"It's what made space travel a common occurrence," said Still, who traveled 7.8 million miles aboard Columbia as commander of two 1997 shuttle flights.
Today's launch of the Atlantis will be its last, and final missions of NASA's other shuttles -- Discovery and Endeavor -- are planned later this year.
"It's the only reusable space vehicle -- ever -- and it may end up being the only one ever," she said. "We could land it on a runway and just fly it again."
As the shuttle program -- begun in 1981 -- winds to a close, it is important that our nation find a way to continue manned flight, Kilrain said.
"At this point, we don't know where the manned space program for our country is going from here because that hasn't been decided," she said. "But I think it would be a shame -- and a disappointment -- if we didn't find a way to continue our manned program."
NASA has said it is retiring its shuttles to focus on new technologies and rockets that could one day get astronauts to asteroids -- and perhaps to Mars.
However, there are no formal plans in place as to how the program will proceed in the post-shuttle era.
"We will still have representation on the international space station," she said. "But the astronauts and everyone interested in space are waiting to see what will happen next."
Kilrain, who retired from the Astronaut Office in 2002 and from the Navy in 2005, is one of only three women to pilot a shuttle. She hopes future space programs will create new opportunities for future generations, too.
"We need to have a program," she said. "Other countries are certainly going to, and China is ramping up its own program. We're not in a space race like we were in the '60s, but we'll have no say in the matter if we have no program at all."
Kilrain, a motivational speaker, now lives in Virginia with her husband and four children.