NASA's chief is worried about China getting back to the moon first. Here's why

NASA Administrator Bill Nelson at the space agency's headquarters in Washington, D.C., on Wednesday. (Elizabeth Gillis/NPR)

There's a moon rock in the lobby of NASA's Washington, D.C., headquarters.

Visitors are urged to rub their fingers over its smooth, worn surface to connect with one of the greatest achievements in human history: the Apollo missions that landed 12 American men on the moon.