There is really nothing at all secret about the work - a mistake is being made here

Colleague of Valentin Danilov

Twenty of Mr Danilov's colleagues have written an open letter in protest at his arrest and demanding his release.

The FSB said he had been trying to sell research on the effects of space on satellites to a Chinese firm.

Russian public television said the charges related to a contract concluded two years ago between Mr Danilov's university, a Chinese aerospace institute and a Chinese national import-export firm.

It said both prosecution and defence were trying to find out if the materials included in the contract were a state secret or not.

Mr Danilov is being held in jail in Krasnoyarsk

One of Mr Danilov's colleagues said his work dealt with the effects of solar activity on satellites, which the FSB might see as sensitive because of its possible use in the development of anti-satellite weapons.

"This is Star Wars stuff...But anyone with experience in the field could have put together what he was doing," the man, who did not want to be named, told Reuters news agency.

"There is really nothing at all secret about the work. Virtually all his research has long been in the public domain. A mistake is being made here."

Bail request

Mr Danilov's lawyer, Yelena Yevmenova, also insisted her client had not given away secrets, and said she would press for the case to be dropped.

"Within two weeks I hope to be able to again ask (for bail)... It is even possible that we could see this case dismissed altogether," she said.

Ms Yevmenova said her client was "as well as can be expected for a man in prison".

An FSB spokeswoman in Krasnoyarsk, Stella Alexeyeva, said Mr Danilov's links with the Chinese company had been under investigation since last May.

His trial was expected to begin in September, she said, when he could face a jail term of 12-20 years.