by The Design
calibration target through both Mastcams. (This problem will be solved for Curiosity’s
successor, Mars 2020, by moving the calibration target just a few centimeters toward the
center line of the rover.) The right Mastcam is somewhat farsighted, with a minimum
6 Michael Malin, personal communication, email dated April 14, 2017
7.2 Mastcam 247
in- focus range of 1.6 meters, so its images of the calibration target are not in focus, but that doesn’t affect the calibration target’s usefulness.
Like the Earth sundials that the calibration target resembles, the Mastcam calibration
target has art and text embellishments. Most of these are inherited from the Mars
Exploration Rover Pancam calibration target, but there is a new motto: “Mars 2012” at the
top of the dial (the year is usually hidden from view behind the gnomon as seen by
Mastcam, but it’s visible to MAHLI), and “to Mars to explore” at the bottom. On the four
vertical sides the following text is engraved:
For millennia, Mars has stimulated our imaginations. First we saw Mars as a wan-
dering red star, a bringer of war from the abode of the gods.
In recent centuries, the planet’s changing appearance in telescopes caused us to
think that Mars had a climate like the Earth’s.
Our first space age views revealed only a cratered, Moon-like world, but later mis-
sions showed that Mars once had abundant liquid water.
Through it all, we have wondered: Has there been life on Mars? To those taking the
next steps to find out, we wish a safe journey and the joy of discovery.
The calibration target is 8 centimeters square and has 7 regions useful for calibration,
including 4 color chips at the corners and 3 grayscale rings around the black gnomon
(central post). Ring-shaped “sweep” magnets underneath the color chips and the lighter
two of the grayscale rings attract Martian dust to them, keeping the centers of the magnets less dusty than the rest of the calibration target. 7 The top of the rover pyro fire assembly has, unfortunately, turned out to be one of the dustiest spots on the rover. The Mastcams
image the calibration target whenever they do multispectral imaging, using the same set of
filters as were used for the science observation. Although the dust is obscuring the areas
intended to be used for calibration, the dust affects the brightness and color of the calibration target in a way that is straightforward to model, so it remains a useful calibration tool.
7.2.2 Using Mastcam
As with the Navcams, Mastcam imaging can either be targeted, or “blind.” To do targeted
imaging, the Mastcam team needs Navcam images to provide spatial information. Targeted
imaging doesn’t just happen at drive stops: Curiosity can perform targeted Mastcam imag-
ing in the middle of a drive as long as the drive has not taken Curiosity beyond the terrain mesh calculated at the last drive stop. Blind imaging doesn’t require Navcam context.
Blind observations include 360° panoramas, Sun and horizon observations (since the posi-
tion of the Sun and of distant landscape features don’t measurably change over the course
of a short drive), and observations in rover-relative locations, like the arm work volume
and ChemCam targetable region.
7 Kinch K et al (2013) Dust on the Curiosity mast camera calibration target. Paper presented at the 44th Lunar and Planetary Science Conference, The Woodlands, Texas, March 18-22, 2013
248 Curiosity’s Science Cameras
Figure 7.8. Mastcam calibration target as seen over time. NASA/JPL-Caltech/MSSS/Emily Lakdawalla.
7.2.2.1 360° panoramas
The rover acquires 360° panoramas with the wider-angle left Mastcam in interesting sci-
ence locations and also roughly every 250 to 300 meters along long traverses in order to
document the landscape. Full panoramas need no specific targeting (except coarsely, to
include the top of Mount Sharp), so they are often taken on restricted sols when the rover’s precise state isn’t known. It takes 23 left Mastcam frames to complete a single tier over the full azimuth range of 360°, at about 8 minutes per tier, and roughly an hour for a typical
complete panorama. One tier is centered near the horizon; each subsequent tier drops by
12°; and a partial tier covers the predicted location of the peak of Mount Sharp.
To save on time and bandwidth, the tiers below the horizon are usually incomplete, with
areas including the rover deck skipped. This is a source of frustration to mission team
members and the public alike, who would like to see a Mastcam self-portrait of the rover
on the Martian surface including the robotic arm (which can’t be imaged in MAHLI self-
portraits). To date, only one Mastcam panorama has included all of the rover deck; it was
taken on sol 1197, at Namib dune.
The higher-resolution right Mastcam requires 9 times as many images to cover the
same amount of terrain as the left Mastcam, so has only taken a 360° terrain panorama
once, in imaging sessions conducted from sols 172 to 198, while at John Klein.
7.2 Mastcam 249
7.2.2.2 Tactical support imaging
The left Mastcams are often used to take 5-by-1 “drive direction” mosaics to survey distant terrain in more detail. Unlike Navcam drive direction panoramas (section 6.4.2), the Mastcam panoramas don’t include right-eye imaging, so do not contain depth information
of tactical value. They can be shot blind as long as the rover drivers have a good estimate of the direction they will want to travel. They are useful for helping rover drivers avoid rocks that could damage the wheels. Other tactical planning products include mosaics of the work
volume in front of the rover to prepare for in-situ work (see Figure 3.12), and mosaics of the region targetable by the ChemCam laser in front of and to the right side of the rover, to
improve ChemCam target selection. The Mastcams are also used to inspect the turret before
and after drilling and sampling operations, to image instrument inlet covers before and after sample delivery, and occasionally to capture movies of sample handling events. They are
used to document the health of the wheels, but due to the position of the mast on the rover’s right shoulder, the Mastcams can only see the wheels on the right side of the rover.
7.2.2.3 Mastcam science imaging
Most science imaging is done through the clear filter (producing RGB color images, with
infrared light cut off) unless otherwise noted.
Science images and mosaics. Both Mastcams are used to obtain targeted observations of areas of scientific interest. The images may be used for science in and of themselves for
study of geomorphology, or may provide valuable context to other types of science data. If
a region of interest is larger than a camera’s field of view, the Mastcam team will sequence a mosaic made of slightly overlapping images that can be assembled on Earth later.
Stereo images. The overlapping fields of view of the two Mastcams allow stereo imaging.
For single observations, the Mastcams usually acquire one full frame through each eye,
but mosaics require a different strategy. Because of the different fields of view of the two cameras, it would be wasteful in data bits to capture and return to Earth full images in both eyes for each spot in a stereo mosaic. So they subframe (that is, crop) Mastcam-34 images
taken as part of a stereo mosaic, returning one subframed Mastcam-34 left-eye image for
every Mastcam-100 right-eye image. Operationally, the team refers to these sequences as
“shrinkwrap stereo,” because the field of view of the Mastcam-
34 image has been shrunk
to some size that contains (“wraps”) the entire Mastcam-100 image. But because the two
cameras’ boresights are toed in by 2.5° (1.5° each), the horizontal position of a Mastcam-100
image within a corresponding Mastcam-34 image depends on the target’s distance from
the rover. This complicates the efforts of mission planners to determine how to subframe
the images. In practice, most shrinkwrap stereo observations are cropped to match the
vertical extent of the Mastcam-100 image (which is the same regardless of the distance to
the target), but the horizontal image dimension encompasses all possible positions of the
Mastcam-34 field of view, trading slightly higher data volume for a major reduction in
planning complexity. Figure 7.3 illustrates the location of the shrinkwrap stereo subframe on the left Mastcam field of view.
250 Curiosity’s Science Cameras
Focus stacks. Mastcam has the capability to take many images at different focal depths and merge them onboard into a single best-focus image and range map. This capability
exists because it was required for the shallow-depth-of-field MAHLI and has only been
used on Mars by Mastcam on two sets of observations: one on sol 193 and another on sol
1051/1052. For more on focus stacking, see section 7.4.2.3.
Clast surveys. After drives, the Mastcams often take a stereo pair of images of the terrain to the right of the rover. These photos are shot blind and cover the field of view of the
ground temperature sensor of REMS boom 1 (see section 8.4.2.1).
ChemCam documentation. Mastcam stereo images usually provide context for ChemCam
laser shot points, especially blind targets and AEGIS targets (see section 9.2.2.2). The
ChemCam team has developed a method to automatically colorize ChemCam images with
lower-resolution right Mastcam color information, helping them interpret their data.
Multispectral imaging for mineralogy. When a target is expected to have interesting
spectral content, the team uses all or some of the science filters to image it. ChemCam
laser targets, brushed spots, and areas associated with drilling, scooping, or sample dump-
ing are usually hit with all fourteen science filters. Where the team expects to see minerals that may contain water – most often found in calcium sulfate veins crosscutting the rocks –
they may perform a “hydration survey” using right-eye filters 0, 3, 4, 5, and 6, or just 0, 5, and 6, to differentiate among more-hydrated or less-hydrated forms of calcium sulfate.
The smaller number of filters and use of just the right-eye camera diminishes the data
volume and simplifies the planning relative to fourteen-filter observations, so hydration
surveys can be small mosaics without generating a prohibitively large data volume.
When Mastcam takes multispectral images, nothing in the file names indicates which
filter was used, but the filters are almost always used in order, e.g. [L0, L1, L2, ... , L6]. If it is a multi-position mosaic, the filter wheel may be spun backwards on every other footprint in order to reduce total wheel rotation, e.g. [R0, R5, R6, shift position, then R6, R5, R0, shift position, repeat].
Photometry. Multispectral observations taken with the left camera filters 1, 2, 3, and 6 of the same spot several times over the course of a day allow scientists to study surface properties of the Martian soil. Photometry surveys are often performed when the rover is
parked for some period, over holidays or during anomaly investigations. They can sequence
photometry observations two or three days in a row, performing them at different times of
day to build up dense temporal coverage.
Atmospheric studies. The Mastcams routinely image the Sun through the solar filters, using the Sun’s known brightness to probe the optical depth (which is related to how much
dust is in the atmosphere). Sun images are usually subframed to 256 pixels square. At the
same time, photos of the sky are usually taken in a direction away from the Sun with left-
eye filters 2 and 5, which have similar bandpasses to the solar filters, to measure aerosol scattering properties. On occasion, Mastcam sky surveys span the sky from horizon to
zenith, with or without multispectral observations. Beginning on sol 939, they also began
to take routine images pointed due north at the distant crater rim as a way to observe the
dustiness of the atmosphere within the crater.
7.3 MARDI: Mars Descent Imager 251
Astronomical imaging. Astronomical imaging has a variety of scientific goals. At night, capturing movies of Phobos and Deimos passing through the field of view at the same
time, or of moons occulting bright stars like Aldebaran, can help constrain the moons’
orbital positions. During the day, the Mastcams can observe Phobos and Deimos transit
the Sun for the same purpose (and can even image large sunspots, from a different perspec-
tive than solar spacecraft, particularly in the Sun images from sol 1000–1047, when a very
large group was visible). Mastcam has also watched Phobos enter Mars’ shadow, probing
for dust in the upper atmosphere. It has targeted other bright sky objects, including Jupiter, Saturn, Ceres, Vesta, and stars like Regulus, and achieved a detection of Comet Siding
Spring. Mastcams have even watched the Sun set, justified for atmospheric science pur-
poses but mostly to produce evocative images of a sunset on another planet. Box 7.1 summarizes Mastcam imaging of astronomical targets.
Box 7.1. Astronomical imaging with Mastcam to sol 1800.
Sunset: 587, 956
Transits of the Sun by Phobos: 37, 42, 363, 368, 369, 713, 1032; 1692; by Deimos:
42; by Mercury: 650, 956.
Photography of Phobos: 45, 635, 662, 964; Deimos: 772, 777, 1732, 1738; 1742.
Sequence of images of Phobos entering or exiting eclipse: 393, 964, 970, 979, 987,
998, 1002; 1730; 1736; same by Deimos: 995.
Phobos over Mount Sharp at sunset: 613.
Phobos and Deimos mutual events, 351, 378, 393, 964.
Siding Spring: 772; with Earth, Phobos, and Deimos, 782; with Deimos 783; with
Phobos 784.
Other: Jupiter 378; Phobos occultation of Aldebaran 387; Jupiter & moons & Phobos
& Deimos 393; Phobos & Jupiter & Deimos & Ceres & Vesta & Saturn & Regulus 606, Regulus 662.
7.2.3 Anomalies
The Mastcams have worked well on Mars, with the first puzzling problem appearing early
in 2017. On sol 1576, atmospheric scientist Mark Lemmon first noticed seeing large dif-
ferences between the zenith atmospheric opacity measurements computed from left and
right Mastcam solar images. Yet images from the two cameras do not have different bright-
nesses when the rover was looking in other directions through different filters. Whatever
caused this change in behavior happened at some time between sol 1490 and sol 1576. 8 At the time of writing, the best explanation appears to be that sand has blown into the right
camera baffle, which flows onto the cameras’ front windows when the rover looks up. The
Mastcam team is working on testing this hypothesis, taking some images looking inside
the Mastcam sunshade on sol 1749.
8 Mark Lemmon, personal communication, email dated June 15, 2017
252 Curiosity’s Science Cameras
7.3 MARDI: MARS DESCENT IMAGER
The Mars Descent Imager (MARDI)’s intended purpose was to help the science team
rapidly identify the location of Curiosity’s landing site. The images would also bridge the gap between the orbital coverage of the site and the Mastcam view from the ground.
MARDI f
unctioned as designed, taking 622 images between heat shield separation and
touchdown, and many more after (see section 2.3.7). By the time Curiosity was launched, the sharp eyes of the HiRISE camera on Mars Reconnaissance Orbiter had made MARDI’s
landing-site-localization function mostly redundant, but the video that MARDI returned
during the descent provided engineers invaluable information on the dynamics of the land-
ing, and provided rover fans with a thrilling movie.
MARDI was not required to operate after landing, so was never tested on Earth for survival
through Mars day/night temperature cycles. It has no heaters. However, it also has no moving parts, so there is no reason to expect it to suffer from Martian conditions any more than
MAHLI and the Mastcams do. Since landing, MARDI has been used to image the ground
beneath the rover, documenting the rock fragments and outcrops along rover traverses.
Curiosity’s MARDI was built by Malin Space Science Systems, who had also built
MARDI instruments for Mars Polar Lander (which crashed) and 2001 Mars Surveyor
(which was canceled). The principal investigator is Michael Malin. The Surveyor MARDI
later flew to Mars on Phoenix, but was not actually used during the landing because of
late-appearing concerns about the spacecraft computer’s interface with the instrument.
Although Curiosity’s MARDI bears the same name as these predecessors, it is a wholly
different instrument. It has a successor instrument already in space, the JunoCam aboard
NASA’s Juno orbiter mission to Jupiter. (Interestingly, JunoCam launched a few months
before MARDI on Curiosity.)
7.3.1 How MARDI works
MARDI is mounted to the left front side of the rover, pointed straight downward (Figure 7.9). 9
It uses the same detector, electronics, and software as MAHLI and the Mastcams (see sec-
tion 7.2.1), with much simpler optics. It is in focus at any distance beyond 2 meters. It obtains color 1600-by-1200-pixel images over a wide field of view of 70-by-55°. Images