Russian cosmonaut Alexander Skvortsov brandished a small toy duck Friday as he and his crewmates prepared to blast off to the International Space Station (ISS) in April.

The tiny toy was picked out by his daughter as an impromptu "weightlessness sensor," said Skvortsov, who will take off from Baikonur on April 2 along with fellow Russian Mikhail Korniyenko and NASA astronaut Tracy Caldwell-Dyson.

"We thought it was light and pretty enough. I think it should bring us luck," said Skvortsov, a uniformed air force colonel, speaking at the Star City training facility outside Moscow.

The astronauts will spend two days in a cramped Soyuz capsule before arriving at the ISS, where they will join US astronaut Timothy Creamer, Soichi Noguchi of Japan and Russian cosmonaut Oleg Kotov.

One of the three Russians will have to sleep on the US side of the space station, since the Russian side has only two beds, officials said.

Skvortsov, 43, and Korniyenko, 49, are both set to make their first space flight after training together.

"The hardest thing in our profession is the waiting. Sasha (Alexander) and I have been waiting 12 years for this flight," said Korniyenko, a former Moscow policeman, who is set to turn 50 in space.

"The most important thing is not to break down, to keep yourself going, to keep training despite all the difficulties. Then you will achieve success," Korniyenko said.

Caldwell-Dyson made her first space flight in 2007. Speaking Russian and English, she said she had "very little time" to train with her Russian colleagues but described it as "rewarding".

"I think the most challenging part we'll face in orbit will be maintaining our team work during the very busy timeline we have," she said.

Earlier Friday the head of Russia's space agency Roskosmos Anatoly Perminov said that a moratorium on space tourism to the ISS would continue "for two or three years," as NASA will remain reliant on the three-seater Soyuz launch.

"There are many people interested. Very many countries have made requests, but now it is physically impossible for us," Perminov said, the Interfax news agency reported.