It was a day of remembrance for Nasa, as it marked the 30th anniversary of the Space Shuttle Challenger explosion.

"I'd like to just take a moment of silence and recognize the sacrifice of all those crew members and how their spirit and their legacy lives on and their achievement in space." said Scott Kelly, astronaut on the International Space Station.

From silence in space, to music and remembrances at the Kennedy Space Center in Cape Canaveral, Nasa honored the six astronauts and one teacher killed on Jan 28, 1986, when a booster engine failed just 73 seconds after launch, causing Challenger to explode.

"They've shown us that exploration is not without risk, that we can learn from our mistakes and be better for them in the end." said Bob Cabana, Director of Nasa's John F. Kennedy Space Centre.

Former astronaut Jon McBride's voice broke as he called out the names of those killed.

It was an equally sombre scene at Arlington National Cemetery - as Nasa Administrator Charles Bolden and other agency officials - laid a wreath honoring the crews of space shuttles Challenger as well as Columbia and Apollo 1.