5.8 SAM AND CHEMIN INLETS AND WIND GUARDS
The final elements in the sample delivery chain are the motorized sample inlets on the top of the rover deck. Three flaps (two for SAM’s inner and outer carousel rings, and one for CheMin) open and close to allow CHIMRA to deliver portions. Mastcam shoots photos of the inlets before and after each delivery in order to check whether wind blew the sample away from the inlet and deposited it on the deck nearby. The rover also uses MAHLI to image the fine mesh grate over the open CheMin sample inlet from time to time, often at night, when the MAHLI LEDs can be used as flashlights to evenly illuminate the interior. The goal of this imaging is to check for clogging by excessively large particles. All these imaging activities are summarized in Table 5.4.Table 5.4. Imaging of the CheMin and SAM inlet ports by Mastcam and MAHLI to sol 1800.
CheMin inlet (Mastcam)
CheMin inlet (MAHLI)
SAM inlets (Mastcam)
SAM inlet (MAHLI)
14
51
71
94
195
282
623
765
884
922
1061
1121
1139
1226
1323
1334
1362
1375
1425
1466
1496
36
74
81
94
195
282
411
558
564
666
774
895
1028
1064
1091
1123
1136
1142
1184
1259
1287
1324
1337
1348
1364
1375
1402
1427
1438
1459
1466
1470
1477
1484
1489
1496
14
90
93
96
114
116
117
196
224
227
281
286
290
353
367
381, 382
413, 415
463, 464
624
653
694
773
887, 888
891
892
928
954
1075
1129
1147
1178
1224
1230
1231
1233
1382
1409
1443
1456
1651
93
96
282
An amusing side effect of the repeated imaging of the sample inlets is that it has been possible to track the motions of bits of gravel on the rover deck over the course of the landed mission (Figure 5.21). This gravel was tossed onto the deck during landing and has rattled around the top surface ever since, occasionally drawing squiggly lines in accumulated deck dust.
Figure 5.21. CheMin inlet and wind guard as seen from Mastcam. Pebbles that have been on the deck since landing leave tracks as the rover’s motion vibrates them across the deck. NASA/JPL-Caltech/MSSS/Emily Lakdawalla.
The difficult experiences of sample delivery in the Phoenix mission caused engineers to be concerned about wind blowing Curiosity’s tiny sample portions away. To mitigate against this possibility, they added spring-loaded collars around the sample inlets, and a corresponding plate over the CHIMRA portion hole. In the event that wind dispersal of sample is found to be a problem, the engineers can deliver sample with the portion plate pressed against a wind guard. This capability has not been used. Mastcam videos of portion delivery recorded on sols 64, 78, 284, and 289 showed the portions dropping straight down for a distance longer than the few centimeters separating the portion hole and sample inlets. The mission has also taken advantage of REMS wind data to select times of day for sample delivery when winds are expected to be minimal.
REFERENCES
Anderson R et al (2012) Collecting samples in Gale crater, Mars: an overview of the Mars Science Laboratory Sample Acquisition, Sample Processing and Handling System. Space Sci Rev 170:57–75, DOI: 10.1007/s11214-012-9898-9
Billing R and Fleischner R (2011) Mars Science Laboratory robotic arm. Paper presented to the 14th European Space Mechanisms and Tribology Symposium, 30 Sep 2011, Constance, Germany
Conrad P et al (2012) The Mars Science Laboratory organic check material. Space Sci Rev 170:479–501, DOI: 10.1007/s11214-012-9893-1
Grotzinger J et al (2014) A habitable fluvio-lacustrine environment at Yellowknife Bay, Gale Crater, Mars. Science 343, DOI: 10.1126/science.1242777
Kuhn S (2013) Curiosity’s scoop campaign, a summary. http://www.planetary.org/blogs/guest-blogs/curiositys-scoop-campaign-kuhn.html Article dated 8 Jan 2013, accessed 6 May 2016
JPL (2014) Lesson Learned: Recognize that Mechanism Wear Products May Affect Science Results. http://llis.nasa.gov/lesson/10801. Article dated 8 Jun 2014, accessed 14 Oct 2015
Kim W et al (2013) Mars Science Laboratory CHIMRA/IC/DRT flight software for sample acquisition and processing. Paper presented to the 8th International Conference on System of Systems Engineering, 2–6 Jun 2013, Maui, Hawaii, USA
Lakdawalla E (2017) Curiosity update, sols 1548–1599: Serious drill brake problem as Curiosity drives through Murray red beds. http://www.planetary.org/blogs/emily-lakdawalla/2017/02031109-curiosity-update-sols-1548-1599.html Article dated 3 Feb 2017, accessed 9 Feb 2017
Limonadi D (2012a) Sampling Mars, part 1: The hardware. http://www.planetary.org/blogs/guest-blogs/20120816-limonadi-sampling-mars-1-tools.html Article dated 16 Aug 2012, accessed 26 Feb 2016
Limonadi D (2012b) Sampling Mars, part 3: Key challenges in drilling for samples. http://www.planetary.org/blogs/guest-blogs/20120821-limonadi-sampling-mars-3-drilling-challenges.html Article dated 21 Aug 2012, accessed 6 May 2016
Manning R and Simon W (2014) Mars Rover Curiosity: An Inside Account from Curiosity’s Chief Engineer. Smithsonian Books, Washington DC
Novak K et al (2008) Mars Science Laboratory rover actuator thermal design. Presentation to the Spacecraft Thermal Control Workshop, 11–13 Mar 2008, El Segundo, California, USA, DOI: 10.2514/6.2010-6196
Okon A (2010) Mars Science Laboratory Drill. Paper presented to the 40th Aerospace Mechanisms Symposium, 12–14 May 2000, NASA Kennedy Space Center
Sunshine D (2010) Mars Science Laboratory CHIMRA: A device for processing powdered Martian samples. Paper presented to the 40th Aerospace Mechanisms Symposium, 12–14 May 2010, NASA Kennedy Space Center
Footnotes
1The arm is described in detail in Billing and Fleischner (2011)
2Use of the arm for sample collection is described in Anderson et al (2012)
3Kuhn (2013)
4The drill is described in detail in Okon (2010)
5Supplementary material to Grotzinger et al (2014)
6Limonadi D (2012b)
7Ashwin Vasavada, personal communication, email dated February 9, 2017
8JPL (2014) Lesson Learned: Recognize that Mechanism Wear Products May Affect Science Results http://llis.nasa.gov/lesson/10801. Article dated June 8, 2014, accessed October 14, 2015
9Manning and Simon (2014)
10James Erickson, interview dated April 10, 2015
11Ashwin Vasavada, interview dated May 1, 2015
12Steve Lee, interview dated September 1, 2017
13Th
e main published source for information on CHIMRA is Sunshine (2010). Cambria Hanson and Louise Jandura explained its intricacies and some last-minute design changes to me in great detail in an interview on June 3, 2016
14Steven Kuhn, personal communication, email dated August 14, 2015
15Vandi Verma, personal communication, email dated April 1, 2017
16Dan Limonadi, personal communication, email dated February 2, 2013
17Ashwin Vasavada, personal communication, email dated November 17, 2017
18There is no published paper about the DRT hardware. Information in this section comes from a paper mentioning the DRT software by Kim (2013) and personal communication with Ashwin Vasavada (email dated February 9, 2017).
19Conrad et al (2012)
20Anderson et al (2012)
© Springer International Publishing AG, part of Springer Nature 2018
Emily LakdawallaThe Design and Engineering of CuriositySpringer Praxis Bookshttps://doi.org/10.1007/978-3-319-68146-7_6
6. The Mast, Engineering Cameras, Navigation, and Hazard Avoidance
Emily Lakdawalla1
(1)The Planetary Society, Pasadena, CA, USA
6.1 INTRODUCTION
The Curiosity mission navigates Mars using a combination of human and artificial intelligence. Both methods rely upon a suite of engineering cameras for situational awareness. The twelve engineering cameras are in six pairs: two redundant pairs each of Navcams, front Hazcams, and rear Hazcams. A remote sensing mast lifts the four Navcams nearly two meters above the Martian surface, while the eight Hazcams are mounted at belly height, four facing forward and four to the rear. The Hazcams and Navcams are flight spares or build-to-print copies of the engineering cameras of the same names on the Mars Exploration Rovers; this not only saved money in hardware, but made it significantly easier to use a modified version of the same rover driving software for Curiosity as for Spirit and Opportunity. The mast also carries the Mastcams and parts of the ChemCam and REMS instruments. Both Navcams and Hazcams are routinely used to gather data for environmental science purposes.
6.2 REMOTE SENSING MAST
Curiosity’s vantage point is a bit higher than most humans’. From the Navcams’ position at 1.9 meters above the Martian surface, Curiosity can see quite far: if the landing site were perfectly flat, the horizon would be 3.6 kilometers away. Of course, Curiosity sits inside a crater, and topography rises above the horizon as far as the rover can see. The nearest foothills of Gale crater’s central mound were about 5 kilometers from Curiosity on landing day. The nearest point on Gale’s rim was 20 kilometers to the north; to the east and west, the visible rim is more like 40 kilometers away. All of this topography is usually visible in Curiosity images of the horizon, although the crater rim and sometimes even the central mountain disappear and reappear over time as the amount of dust in the air waxes and wanes.
The Remote Sensing Mast (RSM) has three motors, of which one, the mast deploy actuator, was used only once to lift the mast permanently to its vertical position.1 The mast’s azimuth and elevation actuators are mechanically capable of panning 362° horizontally and tilting 182° vertically in order to point cameras at every possible target within Curiosity’s view. The elevation mandrel and azimuth twist cap allow the cabling to flex as the mast tilts and rotates. Software prevents the mast from rotating to hard stops, limiting it to panning 360°. Software also limits how far down it can tilt, preventing it from pulling on the cable bundle that runs up the mast to the mast head, reducing its tilt limit by 4°. Thus its tilt can be commanded from –87 to +91°. Two booms containing REMS instrument components are mounted to the mast below the actuators, so their positions are fixed (Figure 6.1).
Figure 6.1. Parts of the remote sensing mast as seen in photos taken during assembly at JPL in 2011. The mast is about one meter tall. In this photo, the two REMS booms are covered for their protection; the covers were removed before flight. NR-A, NL-A, NR-B, and NL-B refer to the right and left Navcams connected to the A-side and B-side computers. NASA/JPL-Caltech/Emily Lakdawalla.
The mast has to be able to point incredibly precisely in order for ChemCam to zap targets selected within Navcam images. The mast’s absolute pointing accuracy is 0.25° (4.6 milliradians), or about 6 Navcam pixels; but its pointing is repeatable to less than a single Navcam pixel. This pointing precision has enabled Curiosity to perform sharpshooting feats like profiling down the side of drill holes (Figure 6.2).
Figure 6.2. ChemCam laser shots are spaced using minute motions of the remote sensing mast. Here, ChemCam laser shots are spaced 1.4 mm apart horizontally in rasters marching down the wall of the Okoruso drill hole. Drill holes are 1.6 centimeters in diameter, and this one was 2.6 meters away from the mast head when the shots were fired. Corresponding mast shot-to-shot angular motion was 0.03° (0.5 milliradians). MAHLI image 1338MH0005880000501506R00, taken at night with LEDs on. Contrast in the image has been increased to emphasize the laser shot points. NASA/JPL-Caltech/MSSS/Emily Lakdawalla.
6.3 ENGINEERING CAMERAS: NAVCAMS AND HAZCAMS
The Navcams are located approximately 1.9 meters from the ground when the rover is level, but their precise elevation depends upon the tilt of the mast head. They are spaced a very wide 42.4 centimeters apart, which gives them depth perception out to a distance of 100 meters. That helps engineers plan long blind or visual odometry drives, the most time-efficient driving modes, as long as the Navcams have a good view of the path ahead. Figure 6.1 shows the positions of all the Navcams. The switch from A-side to B-side cameras after sol 200 moved the rover’s Navcam vantage point downward by 4.8 centimeters.
The fish-eye Hazcams provide Curiosity with situational awareness of the terrain both forward and aft of the rover and in between the wheels, particularly in areas not visible to the Navcams. The Hazcams are hard-mounted to the rover so have fixed fields of view. Figure 6.3 shows the locations of all the Hazcams. They are boresighted 45° below the horizon, with 120° field of view vertically, and 180° corner-to-corner. Because of the wide view, raw Hazcam images are very distorted. The front Hazcams are mounted near the middle of the front of the rover, with the A-side and B-side cameras interleaved, each offset from the next by 8.2 centimeters, giving a stereo separation of 16.4 centimeters for each pair. The front Hazcams provide detailed stereo maps of the area within reach of the robotic arm.
Figure 6.3. Locations of the Hazcams. Top image taken during JPL mobility testing on 3 June 2011. NASA/JPL-Caltech image release PIA14254. Bottom image taken at arrival of the rover at Kennedy Space Center. Credit: NASA/Frankie Martin, release KSC-2011-5909.
When Curiosity switched to the B-side computer, the front Hazcam view of the world shifted to the rover’s left by 8.2 centimeters, resulting in a view that is more obscured (primarily by the shoulder elevation actuator) than the previous view was (Figure 6.4). The rear Hazcams are mounted on either side of the RTG in two pairs spaced 10 centimeters apart, with the A-side rear Hazcams on the rover’s left side and the B-side rear Hazcams to the rover’s right, separated by 1 meter. So when Curiosity shifted to the B-side computer, the rear view seemed to shift left by 1 meter. The new rear view is not substantially different in quality from the old view.
Figure 6.4. Shifting Hazcam points of view between sol 166, on the A-side cameras, and sol 233, on the B-side cameras. The rover did not change position in the time between these two sets of images. The images have been reprojected to correct for the fish-eye distortion of the Hazcams. NASA/JPL-Caltech.
The Navcams and Hazcams have identical detectors, 1024 pixels square. It takes 5.4 seconds to read out a single full-frame image. Rover planners can improve that speed by binning the images or by reading out partial, “windowed” (cropped) images. The cameras are sensitive to light in the 600 to 800 nanometer range – slightly longer-wavelength than human color vision, and similar to the red filter on the Mastcams (Figure 6.5). Only two of the six cameras can be powered simultaneously. So stereo pairs are usually taken at the s
ame time, but front and rear Hazcam pairs have to be taken sequentially.
Figure 6.5. Spectral responsivity of Navcams and Hazcams. From Maki et al. ( 2012 ).
Navcam images of the path ahead and arm workspace are decisional data, required to plan later sols (see section 3.3). It can be tricky to squeeze all the necessary data into the first available downlink, especially if a drive happens late in the sol after the Mars Reconnaissance Orbiter communications pass so only an Odyssey pass is available. Compressing the images reduces file sizes, which allows more images to be returned to Earth. But lossy compression reduces data quality, potentially affecting the quality of the range information that rover drivers use to plan driving and arm positioning. So images that are used for generating range maps are compressed very little, while other images taken only for documentation purposes (for instance, to verify the placement of the robotic arm) are compressed much more.
6.4 USING THE ENGINEERING CAMERAS
6.4.1 Navcam panoramas
With the Navcams’ 45° field of view, it technically takes only eight pairs of Navcam images to cover the complete 360° in stereo around the rover. But to generate good stereo range information for planning, it’s necessary to have substantial overlap between adjacent image tiles, so most 360° Navcam panoramas contain 12 image footprints (where a footprint includes one each of left- and right-eye images) in any tier. Curiosity requires so much overlap because the wide spacing of Curiosity’s Navcams translates into a 21-centimeter offset from their pan axis. Rotating the mast shifts the camera position, making edges of adjacent Curiosity Navcam frames match poorly, particularly close to the rover.
The Design and Engineering of Curiosity Page 25
