New Delhi, Nov. 12 -- NASA's Voyager 1 spacecraft is approaching an unprecedented milestone in space exploration, as it prepares to travel one light-day away from Earth - a distance no other human-made object has ever reached.

Launched in 1977, Voyager 1 is expected to reach the milestone on Wednesday (November 18), when it will be more than 16 billion miles (25.9 billion kilometres) from Earth. At that distance, light travelling from Earth would take 24 hours to reach the spacecraft, according to NASA.

Voyager 1 is already the most distant human-made object from Earth and has continued travelling through space for nearly five decades. Reaching the one light-day mark will add another historic achievement to its long-running mission.

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