The return of a spacecraft is not always considered—equipment has historically been left to circulate our planet on its own, creating a lot of garbage in near-Earth orbit. Everything from broken equipment to paint flecks to abandoned launch vehicle components are circulating and threatening the duration or safety of active missions. The Department of Defense Space Surveillance Network tracks 27,000 pieces of trash, and that is only a small fraction of what is floating around.^a

As Alexandra Navrotsky and Megan Householder wrote in a recent review article, “we have done a remarkable job gumming up the Earth with our refuse. We are doing an equally remarkable job gumming up near space with all sorts of remnants from satellites and rockets.”^b