by The Design
order to scrub the apparatus of any remaining manufacturing residue. 8 They scooped again Figure 3.6. Left Mastcam photo 0061ML0003060000102375E01 documenting the first day of scooping at Rocknest. CHIMRA acquired a full scoop from the site at lower right, then shook out some of the sample to reduce the amount in the scoop, leaving a fresh pile of dark sand on the ripple surface. NASA/JPL-Caltech/MSSS.
8 CHIMRA is pronounced “chimera”
3.5 Mission Summary 125
and delivered the first Martian samples to the laboratory instruments CheMin and SAM
for the first times on sols 71 and 93.
MAHLI captured the first full rover self-portraits at Rocknest on sols 84 and 85 (see
section 7.4.3.5 for more on how MAHLI captures self-portraits). In order to continue analyzing the Rocknest sample while proceeding toward Yellowknife Bay, the rover planners
developed and quickly deployed the ability to drive with cached sample held inside the
CHIMRA mechanism (see section 5.4.5).
Curiosity acquired its first drilled sample on sol 176, at John Klein (Figure 3.7). Analyses
of the first drill samples were interrupted by a major anomaly – arguably the scariest event of the mission after landing – on Wednesday, February 27, sol 200. The event is now known
as “the sol 200 anomaly.” The routine morning uplink revealed that the rover was behaving
strangely, returning real-time telemetry but not performing commanded activities. Engineers quickly diagnosed an issue with the rover’s onboard memory. Later in the day, their concern elevated when more telemetry from Curiosity indicated that it had not gone to sleep as commanded, so was depleting its batteries.
Figure 3.7. John Klein drill site after drilling activities were completed. Mastcam acquired this photo on sol 229, after CHIMRA dumped the remaining drilled sample in two piles.
NASA/JPL-Caltech/MSSS release PIA16815.
126 Mars Operations
Unlike the smaller Spirit and Opportunity rovers, Curiosity has an entire spare com-
puter system available for the rover to switch to. On sol 201, the mission uplinked com-
mands to swap from the A-side computer, with its corrupted memory, to the B-side
computer. Commissioning of the instruments on the B-side computer was completed as of
sol 223 (23 March 2013). The rover has operated on the B-side computer ever since.
As a consequence of the swap to the B-side computer, the rover switched eyes. It has
two pairs of each of its engineering cameras (the Navcams and front and rear Hazcams, see
section 6.3), with complete sets connected to each computer. The switch from A-side to B-side computers moved its Navcam point of view down by 4.8 centimeters. Similarly, the
front Hazcam view of the world shifted to the rover’s left by 8.2 centimeters. The rear
Hazcam view shifted to the rover’s left by about a meter, from one side to the other of the MMRTG. Because the rover’s autonomous hazard-finding software had been trained on
Mars only with A-side images, the project was forced to repeat some of the commissioning
activities using the rover’s new eyes.
During recommissioning of autonomous driving modes, the engineers made the
unpleasant discovery that the pointing of the B-side Navcams shifted very slightly over the course of a sol, likely because their mounting bracket warped with daily extremes of
Martian temperature, enough to confuse the onboard rangefinding software. Over the
ensuing weeks, they had to perform calibration activities to understand the temperature-
dependent behavior. Only after this investigation was complete were they able to test
autonomous navigation capability.
After recovering from the sol 200 anomaly, rover operations almost immediately stood
down again because of solar conjunction. When the Sun is within 3° of Mars in Earth’s
sky, radio communications can be affected by solar radio emissions. Mars landers and
orbiters aren’t directly affected, but because communications aren’t reliable, Earth con-
trollers avoid any activities that might place the spacecraft at risk of needing intervention.
During solar conjunction, from sol 235 to 260, the rover performed only background envi-
ronmental science observations and transmitted a daily “beep” to Earth. After conjunction,
the rover drilled for a second time at a nearby site named Cumberland, on sol 279.
Early impressions of the drilled material suggested that Curiosity had accomplished its
science objectives (listed in Box 1.5). The mission had successfully explored the biological potential of at least one target environment (using SAM to inventory organic compounds) and had gathered the data needed to conclude that the environment was a biologically relevant one (the still water of a lake bottom). The mission had characterized the regional geology of the landing site before landing, and followed that up with successful chemical, mineralogic, and isotopic analyses with the science instruments. The isotopic measurements of water in the
ancient Mars rocks had corroborated orbital science results indicating that Mars has lost much of its atmosphere. And RAD’s successful operation had hit Curiosity’s last goal of characterizing surface radiation. With all the crucial first-time activities complete and minimum mission success achieved, the science team could go on their driving adventure.
3.5.3 The Bradbury traverse
On sol 295, Curiosity departed Cumberland, investigating a few outcrops close to
Yellowknife Bay. Then the rover embarked on a 13-kilometer journey across the floor of
the crater to the southwest, toward Murray buttes and the gap in the Bagnold sand dune
field that would allow the rover to cross it safely and reach the base of the mountain.
3.5 Mission Summary 127
During the time at Yellowknife Bay, engineer Paolo Bellutta had led the effort to map
out a “rapid transit route” for the rover using the traversability algorithms he had devel-
oped during the landing site selection process (see section 1.6.3). It was not the shortest possible path, but sought to minimize drive time by keeping the rover to relatively flat
terrain with good visibility, which would maximize single-sol drive distances. (Being able
to see far ahead permits longer blind drives, which is the fastest driving mode; see section
6.5 for more about the different driving modes.) The traverse was across a region of low, hummocky plains with rare outcrops of rock. From orbit it appeared largely similar to the
terrain Curiosity had already traversed. The rover would be permitted to perform science
observations as opportunities came up, but driving was a higher priority than science. They used autonav for the first time to extend a planned drive on sol 347, and quickly racked up record-breaking drive distances, including one of 141 meters on sol 385.
Long drives also used up time and energy, limiting resources available for science. The
science team selected three locations along the proposed path where orbital images sug-
gested that there was more coherent outcrop, worthy of brief stopovers for science.
Curiosity reached the first site, Darwin, on sol 390, staying until sol 402. On sol 426, the rover passed from terrain that the science team had mapped as “hummocky plains” to a
new landscape, called “rugged terrain” (Figure 3.8). Rugged terrain featured more bedrock in the form of sharp blocks of rock protruding from the plains. The rougher terrain
slowed down autonav, making drive distances shorter. On sol 439, Curiosity approached a
site called Cooperstown to characterize the rugged-terrain rock.
The months after Cooperstown were full of problems. An unsuccessful flight software
update (see section 4.3.2.2) delayed them
at Cooperstown until sol 453. On sol 456, the rover experienced a “soft short” in its MMRTG, later determined to have been caused by
part of the electrical power circuit touching its metal housing (see section 4.2.3).9 The
short spontaneously resolved itself on sol 461 and didn’t recur for a year. On sol 463, the rover drivers commanded a set of MAHLI images of the wheels, which revealed a huge
hole in the left front wheel. They started commanding wheel images after every drive to
monitor the development of the wheel damage. Wheel imaging slowed down driving and
revealed rapidly progressing damage (Figure 3.9 and section 4.6.4).
The mission appointed a Tiger Team led by Rich Rainen (who had managed the rover’s
mechanical team during its construction) to answer three questions: What was causing the
damage? How could the mission reduce or prevent further damage? And what was the life
expectancy of the wheels?10 Following experiments in the Mars Yard, the Tiger Team quickly determined that the rugged terrain was a factor. Sharp-pointed rocks that were
embedded in the ground did not shift when the rover passed over them; instead, they
pierced the wheels. No rover had encountered such embedded, sharp rocks before.
The project directed the engineers to avoid pointy rocks to the best of their ability, take one set of wheel images on every drive, and perform full wheel imaging (five sets of
images interspersed with 60-centimeter drives, in order to present all surfaces of the
wheels to the cameras) once every 100 meters. This effectively ended the use of autonav
for some time, which dramatically slowed the rover’s progress. Moreover, every
9 JPL (2013)
10 Interview of Rich Rainen and James Erickson conducted September 18, 2014
128 Mars Operations
Figure 3.8. Top: typical hummocky terrain. Part of a mosaic of left Mastcam images from sol 412. Bottom: typical rugged terrain. Part of a mosaic of left Mastcam images from sol 437.
NASA/JPL-Caltech/MSSS.
full- wheel- imaging sol advanced the rover only 2 meters toward the destination at the cost of a precious drive sol. One consolation was that sequencing arm activities for wheel
imaging permitted more opportunities for APXS and MAHLI use than the science team
had previously been able to justify. The project began to employ surge sols (see section
3.4.3) in order to make the most of every opportunity to drive.
3.5 Mission Summary 129
Figure 3.9. Development of damage to the left front wheel. MAHLI images taken on sols 177, 411, 463, and 469. NASA/JPL-Caltech/MSSS.
As the engineers performed further tests on wheel damage, a group of scientists and
engineers led by John Grotzinger and Matt Heverly mapped the terrain ahead and drove a
virtual rover through digital terrain models to develop plans for a feasible future long-term drive path that would avoid wheel-damaging terrain. Unfortunately, the previously planned
rapid transit route, which had preferred high ground for visibility, coincided with the worst terrain. In between high ground were depressions filled with sand, which would be kinder
to the wheels, but the valleys had their own problems: driving in depressions meant less
long-distance visibility; required a slightly longer drive distance in order to detour around highlands; and had potential issues with “pinch points” where the rover would have to pass
through relatively narrow and/or steep gaps in order to exit one valley and enter another.
On sol 524, the rover departed the rapid transit route to enter sand-filled valleys. The
rover had to pass over a relatively high sand ripple blocking Dingo Gap in order to enter
the first of the valleys (Figure 3.10). It successfully made the crossing on sol 535.
Driving in valleys provided far more opportunities to study rock layers from the side,
and the science observations improved. On sol 574, the rover approached the third and final Bradbury traverse science stop, named the Kimberley, where three distinct rock units came
together (Figure 3.11). They spent nearly two months at the Kimberley, drilling at Windjana on sol 621. While working at Windjana, the MAHLI instrument experienced and recovered
from its first anomaly, which put the instrument out of service from sols 615 through 626.
130 Mars Operations
Figure 3.10. Dingo Gap, where a tall sand ripple obstructed Curiosity’s progress westward into the safer valleys. In the distance is the rim of Gale crater. Left Mastcam mosaic from sol 530. NASA/JPL-Caltech/MSSS.
Figure 3.11. View from the Kimberley, a mosaic of many left Mastcam images taken on sol 590. In the foreground are layered rocks, the lowest of the three distinct units exposed at the Kimberley. Two more units make up the lower and upper slopes of Mount Remarkable, the
mound at middle right. Curiosity drilled near the toe of that mound at Windjana on sol 621.
In the distance on the left are the lower foothills of Mount Sharp, Curiosity’s eventual destination. In the distance on the right is the rim of Gale crater. NASA/JPL-Caltech/MSSS.
3.5 Mission Summary 131
The pause at the Kimberley allowed the wheel damage Tiger Team to complete their
work. See section 4.6.4 for details on the wheel investigation and results. Wheel imaging at every drive proved that damage was progressing only slowly and at a rate predicted from
Earth experiments. So sol 636 was the last time that the engineers sequenced single sets of wheel images before every drive; after that, they continued doing full wheel imaging
approximately every 500 meters.
Instrument teams began preparing for extended-mission operations. CheMin, for
instance, tested whether they could re-use sample cells. On sol 640 the rover delivered a
Windjana sample to a CheMin cell that had previously held Cumberland material. They
detected no cross-contamination of the Windjana sample by Cumberland and cleared
future deliveries of samples to previously used cells.
On May 30, 2014 (corresponding to sol 645) the team selected a new future traverse
that diverted the rover to the south around a large region of potentially wheel-damag-
ing caprock called the Zabriskie plateau. The new route had the advantage of leading
the rover to rocks that represented the base of Mount Sharp earlier than originally
planned, before crossing over the dune field. They would need to cross a short stretch
of the Zabriskie plateau in order to reach those rocks. The rover climbed onto the pla-
teau on sol 691.
They started using surge sols again in order to make the most of unrestricted drive sols.
They tested a new “sidewalk mode” of MARDI imaging on sol 651 (see section 7.3.2) and used it for science purposes on the drive onto the plateau. As the rover approached the
dune field, it encountered more sand ripples and some valleys filled with rippled sand. The rover bogged down in sand twice, once at Sourdough on sol 672 and again at Hidden
Valley on sol 711. The team backed out of Hidden Valley and modified the path slightly to
avoid valleys containing obvious sand ripples, sticking to places where the sand seemed to
be a thin coating over rock. On the way out of Hidden Valley, they noticed a bit of Mount-
Sharp-related rock that appeared suitable for drilling, but a drill attempt at Bonanza King on sol 733 resulted in the fracturing of the rock, halting drilling. The team elected to abort the sample attempt and drive onward to a better-looking outcrop.
3.5.4 Mission to Mount Sharp
Curiosity arrived at basal Mount Sharp rocks at a site called Pahrump Hills on sol 751, just after the first extended mission began. The Zabriskie plateau had ended, and Curiosity left the rock
units of the Bradbury plains behind. The bright-colored Pahrump Hills outcrop
contained material that the mission had referred to as the “paintbrush unit” when mapped
from orbit, but it was renamed the Murray formation as Curiosity approached. It consisted
of very finely laminated mudstone. Across a distance of 150 meters, the outcrop rose 15
meters of elevation, a convenient vertical slice through hundreds of rock layers. Curiosity drilled into the lowest-elevation spot on the outcrop, at Confidence Hills, on sol 759.
The rover proceeded to walk the Pahrump Hills outcrop three times. On the first circuit
(sols 780 through 799) the focus was remote sensing. On the second circuit (sols 800
through 862) there was more contact science work with APXS and MAHLI to characterize
the rock (Figure 3.12). Finally, on the third trip, Curiosity drilled at two locations, Mojave near the base of the outcrop on sol 882, and Telegraph Peak near the top on sol 908.
132 Mars Operations
Figure 3.12. Left Mastcam panorama of the “work volume” in front of the rover after a drive to an outcrop named Chinle on sol 826, during the second circuit of Pahrump Hills. These kinds of mosaics are used to plan contact science with MAHLI and APXS. Curiosity surveyed the outcrop to study trends in sedimentology and composition up the outcrop. NASA/JPL-Caltech/MSSS.
Unfortunately, as the rover prepared for the second circuit on sol 801, the autofocus laser on the ChemCam instrument failed. By sequencing many observations at slightly different
focal depths the ChemCam team could continue to gather science data, but less efficiently,
and large arrays of shot points were no longer possible. With prodigious effort the team
developed a new autofocus capability using the ChemCam imager, but not until sol 983, so
autofocus was not available for the entire Pahrump Hills campaign (see section 9.2.3).
Another persistent problem began at the Telegraph Peak site: the drill experienced a
soft short in the percussion mechanism on sol 911 that has recurred intermittently on a
