Boeing and SpaceX made numerous advances on their crew transportation systems set to carry astronauts to and from the International Space Station for NASA's Commercial Crew Program. Both companies began building the spacecraft that will fly the flight tests for the program before beginning crew rotation missions. Boeing is building the CST-100 Starliner to fly on a United Launch Alliance Atlas V rocket, and SpaceX is building its Crew Dragon spacecraft to launch atop the company’s Falcon 9 rocket.

The year marked a substantial transition from design of critical elements and systems in previous years to the manufacturing of the spacecraft and launch vehicles, substantial modifications to launch complexes in Florida and the first integrated simulations of the teams that will oversee the flights. Along the way, advances were overseen by NASA engineers and the astronauts who will fly the spacecraft into orbit for the flight tests.

Here’s a look back at 2016: