Consumption of only 0.3% of the originally planned propellant: Deciphering the story behind the "overtime" of the Chang'e-5 orbiter
China News Service, Beijing, January 13th, title: Only 0.3% of the originally planned propellant consumed: Deciphering the story behind the "overtime" of the Chang'e-5 orbiter
Author Gao Shiqi Guo Chaokai
On December 17, 2020, the Chang'e-5 mission orbiter and the returner were separated at a distance of 5000 kilometers from the earth. The returner carried the lunar sample back to the earth, and the orbiter successfully performed the evasive maneuver.
The China National Space Administration recently announced that after completing its main mission, the Chang'e-5 orbiter will launch an expansion mission and set off for the Sun-Earth Lagrangian L1 point, which is about 1.5 million kilometers away from the earth.
Why can the Chang'e-5 orbiter still "work overtime"?
The rocket expert of the China Academy of Launch Vehicle Technology said that this is because the Long March 5 rocket lifted up by the Chang'e 5 probe has a very high accuracy in orbit, which reduces the number of earth-moon orbit corrections of the Chang'e 5 orbiter. The propellant for the orbit correction actually consumed only 0.3% of the original plan, saving a lot of fuel.
After completing the returner escort mission, the Chang'e-5 orbiter has more than 200 kg of propellant left.
With so much fuel available, the "full energy" orbiter naturally has the motivation to continue "working overtime."
Why is the rocket's orbital accuracy so high this time?
This is due to the orbital designers of the China Academy of Launch Vehicle Technology, who specially designed a nearly perfect flight path for the Long March 5 launch vehicle.
Orbital design can be said to be the gene and soul of the rocket's core parameters.
The selection of the flight path of the Long March 5 carrier rocket generally requires two rounds of selection.
The first round is the "sea election".
Chang'e-5 is going to the moon. The ideal launch orbit is that after the stars and arrows are separated, Chang'e-5 can directly "slide" to the near-moon point and then ignite and brake, so as to save propellant and reach the moon quickly.
However, the distance between the earth and the moon is constantly changing, the launch time is different, and the corresponding launch orbit is also different. Therefore, the goal of the first round of sea elections is to determine the launch interval.
Integrating the solar panel illumination angle, communication antenna pointing, lunar surface sampling illumination, and returner measurement and control after the detector is separated, there are 2 to 3 days in October to December every year, and about 50 minutes a day meets the requirements of the ideal launch window.
This audition process can be described as "one in a million".
The second round is "preferred".
Usually a rocket has one orbit, but the third phase of the lunar exploration project puts forward higher requirements on the rocket launch probability and launch window. In order to overcome the impact of typhoon transit and improve the failure adaptability, the orbit designer has carried out a refined plan Monthly multi-track design and key technology verification research.
The launch windows selected by the sea were accurately cut into small windows, and each small window was designed with a corresponding launch orbit for optimization. Finally, the multi-orbit design for the moon to the moon on November 24 and 25, 2020 was confirmed. Each of these orbits Can accurately send Chang'e-5 into the Earth-Moon transfer orbit.
On the day of launch, the Long March 5 carrier rocket can easily choose the best one. From these orbits, choose the best route that best meets the actual situation, and take Chang'e 5 to go on a long journey.
The designers also established a high-precision ground-moon transfer multi-celestial body flight dynamics model algorithm, integrated the influence law of the launch trajectory design parameters, and directly optimized the rocket flight program and changed the position of the orbit point according to the desired target trajectory parameters of Chang'e-5.
In this way, after Chang'e 5 embarked on its journey to the moon, it reduced the number of orbit corrections and saved “overtime” fuel.
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