Argo was a 2009 spacecraft mission concept byNASA to theouter planets and beyond.^[1][2][3] The concept included flybys ofJupiter,Saturn,Neptune, and aKuiper belt object.^[1] A focus on Neptune and its largest moonTriton would have helped answer some of the questions generated byVoyager 2's flyby in 1989,^[1] and would have provided clues toice giant formation and evolution.^[2]

TheArgo mission was meant to compete for theNew Frontiers mission 4 (~$650M). One of the reasonsArgo was not formally proposed was the shortage ofplutonium-238 for the requiredradioisotope thermoelectric generator (RTG) for electric power.^[4] The current launch window for this mission had been particularly favorable. It opened in 2015 and lasted through the end of 2019, so future missions would need to be redesigned for the relevant planetary alignments.^[4]

It was noted that although it offered a Neptune mission at the price of New Frontier's budget, it would be flyby only, limiting the amount of time at Neptune and Triton compared to an orbiter.^[5] However, the advantage would be access to a wide variety of Kuiper belt objects by using agravity assist at Neptune, which would allow a wide range of objects to potentially be targeted.^[5] In addition, with a flyby of Jupiter and Saturn, the Planetary Society compared the mission toVoyager 2.^[5]

During its flybys of the giant planets, there would have been potentially well over 100 other moons that could have been studied, and beyond Neptune, the possibility of visiting Kuiper belt objects.

• New Horizons probe, performed a Pluto flyby in 2015
• New Horizons 2

• Future Planetary Exploration -Argo

• Proposed NASA space probes
• Missions to Neptune
• Triton (moon)

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