Xinhua News Agency, Washington, November 24. An asteroid is about to crash into the earth?
Once such news appears, it will more or less make people living on earth feel a little panic.
In fact, although a large number of asteroids collide with the earth every year, most of them are decomposed in the earth’s atmosphere.
However, the risk of an asteroid hitting the Earth does exist in theory.
According to the American Planetary Society, there are many ideas about the technology to prevent asteroids from hitting the earth. The extreme method is a nuclear explosion, and the more moderate method is to let a heavy spacecraft pass the asteroid, thereby causing the asteroid to deviate from its original orbit.
In between is the kinetic impactor technology, which focuses on one or more spacecraft hitting an asteroid at high speed to change its orbit.
NASA launched a spacecraft named "Dual Asteroid Redirection Test (DART)" on the 24th Eastern Time to guide it to hit a small celestial body in order to evaluate the technology for preventing asteroids from hitting the earth.
This is the first mission of NASA to verify the technology of the kinetic energy impactor, that is, to change its orbit by impacting an asteroid to protect the earth from being hit by an asteroid.
This mission is handed over by NASA to the Johns Hopkins University Applied Physics Laboratory. It will be the first to test whether this strategy of driving away asteroids is realistic: it will test whether the spacecraft can autonomously sail to the vicinity of the target asteroid. And deliberately crashed into it while observing how far the asteroid deviated from its original orbit.
To put it simply, this is a "go and no return" mission to prove the feasibility of using an impact strategy to prevent asteroids from hitting the Earth.
The DART mission spacecraft is relatively small, the main body is about 1 meter square, and there is a solar panel about 8.5 meters long when fully deployed on each side, and it weighs about 610 kilograms when launched.
The DART mission spacecraft is equipped with about 50 kilograms of hydrazine propellant used for spacecraft braking and attitude control, and about 60 kilograms of xenon used to operate the ion propulsion technology demonstrator.
According to NASA, the target asteroid system consists of an asteroid with a diameter of about 780 meters and an asteroid with a diameter of about 160 meters. The latter orbits the former and is also a small satellite of the former.
While revolving around the sun as a whole, these two asteroids occasionally move closer to the Earth.
Among them, the small satellite is the object to be hit in this test.
According to the plan, the DART mission spacecraft will fly for nearly a year after separation from the rocket. It is scheduled for the fall of 2022, that is, when the asteroid system is closest to the earth (about 11 million kilometers), with the help of high-resolution cameras and automatic navigation systems, It hits the small satellite at a speed of about 6.6 kilometers per second.
NASA stated that this small satellite currently has no threat of hitting the earth, and the DART mission spacecraft will not pose a new threat to the earth after it hits it, so it is an ideal asteroid defense test target.
NASA stated that the collision "will change the speed of the small satellite orbiting the asteroid by 1%," which in turn shortens the orbital period of the small satellite by a few minutes and slightly narrows the distance between the two small celestial bodies.
Ground-based telescopes will conduct observations before and after the impact to make detailed measurements of orbital changes.
About two years after the impact, the European Space Agency will launch the "Hera" mission spacecraft to study the impact of the impact on the asteroid system and collect various detailed data, such as the precise mass, composition and internal structure of the asteroid system , And the size and shape of the impact crater left by the DART mission spacecraft.
These detailed data are very important for how to transform the asteroid drive test into a scalable and repeatable technology.
As one of NASA’s planetary defense strategic missions, the DART mission will have the opportunity to collect real asteroid impact data for the first time. In the future, these data can be input into a computer model to calculate the resistance to a small planet that has a risk of impact on the earth. What size spacecraft does the planet need and what speed it uses, etc.
However, in a real planetary defense scenario, there are more factors that need to be considered. For example, some countries may be hit by asteroids, and other countries have the ability to take action to prevent the impact. This requires strengthening international cooperation; in addition, the impact on asteroids Incorrect mass estimates or deflection of the asteroid's orbit may affect the final defense effect.
Therefore, if the danger really comes, to prevent asteroids from hitting the earth, different plans still need to be made according to different types of targets.