Read the following excerpt. it is adapted from president ronald reagan's 1986 televised address after the space shuttle, challenger burst into flames upon takeoff. the explosion claimed the lives of all seven astronauts on board.
today is a day for mourning and remembering. nancy and i are pained to the core by the tragedy of the shuttle challenger. we know we share this pain with all of the people of our country. this is truly a national loss.
we've grown used to wonders in this century. it's hard to dazzle us. but for twenty-five years the united states space program has been doing just that. we've grown used to the idea of space, and perhaps we forget that we've only just begun. we're still pioneers. they, the members of the challenger crew, were pioneers.
and i want to say something to the school children of america who were watching the live coverage of the shuttle's takeoff. i know it is hard to understand, but sometimes painful things like this happen. it's all part of the process of exploration and discovery. it's all part of taking a chance and expanding man's horizons. the future doesn't belong to the fainthearted; it belongs to the brave. the challenger crew was pulling us into the future, and we'll continue to follow them. .

based on the excerpt, what is the purpose of ronald reagan's speech?