Q&A with Steve Clarke, deputy associate administrator for exploration in NASA’s science division (members only)

Northrop Grumman’s Cygnus supply ship set for liftoff Saturday will deliver to the International Space Station the final hardware for a series of ambitious spacewalks later this month to install a new coolant system on the Alpha Magnetic Spectrometer, a $2 billion particle physics experiment seeking the cosmic signatures of dark matter and antimatter.

NASA’s acting administrator said Tuesday he does not expect Russian cosmonauts to start launching to the International Space Station on U.S. commercial crew vehicles until next year. A proposed agreement with Russia to ensure the space station is always staffed with an international crew is awaiting U.S. government approval.

SpaceX’s Crew Dragon spacecraft closed out a six-day test flight in low Earth orbit Friday with an on-target splashdown in the Atlantic Ocean, and officials hailed the ship’s performance before it flies with astronauts for the first time later this year.