Emily Lakdawalla
Page 16
long as they could fit a 9-hour planning period in work-permissible hours within the
16-hour window between the receipt of end-of-sol data from Mars and the time of the next
sol’s uplink.
As days and sols turn over, the beginning of Curiosity’s Mars sol creeps later and later
in the tactical team’s Earth day. If decisional data arrives on the team’s computers after the planned start of work, they don’t have time to analyze the data from Mars before they need
to plan the next day’s activities. For a couple of sols, they can slide the Earth planning
3.4 Tactical Planning Process 117
timeline a little later in the day – starting, say, at 11:00 in the California morning and finishing at 8:00 in the evening – but these “late slide sols” only buy a couple of days on
Mars-like time.
An Earth planning day comes when the decisional data arrive from Mars too late for an
Earth time schedule, in the middle of the day in California. On these “restricted sols,” the team has to plan the rover’s activities without any knowledge of whether the previous sol’s activities executed successfully. If the previous sol included arm work or driving, further motion is usually precluded until the planners can assess the success of the activities, so restricted sols following arm work or driving are heavy with remote sensing. (The engineers do consider it safe to move the mast head to perform imaging and ChemCam opera-
tions despite not knowing the state of the rover.) If the previous sol included a drive, the team has no way of knowing what the immediate landscape looks like around them.
Therefore, they can’t conduct science work with the arm or target remote sensing. When
the mission is in restricted sols, drives can only be commanded at most every other day.
The mission’s first restricted sol was sol 92.
Common restricted-sol activities include untargeted remote sensing in which cameras
or spectrometers shoot in the blind. Some remote sensing observations don’t actually
require detailed position information, like 360° panoramas, or imaging of distant targets
whose positions don’t change much with one drive, like targets on the crater rim, the Gale
central mountain, or sky objects like the Sun, clouds, Mars’ moons, stars, and comets. The
team may also use restricted sols for SAM or CheMin analyses of samples already inside
the rover. Sometimes restricted sols include little activity at all, an opportunity to let the batteries recharge. The restricted-sol period continues until the Mars clock drifts far
enough with respect to the Earth clock for the 9-hour planning cycle to fall within the
16-hour window again. There is a “soliday” – an Earth day in which there is no need to
plan for Mars, one every 38 Earth days – and then the mission comes in for two or three
days of early slide sols to begin a couple of weeks of unrestricted planning. Whenever
possible, the mission tries to plan solidays to fall on weekends.
3.4.3 Weekends, holidays, and surge sols
Even after the transition to Earth time, daily Mars operations imposed difficult demands
on the lives of mission personnel. Operating through weekends was especially hard on
workers with families. Knowing that the mission could continue for years, Curiosity man-
agement worked to reduce the mission planning schedule.
As of sol 180, the mission ended routine Sunday tactical planning, planning two sols
every Saturday instead. During restricted sols, the rover could be commanded to drive on
Saturdays, to allow Mondays and Wednesdays to be used for planning driving sols, with
Tuesdays and Thursdays used for untargeted remote sensing. Fridays could then be given
over to arm activities and/or targeted operations with remote sensing instruments. Sundays
were often used for time- and power-intensive SAM and CheMin analyses and/or untar-
geted weather observations.
As of sol 270, the mission ended routine Saturday planning. From then on, Friday tacti-
cal planning covered three sols, or two with a soliday. And very rarely, the mission reactivated Saturday planning in order to take advantage of unrestricted sols for driving or
drilling, but the project ended this practice in May 2015.
118 Mars Operations
For a few months beginning sol 515 and again on sol 635, in order to maximize the use
of unrestricted sols, the mission employed the concept of “surge sols”. These are engineer-
only (no formal science activity) sols with only a 6-hour planning period. They allow the
team to begin planning very early or late in the Earth day and eke out another day or two
of unrestricted drive sols before flipping over into restricted-sol operation. The project also performed surge-sol planning on weekends during unrestricted-sol periods, again without
formal science team participation.
After the end of the prime mission, around sol 765, the mission reduced planning days
further, producing two-sol plans only three weekdays a week when in restricted sols.
Nowadays, a typical 38-day/37-sol period begins with two or three early slide sols, then two or three weeks of 5-day-a-week unrestricted sol-planning, followed by two or three late
slide sols, then two or three weeks of 3-day-a-week restricted-sol planning, then a soliday.
At the start of Earth time planning, operations were more often in restricted than in unre-
stricted sols. As the team has become more experienced and the planning period has been
shortened (to 8 hours), the mission now enjoys slightly more days in unrestricted sols.
The mission has always reduced the intensity of planning during major United States
holidays like Thanksgiving, Christmas/New Year, and Independence Day. They prepare
multi-sol plans to tide the rover through these periods, usually focusing on routine envi-
ronmental observations. Holiday plans don’t usually generate as much data as regular
plans, so routine orbiter communications (which the rover handles autonomously accord-
ing to a schedule delivered months in advance) during holidays are periods of catching up
on data downlink.
3.5 MISSION SUMMARY
Recounting the daily operations of the rover is beyond the scope of this book. The follow-
ing broad overview is intended to provide context for the discussion of how the rover’s
systems and instruments work in the rest of this book.7 Appendix 1 contains a list of the official mission summaries of each sol of activity. A brief overview of mission activities is in Table 3.2.
3.5.1 Site context
Curiosity landed in the northern floor of Gale crater, at 4.5895°S, 137.4417°E and an ele-
vation of 4501 meters below the Martian datum (Figure 3.3). One of the deepest holes on
Mars, Gale is located at the boundary between Mars’s southern highlands and northern
lowlands. Gale displays clear evidence for water having once flowed from the highlands
surrounding the crater through gaps in the rim and then depositing overlapping alluvial
fans of sediment on the crater floor. One such channel and fan is Peace Vallis, to the
7 This section is based upon my years of reporting for planetary.org on the ongoing adventures of the Curiosity mission. That reporting is based upon mission images, press releases and team blog entries on the JPL and United States Geologic Survey websites, roughly monthly interviews of Ashwin Vasavada, and occasional conversations with numerous other team members
3.5 Mission Summary 119
Table 3.2. Brief summary of major phases of the Curiosity mission.
Sol
Site/drive
>
Date (UTC)
Event
0
1/0008
6 Aug 2012
Landing
21
3/0100
27 Aug 2012
Drive toward Glenelg
57
5/0000
3 Oct 2012
Arrive at Rocknest
102
5/0388
19 Nov 2012
Depart Rocknest, drive toward Glenelg
166
6/0000
23 Jan 2013
Arrive at John Klein in Yellowknife Bay
272
6/0068
12 May 2013
Arrive at Cumberland, Yellowknife Bay
324
7/0000
5 July 2013
Depart Cumberland, begin Bradbury traverse
392
16/0050
12 Sep 2013
Arrive at Darwin (Waypoint 1)
402
16/0328
23 Sep 2013
Depart Darwin, continue Bradbury traverse
439
21/1572
31 Oct 2013
Arrive at Cooperstown (Waypoint 2)
453
22/0484
14 Nov 2013
Depart Cooperstown, continue Bradbury traverse
535
26/0366
6 Feb 2014
Cross Dingo Gap
574
30/0740
18 Mar 2014
Arrive at the Kimberley (KMS-9)
634
32/0204
19 May 2014
Depart the Kimberley
753
42/1020
18 Sep 2014
Arrive at Pahrump Hills
923
45/0558
12 Mar 2015
Depart Pahrump Hills
992
48/1194
22 May 2015
Arrival at Marias Pass
1072
49/0294
12 Aug 2015
Depart Marias Pass, travel south to cross the Stimson unit
1172
51/0592
23 Nov 2015
Approach Bagnold Dunes for first campaign
1248
52/0722
9 Feb 2016
Traveling west toward the Naukluft plateau
1281
53/1284
14 Mar 2016
Climb onto Naukluft plateau
1369
54/2508
12 Jun 2016
Turn south to cross the Bagnold dunes
1427
56/1326
11 Aug 2016
Approach Murray buttes
1454
57/2582
8 Sep 2016
Depart Murray buttes, drive south
1508
59/0936
2 Nov 2016
Enter southern Bagnold dunes
1601
60/3162
6 Feb 2017
Begin second Bagnold Dune campaign
1671
62/1140
19 Apr 2017
Exit dunes, traverse south to Vera Rubin Ridge
(formerly known as Hematite Ridge)
1726
64/0000
14 Jun 2017
Arrive at Vera Rubin Ridge, turn east along ridge base
1812
66/0000
11 Sep 2017
Reach top of Vera Rubin Ridge
northwest of the landing site. But there were many other such channels and fans all around
the rim; Peace Vallis was just one of the last to form, so is the most prominent today.
At the center of Gale crater is a 5-kilometer-tall central mound of layered sediments
formally named Aeolis Mons. The science team refers to the mountain as Mount Sharp,
after Robert Sharp, a pioneering Caltech planetary geologist. Researchers studying orbital
data before the landing were divided on how the mountain formed, but it did seem clear
that different styles of geology prevailed at different times. In particular, the lowermost elevations of the mountain were made of nearly horizontally layered rocks, whereas the
upper, brighter slopes lacked such obvious layering. NASA’s Mars Reconnaissance Orbiter
had spotted spectral signs of clays, sulfates, and hematite in Gale’s lowermost layered
rocks, all of which form in different kinds of wet environments. Reaching the lowermost
slopes of the mountain to study those rocks was a major goal for the science team. Then
they hoped to climb up through the layered rocks to study the history preserved in them.
They never intended or expected to summit the mountain; at best, they hoped to reach the
120 Mars Operations
Figure 3.3. Context map of the landing site. Inset: topographic map of Gale crater from Mars Express. Gale is about 150 kilometers in diameter. Yellow rectangle shows location of main map. Elevation scale is in meters relative to Martian datum. Main map: major landmarks at the landing site. Base image is the Mars Odyssey THEMIS daytime infrared mosaic. NASA/
JPL-Caltech/ASU/Emily Lakdawalla.
3.5 Mission Summary 121
boundary between the lower mound and the upper mound in order to understand what
happened in Mars’ history to change the style of sediment deposition so abruptly.
During the cruise, members of the science team had carefully mapped the geology of
the landing ellipse using orbital images, so they were prepared with a good understanding
of the regional geology and their likely drive route before the landing. The landing placed them several kilometers to the southeast of the end of the Peace Vallis fan. Between the
rover and the mountain lay a linear swath of black sand dunes, later called the Bagnold
dune field, named for Ralph Alger Bagnold, a pioneer in the study of sand’s behavior in
deserts. Most of the dune field was considered hazardous to the rover. However, southwest
of the landing site, the dunes thinned out near a cluster of steep-sided buttes that the mission named the Murray buttes after Bruce Murray, a Mars geologist and early leader in
NASA’s Mars exploration. To reach the interesting rocks at the base of the mountain,
Curiosity faced a lengthy drive – more than 9 kilometers as the orbiter flies, much longer
for a wheeled rover dodging obstacles. At Murray buttes, the rover could cross the dune
field and finally reach the lower mound’s layered rocks. Figure 3.4 is a visual summary of
the rover’s route.
3.5.2 Yellowknife Bay campaign and the sol 200 anomaly
The first order of business upon landing was to establish the basic functions of the rover, like raising the mast, establishing routine telecommunications, and making sure that the
rover’s power and thermal systems were operating as expected. Then the rover stood down
for four sols for an upgrade of its operating system, reprogramming the main computer
from an interplanetary spacecraft into a surface rover. Figure 3.5 provides an overview of the major external Curiosity rover systems relevant to the surface mission.
Initially, the engineering side of the tactical team had more control over Curiosity than
the science team did. Curiosity required a commissioning activity phase to work it through
its engineering and science functions. Even after commissioning ended, there was a long
list of first-time activities that engineers methodically paced through: first drive, first contact science target, first scooping, first use of different driving modes, first drill site, and so on.
Rather than immediately beginning the journey southwest across nondescript-looking
terrain, the project science group decided to start the mission with a drive of about
500
meters east to a location they named Yellowknife Bay, where three distinct rock types
occurred together. While working through its first-time activities, Curiosity would be able to perform productive science there.
Curiosity used all the environmental and remote sensing instruments for the first time
on Mars at the landing site. RAD measured the radiation environment. DAN detected
neutrons from the ground (and also from the MMRTG). Mastcam took photos, testing out
its focal mechanism. ChemCam lasered a rock. REMS took weather data. In the very first
days of operations, the REMS team discovered that one of their wind sensor booms had
been damaged, likely by gravel launched into the air by the force of the descent engines
impinging upon the surface. The wind experiment on REMS has never functioned fully,
but the rest of the REMS sensors have been active since landing.
122 Mars Operations
Figure 3.4. Route map for the mission to sol 1800. Bold text denotes drill or scoop sites. Map by Emily Lakdawalla on a base image of Mars Reconnaissance Orbiter CTX mosaic colorized with Mars Express HRSC image.
3.5 Mission Summary 123
Figure 3.5. Science instruments and major external systems of the Curiosity rover. Top image is a rover self-portrait taken at John Klein on sol 177. NASA/JPL-Caltech/MSSS image
release PIA16764. Bottom image taken June 3, 2011 during mobility testing. NASA/JPL-
Caltech image release PIA14254, annotated by Emily Lakdawalla.
124 Mars Operations
The rover drove for the first time on sol 16. During the next few weeks the rover drivers
slowly increased its driving autonomy, beginning with blind drives, later adding in visual
odometry to increase drive accuracy (see section 6.5 for more on the different driving modes). SAM ingested its first atmospheric sample on sol 18. The SAM team initially
thought they had detected abundant methane in the air, but it turned out to be contamina-
tion from the leak that had happened before launch (see section 9.5.1.3).
Scientists selected a rock they named Jake Matijevic for the first contact science obser-
vations (APXS compositional info and MAHLI photos) on sol 46. The engineers com-
manded the arm to reach out and scoop a sample of sand for the first time at the Rocknest
sand drift on sol 61 (Figure 3.6). They shook the sample inside the Collection and Handling for In situ Martian Rock Analysis (CHIMRA) sample handling mechanism on the arm in