Boeing and SpaceX hope to launch commercial crew ferry ships on long-awaited test flights later this year, but both companies face major challenges getting the spacecraft certified before late 2019 when seats aboard Russian Soyuz spacecraft will no longer be easily available for NASA space station crews, officials told lawmakers Wednesday.

America’s most experienced astronaut says her fully commercial visit to the International Space Station this week is a critical stepping stone on the road to space tourism, private-sector orbital research and development of commercially operated space stations.

Veteran Soyuz commander Yuri Malenchenko, outgoing space station skipper Tim Kopra and British astronaut Tim Peake departed the International Space Station early Saturday aboard the Soyuz TMA-19M capsule and landed in Kazakhstan at 0915 GMT (5:15 a.m. EDT).