Science Priorities for Mars Sample Return

VI.K.Contamination Control

It would also be important that we design an effective strategy for the use of witness plates on MSR to help distinguish carbon compounds in the returned samples from contamination introduced during spacecraft operations and/or sample processing on Earth. We know that sample contamination happens in the terrestrial environment, regardless of how carefully the sample is treated. For example, handling of lunar and meteorite samples has introduced contaminants such as xylan (an amide-based compound) found in lubricant for bolts in the lunar processing cabinets (Wright et al., 1991,1992), Phthalates and siloxanes (Steele 2001), or epsilon amino n-caproic acid formed during hydrolyis of nylon bag material used to contain carbonaceous chondrites (Glavin et al., 2006). Terrestrial microbes are known to be able to propagate on Martian meteorites (Steele, 2001; Toporski and Steele, 2007). A key to identifying and avoiding contaminants such as these is to archive any potential contamination sources during the spacecraft and hardware design and construction ­ a process which has heritage from several sample return missions including Apollo, Genesis, Stardust, and Phoenix. However, this step must be planned for in advance.

VI.L.Documented Sample Orientation

The orientation measurements could in principle be determined, through a combination of telemetry and imagery (the same technique is used on MER, where orientation precision is determined to within a few degrees).  Telemetry includes overall rover orientation from the IMU and joint angles from the arm.  Imagery includes the documentation images of the science target as well as operational imagery showing the arm in place and the position of the instruments (and corer) as the samples are obtained.  This information is already required for sample documentation and safety monitoring of arm operations, therefore determining the orientation should not add any additional requirements on the system. Finally, we need to know the rotational orientation of the core sample. This may be available for indurated samples by comparing images of the surface with MI images taken before drilling.  Although not all samples will preserve the top after drilling, enough may do so to be sufficient to meet the science goals of the mission. Of course alternative methods for marking the rotational orientation might be superior and should be sought.

VI.M.Program Context, and Planning for the First MSR

The MEP lays out a logical progression of missions that build upon the past and lead to the future. In that sense, the recent, current, and planned missions have already and would continue to contribute to a superior first MSR mission (see Section IV.A). We thus believe that a first MSR mission in the next decade would be far better scientifically than any MSR mission that might have been implemented earlier. This validates NASA’s foresight in establishing the MEP many years ago and its belief that Mars holds a special place in planetary exploration. The ND-SAG anticipates that such a productive return-on-investment would continue after the first MSR mission: there is no doubt that the analyses of the returned samples would significantly alter our understanding of Mars and greatly enhance our interpretation of current and future remote sensing data. This conclusion has been “validated” by the Apollo program in which the results from the Apollo-11 returned samples directly and rapidly impacted subsequent Apollo missions and led to the establishment of many of the science objectives for the current spate of lunar robotic missions.

For the first MSR mission, we need to balance the need to keep the mission from becoming overly complex in an engineering sense, while at the same time retaining the essential attributes that contribute to the scientific value. As input to these trades, the ND-SAG team has summarized in Table 11 the various attributes discussed in this report that would improve the science value of MSR, along with a preliminary assessment of the impact of these attributes on mission engineering. Since there are legitimate differences of opinion within the science community on the priority of these attributes, and the planning for a possible MSR is still in its early stages, rather than try to reach consensus on a single set of priorities, three example priority positions are shown in the columns on the right. This illustrates both the commonalities and the differences in how different sectors of the science community value these attributes.

The question naturally arises as to what follows MSR in the MEP. First, we do not consider MSR to be a single-mission event. The great diversity of Mars makes it probable that not all MSR objectives could be achieved at one sample site. Landing site engineering constraints for the first MSR mission prohibit going to certain terrains, such as polar regions and rough topography (e.g., the gullies of “uncertain special regions” or “special regions”). The data gleaned from the first MSR mission would likely stimulate the desire to conduct additional MSR missions.

There is an aspect of a “second MSR mission” that merits our attention, to wit: the MEP may decide, for reasons of program risk reduction, to advocate replicating the riskier elements of the mission, e.g. landing and ascent systems. If such appears prudent and affordable, we could today make a convincing case that returning samples from two substantially different sites on Mars would be eminently prudent. The living example of this risk-reduction philosophy is the MER mission, for which the NASA administrator chose to send two landers.

Table 10 Science priority of attributes of the first MSR.

Notes on Table 11. KEY: H - High priority, M - Medium priority, L - Lower priority **Revisiting a previously characterized site might require only 2 instruments.
The ND-SAG emphasizes that, however important, the first MSR would not be the finale of a science-driven MEP. We know now that other mission types need to be considered for opportunities immediately following the first MSR. There are already high priority proposed and studied mission concepts that are relatively independent of MSR results (e.g., network missions, orbital science) and that could be implemented immediately after the first MSR. Indeed, it is virtually inevitable that the results of the first MSR would lead to new proposals for non-MSR orbital and surface science missions.

The MSR mission would have a significant relationship to eventual human exploration. As shown both in the MEPAG Goals and in this study, information gleaned from the returned samples would be directly related both to the health and well being of astronauts on Mars and to reliable operations on the Martian surface. There is an associated indirect yet important aspect: the detailed knowledge obtained from the returned sample would inevitably inform what science astronauts would do at Mars and how they would do it. For these reasons an MSR mission probably would be required at the landing site eventually selected for human exploration (which may or may not be a prior MSR site). Again we refer to the Apollo missions in which post Apollo-11 mission science was altered in response to findings from returned samples. Lastly, there would be the “proof-of-concept” element of MSR in which the demonstration of the roundtrip to Mars with successful Earth-return bolsters public understanding and conviction that it is indeed feasible for humans to eventually make that sojourn.