In a move that pours cold water on the dreams of a few billionaire space explorers, the US has tightened its definition of the word "astronaut".

New Federal Aviation Administration (FAA) rules say astronaut hopefuls must be part of the flight crew and make contributions to space flight safety.

That means Jeff Bezos and Sir Richard Branson may not yet be astronauts in the eyes of the US government.

These are the first changes since the FAA wings programme began in 2004.

The Commercial Astronaut Wings programme updates were announced on Tuesday - the same day that Amazon's Mr Bezos flew aboard a Blue Origin rocket to the edge of space.

To qualify as commercial astronauts, space-goers must travel 50 miles (80km) above the Earth's surface, which both Mr Bezos and Mr Branson accomplished.

But altitude aside, the agency says would-be astronauts must have also "demonstrated activities during flight that were essential to public safety, or contributed to human space flight safety".

What exactly counts as such is determined by FAA officials.

In a statement, the FAA said that these changes brought the wings scheme more in line with its role to protect public safety during commercial space flights.

On 11 July, Sir Richard flew on-board Virgin Galactic's SpaceShipTwo to the edge of space as a test before allowing customers aboard next year.

Mr Bezos and the three other crew members who flew on Blue Origin's spacecraft may have less claim to the coveted title. Ahead of the launch, Blue Origin CEO Bob Smith said that "there's really nothing for a crew member to do" on the autonomous vehicle.

Those wishing for commercial wings need to be nominated for them as well. An FAA spokesperson told CNN they are not currently reviewing any submissions.

There are two other ways to earn astronaut wings in the US - through the military or Nasa.

The wings spotted on Mr Bezos and Sir Richard following their flights were custom-made pins by their own companies.

However, a glimmer of hope remains for Sir Richard, Mr Bezos and any future stargazers hoping to be recognised as astronauts.

The new order notes that honorary awards can be given based on merit - at the discretion of the FAA's associate administrator.

Astronaut wings were first awarded to astronauts Alan Shepard Jr and Virgil Grissom in the early 1960s for their participation in the Mercury Seven programme. (Adopted from BBC)

Update news