Sunday, August 5, 2012

How to do Science with 300+ Team Members and a Rover on Another Planet

Space missions are special. They take hundreds of people cooperating over many years toward a common goal of success.  It’s a complicated process.  MSL is my first mission, and this is my perspective of how the process works.

There are innumerable interesting scientific questions one can ask about Mars, ranging from how it formed to how it has changed through time geologically to how it has changed through time climatically to the potential existence of life.  The first step in any mission is deciding which of those questions to investigate.  To help guide those decisions, NASA sponsors the Mars Exploration Program Analysis Group (MEPAG).  In addition to other activities, MEPAG maintains a document that outlines the science community’s consensus on the most important scientific questions to address in relationship to understanding Mars.  Any scientist interested in Mars can participate in MEPAG meetings and provide feedback to this “Goals Document”.  Based on the highest priority science investigations, NASA then commissions working groups to study particular mission types, for example an orbiter, a rover, or sample return.  They include evaluations of whether or not the desired science investigations are technically feasible and financially realistic.  Once potential missions are well enough defined, they are evaluated in the context of all of NASA’s planetary science missions by a committee established by the National Research Council.  This committee produces a “Decadal Survey” document, which outlines what NASA should plan for and accomplish within the field of planetary sciences in the next 10+ years.  If funding is available, the NASA Planetary Sciences Subdivision is required to take the appropriate steps to implement technology development, fundamental research, and missions with the priorities provided in the Decadal Survey.  

When a mission to Mars of a certain type and with general scientific goals is a high priority in the Decadal Survey, NASA commissions a large number of studies to define what is technically possible, what is scientifically reasonable, and what fits within the “budget wedge”, e.g. how much money per year over the next decade can be expected minus the amount per year that is already committed for other missions.  Eventually, a mission emerges that is defined by more specific scientific goals. A call for proposed instruments is released to the science community.  This call lays out what types of observations need to be made, how much money is available, limits on the power and weight for instruments, and many more technical details.  In the case of MSL, the call for instrument proposals included a call for imaging instruments (e.g. cameras).  Malin Space Science Systems proposed to build and operate several cameras, and I was on one of those proposals.  Once the proposals are submitted to NASA, a committee of experts evaluates each class of instrument and chooses those that they think are the best for the money and can actually be built - there are many instruments we want that are just too difficult to build so that they can be light enough and low power enough to go on a rover AND work at freezing Mars temperatures AND actually produce good results.  When the proposals are chosen, the selected teams get money to implement what they promised.  Our camera proposal was chosen.  
Problems come up.  Problems are solved.  Designs are changed.  Things are removed.  Things are added.  It has taken 8 years to go from the selection of proposals to the launch of MSL!  (It was actually delayed by 2 years due to some technical problems that emerged in the detailed design, implementation, and testing of the rover.)  

While the engineers are building the rover and instruments, the scientists are learning what the instruments can do, calibrating them, choosing where to land, dreaming up new hypotheses to test, etc.  Many individuals on the team are both engineers and scientists - they have a scientific question that they build an instrument to address, or they build an instrument and find science questions that can be addressed by their analyses.  Other team members are one or the other.  The thing we all share is a focus on mission success.  If the instruments fail, the scientists don’t get their data.  If there weren’t interesting science questions, the engineers wouldn’t have a cool rover to design, build, and test.  
We are now at that critical point where everything changes.  The hardware is all built and about to land on Mars.  The goal on MSL now is to operate the rover and its instruments as productively as possible on another planet.  Curiosity is a robot; every single action is controlled by software.  The software is designed to do some things on its own, like Entry, Decent, and Landing (EDL).  It has to be able to do that autonomously because, right now, it takes 14 minutes for a signal to go from Earth to Mars.  It only takes 7 minutes to land.  Thus, we can’t help Curiosity during EDL; she has to do it on her own.  However, once Curiosity is on the surface of Mars, things can go more slowly.  The team on Earth can decide what to have the rover do, and we can send commands up asking her to do different things each day.  

Putting the daily commands for Curiosity together is now our focus - this is called Operations.  Four times per martian day (called a sol), one of two orbiters around Mars will talk to Curiosity.  In the martian afternoon, the orbiters will receive data from Curiosity and in the martian morning, they will provide commands to Curiosity (and receive more data).  These data include the health of the rover, various essential engineering details, and scientific results.  As soon as these data are relayed back to Earth, the science and engineering teams pore over all the details.  If something is wrong with the rover, Tiger Teams are assembled to figure out what is actually wrong and how to fix it.  If nothing is seriously wrong, the science team uses the new data to plan observations for Curiosity to make the following sol.  Every single observation has to be requested.  For example, if you want to know if there is a rock nearby, you have to ask for a picture and wait a sol (or more) for that picture to come back and then look at it.  Since we need to know where we are, images are taken very frequently.  If we want to know the composition of that rock, it takes more planning.  If we have an image, we know where the rock is, and the ChemCam instrument can then be used to vaporize a bit of the rock with its laser.  It takes another sol to vaporize the rock and get that information back.  If we want more detailed results from the APXS instrument on the rover arm, the scientists have to decide where on the rock they want to analyze.  Then the engineers have to figure out how to move every joint on the arm to get the APXS instrument to that position safely.  If it can work, the scientists and engineers work together to make the detailed software commands that tell Curiosity how many turns of each motor and in what order to move for the instrument to end up safely in the right spot and then make the analysis.  Once everything is proofread and any new commands are tested on the twin rover in the “Mars Yard” at JPL, the commands are sent to Curiosity to execute.  As you can imagine, this takes time!

Every single sol, the engineers and scientists go through this process - making sure the rover is safe, deciding what to have Curiosity do, writing the commands that will be executed, proofreading them many times, and sending them off.  We call these “tactical” activities.  We have roughly 16 hours between the time we get data from Curiosity until it’s time to send up the next set of commands.  It takes a lot of people to do this well!  And the team will be doing it every sol for one Mars year (~2 Earth years)!

As you can imagine, it is easy to get caught up in the details.  However, we have those big science questions that NASA used to define the mission.  The mission has to address those questions; it has to stay on track and not spend all of its time looking at everything that might be interesting.  Thus, there is a management structure for “strategic” planning.  The people who led the instrument teams and a few people appointed by NASA make up a committee that sets the strategic timeline for the mission.  For MSL, the long-term goal is to investigate the rocks that make up Mount Sharp in Gale Crater.  Thus, the committee might give the guideline that the rover can characterize a particular set of rocks for 3 sols, but then has to move toward the main science target.  The tactical planning then has some long-term structure.

My first job in operations is as a Long Term Planner (LTP).  A LTP is assigned to work with the tactical process each sol.  Their job is to make sure the tactical process is consistent with the strategic guidelines.  For example, the LTP would intervene if the tactical planning started a set of analyses that would take 5 sols, but Curiosity was supposed to be moving on in 3 sols.  The LTP also makes sure that important discoveries made by team members during the tactical process get incorporated into the strategic plans.  For example, if those 5 sols of analyses were in response to the discovery of a new feature that was really important for the science goals, the LTP would make sure the guiding committee knew about the discovery, possibly suggesting modifications to the strategic plan.  In addition, the LTPs facilitate scientific discussions and interpretations.  After the activities for the next sol are chosen, the LTP leads a Science Discussion during which team members share the discoveries of the sol, plus discuss interpretations of data, new scientific hypotheses, possible investigations that should go into the strategic plans, etc.  This is a place for heated debates, consensus building, and new insights.  Finally, the LTPs are responsible for keeping track of many details such as things that got forced off the tactical plan due to power or time constraints but are really important, the names of sites and features, etc.  

It’s a great job!

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