Monday, July 18, 2011

Where We Stand Now — Terms and Definitions

(Literally, right now, I'm sitting.)

I'm making the uninformed assumption that my audience consists solely of two types of people:

1) Those who know a lot about MER
2) Those who don't know a lot about MER

For the former: This post will move slow and patience will be rewarded; polish off your skimming skills. For the latter: Time to put your learnin' hats on.

There are, then, two things I want to talk about at this point:

1) Terms and definitions — Engineers live in a world of acronyms, initialisms, and otherwise shortened words. By virtue of the nature of a robotic lander or rover mission, there are many… interesting… ones.
2) Current rover status — Self-explanatory.

These will be split between 2 posts, since the first is rather… big.

Let us begin Operation "LEARN ABOUT MACHINES ON OTHER PLANETS." (Shouting required.)


Terms and Definitions
I will keep this one short. Any other terms and definitions that come up in subsequent posts will have a convenient, if hurried, description.
Sol: A Martian day. In Earth time, it is equivalent to 24 hours, 39 minutes, and 35 seconds, a ratio of 1.027. This small but significant difference is has been a source of pain and suffering for all MER landers and rovers. 
Nominal/Restricted/Slide/Tight (planning modes): This will take some increased wordage. EVERYBODY TAKE A DEEP BREATH. [I deem a carriage return is necessary here]

Pretend that you're a rover. Also pretend that you have solar arrays. It follows that you like to do things during the day when the Sun can directly provide power to your instruments, driving system, heaters, and flight computer. (Or maybe you're a super-rover and you don't need any of that sunlight nonsense. In that case, we call you "the Mars Science Lab.") It then follows that your activities — science and engineering both — are "slaved" to the constraints of the Martian day. 

The similarity in the length of Earth days and Mars days is somewhat of a blessing here, if you're a human operator. You can plan a day ahead while the previous plan is executing, and you can do it all on (something very similar to) the Earth clock. However, that it's a similarity — not an equivalence — is also your Achilles' heel. The 2.7% difference means a drift between Earth and Mars times by that much — almost 40 minutes — every Earth day. Therefore, local solar time on Earth and Mars drift with respect to one another.

(This is a vast oversimplification of time systems for planets.)

So. Right. During the MER prime mission, the MER team worked on the Martian clocks — regular tactical and operations shifts slid by 40 minutes each Earth day. For subsequent extended missions after September 2004, the tactical team created something called "Modified Earth Time" to begin shifting back to Earth time, still planning the rovers' activities in Martian time but constraining shifts to Earth time. Only by the 3rd (and beyond) extended missions in 2005 did they shift to a modified Earth time kind of schedule, with tactical planning only occurring, at most, 5 days a week.

This, then, begs the question: Doesn't this create problems?

Well, yes. But for each problem, the MER team creates a solution. In this case — modified Earth time, 5 days a week — they created several planning "modes"…
Nominal: During Earth day, it is (approximately) Mars night. We plan 1 sol at a time, with the uplink products created just in time to uplink them when the rover wakes up the next Martian morning. At the start of each tactical shift — 8:30am Pacific time — we know the state of the rover for the most critical activities and therefore can accurately plan the next set without trouble. 
Slide: Martian time is drifting! Hold on to your hats! The time at which we uplink is approximately the same every sol, and this is creeping "away" from us in one sense. Therefore, the time at which we know the post-critical-activities state of the rover is also slipping away from us. Therefore, we must slide our start time for building the next sol's plan. We can still plan one sol at a time, and shifts start as late as 12:30pm PST.
Restricted: Now, local solar time on Mars, to which rover activities are slaved, has slipped too much and the time of day on Earth when we would know the state of the rover well enough to plan the next sol's worth of activities is now past our team-imposed limit (12:30pm PST). It's "modified Earth time," remember, and we like to be at work during normal human working hours. Mars day and Earth day are approximately aligned. What we do is "slip backward" — in one sense — and plan multiple sols at once, up to 3 if necessary. By the next planning session — up to 3 days away in Earth time — we don't actually have the latest state of the rover from the latest sol planned. This means any critical activities like driving or instrument arm deployment need to be planned accordingly.

Tight: Now, Mars night is approaching Earth day again, but they're just far enough away from each other that we deem our planning day — a 1-sol plan, by the way — "tight." This means we have limited time in our tactical shift to get the plan ready for the next uplink to the rover.

There are many, many, many subtleties and variables in determining what type each planning shift will be. I have barely scratched the surface here.

Okay, more terms and defs! Science payloads, locked and loaded…
IDD: Instrument Deployment Device. It contains the in-situ science payloads, the ones that require touching the environment — dust, rock, soil, etc. Incidentally, a really cool arm. Incidentally, strong enough to break itself. Incidentally, its "shoulder" actuator is broken. Rarely used, though watch out for increased activity during the Endeavour campaign.
APXS: Alpha Particle X-ray Spectrometer. Does… science. Commonly used.
MI: Microscopic Imager. Does… really tiny pictures. Rarely used.
MB: Mössbauer Spectrometer. Does… science. Rarely used.
RAT: Rock Abrasion Tool. Does… drilling. Rarely used.
Ecam/Navcam: Engineering/Navigation Camera. Does… engineering and navigation camera stuff. Used almost every sol.
Pancam: Panoramic Camera. Does… panoramic and scientific imaging. All those really pretty pictures? This bad boy, right here. Used almost every sol.
Mini-TES: Mini Thermal Emission Spectrometer. Does… science. Currently not used.
Some planning tools that you'll see referenced every now and then:
Maestro: Science activity planner and image viewer. Publicly available.
MAPGEN: Mixed-initiative Activity Plan GENerator. Integrates science plans from Maestro and engineering plans from the tactical team into a high-level resource modeling scheme. It is a spinoff of another JPL-developed tool, APGEN, combining both algorithmic (time- and logic-dependent) and non-deterministic (constraint-based) planning methods. 
SEQGEN: SEQuence GENerator. Command-level expansion and modeling tool developed by JPL. 

And the tactical team on the uplink side…
TUL: Tactical Uplink Lead. The person in charge. The TUL has authority in making tactical decisions over all persons, including the SOWG chair (see below), unless the decision can harm the rover, in which case the Mission Manager can supersede their authority. The TUL is very experienced on the MER project and requires much training.
MM: Mission Manager. The second person in charge. They are, almost always, the most experienced person on the uplink team. Most MMs have been around since Prime Mission. They are trained to see the "meta-problem," to poke and prod the TUL and TAP/SIE and provide oversight.
TAP/SIE: Tactical Activity Planner and Sequence Integration Engineer. This is what I am. The TAP/SIE is the least experienced member on the team, but (ironically) is one of the most critical links in the uplink chain. Anybody hired onto the MER tactical uplink team starts as a TAP/SIE, shadowing certified TAP/SIEs until they can "drive" the uplink process themselves. The end result of the TAP/SIE's work is the integrated sequence of all science, drive, and IDD activities, ready to be uplinked to the rover.
RP: Rover Planner. Two are on shift each planning day. The end result of the RPs' work is the sequence of all drive and IDD activities; these get delivered to the TAP/SIE for integration with the rest of the planned activities.
PUL: Payload uplink lead. For each instrument, there is a PUL. The end result of the PULs' work is the sequence of all activities related to their instrument; these get delivered to the TAP/SIE for integration with the rest of the planned activities, just like the RP sequences.
And the tactical team on the downlink side…
TDL: Tactical Downlink Lead. Collects the downlinked data from the rover system, analyzes it, and provides engineering sequence deliveries to support the uplink process. They also collect input from subsystem engineers, like the telecom and thermal guys, in the context of plan current in the process of being built by the uplink team.
PDL: Payload Downlink Lead. Collects the downlinked data from their particular instrument and analyzes it.
MOB/IDD: Mobility/IDD. Usually an RP as well, though not for that particular tactical shift. Collects the downlinked data from the mobility (drive) and IDD activities.
And the science team core…
SOWG Chair: Science Office Working Group Chair. They are the overseer of the day regarding the science activities. 
Doc: Documentarian. Documents the tactical uplink shift in grand detail.
KOP: Keeper of the Plan. "Owns" the science activity plans in Maestro, and then delivers this to the TAP/SIE
LTP: Long-Term Planning lead. They collect science team inputs and report what the long-term (days to weeks ahead of now) plan is for the rover.
And the meeting names, in order of their occurrence on a given planning day…
Tagup: Engineering tagup. First thing in the morning. The TUL, TDL, MM, SOWG chair, Doc, KOP, LTP, and others talk about the current state of the rover and the general direction for the sols that they are planning that day.
SOWG: AKA "Uplink Kickoff Meeting." The entire team — uplink, downlink, and science — gather to discuss the Tagup highlights as well as the plans for today's shift. We start digging into the details: what specific science activities we're doing, what engineering constraints must be applied, and all sorts of other goodies.
APAM: Activity Plan Approval Meeting. The TAP/SIE combines the science activity plan with the engineering "skeleton" for detailed resource modeling, like temperatures, currents, voltages, and all sorts of other things. Meanwhile, the RPs develop a the details for any drive or IDD activities. At APAM, the TAP/SIE and RPs present their results.
M/Sm: Master/Submaster Walkthrough. The activity plan created by the TAP/SIE is expanded, or detailed, into commands that the rover actually understands; likewise for the RPs' plan. At this walkthrough, the uplink team walks through the each and every command to make sure that they have been created properly for the plan at hand. Dirty details get discussed here.
SRW: Sequence Report Walkthrough. After the last walkthrough, the TAP/SIE collects the science sequences and RP sequences, integrates them into a single sequence, a single product for uplink. The TAP/SIE then models this single product in the SEQGEN software. At SRW, this integrated and modeled sequence is reviewed by the entire team. 
CAM: Command Approval Meeting. The final sequence products are approved for "radiation" — uplink — to the rovers. 

Ok. Deep breath. Current rover status coming soon.

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