NASA will wait two years longer than planned and spend another $40 million (euro28 million) to launch a half-billion-dollar probe to Mars because of an unspecified conflict of interest in the purchasing process, officials said.

The Mars Scout program had scheduled a 2011 launch of the $475 million (euro330 million) Mars atmospheric probe and was going to choose proposals for the mission from two research firms — one in Colorado and the other in Texas.

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. The agency created an entirely new panel, and that caused a delay in awarding the contract, Mars Exploration Program Director Doug McCuistion said Friday.

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 since 1994 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.

NASA officials would not say if it were a personal or organization conflict, which experts say makes a big difference in what happens next.

The conflict issue was not created by NASA, but by one of the firms, McCuistion said.

Steven Schooner, co-director of the government procurement law program at the George Washington University Law School, said the way NASA was handling the conflict and procurement process for the probe was unusual. The agency's secrecy about who is involved makes no sense because "it's eventually going to come out," he said.

Also, he said, "How are the firms competing to know whether they're going to get a fair shake going forward?"

The two teams involved are the University of Colorado in Boulder and the Southwest Research Institute in San Antonio, Texas.

Bruce Jakosky, the head of the Colorado team, said he knows of no conflict on his team.

"I'm incredibly disappointed," Jakosky said Friday. "We think we've got an outstanding mission and we're ready to go."

Craig Witherow, spokesman for the Southwest Research Institute, said by e-mail that he could not comment on the delay or questions about a conflict.

NASA officials said the conflict did not involve S. Alan Stern, the agency's associate administrator for science. Stern was identified in a January NASA news release as the project manager of the Southwest proposal; less than a month later, he was hired to be the space agency's science chief.

Last year NASA amended its procurement process to prohibit Science Applications International Corporation of San Diego from having a role in the probe proposals because the firm was helping the space agency evaluate them.

An SAIC spokesman said no one was immediately available to comment Friday