Emily Lakdawalla

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