What is the primary reason crewed missions to Jupiter are estimated to take six to eight years with current technology?

Answer

The need for a massive deceleration maneuver and resulting fuel mass penalty

A human crew must execute a large deceleration maneuver to enter orbit safely, which requires massive propellant loads, adding significant mass and thus extending the mission time.

What is the primary reason crewed missions to Jupiter are estimated to take six to eight years with current technology?

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