About to usher in the Sun Ling challenge, and lose contact with the earth
How does Zhurong spend the long “holiday” safely
The sun is not only a huge “fireball”, but also a huge noise-making machine. When a celestial body moves to the same line as the sun and the earth, the powerful electromagnetic waves emitted by the sun will submerge the radio signals sent by the celestial body, making it impossible for the earth to accurately communicate with it, causing a temporary loss of communication.
◎Intern reporter Du Peng
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Just after celebrating the 100th day of Zhurong’s landing on Mars, will it lose contact in September? This may seem sensational, but it is true. Starting from about mid-to-late September, many Mars probes, including Zhurong, Curiosity, Perseverance, etc., will gradually lose contact with the Earth.
But the problem is not the probe, but Mars is about to play a game of “hide and seek” with the earth-it will hide behind the sun for more than a month, avoiding the earth. Of course, you don’t need to worry about this. Scientists are well prepared for this.
The “culprit” of the lost connection is Riling
In the opening chapter of the science fiction novel “Three-Body”, the protagonist Ye Wenjie uses the sun as a giant radio signal amplifier to transmit the earth’s signal to the depths of the universe, and finally attracts the “three-body man.” Although it is only a science fiction story, the sun does emit electromagnetic waves and transmit “signals” all the time.
The sun is not only a huge “fireball”, but also a huge noise-making machine. The electromagnetic waves it emits cover a wide range, from short-wave gamma rays and X-ray bands to long-wave radio bands, and the sun is compatible. Therefore, when a celestial body moves to the same line as the sun and the earth, this situation is usually called a solar transit. At this time, the strong electromagnetic waves emitted by the sun will submerge the radio signals emitted by the celestial bodies, making the earth unable to communicate with it accurately, causing a temporary loss of communication.
This is the reason why Zhurong and the orbiter lost contact this time. With the sun as the center, the earth’s orbit is inside, and the orbit of Mars is outside, forming two concentric circles. The revolution period of Mars is different from that of the earth, which is about 687 days. Therefore, the sun, earth, and Mars will travel in the same straight line every once in a while. Especially when Mars moves behind the sun and is placed on both sides of the sun with the earth, it will cause significant solar transit effects.
Sun Zezhou, chief designer of the Tianwen No. 1 probe system, explained that the huge volume of the sun itself will not only block the signal from the Mars probe, but the strong electromagnetic interference it produces will also prevent the Earth from accurately distinguishing Mars from the background noise. The signal of the detector, thus causing difficulty in signal reception. At the same time, the signal uploaded from the earth to Mars will also be covered by the sun’s electromagnetic waves and cannot be reached accurately, causing the effective communication between the two to be interrupted. “The uplink cannot be controlled, and the downlink data is difficult to receive effectively.” Sun Zezhou also added that at this time, it happened that the distance between Mars and the earth reached the farthest 395 million kilometers.
Sun Ling will not only affect the Mars rover, but also affect people’s daily life from time to time. Every year at the spring and autumn equinox, the sun hits the equator directly, and geostationary orbiting satellites also travel over the equator. At this time, the sun, the satellite, and the earth form a straight line, and the electromagnetic interference emitted by the sun will affect the earth’s reception of satellite signals. For example, around the spring equinox and autumnal equinox every year, there are often unstable TV broadcast signals and “snowflakes” on TV screens all over the world. In February of this year, the State Administration of Radio and Television issued a forecast of the time of the satellite solar transit in the spring of 2021 in major cities across the country, stating that during the period from February 25 to March 17, China Star 6A and Asia Pacific 5C will be used for the transmission of my country’s radio and television programs. When the satellite enters the solar transit period, it will affect the reception of TV signals in many cities, including Beijing, Shanghai, and Hangzhou. The duration ranges from a few minutes to ten minutes.
Give Zhurong a “long holiday”
Sun Ling caused the Mars rover to lose contact. Although it sounds terrible, Zhurong and its orbiter are already fully prepared.
Sun Zezhou introduced that during the transit period, the Zhurong rover and the orbiter will suspend all scientific activities, switch to a safe mode, and quietly wait for the transit to pass. But he emphasized that safe mode does not mean stopping work altogether. After a person falls asleep, although he stops his activities, he still needs to maintain the normal operation of various body functions. The same is true for the Mars rover and the orbiter. For example, the orbiter needs to rely on autonomous control to maintain its own flight state, and the Zhurong rover must continue to obtain energy and perform temperature control to ensure that it can quickly resume its working state after the sun’s transit is over. “In this process, the requirements for the autonomy of the detectors may be very high, because in a month or even longer, they need to operate completely autonomously.” Sun Zezhou said, “I am quite relieved, I believe that the two devices can be stable. Spend the sun.”
This self-confidence is largely derived from the excellent working condition of Zhurong and its surrounds in the past 100 days. “In the past period of time, we have had a comprehensive confirmation of the operating status of the hardware and software of the two devices, and we have a bottom line.” Sun Zezhou also mentioned that the work content of the two devices themselves will be better during the period of the day. It is simpler to carry out scientific activities in the past, which helps it to remain stable for a long time, “this is actually a static waiting state.”
Another reason that supports this confidence is the complete preparatory work. Cui Xiaofeng, chief engineer of the Beijing Aerospace Flight Control Center, mentioned that through accurate calculation of Mars revolution period, revolution orbit and other data, as early as in the development stage, the relevant team had accurately predicted the occurrence time of the solar transit and carried out corresponding measures. Prepare. For example, in addition to setting up relevant procedures in advance, after entering the safe mode, Zhurong and the surround will also conduct regular self-checks, that is, self-detection of faults, and can also perform fault handling and fault reconstruction after faults are found. Ensure that one’s own state is stable. “For some problems that may arise in the process of autonomous operation, we have all designed in advance, and have conducted many tests on the ground, so there is basically no need to worry.” In addition, Cui Xiaofeng also mentioned that the loss of connection is not completely without signal. When it is completely in a straight line, there may be no signal. But if it is not completely in a straight line, there may be a little signal intermittently. We will also use very rare signals to monitor the status of the two devices.”
No matter what the situation is, Zhurong and the orbiter are fully prepared. They will also start a new stage of Mars exploration after waiting for the end of the “long holiday” of Sun Ling.
Relay satellites may “break” the troubles of the sun
Riling can be said to be a “frequent visitor” in space activities. In addition to the previously mentioned impacts on geostationary satellites over the equator, space activities such as manned spaceflight and lunar exploration projects have also been affected by solar transits on many occasions. For example, in November 2007, Chang’e-1 encountered a brief period of solar interference during its lunar exploration. However, with the huge 18-meter antenna of the Qingdao ground measurement and control station, the ground control center successfully monitored the Chang’e-1 during the day, and there was no frame loss or garbled.
But compared with the neighboring moon, when Mars, which is 395 million kilometers away, encounters the sun’s transit, the existing communication methods can do little. Cui Xiaofeng also pointed out: “This Sun Ling is the longer time we have encountered in my country’s previous space activities. The longer the time, the greater the potential impact.”
In the future, the distance of deep space exploration will be farther and farther. Is Riling really unsolvable? Relay satellite may be an option for reference. The fundamental reason for the impact of Ri Ling on spacecraft communication is that when the sun, spacecraft, and the earth are almost in the same straight line, the communication signals between the spacecraft and the earth cannot escape the electromagnetic interference of the sun and reach each other, but Relay satellites may be able to solve this problem. Deploying it at a location far away from the electromagnetic radiation of the sun, acting as a “messenger” between the spacecraft and the earth, can make the signal bypass the sun and reach the other party.
A similar idea was actually realized when Chang’e-4 landed on the back of the moon. At that time, in order to solve the problem that Chang’e-4 could not communicate with the earth on the back of the moon, my country launched the Queqiao relay star to the point L2 of Lagrange in advance—a position that can be seen on the back of the moon and the earth, acting as a space between the moon and the moon. The “microphone” allows Chang’e-4 to communicate with the earth indirectly. The orbiter in the Tianwen-1 Mars exploration mission also took on the task of data relay, but because the orbiter is still flying around the fire, it is also unavoidable from the impact of the sun.
As deep space exploration moves further and deeper in the future, relay satellites may become an important tool to effectively avoid the effects of solar transits. But Cui Xiaofeng also believes that at the current stage, the impact of Riling is completely controllable. “As long as we make accurate predictions, careful preparations, and precise implementation, we don’t have to worry too much about the impact of Riling.”
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