Recently, the U.S. Psyche probe completed a deep-space laser communication test with ground facilities 16 million kilometers away, setting a new distance record for optical communication in space. So what are the advantages of laser communication?What difficulties does it need to overcome according to the technical principles and mission requirements?In the future, what is the application prospect of it in the field of deep space exploration?
Technological breakthroughs are not afraid of challenges
In the process of space researchers' exploration of the universe, deep space exploration is an extremely challenging task. Spacecraft need to travel through far, far interstellar space, overcome extreme environments and harsh conditions, and acquire and transmit valuable data, and communication technology plays a vital role. 
Schematic diagram of the Eucharis probe conducting a deep-space laser communication test with a terrestrial observatory.
On October 13, the Psychistan probe lifted off for at least eight years of exploration. At the beginning of the mission, it cooperated with the Haier Telescope at the Palomar Observatory in the United States to test deep space laser communication technology, using near-infrared laser coding to send and receive data with the Earth team. To do this, the detector and its laser communication equipment need to overcome at least 4 types of difficulties.
One is the long distance. In deep space exploration missions, the distance between the target object and the Earth is often measured in "100 million kilometers", which requires extremely high signal strength and stability to ensure accurate data transmission.
The second is signal attenuation and interference. As the transmission distance increases, the radio signal will be significantly attenuated, which will inevitably bring great challenges to communication. Especially in the deep space environment, cosmic rays, dust and other materials will interfere with the communication signal, and the magnetic field and ionosphere of the target celestial body will also destroy the transmission stability of the signal.
The third is bandwidth throttling and latency. Compared to the needs of deep space exploration missions, the communication bandwidth is limited. If the detector wants to efficiently transmit data within the limited bandwidth, it is necessary to use advanced encoding technology and compression algorithms to increase the data transmission rate. In addition, due to distance limitations, deep space exploration missions need to overcome time delays that cannot be ignored, and it is common for a single communication to be delayed by minutes or hours, while approximate real-time communication is very difficult.
Fourth, energy constraints and heat dissipation issues deserve attention. The probe performs deep space exploration missions for a long time under the condition of limited energy supply, and in order to ensure efficient and stable communication, low-power equipment and technology are required. At the same time, the operation of communication equipment will continue to generate a large amount of heat, and how to effectively dissipate heat has also become a challenge.
Researchers have long anticipated and prepared for these difficulties, "prescribed the right medicine", and made breakthroughs in a series of key technologies, laying a good foundation for the Lingshen probe to carry out deep space laser communication experiments.
First of all, the Lingshen probe adopts high-speed data transmission technology, selects laser beam as the transmission medium, and is equipped with a high-power laser emitter, and tries to establish a laser communication link in the deep space environment by taking advantage of the advantages of fast laser transmission rate and high stability.
Secondly, in order to improve the reliability and stability of communication, the Lingshen probe adopts high-efficiency coding technology, which can achieve a higher data transmission rate within a limited bandwidth by optimizing the encoding of data. At the same time, by adopting technologies such as forward error correction coding, it can reduce the bit error rate and improve the accuracy of data transmission.
Thirdly, with the help of intelligent scheduling and control technology, the Lingshen probe has realized the optimal utilization of communication resources. The technology can automatically adjust the communication protocol and transmission rate according to the mission requirements and changes in the communication environment, so as to ensure the best communication effect under limited energy conditions.
Finally, in order to enhance the signal reception capability, the Lingxing probe uses multi-beam reception technology. This technology uses multiple receiving antennas to form an array, which can enhance the reception sensitivity and stability of the signal, and then maintain a stable communication connection in the complex deep space environment.
The advantages are obvious, and there is a mystery inside
It is not difficult for the outside world to find that the laser is the core element of the deep space communication experiment of the Lingshen probe, so what are the specific advantages of the laser that can help the deep space communication to make significant progress?What's the mystery in it?On the one hand, the growing demand for massive data, high-resolution images and high quality in deep space exploration missions will inevitably require higher data transmission rates for deep space communications. In the face of communication transmission distances that often "start" at tens of millions of kilometers, radio waves are gradually "overwhelmed".
Laser communication encodes information on photons, and compared with radio waves, near-infrared light waves have narrower wavelengths and higher frequencies, making it possible to build a more efficient and smooth spatial data "highway" for information transmission.
Schematic diagram of early low-Earth orbit laser communication tests.
This has been preliminarily verified in early low-Earth orbit space tests. After taking relevant adaptive and overcoming atmospheric interference measures, the data transmission rate of the laser communication system was once nearly 100 times higher than that of previous communication methods.
On the other hand, laser communication technology is more adaptable to the deep space environment. In the deep space environment, the probe has to deal with the ubiquitous cosmic rays, and also has to overcome obstacles such as celestial debris and dust during the arduous journey through the asteroid belt and the large star ring, and the radio signal is more susceptible to interference.
The essence of laser is a beam of photons emitted by atoms that are stimulated, and the photons in it have highly consistent optical properties, good directionality, and obvious energy advantages. With its inherent advantages, lasers can better adapt to complex deep space environments and build more stable and reliable communication links.
However, for laser communication to achieve the desired results, it must be precisely aligned. Taking the Lingshen probe as an example, the guidance, navigation and control system of its flight computer plays a key role, and the so-called "pointing, acquisition and tracking system" ensures that the laser communication terminal and the connection device of the Earth team are always accurately aligned, ensuring stable communication, and can also effectively reduce the communication error rate and improve the accuracy of data transmission.
In addition, this precise alignment helps the solar wings absorb as much sunlight as possible, providing ample energy for the laser communication equipment.
Of course, no matter how abundant energy is, it must be used efficiently. One of the advantages of laser communication is the high energy utilization efficiency, which can save more energy than traditional radio communication, reduce the burden of deep space probes under limited energy supply conditions, and then extend the flight range and working time of probes, and harvest more scientific results.
In addition, laser communication theoretically has better real-time performance than conventional radio communication. This is very important for deep space exploration, helping scientists to obtain data in a timely manner and conduct analytical research. However, with the increase of communication distance, the delay phenomenon will gradually become obvious, and the real-time advantage of laser communication needs to be tested.
Looking to the future, there are more possibilities
At present, there are many challenges in deep space exploration and communication, but with the continuous development of science and technology, it is expected that a variety of measures will be used to solve the problem in the future. For example, in order to overcome the difficulties caused by long communication distances, it is possible that future deep space probes will use a combination of high-frequency communication and laser communication technology. High-frequency communication equipment can provide higher signal strength and improve communication stability, while laser communication has a higher transmission rate and lower error rate.
Close-up of a deep-space laser communication device on the Psitron probe.
Specific to the details of laser communication technology, in order to improve bandwidth utilization and reduce latency, deep space probes are expected to adopt more advanced intelligent coding and compression technology. To put it simply, according to the changes in the communication environment, the laser communication equipment of the deep space probe in the future will automatically adjust the coding method and compression algorithm, and strive to achieve the best data transmission effect, increase the transmission rate and alleviate the degree of delay.
In order to overcome the energy constraints in deep space exploration missions and solve the heat dissipation needs, the probe will inevitably apply low-power consumption technology and green communication technology in the future, which can not only reduce the energy consumption of the communication system, but also achieve efficient thermal management and heat dissipation. There is no doubt that with the practical application and popularization of these technologies, the laser communication system of deep space probes is expected to operate more stably, and the endurance will also be significantly improved.
With the continuous advancement of artificial intelligence and automation technology, deep space probes are expected to complete their tasks more autonomously and efficiently in the future. For example, through preset rules and algorithms, the detector can realize automatic processing and intelligent transmission control of data, avoid information "blockage", and improve communication efficiency. At the same time, laser communication systems will benefit from artificial intelligence and automation technologies that help scientists reduce operator errors and improve the accuracy and reliability of detection tasks.
After all, laser communication is not a panacea, and future deep space exploration missions may gradually realize the integration of diversified communication means. Through the comprehensive use of various communication technologies, such as radio communication, laser communication, infrared communication, etc., the detector can play the optimal communication effect in multiple paths and frequency bands, and improve the reliability and stability of communication.
At the same time, the integration of diversified communication means can help to realize multi-task cooperation and improve the comprehensive performance of the probe, which in turn will promote more types and numbers of probes to perform more complex tasks in deep space.
This article was originally published in China Aerospace News Feitian Science Weekly
Text: Sonic.
Edited by Gao Chen.
Review Yang Jian Yang Lei.
Executive Producer: Suo Adi.