The machines continue to perform splendidly across the solar system. Yet the uncertainty that now besets the American space program stems from Earth-bound policy failures and a singular lack of imagination.

While rovers traverse the surface of Mars, and planetary probes uncover the secrets of the solar system, NASA finds itself relying on Russia to ferry astronauts to and from the International Space Station. With geopolitical tensions mounting between Russia and Ukraine, the space agency recently cut off nearly all contact with Roscosmos, the Russian federal space agency. The last remaining joint activity is the ISS flights aboard Russian Soyuz rockets.

Despite continuing budget cuts, NASA is developing several other post-shuttle options to return to space, including a commercial crew spacecraft competition for orbital flights and a new heavy-lift rocket to again venture beyond Earth orbit. Those projects probably won't fly until later in the decade, adding to the uncertainty over the future of human space exploration.