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The functional requirements related to the landing site for the proposed 2018 joint rover mission are derived from those identified by E2E-iSAG (2011), which are endorsed by the JSWG. The engineering considerations that lead to elevation limitations are described in Appendix 3. The E2E-iSAG reviewed previously considered and new sites against four threshold criteria to establish requirements for elevation and latitude that would enable a reasonable number of candidate sites to be considered for meeting the science objectives of the proposed MSR Campaign. These criteria define priorities for the types of science targets that should be available at the landing location. They include: 1) the presence of subaqueous sediments or hydrothermal sediments (equal 1st priority), or of hydrothermally altered rocks or low-temperature fluid-altered rocks (equal 2nd priority); 2) the presence of outcrops containing aqueous mineral phases (e.g., phyllosilicates, carbonates, sulfates); 3) sites of Noachian/Hesperian age, based on stratigraphic relations and/or crater counts; and 4) the presence of igneous rocks with known stratigraphic relations, of any age, as identified by primary minerals.
E2E-iSAG (2011) identified candidate landing sites satisfying these threshold scientific criteria, primarily for the purpose of framing the engineering requirements for landing capabilities. These sites, referred to as “reference landing sites”, were derived from a review of the ~60 landing sites proposed for the MSL mission (Grant et al. 2011), and of ~25 additional community-proposed landing sites identified for possible future missions (originating through a 2010 Future Landing Sites call). These sites are not intended to be favored over any others that may eventually be proposed. A recommendation for the actual site selection process for the proposed 2018 joint rover mission is proposed in Section 5.5 of this report.
Many of the sites considered for MSL, and/or proposed for possible future missions, overlap in science objectives with the proposed MSR Campaign and have been partially, to nearly completely, characterized by high resolution spatial and spectral mapping (e.g., from MRO, MEX, and Odyssey orbiter missions). The E2E-iSAG team chose sites expected to provide a range of science and engineering characteristics that could be used to help define landing and roving requirements. Sites with substantial existing image coverage were favored because such data enable meaningful engineering studies of the proposed MSR Campaign EDL system requirements.
Table 4. The reference landing site set proposed by E2E-iSAG (2011). Note that a mission that could land at these reference sites would also be able to land at Gale Crater (latitude = 4.6 S; elevation = –4.5 km), the landing site for MSL.
The seven reference landing sites identified by the E2E-iSAG are described in Table 4 and range in latitude from approximately 14˚S to just over 33˚N. Elevations range from –0.6 km to approximately –3.0 km (relative to the MOLA aeroid). Ideally, the functional requirements of the proposed 2018 mission’s landing system would encompass the E2E-iSAG (2011) reference landing sites. Additional limitations in either latitude or elevation accessibility would likely reduce the number of candidate sites that could be considered for the proposed 2018 joint rover mission. For example, setting the baseline landing elevation at –1 km, 10 out of the 60 or so sites considered for MSL (Grant et al., 2011) would need to be ruled out (including the Nili Fossae Trough reference site). Dropping the baseline elevation to –1.5 km would further eliminate another 16 sites from consideration, including one more E2E-iSAG reference site, as well as other sites that were highly rated during the MSL selection campaign. Reducing the maximum altitude landing capability to –2 km would eliminate yet an additional 9 candidate MSL sites from consideration, including 3 more E2E-iSAG reference sites (and would put a 4th, NE Syrtis at –2.1 km, at risk). While a maximum landing site altitude of –1 km has some impact on potential landing sites, a majority of the sites proposed for MSL, and those considered as reference sites by the E2E-iSAG, could remain under consideration. This provides a sound scientific basis for establishing –1 km as the site’s maximum baseline for the proposed 2018 joint rover mission. A –2 km landing baseline would mean that a majority of sites proposed for MSL and considered as reference sites by the E2E team, would be eliminated from consideration. Hence, a –2 km or lower landing elevation is established as the threshold elevation recommendation for the mission.
DRAFT REQUIREMENT (L1; JSWG REF #R1): The project system shall be able to land at altitudes of up to [–1.0] km relative to the MOLA aeroid. Threshold requirement: The project system shall be able to land at altitudes of up to [–2.0] km relative to the MOLA aeroid.