Mission type Reconnaissance Power RTG (proposed) | Operator NASA | |
 | ||
Launch date Launch window: 2015 to 2020 Closest approach Neptune: 8-11 years after launch.
KBO: an additional 3-5 years | ||
Argo was a 2009 spacecraft mission concept by NASA to the outer planets and beyond. The concept includes flybys of Jupiter, Saturn, Neptune, and a Kuiper belt object. A focus on Neptune and its largest moon Triton would help answer some of the questions generated by Voyager 2's flyby in 1989, and would provide clues to ice giant formation and evolution.
The Argo mission was meant to compete for the New Frontiers mission 4 (~$650M). One of the reasons Argo was not formally proposed, was the shortage of 238Plutonium for the required radioisotope thermoelectric generator (RTG) for electric power. The current launch window for this mission was particularly favorable. It opened in 2015 and lasts through the end of 2019, so future missions would need to be redesigned for the relevant planetary alignments.