Chinese researchers examine how to keep satellites under the radar

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A research team in Nanjing, Jiangsu Province, has developed stealth technology to be used by small satellites for blind radar detection.

Locating and tracing a small satellite is difficult, even with a large telescope, but some ground radar stations can identify an object as small as a pen orbiting close to Earth, day or night.

The new stealth technology could reduce the strength of radar signals by more than 80%, making the small satellite virtually invisible on a radar screen, Chinese researchers say.

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Radar operators have often swept the skies with electromagnetic waves of different frequencies, interacting with a wide range of materials to ensure they are not missing anything.

The Nanjing team said it could cover a satellite in layers of composite materials with a honeycomb structure that would absorb radar waves at all known operating bandwidths.

A transparent layer of signal absorption material made from rare earth elements has also been added to the satellite’s solar panels, further reducing the chances of being tracked, they said.

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Anti-satellite technology such as high power laser weapons has advanced rapidly in recent years. Small satellite constellations – including those used for communication – face “growing threats,” Professor Kong Xiangkun and colleagues at Nanjing University of Aeronautics and Astronautics (NUAA) said in a report. article published in the Chinese Journal of Astronautics last month.

“The development of stealth satellites is of great importance to counter the detection and surveillance of the enemy,” they wrote.

Coating materials have been used extensively on stealth aircraft, but the extreme environment in space has brought new challenges.

Unlike a stealth aircraft which spent most of its time in an air-conditioned hangar whose skin was frequently inspected and maintained, a satellite was not sheltered and had endure repeated temperature peaks and cosmic ray bombardment for years.

Another problem is the weight. Kong and his colleagues used a large amount of plastic and paper to reduce the weight of the material to about 6 kg per square meter (1.2 pounds per square foot), which is less than most traditional absorbent coverings.

Although only 3 millimeters thick, the stealth shield was physically strong enough to withstand blows and elbows, the researchers said.

But a satellite is a complex system, and the stealth technology would have to work with other components, such as heat management and communication antennas, to get the best results in real applications, they said.

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The first concept of stealth satellites appeared in the 1960s, with the United States and the former Soviet Union leading the way.

The details of these programs were mostly confidential, but the technical challenges seemed enormous. The world’s first known stealth satellite was launched only towards the end of the Cold War.

In 1990, the United States launched Misty, a spy satellite for the Central Intelligence Agency. Misty was known for an inflatable metal shield in gold or silver to deflect radar signals, according to freely available information.

A total of three Misty satellites were launched. They were so expensive that some members of the United States Congress complained that the program had affected the budget of other space activities.

Artist's impression of the American satellite Misty.  Photo: Handout

However, the Misty satellites were on other countries’ watchlists because their shiny shields were so bright against the sun that they had been spotted by backyard astronomers.

The CIA reportedly ended the program in 2007.

Most Chinese research on stealth satellites has been carried out in the past two decades. Although late, Chinese researchers have come up with bold designs.

A research team, led by Professor Kang Guohua of NUAA, for example, proposed a stealth “transformer” satellite in a patent filed in 2017. Most of the time, the satellite circled the Earth in a simple form. similar to an American football. . Only when needed would she expand solar panels and other instruments.

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This solution could reduce the radar signature by more than 300 times, according to Kang’s calculations.

Other suggested strategies include painting the satellite with a special graphene-based black paint to make the satellite blend into the sky at night; or hide the satellite behind space debris to avoid detection.

While not impossible, these ideas had not found immediate use in real applications due to their complexity and technical challenges, according to Kong Xiangkun and colleagues.

A researcher at the Changchun Institute of Optics, Fine Mechanics and Physics in northeast China said the intensification space race between China and the United States would likely lead to a breakthrough in stealth satellite technology.

Large space assets such as the Chinese space station under construction were equipped with radar to detect incoming space debris.

The radar might not be able to detect a small satellite covered in stealth material, said the researcher who asked not to be named because he was involved in a military program.

China is developing technology for a space-based early warning system that uses not only radar, but other detectors such as optical telescopes and heat sensors.

Radar remains the main approach because other detection methods can be affected by environmental elements such as the stars and the sun, according to the researcher.

“The use of stealth technology in space requires new international laws and regulations,” he said.

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