Seeking to lead Houston into a future from aviation to aerospace, the Houston Airport System unveiled preliminary plans on Wednesday to develop a 450-acre spaceport at Ellington Airport.

"I'm absolutely convinced now is the time to start positioning Houston as a major player in this industry," said Mario Diaz, Houston aviation director.

Ellington Airport, a few miles from Johnson Space Center, is only about one-third occupied.

Diaz said Houston needs to seize the future of aerospace, which he believes is increasingly moving from the hands of government and NASA to the private sector.

"In recent years we've seen a dramatic change in the aerospace industry," Diaz said. "With this trend in mind, the question is how does the city dubbed Space City USA in the last century hold on to that title in the 21st century? We think a spaceport is the answer."

Designs: How the spaceport could look

He envisions a facility that would be home to space tourism as well as support aerospace hangars, manufacturing facilities, educational institutions and museums.

Like aviation companies do at other Houston airports, facilities would be leased from the city, providing the bulk of revenues.

In addition to Johnson Space Center, Houston has attributes that would help it succeed as a private aerospace hub, including a skilled workforce and easy access to offshore airspace, said Michael Lopez-Alegria, president of the Commercial Spaceflight Federation, an industry trade group.

"It goes without saying that space and Houston are rather synonymous," Lopez-Alegria said.

He agreed with Diaz that the spaceflight game is changing, and that Houston needs to move beyond relying on NASA alone for its aerospace prominence.

"As important as that legacy is, I think we're on the doorstep of a new era," he said.

Construction costs for such a facility are not clear. Diaz said there are no "concrete numbers" for development of the facility, which would be financed from a variety of sources, including private companies, public bonds and grants. He envisions construction occurring over the next five to 10 years.

Mayor Annise Parker and the Houston City Council have expressed support for the initiative, giving the airport system approval to apply to the Federal Aviation Administration for a spaceport license. The United States has eight spaceports.

The commercial flights being proposed from Ellington Airport would take off from the spaceport like a traditional aircraft, then fly out over the Gulf and up to about 60 miles above the surface. From there passengers would be treated to a view of the Earth seen so far only by astronauts.