JOHNSON SPACE CENTER, Texas (CNN) -- The latest group of men and women who hope to become U.S. astronauts began two years of intensive training Monday at NASA's Johnson Space Center.

Among them is Barbara Morgan, who served as backup to Christa McAuliffe, the teacher who was to go into space but was killed in the 1986 Challenger explosion.

The 31 new arrivals include 25 Americans and six candidates from other nations, including Canada, Brazil, Germany, Italy and France.

Of the group, eight will undergo training to be space shuttle pilots. The other 17 will receive specialized training to become "mission specialists" in NASA parlance, eventually serving as shuttle crew members.

The candidates met Monday with the current astronaut corps after a ceremony led by JSC director George Abbey.

Following their training, the rookies will be assigned primarily to flights concerned with NASA's next major priority, assembling and staffing the international space station.

This new class brings the total number of astronauts to 175.