NASA will wait two years longer than planned and spend another $40 million to launch a half-billion-dollar probe to Mars because of an unspecified conflict of interest in the purchasing process, officials said Friday.

The Mars Scout program had scheduled a 2011 launch of the $475 million Mars atmospheric probe and was going to choose proposals for the mission from one of two Colorado research institutions.

But a "serious" conflict of interest in one of the proposals forced NASA to disband the board formed to pick the proposal, officials said, declining to elaborate.

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The agency created an entirely new panel, and that caused a delay in awarding the contract, Mars Exploration Program Director Doug McCuistion said. And since Mars only comes close enough to Earth to launch probes every 26 months, NASA had to postpone the mission from 2011 to 2013, he said.

NASA will have no Mars mission in 2011, the first time in more than a decade that the U.S. space agency will miss an opportunity to explore the Red Planet, McCuistion said. A European 2011 probe earlier had been postponed to 2013 and only Russia is talking about a 2011 mission, he said.

McCuistion initially said the delay would increase the cost "slightly" because it would involve more years and inflation. Pressed by reporters, he said that meant about $40 million, but it could be less.

"This was not a conflict of interest that could be avoided," McCuistion said. He refused to say who it involved or what kind of conflict it was or who was on the board, saying revealing that type of data could "compromise the competition" between the two proposals.