Space Science: How to Determine the Launch Window of Spacecraft?

202 1 17 At 9: 22 on June, Shenzhou 12 manned spacecraft was successfully launched at Jiuquan Satellite Launch Center. This time point is accurate enough to be described as a "good day" carefully selected by aerospace experts! Do you know why you are so painstaking about the launch time of the rocket? What factors are related to the launch time? To solve these doubts, we need to understand the "launch window" first.

The launch of spacecraft needs to choose the corresponding launch opportunity. The time range during which the spacecraft is allowed to launch is called the launch window. The determination of spacecraft launch window needs to consider spacecraft orbit, spacecraft working conditions, celestial body operating conditions, space debris avoidance, ground tracking, TT&C communication and meteorological requirements.

There are usually three types of spacecraft launch windows.

1) time series window. It is expressed in the form of consecutive months in a specified year and is suitable for interstellar exploration missions. For example, the launch window of Tian Wen 1 rover Zhu Rong is the annual launch window. The closest distance between the Earth and Mars is once every 26 months. At this time, the probe that launches Mars can save fuel faster, and at the same time help it reach the scheduled orbit with the help of Mars gravity.

2) Monthly measurement window. It is expressed in the form of consecutive days in a month, which is suitable for planetary and lunar exploration missions. For example, the lunar probes Chang 'e-1 to Chang 'e-5 in China's previous Chang 'e exploration project were basically launched at the beginning or end of a month.

3) Daymeter window. It is expressed in the form of a certain time of a day to another time, and is suitable for launching spacecraft such as satellites, spaceships and space stations. If it is a satellite launch, as long as the inclination of the orbit and the meteorological conditions of space launch meet the launch needs, the launch window time is generally relatively long, basically about a few hours. But for manned spacecraft, it is very different. The manned spacecraft needs to meet the normal working conditions of the spacecraft and the safety and life-saving requirements of astronauts at the same time, and its launch window time is more accurate.

After the launch, the Shenzhou-12 manned spacecraft has another important task, which is to "hold hands" with the Tianhe core cabin in space. Shenzhou 12 manned spacecraft should track the target aircraft-Tianhe core cabin, so that the two aircraft can reach the same point in space at the same time and at the same speed, and complete the space docking of the two aircraft. For Tianhe core cabin, the launch time of Shenzhou 12 on the ground will directly affect the speed and success of rendezvous and docking. This launch window, which requires extremely strict rendezvous and docking time, is called "zero launch window", that is, the deviation between the rocket ignition and takeoff time and the scheduled launch time cannot exceed 1 second.

Is it complicated just to listen to the sound? The actual operation is even more difficult, because the Tianhe core cabin to be docked is still in a state of high-speed operation around the earth, and the ground-launched Shenzhou 12 needs to find the most accurate docking time to ignite and launch, and everything must be accurate. After the spacecraft is launched into the scheduled orbit, the ground monitoring and control station will measure the orbital inclination difference, flight speed and altitude difference between Shenzhou-12 and Tianhe core cabin, and then send monitoring and control instructions to let Shenzhou-12 perform orbit change, acceleration and other maneuvers. In this process, it is necessary to keep the speed and altitude zero error, and Shenzhou 12 will start the docking system to realize the rapid docking of the space rendezvous.

1) The influence of meteorological conditions for rocket and spacecraft launch should be considered, that is, the time to meet the requirements for rocket and spacecraft launch should be selected according to the weather forecast.

2) According to the actual preparations of rockets, spacecraft, launch sites and measurement and control systems, the launch time is set at the time when each system meets the launch conditions.

3) The working conditions of the ground tracking measurement system should be considered, such as the weather and waves in the sea area where the ocean-going survey ship operates, the visibility of the optical measurement equipment at the launch site, the sun angle, etc.

4) The requirements of launch site and landing site for astronaut search and rescue should be considered. For example, the selected launch time should be conducive to life-saving preparation, landing site prediction and search, and there should be no bad weather such as strong wind, dust and lightning at the landing site.

It only takes a few seconds to launch successfully.

What is behind it?

How many astronauts are there all day?

Accurate calculation gives an accurate score.

Comprehensive control, to ensure foolproof.

Sink and wait for the best time.

Facing the harsh conditions of zero emission window

China astronauts pursue the ultimate attitude.

Over and over again.

The perfect answer to a successful launch

Pay tribute to China astronauts!

Bless China Aerospace!