by The Design
number of occasions (see section 5.3.4.2).
Curiosity departed Pahrump Hills on sol 949 to drive around the northern edge of the
Bagnold dune field through sand-floored valleys. It proceeded across the Murray forma-
tion, among ridges of a new capping rock, initially called the “washboard unit” and later
named the Stimson formation. The scenery was especially fine during this traverse,
because the Stimson erodes into steep buttes.
The ChemCam team recovered autofocus capability as the rover was preparing to travel
from primarily Murray valley bottoms to primarily Stimson higher plains, at a site called
Logan Pass. When Logan Pass proved too sandy for safe travel, the rover turned around
and headed to a new location, Marias Pass, where the newly capable ChemCam serendipi-
tously found some silica-rich rock. After standing down for the mission’s second solar
3.5 Mission Summary 133
conjunction from sols 1005 through 1026, the rover drilled into this silica-rich rock at
Buckskin on sol 1060.
Curiosity turned south, aiming directly toward the dunes. The path took it repeatedly
across the boundary between the Stimson and Murray formations. The team observed
interesting cracks with bright alteration haloes around them all over the Stimson unit.
They drilled into both unaltered and altered Stimson unit at Big Sky (unaltered) and
Greenhorn (altered) on sols 1119 and 1137.
On sol 1174, the rover arrived at the northern edge of the Bagnold dune field. After
some initial reconnaissance, the rover scooped samples at Gobabeb beginning sol 1224.
Unfortunately, the sample processing activities were cut short by an anomaly on sol 1231.
One of the four motors in the CHIMRA sample handling mechanism, the primary thwack
actuator, stalled. Investigation proved that it still worked, but out of caution the engineers modified sample processing activities to rely less on the affected motor (see section 5.4.6.3
for more detail).
Curiosity left the first dune site behind on sol 1248, now traveling west to skirt around
the extreme northern edge of the dunes. On sol 1281 the rover again ascended a steep
boundary between the Murray and Stimson formations to reach a highland called the
Naukluft plateau, where the wind had eroded the sandstone into fantastic shapes. Since the
Naukluft plateau would be the last time Curiosity drove on the Stimson unit, the team
decided to drill again into an alteration halo (at Lubango, on sol 1321) and into unaltered Stimson (at Okoruso, on sol 1332) (Figure 3.13). On sol 1353, the rover descended from the plateau, placing wheels on the Murray formation again. The team drilled at Oudam, the
lowest- elevation site of a long future traverse across the Murray formation.
On sol 1369, they turned south to finally cross the dunes among the Murray buttes. The
rover would remain on Murray formation rocks for many kilometers, with well-exposed
bedrock everywhere, rapidly ascending in elevation. It gave the science team the opportu-
nity to systematically read the layers of the rock to see how the environment changed over
time. To do that, they changed their approach to selecting drill sites. The team began to
drill every time the rover gained 25 meters of elevation. Three such regular drill intervals followed. Marimba, on sol 1422, was just north of the buttes; Quela, on sol 1464, was just
to their south; and Sebina, on sol 1495, was another 25 meters above. Conveniently, the
new regular-interval style of traverse roughly coincided with the start of the second
extended mission on September 1, 2016, corresponding to sol 1448.
Unfortunately, the regular intervals of drilling came to a halt on sol 1536, when
Curiosity attempted to drill at a site named Precipice. A problem had developed in the drill that was unrelated to the intermittent drill percussion problem that first appeared on sol
911. Now the drill feed mechanism would not advance reliably. As of sol 1800, the rover
has not drilled since. It has collected one more sample, a scoop of sand at a site named
Ogunquit Beach at the southern edge of the Bagnold dunes on sol 1651, but did not deliver
the sample to CheMin prior to sol 1800 because of concern about the drill.
The rover continued to advance southward to approach the interesting-chemistry rocks
first seen from orbit, doing science on the way with its other instruments while engineers
investigated the problem with the drill. As of this writing, the rover had climbed onto Vera Rubin Ridge, formerly known as Hematite Ridge. Engineers began testing on Mars a new
mode of drilling without using the drill feed on sol 1848.
134 Mars Operations
Figure 3.13. Curiosity MAHLI self-portrait at the Okoruso drill site. In the foreground is Okoruso. In the middle ground, just below the REMS boom, a bright spot marks the location of the Lubango drill site. Lubango was in an altered halo, Okoruso in unaltered Stimson rock.
NASA/JPL-Caltech/MSSS.
As of sol 1800, Curiosity had attempted sampling in 20 locations, of which 17 resulted
in the successful acquisition of sample and subsequent delivery to SAM and CheMin.
Sample processing related to these 16 drill sites and 2 of the sand scooping sites is sum-
marized in Figure 3.14 and Table 3.3.
3.5 Mission Summary 135
Figure 3.14. Seventeen Curiosity sample sites on Mars. Each is a MAHLI focus stack taken from a standoff distance of 5 centimeters, except for Rocknest (a photo of 150-micrometer sample on the observation tray from a standoff distance of 5 centimeters) and Sebina (a zoom in on a single image from a 25-centimeter standoff distance). As of sol 1800, there was no close-up photo of material sampled from Ogunquit Beach. NASA/JPL-Caltech/MSSS.
Ogunquit Beach
Scoop:
1651
–
1651
–
–
–
–
–
1651
xplanations of
Precipice
1536*
–
–
–
–
–
–
–
–
–
For e
Sebina
–
1495
–
1495,
1496
1496
1496
1533
–
1496
–
Quela
–
1464
–
1465,
1466
1466
1466
1491
1463,
1466
1466
1484
Marimba
1420
1422
–
1425
1426
1426
1457
–
1425
1443,
1456
Oudam
–
1361
–
1362
1364
1364
1418
–
1362
1382
emained inside CHIMRA.
oruso
Ok
–
1332
–
1334
1337
1337
1358
1338
1334
–
h sample r
Lubango
–
1320
&
nbsp; –
1323
1324
1324
1327
–
1323
–
Gobabeb
Scoops:
1224,
1228, 1231
–
1224, 1228
–
1226,
1228, 1251
1226,
1228, 1251
1228, 1241
1226
1224, 1230
Greenhorn
1134
1137
–
1139
1142
1142
1198
–
1139
1147,
1178
y
Big Sk
1116
1119
–
1121
1123
1123
1132
1126
1121
1129
Buckskin
1059
1060
–
1061
1064
1064
1089
1065
1061
1075
graph Peak
ele
T
–
908
–
922
910
930
954
–
922
928,
954
ough sol 1800. As of sol 1800, Ogunquit Beac
e v
Moja
867*,
881
882
–
884
883
889
894
868,
882, 884
884
887,
891, 892
Confidence Hills
756
759
–
762
768
765
781
–
765
773
Bonanza King
726*
–
–
–
–
–
–
–
–
5 .
indjana
W
615
621
–
623
628
704
613, 627
623, 640
624, 653,
694
ead Chapter
Cumberland
–
279
284, 289
279, 464
279, 283,
292
486
–
282
281, 286,
290, 353,
367, 381,
414, 463,
464
John Klein
174, 176,
180
182
–
193, 194
270
229
177, 270
195
196, 199,
224, 227
Rocknest
Scoops:
61, 66,
69, 74, 93
70, 76,
77, 78, 95
79
–
64, 67,
73, 81,
128
84, 85
(stereo)
71, 77, 94
93, 96,
98, 116
ey
Summary of Curiosity drill and scoop campaign activities thr
f
very
very
ve sample
all surv
ve (coarse
ve
vity
Table 3.3.
the activities listed in the leftmost column, r
Acti
Mini-Drill
(*=unsuccessful)
Full drill
O-tray dropof
Pre- and
post-sie
volume
inspection
Drill w
with MAHLI
Pre-sie
fraction) dump
Post-sie
(fine fraction)
dump
MAHLI
self-portrait
CheMin deli
SAM deli
3.6 References 137
Even if the mission were to end tomorrow, scientists would be working on
interpreting Curiosity’s data for decades. Of course, the mission hopes for much lon-
ger survival than that.
3.6 REFERENCES
Allison M (1997) Accurate analytic representations of solar time and seasons on Mars with
applications to the Pathfinder/Surveyor missions. Geophys. Res. Lett. 24(16):1967–
1970, DOI: 10.1029/97GL01950
Bass D, Wales D, and Shalin V (2005) Choosing Mars time: Analysis of the Mars
Exploration Rover experience. Paper presented at IEEE Aerospace Conference, 5–12
March 2005, Big Sky, MT, USA, DOI: 10.1109/AERO.2005.1559722
Cantor B, James P, and Calvin W (2010) MARCI and MOC observations of the atmo-
sphere and surface cap in the north polar region of Mars. Icarus 208:61–81, DOI:
10.1016/j.icarus.2010.01.032
Chattopadhyay D et al (2014) The Mars Science Laboratory supratactical process. Paper
presented at SpaceOps 2014 Conference, 5–9 May 2014, Pasadena, USA
JPL (2013) Rover Team Working to Diagnose Electrical Issue http://mars.nasa.gov/msl/
news/whatsnew/index.cfm?FuseAction=ShowNews&NewsID=1559 Status report dated 20 Nov 2013, accessed 15 Aug 2016
Reichardt T (2015) The man who named the Martian day. http://www.airspacemag.com/
daily-planet/man-who-named-martian-day-180957350/. Accessed 2 Mar 2016
4
How the Rover Works
4.1 INTRODUCTION
Curiosity may look superficially like the Mars Exploration Rovers and Sojourner
(Figure 4.1), but its redundant systems, powerful science suite, and complicated sample manipulation make it a different beast entirely. The rest of this book describes all the components that enable Curiosity to do science on Mars, how they are supposed to work, and
how things have occasionally gone wrong.
Figure 4.2 shows Curiosity’s external parts, Figure 4.3 its internal ones. Its basic dimen-
sions are outlined in Figure 4.4. The aluminum rover body, also known as the warm electronics box (WEB) is a block 163-by-117-by-46 centimeters in size. It is painted white for
thermal control and to reduce the glint of reflected sunlight into cameras. The warm elec-
tronics box supports the other external components and keeps the avionics and science
instruments inside it within a controlled temperature range.
4.2 POWER SYSTEM AND MMRTG
Curiosity draws its power from a Multi-Mission Radioisotope Thermoelectric Generator
(MMRTG). 1 The MMRTG trickles the power that it generates into two rechargeable 42
amp-hour large-cell lithium-ion batteries. The MMRTG generates power using the heat
from radioactive decay of 4.8 kilograms of plutonium dioxide (a ceramic form of pluto-
nium- 238), of which about 69% of the mass was radioactive plutonium-238 when it was
first fueled on October 28, 2008. Plutonium-238 has a half-life of 87.7 years. Power pro-
duction will decline over time, reducing rover activity. Once the MMRTG no longer gen-
erates enough power for survival and communications, the mission will end, probably by
2030, if nothing else ends it earlier. The MMRTG weighs 40 kilograms.
1 The descriptio
n of Curiosity’s MMRTG in this section is based on NASA (2013), Jones et al (2013), and Woerner et al (2012)
© Springer International Publishing AG, part of Springer Nature 2018
138
E. Lakdawalla, The Design and Engineering of Curiosity, Springer Praxis Books,
https://doi.org/10.1007/978-3-319-68146-7_4
4.2 Power System and MMRTG 139
Figure 4.1. Family portrait of the three JPL Mars rovers. In front is Marie Curie, the flight spare of the Sojourner rover, now a museum piece. At left is the Surface System Test Bed for the Mars Exploration Rover mission. At right is the Vehicle System Test Bed for the Curiosity mission. NASA/JPL-Caltech release PIA15279.
4.2.1 How the MMRTG works
A radioisotope thermoelectric generator converts heat into electricity with no moving
parts by taking advantage of the thermoelectric effect. Holding two different electrically
conductive materials at different temperatures and joining them in a closed circuit gener-
ates current. A pair of conductive materials joined in this way is called a thermocouple. A thermocouple has a “hot shoe” and a “cold shoe.” In Curiosity’s MMRTG, the decaying
plutonium heats the hot shoes of the thermocouples. External fins splaying out into the
Martian air chill the cold shoes.
The plutonium dioxide ceramic is split into 32 pellets, each weighing 150 grams. Each
pellet is clad in iridium. The iridium cladding is a safety feature that blocks the alpha particles emitted by the plutonium pellets. It also has a high melting temperature (2400°C), in case the cooling system fails.
The MMRTG was carefully designed to survive a launch accident, like a launch pad
explosion or a midair breakup, without releasing radioactive material into Earth’s
atmosphere or oceans (Figure 4.5). Two pellets go inside a graphite impact shell.
140 How the Rover Works
Figure 4.2. Overview of external components of rover systems. Not all of the robotic arm is visible in this photo because it was taken with MAHLI, which is mounted on the arm. Base image is the MAHLI self-portrait taken at John Klein on sol 177. NASA/JPL-Caltech/MSSS/
Emily Lakdawalla.
4.2 Power System and MMRTG 141
Figure 4.3. Interior of the rover, looking up from below. SAM, CheMin, REMS, AXPS, Mastcam, MAHLI, MARDI, RAD, ChemCam, and DAN PNG and DE are all science instruments. IMUs (inertial measurement units), rover motor controller, and power electronics are all part of the rover avionics. Telecommunications components include the Electra-lite (UHF) radio and X-band transponder, amplifier, and waveguide. Batteries are part of the power system, and the rover integrated pump assembly is part of the thermal control system. NASA/
JPL-Caltech/Emily Lakdawalla.
142 How the Rover Works
Figure 4.4. Dimensions of some large elements of the rover in centimeters. NASA/JPL-Caltech/Emily Lakdawalla.
A carbon- bonded carbon-fiber sleeve encases the impact shell. Two such sleeves are inside