Large constellations of satellites, such as those launched by SpaceX this week, could clutter Earth's orbit with dangerous space junk, experts have warned.
On Thursday, SpaceX launched a rocket carrying the first 60 satellites of its "Starlink" constellation, which is intended to provide internet to remote regions of Earth from space.
Eventually, the company wants to launch nearly 12,000 spacecraft, each weighing nearly 227kg. If successful, the constellation would dwarf the 2,000 satellites that are currently in orbit.
“Large constellations with several thousand satellites need to be designed and operated with much more care than the usual space traffic in order to avoid a disaster”, says Dr Holger Krag, Head of the Space Safety Programme Office at the European Space Agency (Esa).
He says the altitude of the constellation matters and as such, it’s not just SpaceX’s constellations that are a concern.
Several other commercial firms are hoping to launch satellites constellations into space, including UK-based start-up OneWeb and Amazon, which is working on a 3,200-satellite proposal.
One of the main fears is the risk of collision with fragments that may break off from a satellite. “A pound coin in space has the same destructive power as a van travelling at 62mph, and the many fragments produced from a collision can quickly disperse around an orbit,” says Professor Richard Crowther, Chief Engineer at the UK Space Agency.
Starlink’s final orbit will be slightly higher than the International Space Station, but well below the majority of terrestrial satellites. SpaceX says this allows its satellites to burn up in the atmosphere if one malfunctions.
The satellites have also been designed to automatically divert in the face of man-made or natural space debris.
However, Massimiliano Vasile, a Professor in Mechanical and Aerospace Engineering at the University of Strathclyde, is concerned that the automatic steering might not be enough to avert a catastrophe.
“If you have a collision in orbit, the fragments that result from these collisions don’t really stay there,” he said. “They tend to spread over a range of altitudes. So, in the medium term, the chance for the space station to have a much higher risk of a collision certainly exists.”
SpaceX points out that its satellite steering system has been approved by the Federal Communications Commission. It claims that “more than 98 percent of the satellites in its constellation will have no components that survive atmospheric re-entry.”
Currently Esa estimates that there are almost 130 million debris objects in space, ranging from just a few mm in size up to many metres. Of these, over 900,000 are considered big enough to damage or destroy entire spacecraft.
“We need governments to come up with plans and funding for removing the existing large pieces of space debris they put into orbit over the last several decades. So far they've been unwilling to do so,” says Dr Brian Weeden, Director of Program Planning for Secure World Foundation.
“The urgency is similar to that of climate change. The longer we wait to deal with space debris, the bigger the negative impacts will be.”