Mission Design

The majority of the engineering work for this study was spent on propulsion, power, and trajectory trade-offs to define how the science payload could be delivered to Chiron within the given constraints, leaving fewer resources for the definition of the science package. Several trajectories for flights between Earth and Chiron, including both direct and gravity-assisted flyby trajectories, were examined. Launch was determined to occur between 2019 and 2025 depending on the propulsion option, with a cruise-phase duration of between 11 and 13 years.

None of the preliminary propulsion solutions could deliver an acceptable mass to Chiron with an 11-year transit time; however, five propulsion options were determined that could deliver acceptable masses into Chiron orbit with a 13-year transit time as the baseline.

Mission Challenges

Because of the inherent complexities in reaching Chiron, the primary challenges discussed in this study relate to propulsion and the trajectories needed to orbit Chiron. Budgetary assumptions made in the mission study cost assessment do not include the mission launch vehicle. Additional challenges are posed by the availability of plutonium-238 for the ASRGs and the long-term reliability of ASRGs.


Regarding the five propulsion options considered for trajectories into Chiron orbit: the all-chemical option did not deliver a viable payload; the two solar-electric and chemical propulsion options delivered useful masses with reduced science payloads; finally, the two radioisotope-electric propulsion (REP) options delivered a viable payload capable of meeting all science requirements. However, the REP system will likely need more than the two ASRGs assumed available for this mission. This study demonstrated the need for continued investments in long-term communication infrastructure and propulsion technologies before such missions could be attempted.


The Neptune-Triton-KBO mission concept study was performed by NASA’s Jet Propulsion Laboratory, and a follow-on full mission study of a Neptune Orbiter with Probe was conducted by the Johns Hopkins University Applied Physics Laboratory.


This RMA study investigated a set of missions to the Neptune system, including some with the potential for continued travel to a Kuiper belt object (KBO). Several mission architectures were considered, ranging from relatively simple flybys to complex orbiters. This study initially examined a robust orbiter with an atmospheric probe each for Neptune and Uranus, to assess and develop an understanding of the feasibility and technological differences between the two targets. Neptune is discussed here; Uranus is discussed in Chapter 7 of this report.

Science Objectives

• Determine temporal variations of Neptune’s atmosphere.

• Characterize the chemistry of Neptune’s atmosphere.

• Develop an understanding of the structure, dynamics, and composition of Neptune’s magnetosphere.

• Develop an understanding of the chemistry, structure, and surface interaction of Triton’s atmosphere.

• Develop an understanding of the interior structure of Triton.

• Determine the age and geologic processes that shape the surface of Triton/KBOs.

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