Launch window(Launch window)Carrier rocketA relatively suitable time range for launch (i.e. the time range allowed for launch of launch vehicle).The size of this range is also called the width of the emission window.The width of the window varies from wide to narrow. The width is measured in hours, or even in days. The width of the window is only tens of seconds, or even zero.
The launch window is based onspacecraftThe requirements and external restrictions are determined after comprehensive analysis and calculation.Because the relative positions of the sun, the earth and other stars are constantly changing, even when launching spacecraft of the same type and in the same orbit, the launch window is not fixed.Knowing this truth, people will not be surprised that the launch of spacecraft is sometimes in the morning, sometimes in the evening, sometimes in the day, sometimes at night.
For the launch vehicle itself, there is no too strict launch window limit, and it can be launched at any time.However, when launching a carrier rocket, it is usually launched in the evening or before dawn, because the sun is near the horizon at this time, the sky in the launch site area and the area where the rocket flies is relatively dim, and the rocket can be exposed to the sun after it is ignited and lifted to a certain height. The arrow reflecting the sun forms a large contrast with the background sky,Thus, the optical tracking and measuring instrument on the ground can clearly track and measure the rocket's flight path, observe the attitude and external image of the rocket in flight, and the tracking, measurement and observation effect is better.
But when the carrier rocket is used to launch a spacecraft, it cannot be launched at any time.Because each spacecraft undertakes different tasks, and the instruments and equipment installed on the spacecraft have different use requirements, they put forward various requirements and restrictions on the launch window, and these requirements sometimes contradict each other. Therefore, when to choose a launch time, you must consider various requirements, and select a more appropriate launch window after comprehensive balance.
The requirements for satellite orbit accuracy are equal to the requirements for the relative position of the target celestial body and the earth, and also require careful selection of the launch window.For example, when launching a probe to the moon, planets and other stars, it must be launched when the Earth is in a favorable relative position with the target celestial body being detected.However, when launching space detectors, the width of the launch window is generally wide, and some can be calculated in days.
Once the launch window is missed due to the temporary failure of the launch vehicle, or due to weather and other reasons, you can only wait for the next launch window.yes , we haveSpacecraft launchThere is more than one window in a day, and some only have to wait a few days or more before launching.
Window type
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As far as space missions are concerned, there are three kinds of launch windows, namely, annual counting window, monthly counting window and daily counting window.In addition, in order to achieve precise docking during launchZero windowThe formulation of.
Yearbook window
It is expressed in the form of consecutive months in a specified year, and is applicable to interstellar exploration missions, such as launch pairsHalley's CometProbingComet detector。
Month Count Window
It is expressed in the form of consecutive days in a certain month and is applicable to planetary and lunar exploration missions, such as launching lunar probes.
Day Count Window
It is expressed in the form from one time to another within a day, and is applicable to various spacecraft.
For spacecraft launch, three or two launch windows may be calculated at the same time, but the final decision is in the form of a daily window.For the launch of general satellites and missiles, only the daily launch window needs to be specified.For emissionLunar probeUsually, the monthly and daily launch windows should be specified.For emissionHalley's CometIn general, annual, monthly and daily launch windows should be specified for detectors and other interstellar detectors at the same time.[1]
Zero window
It refers to firing the rocket into the air at the pre calculated launch time without any delay or change.
If inTiangong No.1During launch, in order to complete dockingShenzhou VIII spacecraftWhen the rocket is launched into the coplanar orbit with Tiangong-1, it puts forward high requirements for the precision of the rocket's orbit entry.The rocket is required to ignite and take off on time one second after Tiangong-1 passes the launch point, otherwise it will miss the opportunity to dock with me, which is the cause of the "zero window" requirement.
influence factor
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Ground observation
April 24, 1970, in GansuJiuquan Satellite Launch CenteruseLong March 1 carrier rocketLaunch China's firstArtificial earth satelliteDongfanghong No.1The launch time was set at 9:35 p.m. Beijing time. At the Jiuquan Satellite Launch Center, the sun had set for more than an hour and the sky was dark. However, when the carrier rocket rose to an altitude of more than 400 kilometers and put the satellite into orbit, the third stage rocket and satellite that entered orbit could still be exposed to sunlight.At this time, people on the ground can see the third stage rocket and satellite in orbit with the naked eye.
Light conditions
When launchingPhotographic reconnaissance satellite、Earth resource satelliteWhen the satellite is in the middle orbit, the ground target under the satellite's orbit is required to have good lighting conditions, so that the visible light remote sensor on the satellite can well remote sensing the ground image.Therefore, the launch window for launching such spacecraft is selected in the daytime.
On satellites, manned spacecraft and other spacecraft, most of them use solar cells to supply power. When the spacecraft enters orbit, it is hoped that the sun will shine on the side of the earth. At this time, the solar cell wing will be exposed to the sun, and can immediately generate power for the spacecraft.This is a factor to be considered when launching this kind of spacecraft and selecting the launch window.
Recoverable satelliteWhen a manned spacecraft returns to the ground from orbit, it is generally hoped to find the spacecraft after landing in the daytime;At the same time, we hope that the weather conditions are good and there is no strong wind and other bad weather, so that the parachute can be opened easily.When selecting the launch window, consider the situation when returning.
weather conditions
The electronic equipment of rockets and satellites may be damaged when lightning strikes and dark clouds occur within 20km of the flight path;The strong wind above the atmosphere may affect the satellite's attitude and structure.
measuring equipment
After the spacecraft enters orbit, attitude measurement equipment (such asInfrared horizon, sun sensor, etc.) to measure the flight attitude of the spacecraft, so as to adjust the attitude and enter a stable flight attitude.When the attitude measurement equipment on the spacecraft works, the spacecraft, the earth and the sun need to be in a better relative position, and then the flight attitude measurement accuracy of the spacecraft is high.Therefore, this is also a factor to consider when selecting the launch window.
constraint condition
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Generally speaking, the launch window mainly has the following constraints[2]：
a.The sun shines below the satellite（Substellar point）Illumination conditions of ground targets (such as weather, resources and other satellites);
b.Relative relationship between satellite solar panel and solar light (requirements for solar cell power supply);
c.Geometric relationship among the earth, satellite and sun required by satellite attitude measurement accuracy;
d.The satellite temperature control requires that the sun can only illuminate some directions of the satellite;
e.Requirements for the length of time the satellite is in the shadow of the earth (requirements for solar cell power supply);
f.Requirements for landing recovery time (such as recoverable satellites, manned spacecraft, etc.);
h.Requirements for the relative position of the Earth and the target celestial body (such as lunar probe, planetary probe, etc.);
i.Others include ground tracking measurement conditions, meteorological conditions, etc.[2]
Determining the launch window is actually to determine the relative position between the flight path and specific objects (such as the sun, moon, rendezvous objects, etc.) according to the constraints, and also select the appropriate launch environment conditions.[2]
Determine the law
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According to the constraints, the launch windows of various satellites generally have the following rules[2]：
(3) Satellite constellationsOrbital rendezvous, orbital interception and other launch missions.Since satellites (spacecraft) are required to be sent to the predetermined orbital plane in the inertial space, there are more stringent requirements on the launch time, which is determined by the orbital planeInertial spaceDirection in (OrbitAscending intersectionRight Path), which is possible within 24 hours a day.
(4)Lunar probeAnd planetsdetectorThe launch window of is mainly determined by the position of the target object (moon or planet), and the launch must be carried out within the time range when the Earth and the target object are in a certain relative position.[2]
