China’s FAST radio telescope, with a dish the size of 30 football fields, measuring 500 meters in diameter, dwarfing Puerto Rico’s 300-meter Arecibo Observatory, will launch its astronomers into the nation’s role as the new space superpower cinched with its epic landing of the Chang’e-4 Rover this week on the Moon’s far side. FAST could double the known pulsar tally of 2,000, says Peng Bo, FAST’s deputy manager and acting observatory director. It’s also ideal for mapping gas clouds between stars and for listening for signals from alien civilizations.
China is a nation fascinated by space exploration and the possibility of finding advanced alien life, whose appearance might be imminent, says Liu Cixin, China’s preeminent science-fiction author of The Three-Body Problem. “Perhaps in ten thousand years, the starry sky that humankind gazes upon will remain empty and silent,” he writes in the postscript to one of his books. “But perhaps tomorrow we’ll wake up and find an alien spaceship the size of the Moon parked in orbit.”
“Some strange signals have been found, but it’s hard to confirm their origins, because these signals do not repeat,” says Li Di, chief scientist of China’s new FAST Radio telescope and leader of the radio astronomy division of its operator, the National Astronomical Observatories of China (NOAC) in Beijing. “We look for not only television signals, but also atomic bomb signals. We’ll give full play to our imaginations when processing the signals,” Li says. “It’s a complete exploration, as we don’t know what an alien is like.”
“We don’t know when earthlings will discover ET. It could be 1,000 years from now, or in our lifetimes. It could be next year, when FAST gets going on the sky surveys,” said Dan Werthimer, chief scientist for the SETI Research Center at University of California, Berkeley.
Having the world’s largest and most powerful new radio telescope, we can receive weaker and more distant radio messages, said Wu Xiangping, director-general of the Chinese Astronomical Society, “It will help us to search for intelligent life outside of the galaxy and explore the origins of the universe,” he added underscoring the China’s race to be the first nation to discover the existence of an advanced alien civilization.
Peng Bo, has said of China’s new, supermassive radio telescope that “FAST’s potential to discover an alien civilization will be five to ten times that of current equipment, as it can see farther and darker planets.”
According to Douglas Vakoch, president of METI International, an organization that attempts to make contact with alien life if such a civilization were just 300 years ahead of humans–the tiniest fleck on an evolutionary timescale–in terms of technology development, their communication abilities would be so advanced as to be almost incomprehensible to us.
Due to the limitations of current radio technology, Vakoch observed, any radio signals from alien civilizations detected by the dish would have to be strong and deliberately sent with contact in mind, rather than randomly fired out from radio or TV equivalents. “We’d only be able to find the sort of signals that FAST will be looking for: narrow band signals, something that would have a lot of energy put into a carrier,” he said. “An interstellar beacon saying: We are here.”
“Our civilization has only been evolving for tens of thousands of years,” said Dick Manchester, a radio astronomer at Australia’s Commonwealth Scientific and Industrial Research Organization, Manchester in a discussion with Motherrboad.com. “Other civilizations could have had billions of years to evolve. It’s virtually certain that any other civilization we detect would be enormously more advanced than we are. Our history in terms of stellar evolution is absolutely tiny.”
In a stunning landscape of jagged limestone hills in southwestern China, engineers put the finishing touches on a grand astronomy facility in September of 2016 nestled in a natural depression that gathers radio signals from the cosmos. The world’s largest radio telescope catalogs pulsars; probes gravitational waves, dark matter, and fast radio bursts; and listens for transmissions from alien civilizations. The dish will aid efforts to map the distribution of hydrogen throughout the Milky Way and other galaxies, with changing states of hydrogen being an indicator of exoplanets that could potentially sustain life.
It is not just FAST’s sheer size, it is also breaking new ground in radio astronomy with a design that pulls a section of the spherical dish into a gradually moving paraboloid to aim at and track cosmic objects as Earth rotates, bringing the benefits of a tilting, turning antenna to a fixed dish. This innovation “is absolutely unique, nobody has ever done this before,” says Dick Manchester, a radio astronomer at Australia’s Commonwealth Scientific and Industrial Research Organisation (CSIRO) in Sydney.
FAST’s long gestation began in the 1990s, when it assigned astronomers to serve on China’s delegation to the international working group that eventually proposed the Square Kilometer Array (SKA) as a next-generation radio telescope. Astronomers were counting on advances in interferometry to combine radio waves from dozens or even hundreds of dishes, thereby creating a collecting area far bigger than any existing telescope. In the early days of planning, China vied to host the SKA, proposing to build several large dishes in the limestone depressions that dimple its southwestern provinces. Chinese astronomers even did preliminary work on FAST as a prototype.
Instead, the SKA’s backers opted for a design featuring thousands of small dishes. China was dropped from the list of candidate sites in 2006; construction of the first phase of the SKA, in South Africa and Australia, is expected to begin in 2018. Swallowing their disappointment, Nan and his colleagues pushed China to build FAST anyway.
Single dishes excel at observing point sources like neutron stars and at scanning a multitude of frequencies in the search for extraterrestrial intelligence, says astronomer Li Di, who previously worked at NASA’s Jet Propulsion Laboratory in Pasadena, California. Another advantage is that, compared with the multiple dishes in an array, single dishes are “relatively cheap and relatively straightforward to upgrade,” says George Hobbs, an astronomer at CSIRO. “You just keep building better receivers.”
FAST was modeled after the Arecibo telescope. Both are built in karst depressions and supported on steel cable meshes slung like hammocks from supports fixed to the limestone pinnacles. And like the Arecibo Observatory, FAST takes an unusual approach to focusing incoming radio waves.
Radio telescope dishes are typically parabolic because that shape focuses waves from astronomical objects in line with the parabola’s axis to a point above the dish. The telescope’s receivers—or a subreflector—are positioned at that point. But a parabolic telescope must be steerable and able to point at astronomical objects and track them as Earth rotates, because parabolic reflectors distort waves from off-axis targets.
It’s impossible to steer Arecibo and FAST because their enormous dishes are anchored to the ground. So both have a spherical shape, allowing them to collect and concentrate waves from offaxis sources without focusing on a point. Arecibo aims at cosmic objects by shifting the position of the receiver platform to catch the reflected waves. Within the platform, a complex mirror system brings them into focus. But that limits the slice of observable sky to about 20° from zenith; farther from the zenith, the distortion is too great. The correction system also results in a platform weighing about 900 tons. “That mirror system and the whole platform are very big for Arecibo, and it would have been huge for FAST—and heavy,” Manchester says.
Instead, the team designed a system that pulls a roughly 300-meter-diameter section of FAST’s spherical reflector into a subtle parabola, while positioning receivers along the parabola’s axis. “It’s like forming a smaller bowl within a big wok,” Li says. The position of the parabola can be shifted in real time, so that the parabolic axis always aims at a cosmic object of interest as Earth rotates, just as a steerable radio telescope does. FAST can observe up to 40° from zenith. And because it does not need a complex corrective mechanism, its receiver platform can host more instruments than Arecibo’s.
Making an active surface reflector “was a bold move,” Manchester says. To deform the reflector, FAST has 2225 actuators, essentially high-tech winches, anchored into rock beneath the dish. The actuators tug the dish into a parabola by pulling on tie-down cables connected to the dish’s supporting mesh. The mesh’s natural springiness restores the dish’s spherical shape when the actuators relax the tension. Lasers mounted on small posts protruding through the dish check the coordinates of 1000 points on its surface, allowing fine-tuning of the shape.
To make this system work, the engineers solved a host of challenges. For starters, the actuators emit radio interference that is many times stronger than the signal from the sky. There was no suitable commercially available shielding, so they developed their own.
Another problem was caught during the final design review before construction, when engineers belatedly realized that repeatedly stressing and relaxing ordinary steel cables could lead to fatigue failure, the phenomenon familiar to anyone who has bent a paper clip back and forth until it snaps. The FAST team solved this problem by turning to a Chinese-developed cable that’s fatigue-resistant for up to 2 million stress cycles, far more than the 300,000 cycles the FAST cables will endure over the telescope’s 30-year design life.
In January, with most of the dish’s 4450 triangular reflector panels in place but none of its receivers available, Nan had his crew rig up something resembling a spindly fishbone TV antenna and suspend it over the dish. As radio receivers go it was primitive, but FAST’s enormous collecting area enabled it to pick up signals from the Crab Pulsar, a radio source at the heart of the Crab Nebula. “It was amazing that they could do this with a simple antenna,” CSIRO’s Hobbs says.
But as the dish’s construction entered the home stretch, another glitch cropped up. “The actuators are breaking down at a higher rate than anticipated,” Li says. The team is investigating the cause and possible fixes. “Astronomy is easy; actuators are hard,” says Li, who also served as FAST’s deputy chief engineer.
Getting big telescopes working at full potential is always a challenge, says John Ford, formerly in charge of electronics at NRAO’s Green Bank observatory in West Virginia. On Green Bank’s 100-meter steerable dish, actuators used to counter gravitational effects were “failing on us way more than we thought they would,” he says, because water was leaking in and freezing. Waterproofing the actuators was a headache because they are 100 meters in the air. FAST engineers should have an easier time because their actuators are accessible from the ground, Ford says.
For now, Li says FAST operators will use their working actuators to hold part of the reflector in a parabola, point it at the sky, and simply catch whatever signals they can as Earth rotates. It will take 200 days of such drift scan observations to survey the full northern sky, and he expects they will discover as many as 1000 pulsars, adding to the roughly 2500 now known. Astronomers use these radio beacons, powered by spinning neutron stars, to study the interstellar medium and detect gravitational waves. “We will conduct the world’s best survey for pulsars,” Li says.
“Eventually we will get the telescope working perfectly,” vows Zhu Ming, a FAST project astronomer. Manchester agrees: “They’re very close to achieving an absolutely remarkable feat.”
The Last Word
As a postscript to China’s search of alien life, Liu Cixin, the nation’sforemost philosopher of first contact, told The Atlantic’s Ross Anderson that “he doubts the dish will find one. In a dark-forest cosmos like the one he imagines, no civilization would ever send a beacon unless it were a ‘death monument,’ a powerful broadcast announcing the sender’s impending extinction. If a civilization were about to be invaded by another, or incinerated by a gamma-ray burst, or killed off by some other natural cause, it might use the last of its energy reserves to beam out a dying cry to the most life-friendly planets in its vicinity.”
Liu told Ross that he’s hesitant to make connections between his books and the real world, but said that his work is influenced by the history of Earth’s civilizations, “especially the encounters between more technologically advanced civilizations and the original settlers of a place.” One such encounter occurred during the 19th century, Liu observed, “when the ‘Middle Kingdom’ of China, around which all of Asia had once revolved, looked out to sea and saw the ships of Europe’s seafaring empires, whose ensuing invasion triggered a loss in status for China comparable to the fall of Rome.”