Space exploration embodies some of the best of human striving, wedding ingenuity and inspiration into a scientific pursuit that fires imaginations and stirs space's shocking but subtle mystery in our hearts.

Only a century ago on a beach near Kittyhawk, North Carolina, did human beings first achieve sustained flight.

One hundred years later, we have walked on the moon, propelled cameras to the furthest reaches of our galaxy, and begun construction of an international space station.

You know in your bones, too, that humanity is just getting started.

Saturday, we were reminded that our reaching beyond for something bigger than ourselves can sometimes fall short.

In a moment that resonated with the uncertainty of Apollo 13 and the sorrow of the Space Shuttle Challenger, America awoke to a loss that is hard to define and impossible to avoid.

How many of us knew Columbia was returning to Earth that fateful morning?

How many of us, if we had, would have even thought to utter a silent prayer for a safe homecoming?

President Kennedy's challenge to put a man on the moon fired this nation with a singularity of purpose.

But with regular shuttle flights and satellite television, a nation can be forgiven for sometimes forgetting the befuddling marvel of space travel.

Seven explorers faced that marvel with courage Saturday.

Their sacrifice saddens our hearts, but turns our thoughts again to the heavens and the stars above.

The reality of their loss is weighty, but our capacity for wonder and thirst for knowledge live on.

Godspeed, Columbia.