HOUSTON -- Higher than normal concentrations of carbon dioxide aboard the Russian-built Zarya module on the International Space Station may have made some of space shuttle Discoverys astronauts sick on its latest mission.

Led by Navy Commander Kent Rominger, the U.S., Canadian and Russian crew made the first supply flight to the space station in a 10-day mission ending June 6.

NASA spokesman Ed Campion said the astronauts suffered no long-term effects and a team at Johnson Space Center is investigating the incident.

Symptoms apparently included headaches and nausea, but improved when the astronauts returned to Discovery.

Campion added that carbon dioxide samples were taken upon entry and exit to the module, but none were taken during the work there.

Discoverys carbon dioxide scrubbers and ventilation systems were operating properly throughout the mission, he said.

Campion declined to name the astronauts affected, based on medical confidentiality. Each member of Discoverys crew made at least one trip to the Zarya module.

In addition to Rominger, Discoverys crew included Air Force Lt. Col. Rick Husband, pilot; Ellen Ochoa, flight engineer; Tamara Jernigan and Dan Barry, spacewalkers; Canadian Space Agency astronaut Julie Payette and Russian cosmonaut Valery Tokarev.

The 10-day mission included delivering supplies to the International Space Station and making electrical repairs to Zarya module.