The objective of the Comet Nucleus Sample Return (CNSR) concept study is to produce a documented plan for a mission to return a sub-surface sample from an inactive comet. The spacecraft concept is a carrier/lander combination with automated rendezvous and landing capabilities and a robotic arm for docking and sample transfer, based on the Orbital Express architecture. The role of the Navigation and Mission Design Branch (NMDB) in this study includes evaluation of potential targets with respect to launch vehicle and spacecraft propulsion requirements, mission duration, length of the return leg, and Earth re-entry conditions.

In 2008, the NMDB provided the project team with a trajectory analysis report, detailing the results of trajectory analysis and design performed during FY07, including the selection of comet Wilson-Harrington from a list of 97 potential targets as the primary science target, development of an end-to-end, chemically-fueled, multiple gravity-assist trajectory, and a preliminary launch window analysis. Results of a rudimentary low-thrust analysis were also presented, but detailed low-thrust analysis was performed by Glenn Research Center (GRC) using the Mission Analysis for Low-Thrust Optimization (MALTO) trajectory analysis software developed by the Jet Propulsion Laboratory. The GRC-developed trajectory was selected as the baseline since it delivered better performance in terms of shorter mission duration and higher returned payload. The NMDB work turned to refining the chemical trajectory and evaluating the possibility of sending the carrier spacecraft to rendezvous with another target after releasing the sample return vehicle at Earth. The NMDB also supported three CNSR-related studies in the Integrated Design Center (IDC). The first study was conducted in mid-April 2008 in the Instrument Design Laboratory (IDL) to develop the harpoon sampling system conceptual design. The second study was conducted in late-April 2008 to develop the CNSR lander conceptual design. The third study was conducted in mid-May 2008 to develop the CNSR carrier spacecraft conceptual design.

Evolving science goals are refocusing this effort on the concept of a multiple asteroid rendezvous/sample return mission. The NMDB began developing preliminary trajectories for this concept in May 2008 and the work is ongoing.