Mars Exploration Rover Landing Site Memorandum

September 27, 2000

From: M. Golombek and Tim Parker

Re: Preliminary Definition of Mars Exploration Rover Landing Site Engineering Requirements and Initial Identification of Potential Landing Sites

This memo describes the preliminary definition of engineering requirements on Mars Exploration Rover (MER) landing sites, maps these requirements into remote sensing criteria, and uses these criteria to identify potential landing sites. To first order, many of the engineering requirements are the same as for the Mars Pathfinder mission [Golombek et al., 1997], because the landing system is the same. The preliminary engineering requirements stated below have been adopted by the MER Project.

Analysis of the Entry, Descent and Landing (EDL) system and atmospheric profiles indicates that the MER spacecraft are capable at landing below -1.3 km MOLA defined elevation, with respect to the MOLA defined geoid [Smith and Zuber, 1998; Smith et al, 1999]. This requirement stems mostly from the need for an adequate atmospheric density column for the parachute to bring the spacecraft to the correct terminal velocity. Because the landing system has no means to reduce horizontal velocity, low-altitude winds and wind shear together are major concerns and must be below about 20 m/s.

Preliminary analyses of power generation/usage and thermal cycling of the rovers restricts the landing sites to be near the subsolar latitude at arrival to last the required 90 sols. This translates to 15S to 5N for MER-A and 5S to 15N for MER-B, which arrives at Mars about 52 sols after MER-A. Operations considerations require the two landing sites to be separated by a minimum of 37° (solid angle) on the surface.

Surface slopes are an obvious concern for the landing system. Large slopes can spoof the radar altimeter and/or cause premature or late firing of the solid rockets and airbag inflation. Small slopes over large distances can lead to significant additional horizontal velocity and prolonged bouncing by the lander within the inflated airbags. Reconstruction of Mars Pathfinder landing indicates the lander traversed a horizontal distance of about 2 km in 10-20 large bounces across the surface [Golombek et al., 1999a], even though it landed at 3 am local time when winds should have been calm. Slopes can also affect the stability of the lander, rover deployment and trafficability, and power generation. As a result, surface slopes should generally be less than 15°. One relation between measured radar RMS slopes and slope suggests surfaces with < 6° RMS slopes have about 5% of their surfaces with slopes >15° [e.g., Golombek et al, 1997]. Images must appear hazard free (i.e., relatively smooth and flat without obvious hazards, such as fresh craters).

The airbags of the Mars Pathfinder landing system were qualified to protect the lander from damage when landing on 0.5 m high rocks in any orientation [Golombek et al., 1997]. As for Pathfinder, this required a landing site with less than 1% of the surface covered by rocks greater than 0.5 m high. Model rock size-frequency distributions based on Viking, Mars Pathfinder and rocky locations on the Earth [Golombek and Rapp, 1997; Golombek et al., 1999b], generally suggest this requirement can be satisfied at locations with total rock coverage of < 20% as derived from thermal infrared measurements [Christensen, 1986b].

The surface must be radar reflective for the descent radar altimeter to work properly, so radar reflectivity must be greater than 0.05. The surface must be load bearing for the rover and too much dust would coat rocks and could reduce surface lifetime by covering the solar panels. Extremely high albedo and low thermal inertia regions should therefore be avoided [Christensen and Moore, 1992]. Areas with fine component thermal inertia of less than 3-4 x 10 -3 cal cm -2 s -1/2 K-1 or cgs units (equivalent to 125-165 J m -2 s -1/2 k-1 or SI units) should therefore be avoided [Christensen, 1982, 1986a; Mellon et al, 2000].

We plotted the MOLA elevations within the 30° latitude band from 15N to 15S. Because the southern hemisphere of Mars is dominantly heavily cratered highlands, little area is actually below -1.3 km in elevation for MER-A (between 5N and 15S). The largest area below this elevation is in southern Elysium and Amazonis Planitiae. Unfortunately, most of this area (150W to 200W) is dominated by extremely low thermal inertia, with fine component thermal inertias below 3 x 10-3 cgs units and so is excluded. For the latitude band of MER-B (5S to 15N), more area is above -1.3 km elevation. Nevertheless, most of the area between 135W and 190W is excluded on thermal inertia grounds. Areas available to seek landing sites are thus reduced to southern Isidis and Elysium Planitiae in the eastern hemisphere and western Arabia Terra, Terra Meridiani, Xanthe Terra, Chryse Planitia, and the bottom of Valles Marineris in the western hemisphere.

Because of the arrival geometry and the prograde entry into the atmosphere, landing ellipse size and orientation change significantly with latitude and time of arrival. Analysis of the expected flight path angle at atmospheric entry and dispersions produced by the atmosphere yield landing ellipses of 80 km by 30 km for MER-A at 15S up to 360 km by 30 km for MER-B at 15N. In addition, the orientation of the ellipse rotates from 80° at 15S for MER-A to 109° at 15N for MER-B for the opening of the launch window (for MER-A the ellipse orientations rotate about 3° counterclockwise by the end of the launch period; for MER-B the ellipse orientations rotate about 14° counterclockwise by the end of the launch period). Using the preliminary landing site dispersion data from P. Knocke and P. Desai, we used the following ellipses for each 2.5° in latitude for each lander, applicable for the opening of the launch periods. In reality, the ellipse size probably varies smoothly with latitude, although the ellipses used are within about 20 km of the correct length and within a degree of the correct orientation (sufficient for this preliminary identification). Note all ellipse widths are 30 km.

Table 1.
Landing Site Ellipse Data for MER-A and MER-B
Latitude Ellipse Length Ellipse Orientation
(°) (major axis, km) (orientation of
major axis, °)
MER-A
15S-12.5S   86 81
12.5S-10S   97 81
10S-7.5S 109 83
7.5S-5S 120 84
5S-2.5S 132 86
2.5S-0 140 87
0-2.5N 155 87
2.5N-5N 166 88
MER-B
5S-2.5S 132 103
2.5S-0 140 104
0-2.5N 155 104
2.5N-5N 166 105
5N-7.5N 195 106
7.5N-10N 240 107
10N-12.5N 286 107
12.5N-15N 330 109

Next using these landing ellipses, we tried to place them in all locations that are below -1.3 km in elevation, had acceptable fine component thermal inertia values, and were free of obvious hazards in the MDIMs (Mars Digital Image Mosaics). This is exactly the same procedure employed to initially identify potential landing sites for Mars Pathfinder. Only sites that appear smooth and flat in the MDIM without scarps, large hills, depressions or large fresh craters (>5 km) were acceptable.

To our surprise, we found 100 sites for MER-A and 85 sites for MER-B that met these criteria (30 sites overlap). Even though the area available to land north of the equator is at least twice as great as south of the equator, the smaller ellipse size towards the south compensates. For comparison, the landing ellipse for Mars Pathfinder (300 km by 100 km) and the 10° latitude band reduced available sites to just 10 [Golombek et al., 1997]. Virtually all ages and types of geologic mapped units are available for landing including ancient Noachian units, Hesperian channel and plains, and Amazonian volcanics, channel and smooth plains. The Hematite site studied for the Mars Surveyor '01 lander is assessable to both landers, with 4-5 sites for each (TM20B-TM23B; TM9A-TM12A) and 19 sites (VM35A-VM53A) can be placed within Valles Marineris (guaranteed spectacular views). We have not yet evaluated any of these potential sites in more detail, so it is unclear how many would survive the more careful review required to certify a landing site. If the Pathfinder site selection activity is used as a guide, at least half would be eliminated fairly quickly on the basis of inspection of existing MOC images. Nevertheless, this analysis shows a large number of landing sites are available for study for the MER landers. The 30 sites that overlap in area are: TM1A-TM11B, TM2A-TM11B, TM4A-TM12B, TM5A-TM13B, T6A-TM14B, TM7A-TM17B, TM8A-TM16B, TM9A-TM19B, TM10A-TM20B, TM11A-TM22B, TM12A-TM23B, TM13A-TM24B, TM14A-TM25B, XT18A-XT28B, XT20A-XT29B, XT21A-XT30B, XT33A-XT31B, XT34A-XT27B, EP 68A-EP52B, EP70A-EP56B, EP72A-EP57B, EP74A-EP61B, EP75A-EP63B, EP76A-EP64B, EP78A-EP71B, EP80A-EP70B, EP81A-EP72B, EP83A-EP79B, IP84A-IP96B, IP85A-IP98B.

Below is a list of all potential sites identified. This list is not meant to be exclusive or inclusive; it is merely to identify the scope of choices available. Each site is given a unique identifier consisting of 2 letters, followed by a number, followed by the letter A or B, for purposes of communication. The first two letters define the general region in which the landing site is located as follows: wA-western Arabia Terra, TM-Terra Meridiani, CP-Chryse Planitia, XT-Xanthe Terra, and VM-Valles Marineris (all in the western hemisphere), and EP-Elysium Planitia, IS-Isidis Planitia, and SM-Syrtis Major (all in the eastern hemisphere). The number is the unique site number for MER-A or MER-B, which is distinguished by the letter A for MER-A and B for MER-B. The location is for the center of the ellipse; corresponding ellipse sizes can be found in Table 1. The elevation is approximate for the center of the ellipse and is within 0.5 km for elevations -6 km to -2.5 km and within 0.1 km for elevations -2.5 km to -1.3 km. Geologic units from Scott and Tanaka [1986] and Greeley and Guest [1987] are: Npl1 - Noachian Plateau cratered unit; Npl2 - Noachian Plateau subdued cratered unit; Nplh - Noachian Plateau hilly unit; Npld - Noachian Plateau dissected unit; Hr - Hesperian Ridged plains; Hch - Hesperian Channel Material; Hvr - Hesperian Vastitas Borealis Formation, ridged; Hs - Hesperian Syrtis Major Formation (volcanics); Ael1 - Amazonian Elysium volcanics, Achu - Amazonian Channel material; Aml - Amazonian Medusae Fossae Formation; Aps - Amazonian Smooth Plains; Apk - Amazonian knobby material; Avf - Amazonian Valles Marineris floor material; S - Smooth plains material within craters.

Those at JPL (or with special access) can look at the maps on the MER library web site at: http://mars03-lib.jpl.nasa.gov/ (click on Work Area, then Project Science, then Science Team Meetings, then Athena Science Team Meeting Sept. 18-19, 2000, then Potential landing sites; viewgraphs under Golombek). The ellipses are drawn on an MDIM basemap with MOLA elevation in color, and with the geologic maps of Scott and Tanaka [1986] and Greeley and Guest [1987] in color. We will also have this material on an open web site for the community soon.

Table 2.
Potential Landing Sites for MER-A and MER-B
Site ID: A = MER-A, B = MER-B
Geological Units: Scott & Tanaka [1986], Greeley & Guest [1987]
Latitude: ± 0.2° (°N, °S), relative to MOLA geoid
Longitude: ± 0.2° (°W)
Site ID Location of
Ellipse Center
(Lat: °N/S, Lon: °W)
Elevation (km) Geological Unit
MER-B, Western Hemisphere
wA1B 14.4N, 7 -1.9 Npl1
wA2B 13N, 10.7 -1.7 Npl1
wA3B 9.2N, 6 -2.1 Npl2
wA4B 7.8N, 10.8 -2.0 Npl1
wA5B 11.2N, 17.6 -1.9 Hr
wA6B 8.6N, 18.6 -2.1 Hr
wA7B 6.5N, 15.2 -1.9 Hr
wA8B 10.7N, 23.7 -2.5 Npl1
TM9B 6N, 2.7 -1.3 Npl2
TM10B 5.6N, 8.3 -1.7 Npl1
TM11B 4.2N, 7.8 -1.8 Npl2
TM12B 4N, 13.5 -2.1 Hr
TM13B 2.3N, 12 -1.9 Hr
TM14B 0.9N, 6.7 -1.6 Npl2
TM15B 0.3N, 9.7 -1.9 Hr
TM16B 0.6S, 11.2 -1.9 Npl1
TM17B 0.5S, 9 -2.1 Hr
TM18B 1.2S, 9.5 -1.7 Hr
TM19B 1.2S, 5.3 -1.3 Npl2
TM20B 2.3S, 6.2 -1.3 Npl2
TM21B 2.5S, 3.3 -1.3 Npl2
TM22B 3.2S, 7.1 -1.7 Npl2
TM23B 3.4S, 3.1 -1.4 Npl2
TM24B 2.8S, 10.1 -1.8 Hr
TM25B 3.6S, 10.1 -1.7 Hr
TM26B 4.6S, 10.1 -1.7 Hr
XT27B 1.9S, 22.5 -2.1 Npl2
XT28B 1.2S, 24.5 -1.8 Npl2
XT29B 1.0S, 27.7 -1.7 Npl2
XT30B 1.2S, 30.6 -2.0 Npl2
XT31B 4N, 26.2 -1.8 Npl2
XT32B 4.5N, 34.6 -1.9 Npl2
XT33B 3.2N, 38.4 -1.6 Npl2
XT34B 6.2N, 40.6 -1.6 Npl2
CP35B 0.4S, 33.8 -5.5 Hch
CP36B 8.2N, 33.0 -4.0 Hch
CP37B 10.5N, 45.6 -2.5 Hr
CP38B 11.8N, 45.4 -2.5 Hr
CP39B 14.1N, 47.0 -3.0 Hr
MER-B, Eastern Hemisphere
EP40B 14.2N, 201.3 -2.1 Ael1
EP41B 14.3N, 204.0 -1.9 Ael1
EP42B 13.4N, 203.1 -1.9 Ael1
EP43B 12.4N, 203.0 -2.1 Ael1
EP44B 11.5N, 204.1 -2.5 Ael1
EP45B 7.2N, 201.0 -3.0 Achu
EP46B 12.6N, 208.7 -1.9 Ael1
EP47B 11.2N, 207.4 -2.5 Ael1
EP48B 9.2N, 206.8 -2.5 Ael1
EP49B 7.4N, 205.6 -3.0 Ael1
EP50B 6.6N, 207.6 -3.0 Ael1
EP52B 5.3N, 208.0 -3.0 Achu
EP53B 11.0N, 211.8 -2.1 Ael1
EP54B 8.2N, 211.7 -2.5 Ael1
EP55B 5.6N, 213.7 -2.5 Achu
EP56B 4.4N, 213.6 -2.5 Achu
EP57B 4.2S, 212.1 -1.7 Aml
EP58B 10.7N, 219.5 -2.5 Aps
EP59B 7.2N, 217.0 -3.0 Ael1
EP60B 6.5N, 219.6 -3.0 Aps
EP61B 3.7N, 216.0 -3.0 Achu
EP62B 3.6N, 218.5 -3.0 Aml
EP63B 0.7S, 216.9 -2.5 Aps
EP64B 1.5S, 217.8 -3.0 Aps
EP65B 14N, 223.8 -2.5 Aps
EP66B 115N, 224.1 -3.0 Aps
EP67B 9.2N, 221.2 -3.0 Aps
EP68B 5.6N, 222.9 -3.0 Aps
EP69B 3.6N, 223.4 -3.0 Aps
EP70B 3.1N, 225.0 -3.0 Aps
EP71B 1.6N, 220.6 -3.0 Aps
EP72B 0.4S, 224.9 -3.0 Aps
EP73B 12.9N, 225.6 -2.5 Aps
EP74B 8.8N, 225.9 -2.5 Aps
EP75B 6.8N, 227.6 -2.5 Aps
EP76B 14.1N, 230.1 -3.0 Hr
EP77B 13.0N, 232.5 -3.0 Hr
EP78B 11.2N, 236.1 -2.5 Hr
EP79B 3.7N, 235.5 -1.6 Apk
EP80B 13.9N, 244.1 -2.5 Hr
EP81B 12.1N, 245.2 -2.5 Hr
IP82B 14.1N, 236.6 -3.5 Hr
IP83B 13.5N, 265.1 -3.5 Aps
IP84B 12.8N, 265.8 -3.5 Aps
IP85B 11.6N, 265.5 -3.5 Aps
IP86B 11.0N, 268.7 -3.5 Aps
IP87B 9.7N, 266.4 -3.5 Aps
IP88B 8.3N, 268.1 -3.5 Aps
IP89B 13.7N, 271.2 -4.5 Aps
IP90B 14.0N, 274.6 -4.5 Hvr
IP91B 11.2N, 275.5 -4.5 Hvr
IP92B 8.9N, 272.1 -4.5 Hvr
IP93B 8.2N, 274.6 -4.5 Hvr
IP94B 6.9N, 271.0 -4.5 Hvr
IP95B 5.6N, 272.0 -4.5 Hvr
IP96B 4.6N, 272.3 -4.5 Aps
IP97B 5.7N, 276.6 -4.5 Aps
IP98B 4.7N, 276.4 -4.0 Aps
SM99B 8.1N, 279.7 -4.0 Hs
SM100B 7.1N, 280.3 -2.5 Hs
MER-A, Western Hemisphere
TM1A 4.6N, 7.8 -1.8 Npl2
TM2A 4.0N, 7.1 -1.7 Npl2
TM3A 3.7N, 10.1 -1.7 Npl1
TM4A 4.2N, 13.1 -1.9 Hr
TM5A 2.0N, 11.0 -1.8 Npl1
TM6A 0.9N, 6.6 -1.6 Npl2
TM7A 0.2S, 8.9 -1.9 Hr
TM8A 0.2S, 10.4 -1.9 Hr
TM9A 1.2S, 5.6 -1.3 Npl2
TM10A 2.2S, 6.6 -1.7 Npl2
TM11A 3.4S, 6.9 -1.6 Npl2
TM12A 3.6S, 2.9 -1.3 Npl2
TM13A 2.9S, 10.5 -1.8 Hr
TM14A 3.8S, 10.1 -1.8 Hr
TM15A 8.6S, 6.7 -1.9 S
TM16A 9.4S, 6.6 -1.9 S
TM17A 11.0S, 7.2 -1.4 Npld
XT18A 0.4S, 24.5 -1.8 Npl2
XT19A 1.1S, 25.2 -1.7 Npl2
XT20A 1.0S, 27.7 -1.8 Npl2
XT21A 1.5S, 30.7 -1.7 Npl2
XT22A 4.7S, 16.7 -1.9 Npl1
XT23A 5.4S, 17.7 -1.8 Npl1
XT24A 5.3S, 12.8 -1.9 Npl1
XT25A 5.7S, 12.4 -1.8 Npl1
XT26A 7.7S, 15.5 -1.8 Nplh
XT27A 7.7S, 13.6 -1.5 Npl1
XT28A 7.2S, 11.4 -1.6 Npl1
XT29A 9.3S, 15.5 -1.5 Npl1
XT30A 8.8S, 11.7 -1.4 Npl1
XT31A 10.8S, 15.8 -1.4 Npl1
XT32A 10.7S, 10.7 -1.4 Npl2
XT33A 4.2N, 26.3 -1.4 Npl2
XT34A 1.9S, 22.7 -1.9 Npl2
MER-B, Western Hemisphere, Valles Marineris
VM35A 9.4S, 34.5 -5.0 Hch
VM36A 10.2S, 36.6 -4.5 Hch
VM37A 11.1S, 37.9 -4.0 Hch
VM38A 8.2S, 40.5 -3.5 Hch
VM39A 12.8S, 40.0 -3.5 Hch
VM40A 8.8S, 42.9 -3.5 Hch
VM41A 14.0S, 42.0 -4.0 Hch
VM42A 7.7S, 50.7 -4.5 Avf
VM43A 13.9S, 57.5 -5.5 Avf
VM44A 13.1S, 62.5 -4.5 Avf
VM45A 12.0S, 67.7 -4.5 Avf
VM46A 13.6S, 70.6 -3.5 Avf
VM47A 6.2S, 70.1 -5.0 Avf
VM48A 7.1S, 72.5 -5.0 Avf
VM49A 9.2S, 73.5 -4.0 Avf
VM50A 9.7S, 73.8 -3.5 Avf
VM51A 10.1S, 73.0 -3.5 Avf
VM52A 10.5S, 72.5 -3.5 Avf
VM53A 8.8S, 77.7 -3.5 Avf
MER-B, Eastern Hemisphere
EP54A 11.4S, 181.9 -1.5 Aml
EP55A 14.2S, 184.8 -1.9 Hch
EP56A 14.6S, 188.1 -1.6 Npl1
EP57A 9.0S, 191.4 -3.0 Apk
EP58A 9.9S, 191.5 -3.0 Apk
EP59A 10.4S, 191.6 -2.5 Apk
EP60A 13.1S, 194.1 -1.6 Npl1
EP61A 11.8S, 195.5 -1.9 Apk
EP62A 9.7S, 198.2 -1.8 Apk
EP63A 12.6S, 196.5 -1.6 Npl1
EP64A 14.8S, 197.5 -2.1 Npl1
EP65A 8.7S, 202.6 -1.7 Apk
EP66A 4.0N, 206.5 -3.5 Achu
EP67A 4.6N, 209.6 -3.5 Achu
EP68A 3.5N, 209.2 -3.5 Achu
EP69A 9.3S, 209.5 -1.7 Npl1
EP70A 4.0N, 213.5 -3.5 Achu
EP71A 1.2N, 212.0 -3.5 Achu
EP72A 4.2S, 211.4 -1.7 Aml
EP73A 5.5S, 212.0 -1.7 Aml
EP74A 4.2N, 216.6 -3.5 Achu
EP75A 0.7S, 217.2 -3.5 Aps
EP76A 1.4S, 217.5 -2.5 Aps
EP77A 4.5N, 220.5 -3.5 Aps
EP78A 1.7N, 221.0 -3.5 Aps
EP79A 4.5N, 224.4 -3.5 Aps
EP80A 3.2N, 224.3 -3.5 Aps
EP81A 0.2S, 224.7 -3.5 Aps
EP82A 5.8S, 222.4 -4.5 S
EP83A 3.5N, 234.7 -1.7 Apk
IP84A 4.5N, 271.9 -4.5 Aps
IP85A 4.5N, 271.9 -4.5 Aps

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