Saturday, June 30, 2012

New and updates — and stirring the pot of rumors

How is Opportunity doing? Well… good. Prett-ay good.

Daily Solar Power Is Off the Hizzay

While I idly watch, MER-B's power is shooting through the roof: 600 Watt-hours* predicted. As a reference, we were soaking in about 250 W-hours at the dead of Martian winter (middle of March here on Earth). Tau — a measure of atmospheric opacity — is at an all-time mission low (which means clear skies), and we've had several significant dust cleaning events (which means clean solar arrays). This increase in power is all in spite of the now low northerly tilts that Opportunity is at — you know, the thing that kept her alive in the depths of winter.

If I were so inclined to get in trouble, I'd post the watt-hours plot our Power team puts together. But I'm not so inclined! For that, we'll have to follow our glorious mission manager updates.

Opportunity's Location, Recent Activities, and Future Plans

Opportunity has been skirting the rim of the Cape York geological feature since she departed from her winter parking in the northern havens:

There's been a discovery of new Gypsum (errr, presumably Gypsum) veins:

And we've found a nice juicy spot for a RAT hole — a target named "Grasberg":

Unfortunately, the Mars Odyssey (ODY) spacecraft went into "Safe Mode" a few weeks ago. MER has always been incredibly reliant on ODY for data downlink via the relay chain, and when ODY goes down, MER has to stand down for a few sols. MRO also provides good relay support, but much more rarely than ODY. We have to schedule "passes" with these spacecraft strategically, i.e. weeks ahead of time, so that their teams can piece together their multi-week set of commands appropriately to handle the relay supports. Changing them tactically, i.e., the day of the relay pass or otherwise shortly before then, is a difficult process and things like geometry and spacecraft sequence engineering constraints can bite us.

There is a lot of so-called unsent data on board Opportunity that prevents the team from scheduling data-intense activities (like hi-res Pancams, MIs, or mobility data). As such the work on Grasberg and the surrounding territory is slow.

For the future: We plan to cross the skirt of Cape York to the north to look at the transitional layers (do I sound like a geologist yet?) thereon. Then, southward back from whence we came — to the first entrance into the Endeavour Crater on the south side of Cape York, and then further sound to Cape Tribulation. Betcha we get there before next Martian winter — those RPs are itching to drive the heck out of Oppy, and they're damned good at it, too.

A Mission Milestone -- Sol 3000 
According to my highly technical (read: I cheated and used SPICE again) analysis, Opportunity will hit Sol 3000 at 2012 JUL 02 01:51:32.572 UTC, or 2012 JUL 01 18:51:32.572 PDT.

Holy… what? Seems about right: I started work on the MER project nearabouts sol 2350, which was nearabouts July 2010. 

At the moment I'm not grasping what this really means… I haven't had the time to let it soak in yet. It's just unreal

Rest assured, the MER team is having a big get-together brunch this weekend to celebrate.

Allow me to stir the rumor mill!

I've received several emails asking me about my rumored move away from MER to the Mars Science Lab (MSL) project at JPL. Let me settle all the rumors now: Confirmed. In fact, I left the MER project about two months ago.

Much as I loved working on the MER program, opportunity (pun not intended) awaited me on MSL. It was not a decision that I made without a lot of careful thought — I sat around for a few months working up to actually making the decision. 

There are several good bits to come out of this move, however:

1) I have no plans to discontinue this blog. I never did! MER impacted me in a way that I'll never forget. I'm always going to be plugged into Oppy's updates. She is quickly approaching the off-earth traverse distance record and I want to be blogging about it. No question about it.

2) A large portion of the MSL tactical uplink team comes from MER. ("Gee, you know, it would be prudent of us to hire people who have done all this before…") I see a lot of familiar names and I'm finally meeting some past "MER Legends." Granted, MSL is a new kind of beast, very very unlike MER, but the overarching process of getting 1's and 0's to her is the same. Experience counts.

3) I don't have to move offices! MSL owns floors 4 and 6 of building 264 at JPL, and MER (along with Odyssey and MRO) takes up floor 5. So I still get the chance to swing down to say hello to the MER folks every now and then. In fact I still use the coffee machine in their break room, because if I'm ever going to drink anybody's office-coffee-club coffee, I'm going to drink MER's. **

And several unfortunate ones:

1) I have less time to stay focused on generating consistent, reliable posts here. I'm working crazy hours and will soon be transitioning to "Mars time" shift schedules when we land on Sunday August 5th. POWER THROUGH!

2) I can't blog about MSL, at least not in the capacity that I'm granted here by the PR folks at JPL. 


I've received some good, insightful comments about the Radio Science posts (here and here). I responded with a little too much brevity; and the comments pointed out that I lacked a sense of clarity in the posts! Good catches all a round.

I plan on some supplemental pieces on Radio Science whenever the results go fully public.


*Watt-hours = Energy. Watts are energy (specifically, Joules) per unit time; multiply by a time unit and you get Joules back. You may be asking, "Why not just say 'joules', then?" If we were to express it as Joules — Watt-seconds — we would have these huge numbers that are hard to grasp. Watt-hours are a convenient (though inconsistent!) way of bringing a numb back down to something the human brain to contextualize. It's a colloquial engineering term.
**They've got this old school diner coffee machine that is meant to stay on 24 hours a day; oh boy have I been using it. Late nights on MSL have caused me to leave these silly notes next to the MER coffee machine — something to the effect of "LEAVE ON FOR MATT, 06/29/12 evening" — so nobody turns off my caffeine supply. Sometimes, on top of my note someone from MER will leave me donuts. I love these people…

Sunday, June 10, 2012

Happy 3000th, Spirit

About 3 hours and 32 (Mars) minutes ago, it was zero hundred of Sol 3000 for the Spirit rover. (This means Opportunity's 3000th sol is only a few weeks away.)

Wonder how many sols more it will be until a human stops by and designates the final resting place of Spirit as a historic monument of humanity?

Saturday, June 9, 2012

The Radio Science Campaign, Part 2/2 — The Results


Really, this took much longer to put together than I had imagined. There were a few technical snags — most of which are explained by the fact that I'm a bad programmer — but we finally have something worth discussing.

In Part 1, I talked about the basic science behind the Radio Science campaign that Opportunity undertook from January through the middle of May. Now, we have the results from that. Where in the sky was the Earth when Oppy was doing the experiments? Why does it matter? How did that change over time? How do the various variables relate? How can we easily represent all of this?

I've boiled it down to three plots. First, a few disclaimers and notes:

1) Since I'm not allowed to use operations data or products to create these plots, I have to play stupid and guess at which times of the Martian day to look at the data. As always, I used the SPICE toolkit for the geometric computational heavy lifting. Based on this data and what I remember from all those tactical shifts, I could piece together the relative time of Martian of day at which these happened. I looked at the orientation data of the High Gain Antenna (HGA) to see when it was moving and then — by hand! by hand! — picked out the ones that were "obviously" RS-DTE experiments rather than just the regular DTE/DFE's (see Part 1) when the HGA is also moving. The RS-DTE's are easy to pick out simply by time of day.
2) No durations shown here, just middle of the guessed window. Close enough! Most windows were about half an hour in length.
3) All Martian times of day (TOD) are Hybrid Local Solar Time (HSLT; we also just say "LST"), which is consistent with the rover's flight software.**
4) The plots of position of Earth in the sky (azimuth, elevation) are just showing where the Earth is, not where the antenna was actually pointing. I've done this for simplicity, and because backing out the real position of the HGA difficult. There are ~5 degrees of error here, which, for the purposes of this blog, is well under my "do I care?" radar.

The Evolution of Earth Elevation

We like to schedule DFE/DTE communications with our rover at the same time of Martian day. This gives us predictability, consistency, and flexibility in the plans from sol to sol. However, even if we could get the time on the DSN to do that (nobody can, it's a shared resource), geometry plays a big role. Both planetary geometry and the relationship of Earth and Mars time (i.e., the length of their day) have effects on when we can schedule communications passes — and remember, RS-DTEs are simply communications passes without much data going between the rover and Earth. 

First, as you may know, the Mars day is not equivalent to the Earth day — though it is very close. It's roughly 24 hours and 40 minutes, depending on what you mean by "day". Are we talking solar day? Mean solar day? Hybrid solar day? Then we get different values. The variance of this couples with the fact that, simply due to the relationship of Earth's position to Mars' position over time as they move through the solar system, the Earth will be at different parts of the sky at different times of the year. 

Put it all in a big confusing pot, and baby you got a stew goin'.

Right. So. How we best show this? The plot below shows this basic relationship: I've plotted elevation of the Earth from the local-level horizon at Opportunity's position on Mars at the same time LST (hybrid! hybrid!) from Sol 2800 to Sol 2971, which corresponds roughly to the times of the Radio Science experiments.

I could have picked any arbitrary time of day. The point is to show how the same time of day doesn't give you the same Earth position. We can see that sometime in the middle of February the elevation peaked. This pattern would repeat over and over if I had simply extended the time back. 

The lesson here is this: Earth elevation and Martian time of day only approximate proxies for one another.

Right, so, we see that elevation drifts. How did the RS-DTEs take account for this, or take advantage of this?

The RS-DTE Observations

One of the key characteristics of good RS-DTEs is a low Earth elevation angle. This exaggerates the Doppler-shifted signal, reducing the noise and clarifying the meaning of the data. We know that the Earth will probably be at low elevation angles in the morning and late afternoon, so it would be prudent to schedule our RS-DTEs there. When you slap on operational constraints — can we get that time with the DSN? do we have the solar energy to do it at that time of day? are we doing other things on the rover that preclude HGA movement? etc. — you get large variation from sol to sol in the time of day, and consequently the elevation angle of Earth, for each observation. 

The plot below shows all of the measurements that I gleaned from the SPICE kernels (see above). Details:
1) Left axis (blue): Elevation angle of Earth in degrees during the observation
2) Right axis (green): HLST Time of Day of the observation
3) Bottom axis: Time (duh)

Here are my observations:
> We tried for a lot of elevations under 30 degrees. Notice how we were getting those early on — then the power got too low, and we had to sacrifice the quality of the data for the survival of the rover, so we scheduled the RS-DTEs at an earlier time of day when there was more sun on the arrays.
> Another driver for the earlier and earlier times of day of the observation is found in the first plot from above: The Earth was lower and lower in the sky at the same time of day, and we wanted to hit particular windows of elevation angles, we ended up moving observation times to get the elevation angles right.
> The earlier the measurements got, the more we (presumably) doubled these tracking passes with the DSN as uplink passes to load the next sol's set of plans on board. Win win!

Finally, where was the Earth in the azimuthal direction relative to North? Here we have a plot of azimuth angle clockwise from North and elevation in concentric circles,

North is up (0 degrees azimuth); East is to the right (90 degrees azimuth). For each of the observations, the azimuth was roughly the same; this has mostly to do with the orbits of Earth and Mars, less to do with local solar time. Of course, you can't tell the direction of time in this plot, but that's not the point!

The End of RS-DTEs

There is an incredible amount of input going into these observations; a hundred constraints and a hundred desires. Now we're driving and hunting down veins, leaving radio science to next Martian winter — about an Earth year and a half from now. 

I hope this was educational!


*No, I don't have a Twitter account. No, I don't want one. hashtag PleaseLeaveMeAloneAboutIt
**Fun fact: MSL will be using "mean" solar time — "LMST". It matters.