Following completion of its Centaur dual engine system, the rocket set to send American astronauts back to the International Space Station is in its final assembly stage at United Launch Alliance’s (ULA) factory in Decatur, Alabama.

ULA’s Atlas V rocket will power Boeing’s CST-100 Starliner spacecraft in the first astronaut mission launched from American soil since the final Space Shuttle launch in 2011.

Since the last Shuttle mission, American astronauts have been flying to the Space Station on Russian rockets.

Before sending astronauts, ULA will conduct an Orbital Flight Test. Both the test and the eventual mission will be launched from Cape Canaveral, Florida, though a date hasn’t been set for either.

Aside from its role in manned space missions, ULA also plays a critical role in the exploration of Mars.

On Wednesday, ULA President and CEO Tory Bruno testified before the Senate Subcommittee on Space, Science, and Competitiveness about his company’s work in space exploration and his hope for the future of the same.

“Acts of Congress and presidential directives reflect the high priority that the United States Government has long placed on human space exploration,” Bruno said. “With this continuing commitment, Americans will surely land on Mars as they landed on the Moon.”

ULA rockets have been responsible for powering all U.S. missions to Mars.