PSJC #2 Jan 16 2008

MARCO POLO Mission and Proposed Work

Humberto Campins

Mission Summary: MARCO POLO is a near-Earth object sample return mission to a primitive asteroid whose objective is to return samples that are otherwise not available among known meteorites. Primitive bodies are leftover building blocks from the earliest era of Solar System formation and may have contributed water and organics to Earth, thereby providing a foundation for life. Primitive meteorites are among the least frequently sampled by falling to Earth and all samples received are biased by their ability to survive atmospheric passage. Direct investigation of both the fresh regolith and fresh lithospheric fragments is also impossible by any means other than sample return. MARCO POLO will conduct a broad in situ analysis of the target and the geologic context for the samples prior to their acquisition. Sample return enables the power of the Earth's laboratories to identify major chronological events in solar system history, to search for pre-solar material yet unknown in meteorite samples, and to characterize in depth the nature of organic compounds that may be present. MARCO POLO thus directly addresses the top level NASA strategic planning goal to: Advance scientific knowledge of the origin and history of the solar system, the potential for life elsewhere, and the hazards and resources present as humans explore space (NASA Science Plan 2007, page 5).

Proposed Work by US Investigators During Assessment Phase: The MARCO POLO proposal presents four mission options, whose scientific return and scientific merits are to be assessed relative to the total mission cost. A major component of the proposed work by US Investigators will be to contribute to the full identification and development of the science return for each mission option and to more fully demonstrate the scientific case for the MARCO POLO mission relative to NASA's objectives. The four mission options are:

1. Baseline: Mother spacecraft (MSC), separate surface lander (SIFNOS), capability for multiple sampling and full recording of the sample acquisition, a re-entry capsule, and scientific payloads for in situ characterization.
2. Add a subsurface drilling capability to the SIFNOS lander.
3. Perform the landing, sampling, and drilling by a single spacecraft (no separate lander).
4. Touch & go sampling by the MSC only, with no lander.

In addition to the scientific assessment of the mission options, US Investigators will participate in the evaluation and groundbased reconnaissance of potential mission targets. Current targeting options for the MARCO POLO mission include the following near-Earth objects:

• (4015) Wilson-Harrington, a dormant comet, that can provide insights into the unknown link between asteroids and comets;
• Primitive D-type asteroids such as 2002 AT₄ and 2001 SG₂₈₆;
• The primitive C-type double asteroid 1996 FG₃, which in addition to early solar system history, provides insight into the binary formation process.

Particularly important to the success of the MARCO POLO mission is the placement of the target body and sample within the broad context of the solar system. While groundbased measurements can access numerous small solar system bodies, only very few bodies can be directly sampled by missions. Thus the context of the sampled body, within the broader solar system population, must be understood as part of the scientific assessment for the MARCO POLO mission. The team of 12 US investigators named within the ESA proposal, and their proposed contributions during the assessment phase, are summarized in Table I [not included --Ed.]. The members of the US investigator team have the background and the capability to bring specific strengths and contributions to the MARCO POLO mission during the assessment phase. These strengths and contributions, include:

• Evaluation of the science return of the mission options and the mission targets, as described above, to make a final recommendation on overall mission design. The resulting science return can be affected to ensure alignment with NASA objectives.
• Capabilities and experience to: perform groundbased reconnaissance of the proposed targets (as well as potential new ones), to evaluate and model existing data on targets, and to use the derived information on target characteristics as critical input for the final mission design. These physical observations have the capability to characterize the radius, albedo, thermal inertia, shape and surface composition of the potential targets based on visible and infrared observations.
• Carry out laboratory analysis of primitive meteorites for a wide variety of grain sizes to try to estimate the mineralogy surface characteristics (and possible organic chemistry) of the potential targets, where this understanding will impact mission design and target selection. These analyses will include spectroscopic, x-ray diffraction, and x-ray fluorescence measurements.
• Apply knowledge from current photometric models, and develop new ones, specific to the low albedo surfaces to be encountered for MARCO POLO mission targets. These model results will be used to set sensitivity requirements for remote sensing instrumentation and will affect mission planning (e.g. exposure times) so as to achieve the target and sample characterizations specified within mission options.
• Evaluation of the reconnaissance phase imaging requirements to achieve a global characterization of the target asteroid, particularly with regard to its cratering distribution and inference of its likely collisional history.
• Expertise in the mechanical properties of asteroid regoliths, the modeling, and the design of experiments for various possible surface structures, and the effects of those properties on the surface interactions; including anchoring, drilling and sample collection.
• Expertise in planning and implementing procedures for the collection, return, and recovery of samples. Additional expertise to prepare a more extensive description and plan for sample handling and curation.
• Evaluation of the mission design requirements to achieve the acquisition of samples most likely to supply the detailed solar system chronology central to the overall mission science objectives.

Short List of References Documenting Expertise to be Contributed by US Investigators.