Editor's note: Meg Urry is director of the Yale Center for Astronomy & Astrophysics and the chair of the Yale physics department. Her nearly three-decade career of space study includes a 14-year stint at the the Space Telescope Science Institute, the home of the Hubble Space Telescope, where she headed the Space Science Selection Office, sifting through thousands of applications from scientists each year hoping to use the telescope. This piece was written in association with The Op-Ed Project, an organization seeking to expand the range of opinion voices to include more women.

(CNN) - Atlantis, the last space shuttle, returned to Earth on Thursday and will go to its post-retirement gig at the Kennedy Space Center Visitor Complex. After more than 30 years and 135 shuttle flights by literally hundreds of astronauts, NASA has reason to be proud.

But for any terrestrial mourners out there, I have some tissues and another perspective: It's time.

The shuttle is an aging workhorse that should be put to pasture - it's time for a new direction for the space program.

The private sector should take over routine spaceflight while NASA develops new, more technologically current vehicles that can carry human explorers well beyond low Earth orbit.

Just as importantly, NASA should continue its wildly successful program of robotic space science, which has returned an incredible wealth of knowledge for pennies on the human-spaceflight dollar.