As NASA aims to return astronauts to the moon, a multibillion-dollar question mark looms: What will the space agency do when the International Space Station retires?
As the US sets its sights on establishing a permanent base on the moon, its foothold in an area of space much closer to home is growing more uncertain.
Located in low-Earth orbit — or LEO, a region that stretches up to 1,200 miles (2,000 kilometers) ... [12046 chars]