WASHINGTON - To soar far away from Earth and even on to Mars, NASA has dreamed up the world's most powerful rocket, a behemoth that borrows from the workhorse liquid-fuel rockets that sent Apollo missions into space four decades ago.

But with a price tag that some estimate at $35 billion, it may not fly with Congress.

NASA Administrator Charles Bolden and several members of Congress on Wednesday unveiled the Obama administration's much-delayed general plans for its rocket design, called the Space Launch System. The multibillion-dollar program would carry astronauts in a capsule on top, and the first mission would be 10 years off if all goes as planned. Unmanned test launches are expected from Cape Canaveral, Florida, in six years.