Boeing will be the first commercial company to carry a NASA astronaut to space in July 2017 under a contract with the US space agency, followed by its competitor SpaceX, officials said Monday.

NASA is funneling billions of dollars to both companies so that they can replace American access to the orbiting International Space Station after the US space shuttle program was retired in 2011.

The announcement of $4.2 billion for Boeing and $2.6 billion for SpaceX was made in September 2014.

However, a legal challenge by Sierra Nevada -- which was developing a space-shuttle-like vehicle called Dream Chaser and was closed out of the competition -- meant that officials could not reveal many details until now.

The US Government Accountability Office (GAO) denied the protest by Sierra Nevada earlier this month, allowing NASA and its partners to speak publicly about the contracts and future plans for test flights.

Commercial Crew Program Manager Kathy Lueders said at a press conference in Houston, Texas that Boeing would be the first to make two contracted missions to carry NASA astronauts, since it has completed two milestones so far, and SpaceX just one.

"Our goal is to have two robust providers," Lueders added.

- July 2017 -

A NASA astronaut and a Boeing test pilot will make the first crewed test flight on the spacecraft called Crew Space Transportation-100, or CST-100 for short, in July 2017, said John Elbon, Boeing's vice president and general manager of space exploration.

"The first services mission then will begin in December of '17," he told reporters, referring to the first official trip to the International Space Station with crew on board.

SpaceX's upgraded Dragon crew vehicle is on track for an unmanned test flight in 2016, followed by a test flight including crew on board in early 2017, said vice president Gwynne Shotwell, who did not give specific dates.

In 2012, California-based SpaceX became the first commercial company to deliver supplies to the International Space Station with its Dragon cargo ship, which is being modified to become a crew capsule.

- Ending dependence -

Since the 30-year space shuttle program ended in 2011, the United States has relied on Russia's Soyuz capsules for astronaut transport at a cost of $70 million per seat.

The cost per seat in the new US commercial industry would be approximately $58 million, an average cost teased out over the course of a five-year mission plan, said Lueders.

NASA administrator Charles Bolden said the rise of private industry in reaching low-Earth orbit means that the US space agency will be able to focus on sending humans to Mars by 2024.

"We made the conscious decision that if we are going to go to deep space, we need to turn over things that we are relatively sure we know how to do -- access to low-Earth orbit -- to American industry," Bolden said.

Another key benefit for the United States is ending its costly dependence on the Russian space agency.

"I don't want to ever have to write another check to Roscosmos after 2017, hopefully," Bolden added.

Both Boeing and SpaceX must show they can successfully complete a test flight with one astronaut aboard before moving on to between two and six more flights contracted with NASA to deliver astronauts to and from the space station.

The spacecraft will launch from Cape Canaveral in Florida.

Boeing's acorn-shaped space capsule, the CST-100, is designed to be re-used up to 10 times, and SpaceX's sleek white Dragon Version Two, or Dragon V2, is also a reusable space capsule.

Both can carry up to seven people to the space station, which circles the planet in low-Earth orbit.