China's fastest rocket carries deep space dream

 A Long March-5 rocket blasted off Thursday at the Wenchang Spacecraft Launch Site in south China's Hainan Province, carrying the country's Mars probe, Tianwen-1.

   It is the first time that the Long March-5 carrier rocket, currently China's largest launch vehicle, is put into practical use after a series of trial launches.

   It is also the first time the Long March-5 exceeded the second cosmic velocity, the fastest China's carrier rockets have gone to date, said Li Dong, the rocket's chief designer at the China Academy of Launch Vehicle Technology (CALVT).

   The rocket did not separate from Tianwen-1 until it accelerated to over 11.2 km per second, the second cosmic velocity or escape velocity. At that speed, Tianwen-1 went into the Earth-Mars transfer orbit, overcoming the gravitational pull of Earth and embarking on an interplanetary journey, Li explained.

   The rocket, codenamed Long March-5 Y4, has a total length of almost 57 meters, equivalent to the height of a 20-story building. It has a 5-meter-diameter core stage and four 3.35-meter-diameter boosters.

   The rocket uses environment-friendly propellants, including liquid oxygen, liquid hydrogen and kerosene. It has a takeoff mass of 869 tonnes and can carry a payload of 14 tonnes to a geostationary transfer orbit.

   As the relative positions of Earth and Mars are constantly changing, a space mission from Earth is like shooting at a moving target. The researchers have designed a record number of trajectories targeting multiple narrow time windows to ensure the probe's precise entry into the preset orbit, said Wang Jue, general director of the rocket research team at CALVT.

   The Mars mission has a 30-minute launch window each day for 14 consecutive days from late July to early August. The rocket team subdivided it into three 10-minute launch windows with different trajectory parameters, said Wang Jue.

   A total of 42 launch trajectories have been designed, more than any other Chinese space mission and the rocket can switch among them automatically, Wang Jue said.

   Tianwen-1, comprising an orbiter, a lander and a rover, weighs nearly five tonnes, a tonne heavier than the Chang'e-4 lunar probe. It is the heaviest deep space probe that China has launched so far.

   "Relying on the strong carrying capacity of the Long March-5, China will push its deep-space exploration from the moon to the planets," said Li Minghua, top director of the Long March-5 team at CALVT.

   Previously, the Long March-5 successfully launched the Shijian-20 satellite. The Long March-5B carrier rocket, a modified version, sent China's new-generation manned spaceship for test into space.

   Based on the experience of these launches, engineers have improved the technology and reliability of Long March-5 Y4, covering multiple systems like its control system, measuring system, body structure, and ground support system.