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Daniel Limonadi is a senior flight systems engineer at the Jet Propulsion Lab in Pasadena.

Sampling Mars, Part 4: Commissioning the Rover and Sampling System

Posted by Daniel Limonadi

2012/08/22 07:04 CDT

Topics: explaining technology, Curiosity (Mars Science Laboratory)

All right, now that you know a little about the hardware and science instruments, and some of the key general challenges associated with doing sampling operations on Mars, let’s talk about how we are commissioning the rover and, in particular, the sampling system after landing on Mars....

Due mainly to the increased complexity of the instruments and engineering systems (especially the SA-SPaH subsystem) on the Curiosity rover, but also taking advantage of the longer expected life, we will be spending a longer time than past missions getting through system commissioning activities after we land on Mars.  Most past Mars lander missions have had relatively quick commissioning phases. Opportunity and Spirit were basically commissioned once they drove off their landers on sols 7 and 12, respectively. (A sol is a Mars day, which is 24 hours and 39 minutes long.) For Phoenix, it was about 3 weeks. The short commissioning time for these missions was partly driven by the fact that these missions had short primary mission durations of only 90 sols,  so they were in a big hurry to get going.

Curiosity, on the other hand, has a minimum required lifespan of 669 sols, or 1 Mars year. For perspective, orbiting spacecraft can take 2 months or more to complete a careful checkout of their instruments and engineering systems. It really depends on the complexity of the system; on how much checkout needs to get done in space versus what could get done before launch; and on how much time pressure there is on the mission.  Anyway, back to Curiosity…

The commissioning phase for Curiosity is spread over threemain bins of activities.  Two of them are part of the formal early “Characterization Activity Phase” (CAP), and one of them is a more broad and stretched-out-in-time bin we call “First Time Activities” (FTAs).  CAP is broken into CAP 1A and CAP 1B, CAP 2A and CAP 2B.  Broadly speaking, CAP 1 checks out most of the rover and CAP 2 checks out specific contact science and sampling system functionality and performance.

Together CAP 1, 2 and a nominal science “intermission” period between them are expected to take around 30 sols, but might go quicker or slower depending on how things unfold on Mars and how the rover performs.  While there is science sprinkled throughout CAP, now that CAP 1B is complete we will be dropping in more and different flavors of targeted science activities into the remaining engineering checkout activities. So while we have a long commissioning phase, we won't wait for it to be over to begin science activities.

CAP 1A was focused on establishing basic health and safety of the spacecraft, most notably the health of the UHF link to Mars Odyssey and Mars Reconnaissance Orbiter, establishing the X-band high gain antenna link to Earth for morning command sessions, deploying the remote sensing mast, and taking initial pictures of the surroundings.  CAP 1A was complete at the end of sol 4.  We performed CAP 1A on the version of software that the spacecraft completed Entry Descent and Landing on.

The transition to CAP 1B was kicked off by booting into and checking out the surface software load (loaded in late cruise into flight computer memory, but we held off booting into it until after the initial core system checkouts on Mars).  After transitioning to the new flight software load, which we completed on sol 8, we began to performbasic functional tests of more of the instruments and remaining mechanisms on the new surface flight software image. We finished that today with our first drive.

Bradbury Landing

NASA / JPL / Damia Bouic

Bradbury Landing
Scour marks and wheel tracks mark the spot where Curiosity first touched down on Mars on August 5, 2012. The site has now been named Bradbury Landing in honor of the writer and futurist Ray Bradbury.

There is an “intermission” that the science team will have between CAP 1B and CAP 2. The intermission will include initial drives away from the landing site, more in-depth ChemCam and Mastcam characterization and science observations, and the first SAM atmospheric science experiment.  The total length of this period depends on how long the science team wants to drive before carrying on with sample chain checkout activities.  The key flavor difference of intermission is that science is more in the driver’s seat and not trying to squeeze in between higher priority engineering checkout activities that have priority during CAP 1 and 2.  Our current plan is to complete a significant fraction of our drive to Glenelg during intermission.

CAP 2A is focused on checking out enough of the SA-SPaH subsystem, primarily the robotic arm, to allow us to green-light contact science activities after it is done.  We have to confirm that the placement accuracy of the arm after landing is in line with our expectations. We will take high-resolution images of the external and internal surfaces (where accessible) of the turret-mounted hardware.  We'll place APXS and MAHLI on their calibration targets to help finish checking out those instruments.  This will take around 4 sols.  When we are done, the science team can chose to do contact science, placing APXS and MAHLI on rock or regolith targets.

Curiosity deploys the robotic arm for the first time, sol 14

NASA / JPL / Damia Bouic

Curiosity deploys the robotic arm for the first time, sol 14

Although the Dust Removal Tool (DRT) is part of the contact science suite of the rover, DRT use will likely not be allowed yet because there is some residual testing that needs to get done on Earth before we allow use on Mars, and the rover test bed schedule shows us not getting to those final Earth tests until late in August or early September.  Yes, we are still checking out some of our system functionality on Earth, because we were constrained enough in resources during cruise that we had to prioritize landing and non-sampling activities and delay preparations for sampling. This is another place where the project took advantage of the expected long life of the mission to manage the overall workload.  In addition, we’ve had some unexpected technical issues with the system, as is often the case when doing new things.  Working through these issues has sidetracked some of the team and contributed to the delay.  It is nice to have the time to make sure we are ready to go, and to ensure as much as we can that we know how to safely and reliably operate this complicated part of the mission.

CAP 2B is the last CAP activity. It's focused on some core activities we need to do before we do our first surface sampling activities.  It includes a second round of robotic arm checkout, most notably preloading the drill onto the Organic Check Material assembly mounted to the front of the rover.  After the initial preload is performed, the rover will wake up roughly every 2 hours during the night and read an embedded force / torque sensor inside the arm to characterize how the preload changes during the thermal cycle. CAP 2B should last around 2 sols. The reason we preload the arm and drill against the rover body itself is to make sure we understand how just the rover system behaves during a thermal cycle on Mars. (As I explained in my last post, the aluminum body of the rover and the titanium arm expand and contracts several millimeters with the daily temperature swings.)

Curiosity's complex sampling system

NASA / JPL-Caltech

Curiosity's complex sampling system
Components of Curiosity's Sample Acquisition, Processing and Handling (SA-SPaH) subsystem and where they are located on the rover.

During CAP 2B we also do a detailed imaging checkout of the internal and external surfaces of the turret hardware, most notably CHIMRA.  This is important in order to capture the “clean” beginning-of-mission reference state of the hardware and to make sure everything looks nominal. The last thing we do during CAP 2B is to place the arm into two of the poses where we spend a lot of time vibrating to move sample around.  We run the CHIMRA vibration actuator through a frequency sweep in each pose in order to confirm that the system dynamics (i.e. frequency response of the arm / turret system when being vibrated) on Mars are within our design criteria.  Depending on the results of the dynamic characterization we might chose to change the nominal operating frequency of the vibration actuator, but we don’t expect to have to make any adjustments.

CAP activities are generally pre-canned and well tested on Earth prior to execution on Mars.  Once we are done with CAP, we move on to a more nominal tactical and strategic planning cycle for surface operations on Mars.

Due to the complexity of Surface Sampling and Science (SSS) activities, a large fraction of fully checking out SSS functionality is done after this transition to nominal surface operations, under the guise of First Time Activities (FTAs).   FTAs are complex. They involve routine activities, like contact science, scooping, and drilling, as well asthings we may rarely or never  do on Mars, like changing out a drill bit.  We treat the first time we do these things as a special event, essentially like a residual checkout activity.  We make sure all our relevant testing and other preparations are complete and that the project management agrees we are ready to execute the activity safely.

Basically every major sampling function like the first time we scoop, the first time we drill a rock, the first time we drop off a sample, is classified as a FTA.  In addition, we have FTAs that lead up to other FTAs. For example, before we do our first contact science and sampling activities on Mars, we will repeat our arm preload test from CAP 2, but this time on Martian terrain.  We'll do this in order to characterize how arm loads change and how the mobility system behaves during the diurnal cycle with the arm actuallytouching Mars.  This activity helps us understand what kind of risk we might be taking by placing an instrument on a rock in the event there is a fault that leaves the arm and instrument in contact with the rock.

There is a first time activity plan for SSS that lays out all of the activities, the dependencies, and rough durations for all of the entrees.  We will be executing this plan starting after CAP.  I will leave the details of the plan to future blog entrees (and/or other media releases).

Well, that wraps up our initial foray into the Curiosity Surface Sampling and Science system.  Hopefully this quick hardware overview, description of some of our design and operations challenges, and description of how we will do initial commissioning of the system has helped you understand this complex machine a little more.  The team and I are looking forward to actually executing our plans and sharing real results with you!In the meantime, we’ll all need to be patient as we carefully checkout this complicated system and its interactions with Mars.

I also want to send a shout out to Michael Scruggs, Guy Webster, and Emily Lakdawalla, who helped me by doing a review of this blog to help make it more readable and catch general mistakes.  Thank goodness for great editors!

Per Aspera Ad Astra

 

Or read more blog entries about: explaining technology, Curiosity (Mars Science Laboratory)

Comments:

Keith Hearn: 08/22/2012 11:58 CDT

Thanks for these blogs. You've done a great job of explaining details I haven't seen elsewhere.

Torbjörn Larsson, OM: 08/23/2012 10:14 CDT

Yes, thank you for the tour de Curiosity! I wanted to ask about sampling one of Curiosity's main science targets, organics as a basis for habitability. At the present it is unclear to me if Curiosity can detect organics in all martian conditions. The SAM is the "organic chemistry laboratory". Apparently it uses pyrolysis on soil samples (post #2). In post #1 you inform us in the comments that "our hardware design was fully committed and in fab" at the time the Phoenix results came back. Can Curiosity avoid a non-detection by having heat activated oxidants breaking down organics as would have been the case for any organics Phoenix had uncovered? The conclusion as far as I understand was that the detected perchlorates there were sufficient to break down and conceal trace amounts of organics. And it is likely something similar happened to the Vikings experiments. One way to put it is: if Curiosity would have landed where Phoenix did would it make roughly the same analysis? In other words, is a positive organics detection depending on having more fortunate circumstances? I keep forgetting what has been said on its organics detecting capabilities.

entity666: 08/23/2012 12:43 CDT

There are noticeable human footprints viewable in the photos taken by the Left Nav Cam during wheel inspection. http://www.break.com/usercontent/2012/8/22/foot-prints-next-to-mars-rover-2361531

limonadi: 08/23/2012 11:54 CDT

Keith - my pleasure! I'm glad you found them useful. Torbjorn - you raise a very good point, one the project tried to deal with. This would best be answered by a member of the SAM team but I'll take a crack at it based on discussions I've heard and what I know of the instrument: 1) this is a credible threat if indeed there are perchlorates or similar oxidizers, however, there seems to still be some controversy regarding how much of the science community believes that result, I'm just an engineer. 2) 9 of the 74 sample cups inside SAM are pre-filled with wet chemistry derivitization fluid (2 different types, 1 type in each cup). For these cups the instrument "punctures" the seal prior to SA-SPAH pouring solid sample down the inlet. The SAM team tried to select fluids that would allow organics to be detected upon heating even in the presence of some amount of oxidizer; 3) while there might be oxidizers in the soil, the general consensus is that it is unlikely they would be in the rocks (or at least in most of the rocks) so hopefully the risk from drilled sample is significantly less and the regular cups would still be usable for detecting organics in rock sample. The SAM team actually was originally proposed at the start of the mission with these wet chemistry cups. The formula might have been adjusted after the Phoenix results, but I am not 100% sure. Hope that helps. If you search on the SAM instrument you might find a paper or article that does a better job explaining this.

rickyjames: 08/24/2012 09:51 CDT

Fantastic overview, Daniel, thanks. I am wondering about details on just how the TLS is going to be used to monitor methane. Questions: 1. When do we start looking for methane / taking atmospheric gas samples in general? Is there going to be a delay to allow hydrazene to disperse? 2. WIll atmospheric samples be taken continuously when the SAM is not processing a soil sample, or periodically on some schedule? Is this enough of a low power operation where continuous / ongoing monitoring is possible to build up methane detection statistics? 3. I understand that the TLS can differentiate between the CH3D, C12H4 and C13H4 forms of methane and that the ratios of these can help determine if the methane is of biological or geological origin. Will the methane results be kept to the science team for publication or announced as we go along in the mission? Any pre-determined protocol rules in place to handle the PR associated with a discovery of biogenic methane? 4. What's your personal gut feeling - methane results to date are will o the wisps that don't really exist, or Curiosity is gonna prove it's there once and for all? Thanks for your comments, and good luck!

Torbjörn Larsson, OM: 08/24/2012 10:46 CDT

Daniel, thanks for the excellent help! That was exactly what I was looking for. You work through all the differences in the experiment and the predicted differences in the samples. I can't say I understand all those differences (not a chemist), but now I know what to look for and where to find it! Which is useful to me, I have a long standing interest in astrobiology, so Curiosity with its astrobiology (chemistry, geology) is a hot experiment.

Torbjörn Larsson, OM: 08/24/2012 10:55 CDT

Let me be more precise: I have studied astrobiology some, and never really let go. As they say, students never grow old.

limonadi: 08/24/2012 11:17 CDT

rickyjames - I will try to answer the questions I know enough about and will skip the ones I don't: 1) the first SAM atmospheric gas analysis is actually happening overnight on sol 18 (basically as we speak). Some of the Data will be showing up in the ~3am (mars time) UHF pass. Note that this first atmospheric analysis is aimed at engineering checkout of the system and is not optimized for very sensitive readings from the internal instruments - there is a follow up atmospheric run coming up later that will hopefully push the instrument closer to its full detection sensitivity. Re: the hydrazine - we did the math on that and feel that by now the close to the rover thruster plume products have dissipated below level SAM cares about (there is not really any hydrazine in the thruster output - it is all water, amonia, etc). Before landing we looked at what happens with the unspent hydrazine that spilled out at the descent stage impact location and the prediction is that it reacts with the CO2 atmosphere and makes carbazic acid, but at a level below what we think poses any kind of concern given how far away it is - the sampling team wants to stay away from the descent stage though due to contamination concerns; 2) SAM in general takes a lot of power to run. Even a "simple" atmospheric sample analysis takes around 4+ hours, and can go longer for the more complicated versions when they try to decrease their minimum detection thresholds. So, no, planning an atmospheric analysis with SAM is a substantial thing that we schedule in advance and don't just have going on in the background. RAD and REMS work the way you are thinking - low power, internal alarm clocks that turn them on / collect data / turn off... then dump data to rover when it is awake; 3) TLS (and the quadrupole mass spec as well I think, but at lower sensitivities - not 100% sure) can distinguish between between carbon isotopes. The longer the analysis run (increased integration time on TLS, or doing enrichment sequences which SAM can also do) the more sensitive the instrument becomes. My understanding is that while SAM/TLS will be able to look at carbon isotope ratios in the Methane, this will only "lean" or hint the investigation toward biogenic or non-biogenic sources - it is not a definitive bio marker. I.e. it will be one clue but not enough to prove the case. Since I am not a member of the science team I am not super tuned in on the data release plans they have. 4) I'd bet a beer that there is methane, but not much more than that ;-) We are all looking forward to finding out!

limonadi: 08/24/2012 11:20 CDT

Torbjorn - glad you are enjoying using your old skills following this mission. We are glad to have the opportunity to make the data available by building and operating the s/c!

memcinto: 08/30/2012 04:58 CDT

Wonderful blog posts - thank you so much! I just can't get enough of the gory details - it just makes it more and more interesting! Keep us posted, and thanks again!

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