of the weight of an optional lower stage rocket to the weight of a direct upper stage rocket to 2.5 or less, and reducing the weight of the direct upper stage rocket and a payload at the point of time of starting point contact of the direct upper stage rocket, from the weight of a space launcher at the time of starting point contact of a stage, in each stage rocket.

CONSTITUTION: In launching a multistage rocket having a payload 14 at an end into a space, the ratio of the weight of an optional lower stage rocket 11 to the weight of the direct upper stage rocket 12 is made 2.5 or less. Moreover in the weight of each rocket in each stage 11, 12, and 13, the weight of the direct upper stage rocket and the payload 14 at the point of time of starting the firing of the direct upper stage rocket is recuced from the weight of a space launcher at the point of time of starting the firing of this stage.