Americans search for answers to shuttle tragedy.

Byline: Martin Merzer, Phil Long and Seth Borenstein

CAPE CANAVERAL _ Few Americans knew the names of the seven astronauts on shuttle Columbia when the aged orbiter left Earth 16 days ago. Now their loss in another shocking space tragedy leaves the nation searching for answers:

How did this happen? When and how will Americans return to space? Should they return to space?

"The cause in which they died will continue," President Bush told the nation Saturday, a nation stunned again by sudden, saddening loss, this time of the entire crew aboard a spaceship that disintegrated over Texas. "Our journey into space will go on."

Initial speculation about the cause of the accident focused on possible damage sustained by the shuttle's left wing during blastoff 16 days earlier.

The astronauts _ a cross section of America and an Israeli pioneer _ never had a chance. Astronauts have no way to escape a shuttle as it glides to a landing without power at 13,000 miles per hour.

The crew included three U.S. military officers and one of the nation's few black astronauts and a woman who immigrated to America from India. Five were married. Between them, the astronauts of shuttle Columbia had 12 children.