The rules of the game are that participants must land a rover on the lunar surface, run it for at least 500 metres and send video images and data back to earth, he told reporters on the sidelines of the 58th International Astronautical Congress.

"The Google Lunar X Prize calls on entrepreneurs, engineers and visionaries from around the world to return us to the lunar surface and explore this environment for the benefit of all humanity," he said. The announcement, made about 10 days back, has received over 150 expressions of interest and seven persons have signed up by making an initial payment of $1,000.

 "We are confident that teams from around the world will help develop new robotic and virtual-presence technology, which will dramatically reduce the cost of space exploration," said Alexander.

The total prize money for the competition is US$30 million, of which US$ 20 million would go to the winner while the runners up will get US$ five million. Another US$ five million dollars will be given as performance bonuses to the participants.

An international panel of experts will judge the entries, which have to land on moon before the end of 2014, Alexander said.

The registration will cost US$ 10,000 this year and those signing up in 2008 will have to pay US$ 25,000 while others have to cough up US$ 50,000 as the entry fee.

The participants are free to use any launch vehicle to put the project in orbit but have to ensure that the same facility is made available to other participants to maintain equal opportunity.

To keep up the excitement, the US$ 20-million Grand Prize will be awarded to missions that meet the criteria before December 31, 2012.  Thereafter, the amount will drop to US $15 million until December 31, 2014.