It was one of those moments, whether epic triumph or epic tragedy, that burns in your mind forever. Where were you when JFK was shot? When Armstrong stepped foot on the moon? When Challenger was lost? On September 11? When Baghdad fell?

On February 1, 2003, America and the world lost seven brave souls who cheerfully gave their all and knowingly risked their lives so that humankind could benefit from the knowledge to be gained by 16 days of scientific research in space. When mission STS-107 ended in tragedy over the southwestern United States, the anguish of our loss was felt around the world.

How we respond to national tragedy is the measure of our character. The effect of the attacks of Dec. 7, 1941, and Sept. 11, 2001, was that our enemies had awakened a sleeping giant. We can be equally proud that our response to the loss of Columbia has not been to retreat from our exploration of space, but rather to strengthen our resolve.

As President Bush said in eulogizing the crew of Columbia, our desire to reach out into space and explore the unknown is a desire that is written on the human heart. The exploration of space is a divine quest for answers to the great questions of existence. Are we alone in the universe? Are there now or have there ever been other forms of life? If we can answer these questions, what, then, is the meaning of life?

Of course exploration brings more than new knowledge and the uplifting of the human spirit. As with the conquest of the seas and the exploration of the American West, the exploration of space demands and drives the creation of new technology and opens up vast new economic frontiers. The gift of space exploration to human kind - scientifically, technologically, economically and spiritually - is so great that the families of the Columbia astronauts, even in the depth of their personal grief, unanimously and without hesitation proclaimed that yes, the journey must go on!

Our nation has responded with character and resolve. NASA has searched its soul, laid bare its defects of character, and moved forward purposefully so the journey may continue.

Most importantly the Administration, with the bi-partisan support of key leaders in Congress, has taken a fearless inventory of where we are and where we must go in space. As a result, a new mandate for NASA - the most powerful, direct and purposeful since John F. Kennedy's cold war mandate to land men on the moon - has been established.

Back to the Moon, and On to Mars! Extend human presence throughout our solar system and, one day, beyond! This is a vision worthy of the sacrifices of Apollo 1, Challenger and Columbia: to break free of low earth orbit, where we've been stuck since Apollo 17, and return to the challenge of boldly going where no one has gone before.

To be sure, there will be critics. Some are already saying that the current NASA funding of 86 one-hundredths of one cent from each tax dollar is enough, and that our future is not worth increasing NASA's budget to 87 one-hundredths of one cent as the President has proposed. (That's right. NASA gets less than one cent from each tax dollar, and the new space exploration program will remain at that low level.)

The critics need to be heard, but not necessarily heeded. There have always been those who lacked courage, commitment or vision. They proclaimed that man would never fly. We did. They said that the accomplishments of the 19th century would never be eclipsed in the 20th century. They were. They said we'd never fly across oceans or land a human on the Moon. We have.

As Teddy Roosevelt said, "It is not the critic who counts . . . the credit belongs to the man who is actually in the arena." The jackals may bark, but the caravan passes on.

It is not a question of whether humans will move out into the final frontier of space. It is only a question of whom and when. Whether the United States will maintain its space leadership, or whether we will let other nations take the lead and reap the rewards.

On the anniversary of the loss of Columbia, we should be mindful that those who have paid for this great cause with their lives were aware of the risks, accepted them, and journeyed into space for all of us. The loss of these heroes was not our first, nor shall it be the last. Their sacrifice has not been in vain. The great journey of human kind from the darkness of our caves to our eventual enlightenment must continue.

Hail Columbia! Godspeed, the journey continues.

Elliot G. Pulham is president and chief executive officer of the Space Foundation, a leading non-profit space and education advocacy organization (www.spacefoundation.org) and a member of the board of the Columbia Shuttle Memorial Trust (www.columbia7trust.org), which works to raise funds for the families of the Columbia astronauts.