How 23 giant Chinese rockets could save the world from ‘doomsday’ asteroid

Stephen Chen, South China Morning Post

Posted at Jul 06 2021 01:29 PM

China’s space programme could one day save the world, with massive rockets travelling for years to defend the planet from huge asteroids capable of wiping out entire cities, according to the government.

This saviour role is unexpected given these are the same machines seen as a threat by many, including the United States, just weeks ago; the main 20-tonne section from one such rocket fell back to Earth in May in an uncontrolled re-entry. It fell into the sea or burned up beforehand, although last year fragments from another rocket were said to have hit two villages in the West African country, Ivory Coast.

Now a new government-funded study says China can launch 23 Long March 5 (CZ-5) rockets – the largest in its fleet, weighing almost 900 tonnes on take-off – to break up the rocky objects in our solar system. Some asteroids are as small as pebbles but others are hundreds of kilometres across. An asteroid about 500 metres (1,640 feet) wide could kill millions.

Although the chance of one colliding with the Earth is currently low, there is one called Bennu which could hit in about a century. Researcher Li Mingtao and his colleagues at the National Space Science Centre in Beijing have been commissioned to find out how China can step in and try to ensure humans do not go the way of the dinosaurs. The asteroid that led to their extinction was around 10km (6 miles) wide.

To change the course of a giant asteroid hurtling towards us at terrifying speeds, a lot of kinetic energy would be needed. Nuclear weapons might do the job but such a blast could break the target into several threatening chunks.

In their proposal, the space centre team suggested launching 23 CZ-5 rockets from various sites across China, at the same time. The spacecraft would have to travel for almost three years to reach their target.

On top of each rocket would be a deflector, a device designed to avoid breaking up the asteroid. Each rocket would “hit” the asteroid, one after another, by way of a gentle nudge.

This would only change the course of a Bennu-sized asteroid slightly, but enough to make it pass safely at a distance about 1.4 times the radius of the Earth and save some cities from annihilation, according to Li’s calculations.

“[It is] possible to defend against large asteroids with a nuclear-free technique within 10 years,” said Li and colleagues in a June paper published in Icarus , an international journal for solar system studies.

The CZ-5 is the backbone of China’s space programme, a more-than-handy workhorse used in space station construction and Mars exploration. The problem is its size becomes an issue during free fall back to Earth, travelling at thousands of miles an hour.

Western authorities including the US Space Force have said they carefully tracked each CZ-5 after each launch. In May US Defence Secretary Lloyd Austin hoped the rocket of concern at the time would “land in a place where it will not harm anyone. Hopefully in the ocean, or someplace like that.”

He also said there was a need to make sure “those kinds of things” were taken into consideration when planning and conducting operations. Some Western media warned readers that the debris might hit big cities.

That did not happen but led to an increased focus on China’s responsibility as a space power.

In the Icarus paper Li and his colleagues said fuel not used during the rocket launch could give extra thrust during the flight towards an asteroid, and the rocket fuselage also increased the total mass of the deflector. They said existing rockets only had to undergo small modifications such as adding a few small thrusters.
A similar mission proposed by researchers with Nasa and California’s Lawrence Livermore National Laboratory in 2018 would require the launch of 75 Delta IV heavy rockets, according to the two organisations and mentioned by Li.

Known as HAMMER (Hypervelocity Asteroid Mitigation Mission for Emergency Response), the US plan would deliver more than 400 tonnes of deflectors, nearly twice as many as in the Chinese proposal, but with a flight time nearly a year shorter, to achieve similar results.

The US mission would be more expensive than the Chinese one, Li said. The Chinese plan also needs less preparation time. While the American approach would need to discover an asteroid 25 years before its potential collision with Earth, China’s plan could cut the lead time to just a decade.

Overall, the Chinese approach, involving what is called the Assembled Kinetic Impactor, could greatly improve deflection efficiency and reduce both launch costs and lead time, the paper said.

A space scientist at Beijing’s Tsinghua University said competition between China and the US would accelerate the development of space technology.
“The problem is, when the doomsday threat comes, politics may override science and lots of time may be wasted on debates to decide which country should take the lead,” said the researcher, who did not want to be named because of the sensitivity of the issue.

China has been challenging US dominance in space for some time. It already has a rover on Mars, is building a space station, exploring the far side of the moon and studying lunar samples recently retrieved by robots.

The US launched its first asteroid defence programme decades ago. It has the only asteroid-warning radar system on Earth and one of its spacecraft is returning home after obtaining samples from Bennu, the asteroid that could hit us in about a century. In 2025 China is expected to launch its own spacecraft to retrieve asteroid samples.

China is also building a planetary defence system with what will be the most powerful radar in the world, according to researchers involved in the project. It will be made up of large radio telescopes across the country and be able to track more targets than its US counterpart.


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