The rocket is launched vertically, taking into account the following main factors.
① The launch vehicle is huge, with a length of more than ten meters to tens of meters and a diameter of several meters to more than ten meters. If it is launched at an angle, it must have a sliding track that is longer than the rocket body. This kind of slide rail is not only quite bulky, has poor stability, and is difficult to walk, but the vibration generated during launch will inevitably affect the rocket's hit accuracy. What's more, to place the slide rail, you must have a very open and flat launch site. At the same time, since the rocket is in an inclined state, a high-temperature, high-speed, and high-pressure gas flow will be ejected from the tail when the ignition is started, so a fairly long safety zone is also required.
② Rockets spend most of their flight in space outside the atmosphere. Vertical launch is conducive to quickly passing through the atmosphere and reducing the loss of flight speed due to air resistance. Of course, the vertical flight time should not be too long, otherwise the rocket's flight speed will suffer a great loss under the influence of gravity. Therefore, the vertical flight segment of the Zhaoqian launch vehicle is generally within the range of 4 to 10 seconds.
③ The use of vertical launch can simplify the launch equipment. All its launch pads can be designed to be very compact, and it is easy to move the rocket erected on the launch pad within 360°, thus Meet the need to change the shooting direction and ensure the stability and concealment of the rocket system.
④The propellant used in large launch vehicles is generally liquid. Therefore, launching in a vertical state facilitates precise filling or discharge of propellant.
⑤Most launch vehicles now use inertial control systems. It requires the rocket to accurately determine its initial baseline and zero adjustment before launch, so as to ensure that the payload can accurately enter the earth's orbit. Vertical launch is much more convenient to achieve this requirement than tilt launch.
⑥The thrust-to-weight ratio of the launch vehicle (the ratio of the rated ground thrust of the rocket engine to the take-off weight of the rocket) is generally relatively small. For example, the thrust of the V-2 rocket is 26 tons (according to regulations, the push unit is "Niu", for the convenience of comparison, the thrust unit here is still ton force), the take-off weight is 13 tons, and the thrust ratio is 2. The thrust-to-weight ratio of current launch vehicles is about 1.2 to 1.6 (the thrust-to-weight ratio of solid rockets can reach more than 2.0). The rocket is placed vertically on the launch pad. When launching, as long as the thrust slightly exceeds the take-off weight, the rocket can take off. As the propellant continues to be consumed, the weight of the rocket gradually decreases and the flight speed becomes higher and higher. It can be seen that vertical launch is very beneficial to the acceleration and energy utilization of the rocket.