Starlink's satellite blitz and the issue of close encounters in space

The world’s richest man, Elon Musk, has a talent for getting involved in controversy. The latest centres on his plans to provide broadband internet through the constellation of Starlink satellites. When Starlink launched, astronomers complained the shiny new objects hurtling across the sky seriously interfered with astronomical observations. Musk tried to cut the albedo (the amount of light reflected) of these satellites to comply with academic pressure.

Now, the Chinese are complaining the Starlink satellites present a safety hazard. The Chinese space station, Tiangong, had to dodge and weave to narrowly avoid catastrophic collisions twice, in July and in October.

Starlink, which is a division of SpaceX, has already launched over 1,600 satellites and it has permission from the US to launch up to 12,000 in its bid to provide internet access. (Musk plans to offer these services in India, although he has been prohibited from offering pre-booking.)

China has complained to the UN and asked for diplomatic support from other nations, which are signatories of the outer space treaty. Independent sources confirmed that the space station was indeed in grave danger.

Starlink satellites came within 3 km of the station on at least one occasion. Given combined speeds in excess of 25,000 kmph, a collision with a 200 kg satellite would have completely destroyed Tiangong, instantaneously killing any astronauts and, of course, obliterated the satellite, too.

The last decade has seen increasing problems with space junk and live satellites. Junk consists of debris that includes dead satellites still in orbit, as well as bits and pieces of destroyed satellites. Anti-missile demonstrations by China and India have smashed satellites and added to the clutter.  

Space navigators try to keep track of at least 30,000 such pieces of debris, all travelling at very high speeds. These range in size from 2.5 cm in diameter up to refrigerator-sized. A 2.5 cm bullet travelling at 800 kmph can penetrate a car — imagine what a fridge travelling at 20,000 kmph can do.

Apart from this, live satellite launches have increased multi-fold, making space even more crowded. Although the paths of live satellites are easier to plot, or change, the sheer numbers make accidents more likely. Much of the data is derived and crunched by The Socrates (Satellite Orbital Conjunction Reports Assessing Threatening Encounters in Space) database. This is managed by CelesTrak (https://celestrak.com/), and provides information about satellite orbits and models their trajectories to assess collision risk.

Starlink satellites are said to be autonomously programmed to avoid collision. But they are involved in about 1,600 “close” encounters every week, about 50 per cent of all such incidents, according to Hugh Lewis, head of the Astronautics Research Group at the University of Southampton, UK. That includes 1,100 encounters between Starlink satellites and about 500 involving other spacecraft. A “close encounter” is a situation when two space objects pass within a distance of 1 km. Lewis, who is reckoned to be the world’s leading expert at this, says the number of close encounters picked up by Socrates has more than doubled since Starlink launched.

The International Space Station has often had to dodge such “junk”. Nasa postponed a planned space-walk at the ISS in November due to concerns over debris. While there has been much talk about initiatives to clean up space junk, little has happened in the way of concrete engineering projects.

Not surprisingly social media exploded with criticism of Starlink, and by extension, Musk, along with his other company, Tesla. Chinese social media users talked up all sorts of conspiracy theories, including speculation that this was a plot by the US military to knock out China’s space programmes.

Even if we discount those, it’s a serious problem and Starlink is not the only offender. Its rival, OneWeb, which has over 250 satellites, is involved in 80 close encounters with other operators’ satellites every week. OneWeb is also attempting to provide satellite internet services in India in a collaboration with Bharti Airtel.

Given the technological trends, the numbers of satellites in space will rise exponentially over the next few years. The space junk problem has to be solved, and urgently at that.