Two former top NASA officials unveiled plans Thursday to sell manned flights to the moon by the end of the decade, in an announcement 40 years after the last human set foot there.

Spaceflight, long the province of national governments, has moved toward increased commercialization in recent years, with private companies for the first time successfully launching rockets into orbit.

The US space agency, in the hopes of keeping costs down, even retired its space shuttles in 2011. NASA has instead paid for space on Russian craft to get people and supplies to the International Space Station -- and, more recently, on one built and operated by SpaceX that carried just cargo.

But with ever shrinking budgets, manned flights beyond Earth's orbit have been put on hold, with the US space agency relying on robots to do its exploring of the rest of the solar system.

The Golden Spike Company, its name a reference to the spike that completed the first railway to traverse the United States, aims to take part in the new wave of private spaceflight, as well as open up new frontiers by getting humans back into outer space.

The company estimates it will cost $1.5 billion for a round-trip expedition to the moon, a price tag it says is roughly equivalent to the amount government-funded space programs spend to send robots there now.

Golden Spike said it can reduce costs by "capitalizing on available rockets and emerging commercial-crew spacecraft."

The company aims to sell flights "to nations, individuals and corporations with lunar exploration objectives and ambitions," it said, adding that the estimated prices "are a fraction of any lunar program ever conceived."

Golden Spike has been working on its business plan for the last two years, and the unveiling comes a day before the 40th anniversary of the launch of Apollo 17, the last mission that put humans on the moon.

The two entrepreneurs behind the company include a former Apollo flight director, Gerry Griffin, who also directed NASA's Johnson Space Center, and planetary scientist and former NASA science chief Alan Stern.

The company counts high-profile politicians among its advisers, including former speaker of the US House of Representatives Newt Gingrich, and Bill Richardson, a former New Mexico governor and a top official under president Bill Clinton.

The Apollo space program ran from 1963 to 1972, and included the iconic Apollo 11 mission that saw Neil Armstrong take the first steps on the moon.

The last mission launched on December 7, 1972, and returned to Earth 12 days later, after astronaut Eugene Cernan took the last steps on the moon by a human to date.

SpaceX, founded by PayPal co-founder Elon Musk is one of several private firms working with the US space agency to send flights to and from the ISS, and the first to become operational.