HOUSTON (AP) -- The NASA turbojet notoriously known as the "vomit comet" for its use in training astronauts for weightlessness made its final flight Friday. Few among the two dozen seasoned passengers aboard got sick.

"It's inevitable," test director John Yaniac said.

NASA's "Weightless Wonder" KC-135, a four-engine turbojet, was more commonly used by researchers to conduct experiments in a zero-gravity environment.

Yaniac proudly told those who attended a post-flight briefing that over the years, the plane's crew had cleaned up at least 285 gallons of vomit.

"They are there to do the research in the microgravity environment so if it means cleaning up a little bit of vomit then so be it, we do it," Yaniac said of researchers who conduct experiments as the plane climbs and dives.

Everyone aboard the plane carries a "sick bag" in their flight suit; plastic bags are available to lock away the odor, said Donn Sickorez, who coordinates college students who conduct experiments aboard the plane.

"It's just not a big deal," said Sickorez, who was ill his first time up. "The point is to enjoy it and get good scientific data and not to feel bad."

The KC-135's final flight lasted almost three hours and made 50 of the steep climbs and dives it used to achieve between 20 and 30 seconds of weightlessness at a time.

During the flight, researchers evaluated tile repair tools in a zero-gravity environment. Two astronauts assigned to the next shuttle mission, Steve Robinson and Soichi Noguchi, were among about two dozen aboard.

NASA got two KC-135s from the military, which originally used the aircraft for cargo and refueling. The first KC-135 _ used in the movie ''Apollo 13'' staring Tom Hanks _ was retired in 2000 and is on permanent display at Ellington Field, not far from the Johnson Space Center.

The final KC-135 will have its usable parts sold off and be placed in permanent storage in Arizona. It will be replaced by a C-9 aircraft next year.

Yaniac said since the second KC-135's first flight in 1995, more than 2,000 students and 460 college teams have conducted experiments on board.

"We're a laboratory just like any other laboratory at JSC," he said. "We just have to go into the sky to do it."

The aircraft made its final landing at Ellington Field late Friday afternoon, where it was greeted by two Air Force fire engines. With their lights going, the fire trucks escorted the plane down the runway. They pulled ahead as the aircraft approached Hangar 990 and then opened their water hoses, spraying an arch of water over the plane as it completed its final voyage.

One of those aboard held an American flag out the cargo door.

"It's the end of an era," Yaniac added. "It's the closing of one door and the opening of another."

Some traditions won't stop, however. The first person to vomit in the C-9 will probably get "a little plaque -- all in good fun of course," Yaniac said.