NOORDWIJK, Netherlands -- The head of Europes International Space Station (ISS) program condemned as "irresponsible" the Russian governments plans to send a millionaire U.S. tourist to the orbiting facility and suggested that the other station partners have a right to block the move.

Jorg E. Feustel-Buechl, director of manned spaceflight and microgravity at the European Space Agency (ESA), said Russia had no right to send "amateurs" to the orbital complex until its safety and security are fully assured.

"It is irresponsible to send amateurs to ISS as long as it has not been proven and is completely operational," Feustel-Buechl said. "Imagine that something happens, something like the Challenger accident, when NASA sent a school teacher aboard the shuttle. It dealt a real setback to the space program."

U.S. millionaire Dennis Tito is preparing for an April 30 flight to the station as part of a three-cosmonaut crew that will deliver a fresh Soyuz spacecraft to the complex and return a week later in the Soyuz now docked there.

Tito agreed last year to pay an estimated $20 million to a private company, MirCorp, to fly to Russias Mir space station. After Russian authorities decided to deorbit Mir in March, Amsterdam-based MirCorp lobbied the Russian Aviation and Space Agency (Rosaviacosmos) to have Titos flight re-routed to the International Space Station.

Tito signed a roughly $20 million contract last week with Rosaviacosmos, the Gagarin Cosmonaut Training Center, and Korolev, Russia-based Rocket Space Corporation Energia late last month that guarantees the former NASA engineer a seat on the upcoming Soyuz flight.

Feustel-Buechl said that if Russia proceeds with the Tito mission, it will be in violation of an intergovernmental agreement signed by Russia and the other space station partners -- the United States, Europe, Japan and Canada.

Tito and some U.S. and Russian officials, however, question whether Europe or any partner has a right to intercede in the matter. Tito told SPACE.com in a Jan. 31 telephone interview from a Moscow hospital where he was recovering from a slight bout with pneumonia that his contract is not contingent upon NASAs approval.

"The only contingency in that agreement is the formal approval of the [Russian] State Interdepartmental Commission for myself to be on the crew, and that pretty much is a formality that in part involves making the final medical check," he said.

An official with the Gagarin Cosmonaut Training Center in Moscow agreed that NASA and the other partners have little say in the matter. "We dont need NASAs permission to select the visiting crew, but we still notify them," said the Russian official, who asked not to be named.

NASA officials also challenged part of Feustel-Beuchls interpretation of the intergovernmental agreement.

According to NASA officials interviewed for this article, the International Space Station Intergovernment Agreement does not specifically address civilian or commercial visitors. However, they said the agreement does obligate all partners to operate the space station "in a manner that is safe, efficient and effective," NASA officials said. Memoranda of understanding between NASA and its ISS partners govern decisions related to crew matters.

Those memoranda provide that crew selection must be the subject of consensus among the space station partners in the interest of safety and the limited crew-flight opportunities.

For its part, Europe will not approve the Tito trip, Feustel-Buechl said: "This is clear nyet on my side."

NASAs official opinion on Titos flight plans is less clear. Tommy Holloway, NASA space station project manager, has made discouraging remarks on several occasions about the Tito flight, but publicly admits there may be little NASA can do to prevent his flight beyond pressuring Russia to reconsider.

"The Russians have the key to their spaceship...so from a physical point of view I dont have any way of keeping the Russians from launching a rocket with somebody else in it," Holloway told reporters during a Jan. 11 press conference in Houston. "On the other hand, we do have a great deal of interaction and program management interface with the Russians and I expect that we would be able to influence decisions they make along the way," he said.

Officials at NASA Headquarters in Washington declined to say whether or not Tito will be allowed to visit the International Space Station.

Asked if NASA has the ability to veto or otherwise block Russias decision to take Tito to the station, NASA spokeswoman Kirsten Larson said that the matter had yet to be discussed between NASA and Russian station officials.

"The decision about whether Tito flies will ultimately be made by consensus between the U.S. and Russia, with input from the international partners," Larson told Space News. "Russia and the U.S. continue to discuss the issue until we reach a mutually agreeable consensus."

She said NASA space station officials plan to discuss the Tito issue Feb. 12 during a high-level meeting with their Russian counterparts at NASAs Johnson Space Center, Houston.

Feustel-Buechl insisted all the international partners are entitled to a say in whether Tito is allowed to visit the station.

Larson said NASA realizes that decisions about commercial activities and the flight of civilians aboard station are important to all of the partners. NASA will report to the international partners following the Feb. 12 meeting and seek their input, Larson said.

Space News correspondent Simon Sardzhyan contributed to this article from Moscow. Todd Halvorson, SPACE.coms Cape Canaveral bureau chief contributed from Florida.