The star pair serves as a reference target for the galaxy, allowing the spacecraft to find the “way home”

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The star pair serves as a reference target for the galaxy, allowing the spacecraft to find the “way home”

At the same time, we can also monitor the flight status in space By combining all the information (the position in the universe and the distance to the earth), we can determine the position of the spacecraft in the solar system and provide this information to the spacecraft.

We can also use Doppler frequency shift to evaluate the speed of a spacecraft away from the earth. By using dish antenna arrays scattered on the earth, we can measure the spacecraft signal reaching between two dish antennas. When we combine these data and position information, a complete six-dimensional information of the spacecraft-three-dimensional position and three-dimensional velocity will be generated.

The star pair serves as a reference target for the galaxy, allowing the spacecraft to find the “way home”(1)

painted by the artist The Voyager probe enters interstellar space

This method relies on a network of ground-based radar systems, which all maintain communication with spacecraft. This technology is suitable for spacecraft in the solar system, as well as NASA” Voyager, but any interstellar mission requires a new method-they must achieve autonomous navigation. In principle, these spacecraft can use airborne navigation systems, such as clock systems and gyroscopes, but interstellar The mission will last at least several decades, and the small errors and uncertainties of the airborne system will undoubtedly cause the spacecraft to deviate from orbit.

Another option is to use pulsars. Pulsars are rotating celestial bodies that flicker or pulsate periodically. Since each pulsar has a unique rotation period, these celestial bodies can be used as deep space missions. The reliable indicator of the This method is only suitable for a relatively small bubble region near the solar system, because the measurement of the rotation period may be contaminated by interstellar dust. Once the position of the pulsar cannot be distinguished, it will be lost in space.

The star pair serves as a reference target for the galaxy, allowing the spacecraft to find the “way home”(2)

Hence the interstellar spacecraft A simple and reliable method is needed to estimate their position in the galaxy. A recent paper proposes a solution-the stars themselves.

This technology is based on an earlier concept-parallax. If you put your fingers in front of your nose and close your eyes alternately, you will see your fingers wobble, and when you switch from one eye When it comes to the other eye, its obvious position change comes from the new perspective. If the distant celestial body is observed in the same way, the swing amplitude of the celestial body will be very small.

It is through the parallax method that scientists can measure the distance to a star for the first time. Through the parallax method, they can determine the position of the spacecraft away from the earth’s home. Before the launch of the spacecraft, we loaded the spacecraft with an accurate map of stars, which can provide the positions of all known stars in the vicinity of the Milky Way. Then, when the spacecraft accelerates away from the solar system, it measures the relative distances between multiple pairs of stars. With the flight of the spacecraft, the stars closer to the spacecraft seem to be moving significantly, while the stars farther away are relatively stationary.

By measuring multiple pairs of stars, and comparing the measurement results with the original earth catalog information, the spacecraft can calculate the specific positions of the stars and the distance between the spacecraft and these stars, thus providing a good The device provides a precise 3D position in the galaxy.

The star pair serves as a reference target for the galaxy, allowing the spacecraft to find the “way home”(3)

Measure the spacecraft The flight speed of is indeed a bit tricky. It relies on a peculiar special theory of relativity. Due to the finiteness of the speed of light, if the spacecraft flies fast enough, celestial bodies may appear in different positions instead of real positions. Specifically, the position of a celestial body will be changed in the direction of your movement. This effect is called “distortion” and can be observed from the earth. As the earth revolves around the sun, the sun seems to be slightly in the sky. swing.

As long as the spacecraft’s flight speed is fast enough (if we want interstellar missions to last for decades, instead of thousands of years, the spacecraft must reach a certain speed), the airborne system can measure this Distortion effect, by recording which stars have deviated from the expected position and the degree of deviation, the spacecraft can calculate its own 3D velocity.

Through the parallax measurement, the spacecraft can recover its complete six-dimensional coordinates in the Milky Way, knowing where it is and where it will reach.

How accurate is this technology? According to the latest research report, if the spacecraft can measure the positions of 20 stars, and the error does not exceed 1 arc second (1 arc second is 1/60 of 1 arc minute, and 1 arc minute is 1/60 of 1 degree), then The spacecraft can determine its position in the galaxy, with a distance accuracy of ±3 astronomical units, and a velocity accuracy of ±2 km/s. An astronomical unit is the average distance between the earth and the sun, which is about 150 million kilometers. Therefore, an error of 3 astronomical units is equivalent to an error of 450 million kilometers. Although this is a very long distance for humans, it is separated by a number of stars. Compared to thousands of astronomical units, this error is insignificant.

At present, astronomers have measured the precise positions of more than 20 stars, so we can load hundreds of millions of stars into the spacecraft to facilitate space navigation. Every celestial body that a spacecraft can measure will help to more accurately determine its specific location, but what we need most is an interstellar spacecraft that can continue to perform space missions. (Ye Qingcheng)