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Launching Science: Science Opportunities Provided by NASA’s Constellation System
Assessment of the Mission Concept for Further Study
This mission is enhanced by the Constellation System. The Ares V with a dual-engine Centaur upper stage would have significant excess capability to allow various Titan exploration options, including reduced travel times and/or elimination of Earth gravity assist. Excess mass capability provided by the Ares V could be used to simplify the spacecraft design and therefore lower cost.
The potential impact on science for the proposed mission is mixed. Although a Titan science mission could have significant impact on science, the science goals of the Titan Explorer as presented to the committee are obsolete, having become outdated following a new understanding of Titan with the results of the Cassini mission and the Cassini Equinox Mission (Cassini’s extended mission). As currently conceived, this mission will require aerocapture, a technology that has not been used before. Also as currently conceived, the mission will require solar-electric propulsion and next-generation ion engines. Furthermore, the proposal did not address the planetary protection issues surrounding taking Advanced Sterling Radioisotopic Generators to Titan’s surface on the airship.43 By studying Cassini’s experience, it will be possible to improve on the science definition, justify the instrument selection, and make a compelling case for advanced technology such as a blimp(s), balloon(s), or other method for moving through Titan’s atmosphere. NASA is currently undertaking studies for a Titan mission that would use an EELV based on science-definition teams established in the wake of the Cassini mission. These efforts would naturally support any potential Ares V-based Titan exploration effort.44
The technical maturity of the Titan Explorer mission concept is relatively high. The instrument package, although scientifically outdated, requires no new technology and has a high TRL rating. This mission would require aerocapture, a technology that has not been used before and is at TRL 3 to 6. The mission would require solar-electric propulsion and next-generation ion engines.
In summary, although the potential scientific impact of a Titan Explorer mission using the Constellation System is potentially high, this particular mission concept was weakened because it did not incorporate recent Cassini scientific results, placing the mission in the “deserving of further study” category. The committee concluded that with an appropriate science discussion the concept would be more highly ranked, and the basic concept of a Titan mission should not be penalized for a poor presentation. NASA can revisit the potential for Ares V Titan missions after the agency has made a decision concerning the next outer-planets flagship mission.
For example, the warm radioisotope generator could melt part of the surface and create its own mini-environment. It is possible, albeit remotely so, that microorganisms brought from Earth on the spacecraft could then flourish in this environment, contaminating it.
J. Leary and the Titan Explorer Team, “Titan Explorer NASA Flagship Mission Study,” Johns Hopkins University Applied Physics Laboratory, Laurel, Md., August 2007; R.D. Lorenz, “A Review of Balloon Concepts for Titan,” Journal of the British Interplanetary Society 61:2-13, 2008; R.D. Lorenz, “Titan Bumblebee: A 1-kg Lander-Launched UAV Concept,” Journal of the British Interplanetary Society 61:118-124, 2008.