The chance that SpaceX’s planned Starlink satellite constellation will cause an injury or death is 45 percent every six years, according to an IEEE Spectrum analysis of figures submitted by the company to the U.S. Federal Communications Commission.

Elon Musk hopes the nearly 12,000 satellites in the constellation will eventually carry half of all Internet traffic. The satellites will use laser and radio links to provide fast, cheap Internet access to people all over the world—and the associated service fees could help Musk fund his dream of colonizing Mars.

But what goes up, must come down, and the sheer scale of SpaceX’s orbital network means that it may only be a matter of time before the world sees the first injury or death from a plummeting satellite.