The commander of the seven-person mission, Eileen Collins, is the mother of a 4-year-old boy and a 9-year-old girl. She and three other parents are scheduled to be launched into space at 3:51 p.m. EDT Wednesday.
Collins told ABC she's been preparing her daughter for the mission.
"I start with the fact that I believe my job is a very important job to the human race as a whole, that my job could make life better here on Earth and that I really believe in what I am doing," she said.
Collins said her son is still too young to understand her work.
The three other parents to be aboard the shuttle are Jim Kelly, who has four children; Japanese astronaut Soichi Noguchi, with three children; and astronaut Charlie Camarda, who has an 18-year-old daughter.
They all said they have tried to reassure their families.
Camarda told ABC he has explained to his family "the amount of people we have working on this and the good people we have across the country making sure every 't' is crossed every 'i' is dotted."