Kathy Sullivan has seen her share of highs and lows.

Sullivan, the first U.S. woman to walk in space, a veteran of three shuttle missions and an enshrined member of the U.S. Astronaut Hall of Fame, took a perilous journey downward this week.

She became the first woman to reach Challenger Deep, the deepest known point on Earth, in the South Pacific.

On Monday, shortly after completing the expedition in their submersible, Sullivan and her fellow diver Victor Vescovo — who was already one of just a handful of people in the world to reach Challenger Deep — coordinated a call with the International Space Station.

"As a hybrid oceanographer and astronaut this was an extraordinary day, a once in a lifetime day," she said in a statement released by EYOS Expeditions, which supported the expedition.