Mind that satellite! The mission to clean up dangerous space junk

In November of last year, the five astronauts and two cosmonauts on the International Space Station were ordered to take refuge in their capsule for fear of being hit by flying debris. It was a crazy way to start a mission, and the crew of the outpost had arrived.

The incident showed how hairy Earth has become, and it wasn't a one-off. Two weeks later, controllers received another alert that the space station might be hit by more debris. The planned spacewalk was delayed because the astronauts could be in danger if they went outside. The space station was forced to dodge a US rocket body before the week was over, because of warnings before. It was reminiscent of the movieGravity, in which debris from a shot-down satellite damages not just the ISS but the Hubble space telescope and a visiting space shuttle.

It's a problem in low Earth orbit because it's where everyone wants to be and there have been accidents in the past. LEO is any altitude up to 1,200 miles. Many of the satellites are higher up, but the orbits is less cluttered.

Since the early days of the space age, there has been more junk in the sky. At first, no one was worried about space being a big place. Over the past six decades, the amount of tumbling debris and its combined mass has risen. Hundreds and then thousands of satellites were launched by the military, space agencies and private operators. The void it used to be is not there anymore.

A mix of spent rocket parts, dead satellites and fragments of hardware is doing their best to defy the rule that what goes up must come down. Old space kit can stay above the atmosphere for centuries, even millennia, where it can smash into other objects. The UN Office for Outer Space Affairs says that if the Romans had launched a satellite into a 750-mile-high orbit, it would fall back to Earth.

There’s potential for space junk to be weaponised, to render entire orbits unusable

"I think it's fair to say that space is becoming congested," says Wing Commander Thom Colledge, the station commander atRAF Fylingdales in the North York Moors. The base is an early warning system for intercontinental missiles. The same radar that watches for nukes also looks out for space accidents. As more and more satellites are launched, they are at increased risk of colliding.

About 30,000 items of space junk larger than 10 cm are monitored by the US Space Surveillance Network. The network gives operators time to assess the risk and move if necessary. There are more than 100,000,000 pieces that are too small to be tracked. Micrometre-sized particles can chip windows and dent solar cells, while millimetre-sized particles can destroy satellite cameras. A fragment at 1 cm can take out a satellite. Operators may never know what happened.

The military-private partnership performs space debris tracking at Fylingdales, with the RAF operating the radar and analysts from Serco interpreting the data. The nine-storey building on the moors has been a striking landmark for the past 30 years. The three square sides of the building form the solid state phased array radar, or SSPAR, which provides a panoramic view of space up to 3,000 miles high. The radar tracks objects by focusing a beam of energy on a region of space and analyzing the reflections that bounce back.

Visitors must ditch their phones and laptops to get inside the pyramid radar station, which doubles as a workplace. The operations centre is where the real work takes place and we pass it on the way to the training room. It has a thick metal door with a hand wheel that would look out of place on a submarine.

All the time, warnings of potential crashes are issued. The UK Space Agency gets thousands of notifications a month from the US Space Network. Drawing on data from other sites around the world and the UK, these are risk-assessed. Jacob Geer, head of space surveillance and tracking at the agency, said that the service will be rolled out to the rest of the country this year.

There is a cost to taking evasive action if the risk of collision is more than one in 1,000. A satellite's lifetime can be shortened by the use of debris. CharlotteNewton, a Serco space, says that avoidance manoeuvres can sometimes be incorporated into pre-planned station-keeping burns.

There are other drawbacks to moving a satellite. If a satellite has to dodge debris, it could end up in a less useful position. This could affect what can be seen and when. There is a chance that space junk could be weaponised, to disrupt and degrade what others can do, and render entire orbits unusable.

Sometimes crashes can't be avoided. Observers can't do anything when two dead satellites are about to collide. One of the satellites will usually have a chance to make a move. When two satellites are involved, the dance becomes more complicated. There is no accepted right of way. Disaster is often averted by those with most to lose.

Mega-constellations are one of the biggest challenges for satellite operators. Hundreds and possibly thousands of small satellites are being launched by companies such as OneWeb to provide services such as global broadband access. The benefits of the satellites will add to the congestion. Esa took evasive action to avoid an operational satellite for the first time in 2019. The Aeolus Earth observation satellite fired its thrusters to avoid a Starlink satellite. Others had close shaves. In December, China criticized the US for threatening the lives of astronauts on board its space station after it was forced to dodge one Starlink in July and another in October. The US would have let China know if there was a chance of a collision.

One theoretical concern is called Kessler syndrome, where the debris from one collision sets off more collisions

There are accidents in space. The most spectacular was in February of 2009, when an operational Iridium communications satellite slammed into a dead Russian military satellite. The impact created thousands of fragments that threaten satellites today. The incident made headlines, but many more suspected collision are never confirmed because satellites are taken out by fragments too small to track.

There are some particularly risky objects in the debris that has accumulated. Old Russian rocket bodies are prone to explosion, leaving their paths strewn with debris. Large satellites such as Esa's doubledecker bus-sized Envisat are sitting ducks. A big collision with Envisat could add a lot of debris to low Earth orbit. Kessler syndrome is a theoretical concern for the future, where there is so much junk in a particular orbit that the debris from one collision sets off a chain reaction of more collision, and more debris, until the orbit is off limits for years.

The risk that space debris poses to satellites has not stopped countries from adding to the problem when they want to. In 2007, China destroyed a weather satellite with a missile, increasing the amount of space debris in low Earth orbit. The US and India cluttering the environment even more in 2008 and 2019. More than 1,500 fragments were created by Russia's act of orbital vandalising last year. This week, the US announced a national ban on further so-called direct-ascent anti-satellite missile testing and urged other countries to follow suit, claiming it wanted to establish a new international norm.

Space agencies are taking action to deal with a growing problem. Better instruments can be built to track debris and satellites more accurately. Satellites carry reflectors that allow operators to track their trajectory precisely. Esa hopes to have a laser range station in Tenerife in the next two years to be able to track space junk with more powerful lasers. The number of false alarm collision alerts should be slashed by having more precise information on the positions of satellites. Teams of engineers are not needed to execute every sidestep and swerving because of further efforts.

The UN Office for Outer Space Affairs has published guidelines for space debris mitigation and long-term sustainable outer space activities. Operators are supposed to remove satellites from the sky in 25 years. Satellites that are more than 20,000 miles high will be pushed up to a graveyard orbit out of harm's way. Satellites should be steered into the atmosphere to burn up on re-entry. Operators of large satellites are advised to time their re-entries so they land in the Pacific.

Not everyone follows the guidelines. Most of the satellites in low Earth orbit are simply abandoned once their work is done.

Esa's approach to the problem is to come up with cost-effective ways to remove dead satellites, rocket parts and large chunks of debris, and hope regulators endorse those that work. Krag favors a similar approach to national park protection, where people must leave with whatever they bring in, if a satellite reaches the end of its life.

It will soon be clear how well that works. Astroscale, a Japanese tech firm with a facility in Oxford, hopes to offer a satellite removal service in the next few years. The ClearSpace-1 mission aims to be the first to remove a piece of space debris. The same mission will test a propellant kit developed by D-orbit, an Italian firm with offices in Oxford, that will steer the spent rocket body back to Earth.

It becomes almost corporate good practice to show that you are sustainable, to make it possible for a company to come and retrieve or service your satellite at the end of its life, or to make it possible for a company to do that. The UK can build expertise for theorbital economy by developing knowhow to retrieve dead satellites.

Krag says that the lack of technology and the lack of disposal means that dozens of objects are left behind every year. It is similar to plastic in the ocean. Would you start cleaning up the old stuff when people add more? No. You are focused on stopping them from adding more. We need to do the same with space debris.