David Brown, Rick Husband, Laurel Blair Salton Clark, Kalpana Chawla, Michael P. Anderson, William C. McCool, Ilan Ramon.

I saw a newspaper ad not long ago, a double-spread of solid black across the bottom third of both pages. On the left, two white dots, fairly close together, marked Earth and Moon. One line of copy on the opposite page read: Mars is eighty yards to your right. With a helpful little arrow.
If you have to ask why we go, you've already been left behind.
By the way, as Charles Johnson reminded us not long ago, there are only two flags on Mars so far:

With a heart of furious fancies
Whereof I am commander;
With a burning spear and a horse of air
To the wilderness I wander.
By a knight of ghosts and shadows
I summoned am to tourney
Ten leagues beyond the wide world's end --
Methinks it is no journey.
-- Tom O'Bedlam