CAPE CANAVERAL, Fla. -- Two U.S. astronauts aboard the International Space Station took time this week to beam back special Memorial Day greetings to American military troops while paying tribute to those who lost their lives in the defense of the nation.

Circling some 240 miles (384 kilometers) above Earth, American flight engineer Susan Helms called Memorial Day "a special day for all Americans."

"As a colonel in the U.S. Air Force, I know first-hand the importance of military service in maintaining our freedom and preserving all those values that we Americans hold dear," the veteran astronaut said. "It's to the credit of the men and women who gave their lives in defense of freedom that we are here today."

Voss, a retired Army colonel, said that he and Helms "see the world without boundaries" during the 16 orbits of Earth each day and that they routinely celebrate holidays and anniversaries.

"However none affects us as deeply as Memorial Day," he said.

"It's an opportunity for all Americans to pause and reflect on those who made the ultimate sacrifice in our nation's service," Voss added. "And we salute the commitment and dedication of those who carry on their legacy, proudly defending our freedom into the 21st century."