Astronaut Scott Kelly and cosmonaut Mikhail Kornienko ended a record-setting 340-day stay in orbit with a fiery plunge to Earth Tuesday, settling to a jarring rocket-assisted touchdown in Kazakhstan to close out a medical research voyage that may help pave the way for flights to Mars.

Loaded with more than 6,000 pounds of supplies, experiments, and hardware, a SpaceX Cargo Dragon freighter docked with the International Space Station at 1:40 p.m. EST (1840 GMT) Monday, one day after taking off from NASA’s Kennedy Space Center in Florida. This was the first Dragon cargo mission to automatically dock with the space station.

NASA is sure enough that Boeing and SpaceX can safely launch astronauts to the International Space Station by early 2019 to hold off paying Russia to keep flying U.S. crews to the research complex, and one official says a deadline to order parts for new Russian Soyuz crew capsules may have already passed.