Emily Lakdawalla
Page 27
spot in the center. So Curiosity moves the arm while brushing to sweep out the center,
creating an oval spot. The entire brushed area is contained within a 60-millimeter circle.
Figure 5.16 shows two different kinds of brushed spots. The size of the brushed spot depends upon how close the brush gets to the surface. Originally, Curiosity brushed at a
height of 1 centimeter, which produced a brushed spot about 46 millimeters in diameter.
Concern that the bristles could wrap around the center post following the discovery of the
bent bristles led them to use a higher standoff of 1.5 centimeters thereafter, which
5.6 Organic Check Material 211
Table 5.2. Summary of dust removal tool (brush) to sol 1806. List courtesy Ken Edgett.
Bradbury Group
Pahrump Hills
North of the dunes
Among the dunes South of the dunes
150 Ekwir
722 Bonanza
975 Albert
1358 Oudam
1681 Duck Brook
169 Wernecke
King
998 Ronan
1366 Auberes
Bridge
291 Cumberland 755 Maturango
999 Wallace
1380 Koes
1695 Mason Point
612 Windjana
758 Moenkopi
1057 Buckskin
1416 Chibia
1702 Fern Spring
767 Morrison
1092 Ledger
1418 Marimba
1710 White Ledge
805 Pelona
1105 Winnipeg
1436 Conda
1715 Timber Point
806 Ricardo
1109 Cody
1444 Ganda
1736 Winter Harbor
808 Rosamond
1114 Big Sky
1474 Jwaneng
1744 Mingo
809 Mojave
1119 Big Sky 2
1477 Catumbela 1806 Robinson Rock
813 Punchbowl 1130 Greenhorn
1484 Serowe
814 Afton
1157 Augusta
1491 Sebina
Canyon
1166 Swartkloofberg 1511 Penobscot
815 Topanga
1245 Kudis
1523 Sutton
819 Mescal
1251 Kuiseb
Island
824 Puente
1259 Gorob
1531 Precipice
828 Pickhandle
1266 Stockdale
1586 Belle Lake
830 Goldstone
1273 Schwarzrand
844 Santa Ana
1275 Mirabib
853 Tecoya
1279 Khomas
880 Mojave 2
1287 Sesriem
905 Telegraph
Canyon
Peak
1293 Brukkaros
936 Hyrum
1300 Bero
1318 Lubango
1330 Okoruso
1341 Kwakwas
1348 Meob
1355 Inamagando
produces a brushed spot about 40 millimeters in diameter. Either way, the cleared area is
slightly wider than the field of view of APXS, so even with positioning uncertainty,
APXS’s field of view will be entirely in the brushed area.
When the brush interacts with very soft rocks, the wire bristles may scratch the surface.
If the rock is extremely soft, wires near the center can get hung up on a protuberance and
actually drill into the rock (see Figure 5.17 for an example).
5.6 ORGANIC CHECK MATERIAL
A palette on the front center of the rover contains 5 cylinder-shaped bricks of hermetically sealed organic check material provided by the SAM team (Figure 5.18).19 It is intended to check the cleanliness of the whole SAM sample processing pathway, to ensure that any
19 Conrad et al (2012)
212 SA/SPaH: Sample Acquisition, Processing, and Handling
Figure 5.16. Moenkopi (left), brushed on sol 758, was a raised feature. Maturango (right), brushed sol 755, was a flat spot, and the brush was moved during brushing. The Confidence Hills drill site is in the background. Drill holes are 16 mm across; brushed spots are at least 45 mm across. Left Mastcam image 0758MH0001900010204611C00. NASA/JPL-Caltech/MSSS.
organic materials detected by SAM in Martian material really do come from Mars and are
not Earthly contamination left behind on the external parts of the sample processing chain: the drill, CHIMRA, and sample inlets. The five bricks are identical. They are composed of
a ceramic that has been doped with a minute amount of fluorinated hydrocarbon chemical
that can be detected by SAM. Each brick is covered with a foil seal. It can be drilled and
sampled just like a rock, and the sample dropped into SAM. Drilling it breaks the seal, so
each brick can be used only once. Figure 5.19 shows how the rover would position the drill on one of the bricks for sampling.
The organic check material has not yet been used. (For more information, see 9.5.1.12.) The
team tested the process of positioning the drill to sample the organic check material on sols 34
and 1076, taking images with MAHLI to document turret positioning (Figure 5.19). They also performed imaging of the organic check material with the MAHLI cover closed on sol 1416.
5.7 Sample Playground 213
Figure 5.17. Scratches and drilling near the center of a brushed spot at Pelona, at the Pahrump Hills site, sol 805. MAHLI images 0805MH0001900010300492C00 and
0805MH0003070010300514C00. NASA/JPL-Caltech/MSSS.
5.7 SAMPLE PLAYGROUND
Immediately in front of the mast is a suite of tools intended to allow the rover to study the properties of drilled or scooped sample. This “sample playground” was a late addition to
the rover design, added after the experience of the Phoenix mission, which had a difficult
time handling clumpy Martian materials (see section 1.5.11). 20 The sample science team looked at how their mature design might be vulnerable to clumpy soil, and developed a set
of tools to help them investigate sampled material before committing to delivering it to
CheMin and SAM.
The sample playground comprises the science observation tray, engineering tray,
CheMin surrogate funnel and soil capture plate, dust removal tool scratching post, and two
portion pokers (Figure 5.20). Sols in which science cameras were used to image parts of the sample playground are listed in Table 5.3, but the playground is also often captured in Mastcam and Navcam views of the work volume, and in MAHLI self-portraits.
The science observation tray, also known as the “O-tray”, is a circular titanium plate 75
millimeters wide. The rover can drop portions of drilled or scooped sample onto it for
20 Anderson et al (2012)
214 SA/SPaH: Sample Acquisition, Processing, and Handling
Figure 5.18. The organic check material mounting plate bolted to the front center of the rover contains five foil-capped cylinder-shaped bricks of ceramic material. Between the five bricks are smaller drill positioning pads, places for the drill contact stabilizers to press during drilling. Below the mounting plate is one of the two spare drill bit boxes and the four front Hazcams. Mosaic of four MAHLI self-portrait frames taken on sol 1065.
NASA/JPL-Caltech/MSSS.
investigation with APXS, MAHLI, and mast-mounted cameras. It was intended to provide
a surface of known composition on which to perform APXS observations of sampled
material. Unfortunately, vibration from CHIMRA, necessary for portion delivery, appears
to transfer through the rover arm to the body and cause delivered portions to “walk” off of the sample tray (see Figure 5.20 for an example). This behavior, which is much worse on Mars than it was in the Earth test
bed, has prevented much use of the observation tray for
science. The APXS team has developed a different method of measuring the composition
of drilled materials by studying the composition of pre- and post-sieve dump piles. The
APXS team has also occasionally taken advantage of the vibration-induced cleaning of the
observation tray to perform measurements of the composition of airfall dust.
5.7 Sample Playground 215
Figure 5.19. A test of the drill’s positioning on one of the organic check material bricks. From this point of view, you can see the tubular inlet and outlet ports that allowed the SAM team to dope the ceramic bricks with a fluorinated compound after they were sealed in their can-shaped housings. Navcam image NLB_493020688RAD LF0490814NCAM00467M1, sol
1076. NASA/JPL-Caltech.
216 SA/SPaH: Sample Acquisition, Processing, and Handling
Figure 5.20. Parts of the sample playground seen from above by Mastcam and from the right side by MAHLI. In the top image, two portions have been dropped to the center of the observation tray. CHIMRA vibration transferred through the arm to the rover body has caused the first portion to “walk” off the tray during delivery of the second portion. Delivery of both portions has also shifted some of the accumulated dust off of the tray. Mastcam image
ML0005780000102730E01 and MAHLI image 0544MH0003460000201460C00. NASA/
JPL-Caltech/MSSS/Emily Lakdawalla.
5.8 SAM and CheMin Inlets and Wind Guards 217
Table 5.3. Sols with
Mastcam
MAHLI
targeted imaging of
the sample playground
70
37
(mostly of the observation
76
73
tray).
77
93
78
95
79
177
81
544
95
571
284
572
289
The rest of the sample playground elements have not been used on Mars. The engineer-
ing tray, located closer to the rover body than the observation tray, has a checkerboard
pattern made of 0.25-inch (6.35-millimeter) squares. It was intended for use in estimating
the volume of portions dropped to SAM and CheMin. To the left is the CheMin surrogate
funnel and soil capture plate. If there are concerns about soil clumping and potentially
clogging the CheMin inlet funnel, the drop can be tested with the surrogate funnel. On the
right side of the engineering tray, a palette of screw heads provides a place to clean off the DRT in the event that Martian material clings to its brushes. Finally, two portion pokers,
one pointing vertically and one horizontally, provide Curiosity with the capability to poke out the CHIMRA portion hole if it should become clogged with material. However, the
inverted funnel shape of the CHIMRA portion hole makes it very unlikely that material
could pass all the way through CHIMRA and then clog the portion hole; the portion pokers
have not been used and hopefully never will be.
5.8 SAM AND CHEMIN INLETS AND WIND GUARDS
The final elements in the sample delivery chain are the motorized sample inlets on the top
of the rover deck. Three flaps (two for SAM’s inner and outer carousel rings, and one for
CheMin) open and close to allow CHIMRA to deliver portions. Mastcam shoots photos of
the inlets before and after each delivery in order to check whether wind blew the sample
away from the inlet and deposited it on the deck nearby. The rover also uses MAHLI to
image the fine mesh grate over the open CheMin sample inlet from time to time, often at
night, when the MAHLI LEDs can be used as flashlights to evenly illuminate the interior.
The goal of this imaging is to check for clogging by excessively large particles. All these imaging activities are summarized in Table 5.4.
An amusing side effect of the repeated imaging of the sample inlets is that it has been
possible to track the motions of bits of gravel on the rover deck over the course of the
landed mission (Figure 5.21). This gravel was tossed onto the deck during landing and has rattled around the top surface ever since, occasionally drawing squiggly lines in accumulated deck dust.
The difficult experiences of sample delivery in the Phoenix mission caused engineers
to be concerned about wind blowing Curiosity’s tiny sample portions away. To mitigate
against this possibility, they added spring-loaded collars around the sample inlets, and a
corresponding plate over the CHIMRA portion hole. In the event that wind dispersal of
218 SA/SPaH: Sample Acquisition, Processing, and Handling
Table 5.4. Imaging of the CheMin and SAM inlet ports by Mastcam and MAHLI to sol 1800.
CheMin inlet (Mastcam)
CheMin inlet (MAHLI)
SAM inlets (Mastcam)
SAM inlet (MAHLI)
14
36
14
93
51
74
90
96
71
81
93
282
94
94
96
195
195
114
282
282
116
623
411
117
765
558
196
884
564
224
922
666
227
1061
774
281
1121
895
286
1139
1028
290
1226
1064
353
1323
1091
367
1334
1123
381, 382
1362
1136
413, 415
1375
1142
463, 464
1425
1184
624
1466
1259
653
1496
1287
694
1324
773
1337
887, 888
1348
891
1364
892
1375
928
1402
954
1427
1075
1438
1129
1459
1147
1466
1178
1470
1224
1477
1230
1484
1231
1489
1233
1496
1382
1409
1443
1456
1651
5.8 SAM and CheMin Inlets and Wind Guards 219
Figure 5.21. CheMin inlet and wind guard as seen from Mastcam. Pebbles that have been on the deck since landing leave tracks as the rover’s motion vibrates them across the deck. NASA/
JPL-Caltech/MSSS/Emily Lakdawalla.
sample is found to be a problem, the engineers can deliver sample with the portion plate
pressed against a wind guard. This capability has not been used. Mastcam videos of por-
tion delivery recorded on sols 64, 78, 284, and 289 showed the portions dropping straight
down for a distance longer than the few centimeters separating the portion hole and sample
inlets. The mission has also taken advantage of REMS wind
data to select times of day for
sample delivery when winds are expected to be minimal.
220 SA/SPaH: Sample Acquisition, Processing, and Handling
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