strated) mobility systems such as balloons (a technology that also has some applications on other atmospheric bodies). The committee also notes that most of the technologies required to address the decadal survey objectives have been demonstrated on prior missions. For instance, Soviet-era Venus missions not only successfully reached the surface, but also operated there for up to an hour, proving that surface missions are possible.

In the decadal survey, the VISE mission concept was discussed in terms of what it could contribute to a future flagship-class Venus sample return mission. While such an approach has significant merit, the committee warns that placing a technology demonstration for a future mission in the critical path of VISE mission success is unwise, particularly given the technical challenges for Venus sample return. Nonetheless, future Venus exploration beyond a VISE mission would require major technology development and demonstration, so that the inclusion of demonstration technologies in a VISE mission on a non-interference, non-critical-path basis is justified.

Mission-Specific Recommendations

The committee concluded that a VISE mission that addresses a significant number of the decadal survey objectives is tenable. Such a mission would make use of technologies that have been successfully demonstrated in prior missions to the Venus surface and near-surface environment. The committee also concluded that several of the VEXAG goals should be included with the goals established in the decadal survey, particularly the VEXAG goals concerning understanding the thermal balance of the atmosphere and gathering global mineralogic data.

The challenges associated with landing in a region not previously sampled, collection of a sample, and lofting to a more clement altitude are the source of greatest technology and cost risk. Consequently, the New Frontiers announcement of opportunity should not preclude a mission that addresses the major goals for chemical sampling of the mid- to lower atmosphere on Venus and characterizing atmospheric dynamics, but lacks a surface sampling component. On the other hand, a mission that only addressed surface sampling would not be acceptable.

The science goals for this mission, which are not in priority order, should be to:

  • Understand the physics and chemistry of the atmosphere of Venus through measurement of its composition, especially the abundances of sulfur, trace gases, light-stable isotopes, and noble-gas isotopes;

  • Constrain the coupling of thermochemical, photochemical, and dynamical processes in the atmosphere of Venus and between the surface and atmosphere to understand radiative balance, climate, dynamics, and chemical cycles;

  • Understand the physics and chemistry of the crust of Venus, for example, through analysis of near-infrared descent images from below the clouds to the surface and through measurements of elemental abundances and mineralogy from a surface sample;

  • Understand the properties of the atmosphere of Venus down to the surface through meteorological measurements and improve understanding of zonal cloud-level winds on Venus through temporal measurements over several Earth days;

  • Understand the weathering environment of the crust of Venus in the context of the dynamics of the atmosphere and the composition and texture of surface materials; and

  • Map the mineralogy and chemical composition of the surface of Venus on the planetary scale for evidence of past hydrologic cycles, oceans, and life and constraints on the evolution of the atmosphere of Venus.

COMET SURFACE SAMPLE RETURN

Scientific community interest in a Comet Surface Sample Return (CSSR) mission has been very high for many years. The advantages of such a mission have been stated in many documents including the decadal survey. Flyby missions to comets are fairly simple, and the Deep Space-1, Stardust, and Deep Impact missions have produced remarkable data. Rendezvous missions such as the ESA’s Rosetta mission (Figure 2.3) are more challenging, and a sample return mission can take twice as long as a rendezvous mission, thereby increasing cost and risk. The decadal survey concluded that bringing back a warm (i.e., non-cryogenic) sample was within a New Frontiers mission budget. While cometary science goals make the return of a cryogenic core sample highly desirable, such



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