Sir Richard Branson's bid to take passengers into orbit is dead-end and dangerous technology, Australian astronaut Andy Thomas says.
Sir Richard's Virgin Galactic organisation was celebrating last week after successfully launching a rocket plane into space for the first time.
SpaceShipTwo, VSS Unity, reached an altitude of 82,682 metres after being released by its carrier plane at 13,106m. It reached a top speed of 2.9 times the speed of sound.
Dr Thomas said he supported what Sir Richard was doing because he was "spinning off" the capability to launch satellites.
But he was less enthusiastic about the idea of taking tourists into orbit.
"It's true that he will fly to the edge of space, but he can't stay there. He falls right back down," Dr Thomas told reporters in Adelaide on Monday.
"It's really just a high altitude aeroplane flight and a dangerous one at that.
"As a technology to get humans out into space it's a go nowhere, dead-end technology."
During his time with the NASA space program, Dr Thomas flew into space four times and spent time on both the Mir and International Space Station.
After last week's successful flight, Sir Richard said his group would now press on with its test program.
"Today we have shown that Virgin Galactic really can open space to change the world for good," he said.
