Opening a simulation diagram on the computer, astronomer Liu Jing shows the blue Earth surrounded by countless dots in the dark space.
The dots are space debris.
As vice director of the Space Debris Monitoring and Application Center under China's National Space Administration, Liu raises a series of astonishing figures.
Humankind has launched more than 6,000 spacecraft, with some 1,300 still in operation, while others are now trash in space. So far, more than 17,000 pieces of space debris have been recorded.
Experts estimate there are more than 23,000 pieces of debris larger than 10 cm, more than 500,000 pieces larger than 1 cm, and over 100 million larger than 1mm in space.
"There is an estimated risk of collision between spacecraft and debris each week. China's satellites face the risk of coming close to debris every month," Liu says.
"If the situation continues, a large space collision will happen every four to nine years. And if no effective measures are taken, the chain reaction between the space debris will bring the intensification of space to a critical point."
Scientists estimate there have been more than 200 spacecraft destroyed in the space era, with an increasing number of collisions in recent years.
In 2007, a European satellite, Meteosat-8, was hit by unrecorded debris and pushed out of orbit. In 2009, a Russian satellite collided with a U.S. satellite, producing a large amount of debris. In 2013, an Ecuadorian satellite was destroyed when it collided with debris from a rocket launched by the former Soviet Union in 1985.
By Sept. 1, 2015, more than 1,300 satellites were in earth orbit: more than 500 were from the United States, more than 140 from China, and more than 130 from Russia.
Many countries, including the United States and Russia, are stepping up the development of small satellites. Many more small satellites are expected to be sent into space, intensifying the orbit and frequency resources and raising the risks of collision.
Liu says more than 10,000 pieces of debris are distributed in a belt between 800 km and 1,000 km above the Earth, the most dangerous region in space.
Scientists say the main sources of debris include remains of satellites and rockets, tools and miscellaneous items discarded by astronauts during extravehicular activities, and fragments broken off spacecraft as a result of aging.
Liu says pieces larger than 10 cm can be detected by ground-based telescopes and radar. "Those smaller than 10 cm and larger than 1 cm are the most dangerous as they cannot be detected by any equipment, but can be disastrous."
Experts can add layers of special materials to protect spacecraft from damage caused by pieces smaller than 1 cm.
"The problem of space debris is too serious to ignore. We must take measures to curb the growing speed of the debris," Liu says.
Scientists are looking for ways to deal with the trash. They have monitored and collected debris samples from space, and set up computer models to analyze the distribution and development patterns of the debris. They are also developing space robots to clean up orbiting debris.
China set up the Space Debris Monitoring and Application Center in June this year. Its main tasks include monitoring debris and near-earth small celestial bodies, studying and determining their risks, and establishing a database of space debris, says Liu.
The center will also provide risk evaluation services for users at home and abroad, offer emergency support, and conduct international cooperation and technological exchanges.
China needs to strengthen supervision of space debris to curb its increase. It should also strengthen research on related laws, and actively participate in making international rules for outer space, Liu adds.
