NASA chief Mr Daniel Goldin criticised cosmic tourist Mr Dennis Tito today for causing stress at the US space agency.
"The current situation has put an incredible stress on the men and women of NASA," Mr Goldin told members of a US House of Representatives panel on space and aeronautics.
"They are dedicated to safety and Mr Tito does not realise the efforts of thousands of people in the United States and Russia that are working to protect his safety and the safety of everyone else, taking extraordinary means," Mr Goldin said.
Mr Tito, a 60-year-old California multimillionaire, paid Russia $20 million to travel aboard a Russian Soyuzspacecraft to the International Space Station.
NASA and the space agencies of Europe, Japan and Canada objected to Mr Tito's flight, saying he was inadequately trained and might dangerously distract the station crew.
Lofted into space last Saturday, Mr Tito arrived at the station on Monday. He will stay for about six days, then return to Earth aboard an older Soyuzthat is about to be retired.
Mr Goldin also praised aspiring amateur astronaut and director Mr James Cameron for delaying any trip until the time is right.