What I Learned Today

I recently joined the Mars Exploration Rover team as a TAP/SIE (Tactical Activity Planner / Sequence Integration Engineer) for the Opportunity rover. That means it’s my job to sit in on the morning SOWG (Science Operations Working Group) meeting, in which the rover’s scientific goals for the day are set, and then work with payload, thermal, downlink, mobility, and other experts to come up with a plan to achieve those goals. What pictures will we take? When? Where will we drive? Is there enough power?

Reading the training documents only gets you so far. I’ve just begun “shadowing” the current TAP/SIEs so that I can learn on the job, watching over their shoulders through a day of planning. My first shift was on Wednesday, and it was supposed to be an “easy” day: pick one of two rock targets, drive towards it, and take some pictures looking backward at yesterday’s tracks.

Scientists dialed in from all over the country for the SOWG meeting. After some debate and consultation with the Rover Planners, they settled on the rock that had the easiest approach. The scientists signed off and we went to work building the plan.

The TAP/SIE’s job is facilitated by a bewildering array of scripts and tools. These allow for the setup, development, refinement, and checking of the plan. Are power or thermal constraints violated? Do we have enough onboard storage space for the new images to be collected and enough downlink allocation to get them back to Earth?

While the RPs (Rover Planners) settled in to their job of constructing the drive sequence, we worked on the full sol’s plan (a day on Mars, which is 24 hours and 40 minutes in Earth time, is called a sol). Very quickly we realized that the planned drive, despite covering only a couple of meters, would drain the rover’s battery dangerously low. Opportunity was starting the sol at only 80% charge because of two long instrument observations the previous sol.

We modified the plan to give the rover a morning “nap” in which it could sun itself and collect power, like a desert lizard. That helped the power situation, but not enough. Several iterations later, we finally squeaked by at 0.1 Amp-hour above the required threshold.

Meanwhile, the RPs were growing concerned about a different problem. To reach its goal, Opportunity would have to straddle a rock that, while small by human standards, could pose a risk to the rover’s instrument arm, which dangles slightly down when stowed for driving. The RPs put their 3D simulation of the rover and the terrain up for all to see, and we stared at the screen while they spun the rover and tried to examine the rock from all angles.

“Can we raise the arm while it drives over the rock?” I whispered to the TAP/SIE I was shadowing. “It’s risky to do that,” she whispered back. “The arm bobs around, especially going over a big rock.”

A few minutes later, a scientist on the telecon asked, “Can’t we just put the arm up?” but was quickly shot down by the TUL (Tactical Uplink Lead, head planner): “Too risky.” The TAP/SIE and I grinned at each other.

Ultimately, it was deemed too dangeous to drive over the rock with our current data (images the rover had taken the sol before), and they decided to drive up to that rock and stop. Post-drive imaging would illuminate the obstacle in more detail.

At the end of our shift, which apparently was two hours later than usual, we had a plan. We ran it through multiple checks and re-checks and manually confirmed all of the sequences. The final walk-through was punctuated with “check!” coming from different areas of the room as each person confirmed that their part was correctly represented. The plan was finalized and transmitted to the rover using the Deep Space Network later that night.

There’s nothing like seeing a job in action. I learned a lot about the steps involved in planning and (unexpectedly) a lot of re-planning. For the rover, today is “tosol” and yesterday is “yestersol.” I got to practice the phonetic alphabet, which is used to communicate letters (in rover sequence ids) with a minimal chance that they will be misheard. I even got to help out a bit as a second pair of eyes to catch typos, spot constraint violations, and suggest alternative solutions. And I’ll be back on shift next Monday!

Opportunity is near Endeavor Crater, working its way along a ridge that is at the perfect tilt to keep its solar arrays pointed toward the sun. This is important because Winter Is Coming, even on Mars, and we want to keep it sufficiently powered to make it through to spring — its fifth spring on Mars. (Opportunity landed 9.5 Earth years ago!)

I guess it’s not surprising that someone would find a way to monetize the exoplanet craze. A startup named Uwingu will now charge you $4.99 for the chance to nominate a name for an exoplanet (plus a downloadable certificate). Not a specific exoplanet, mind you. No, they’re simply compiling “a baby book of names” for astronomers to consult, should they choose to.

That’s right, there’s no guarantee that your suggestion will ever be used, and since it’s not associated with any particular planet, no chance for you to make it suit the planet’s characteristics. (That makes the baby-name analogy more apt, actually, since most parents choose names before the child is born.)

But if so, why should Uwingu get to collect $4.99 for it? And what will they do with the funds?

“Our goal is to award up to half of all Uwingu’s proceeds to The Uwingu Fund, which will provide grants to scientists and educators to conduct space research, education and exploration projects,” says Uwingu. Their first call for grant applications will happen in mid-2013.

But wait, there’s more!

You can pay them $0.99 to cast a vote for the best name, a contest that closes on April 22. Just $0.99 for each vote! What happens to the winning name? They want to assign it to Alpha Centauri Bb, but since they have no authority over official naming, nothing will actually happen. It would be like a band of people deciding to rename New York to be “The Big Apple.” Sure, you can use the name colloquially, but no one’s going to start changing road signs or the name over City Hall or birth records.

So far they’ve received 1230 nominations and 4933 votes, or $11,021. The most popular name is currently Rakhat.

The International Astronomical Union (IAU), which oversees the offical naming of astronomical bodies, is apparently not on board with this at all.

“Such certificates are misleading, as these campaigns have no bearing on the official naming process — they will not lead to an officially-recognised exoplanet name, despite the price paid or the number of votes accrued.”

Uwingu CEO Dr. Alan Stern stated, “This is a first step in democratizing planet naming.” . . . which should be democratic why?

Far be it from me to dissuade any popularizing of science and astronomy. But this seems overly opportunistic, reminiscent of those “Name a Star” scams (check out some words of wisdom from the IAU). It would be one thing if they were compiling a list of names as the outreach-based, public awareness effort they claim it is. But the charges they levy instead highlight it as a semi-deceptive money-making venture, playing on people’s desire to be involved but not delivering what most people think they’re paying for.

The summer and winter solstices happen around the 20th of June and December, respectively. Around the 20th? That seems rather… imprecise, for an astronomical event with a precise definition: the time at which the Sun reaches its “highest or lowest excursion relative to the celestial equator on the celestial sphere” or, for the viewer standing on the Earth, its highest or lowest altitude from the horizon. This is determined by the Earth’s orbit and corresponds to the time at which your current hemisphere’s pole points most closely to, or farthest from, the Sun. So why doesn’t it happen at the same time each year?

Inspired by an awesome book I recently acquired (“Engaging in Astronomical Inquiry” by Slater, Slater, and Lyons), I decided to investigate. I used the Heavens Above site to pull up historical data for the summer and winter solstices going back to 1980. I plotted the time for each solstice (in Pacific time) as its offset from some nearby day (June 20 or December 21). And sure enough, here’s what you get:

The solstice time gets later by about 6 hours each year, until a leap year, when it resets back by 24 – 6 = 18 hours.

Of course, the solstice isn’t really changing. The apparent change is caused by the mismatch between our calendar, which is counted in days (rotations of the Earth), and our orbit, which is counted in revolutions around the Sun. If each rotation took 1/365th of a revolution, we’d be fine, and no leap years would be needed. But since we’re actually about 6 hours short, every 4 years we need to catch up by a full rotation (day).

Now, we all know about leap years and leap days. But this is the first time I’ve seen it exhibited in this way.

Further, you can also see a gradual downward trend, which is due to the fact that it isn’t *exactly* 6 hours off each year. It’s a little less than that: 5 hours, 48 minutes, and 46 seconds. So a full day’s correction every four years is a little too much. That’s why, typically, every 100 years we fail to add a leap day (e.g., 1700, 1800, 1900). 11.25 minutes per year * 100 years = 1125 minutes, and there are 1440 minutes in a day. But that’s not a perfect match either… which is why every 400 years, we DO have a leap day anyway, as we did in the year 2000.

This is what, in computer science, we call a hack.

And now it is evident why for every other planet, we measure local planet time in terms of solar longitude (or L_s). This is the fraction of the planet’s orbit around the Sun, and it varies from 0^o to 360^o. It’s not dependent on how quickly the planet rotates. It’s still useful to know how long a planet’s day is, but this way you don’t have to go through awkward gyrations if the year is not an integral multiple of the day.

By the way, you can get a free PDF version of ‘Engaging in Astronomical Inquiry’. If you try it out, I’d love to hear what you think!

We’ve heard many discoveries over the past decade of planets around other stars. Today astronomers announced the detection of seven new comets around other stars. You can read more here: “Exocomets may be as common as exoplanets”.

Why should we care? Well, comets are a lot smaller than planets, so it’s impressive that they can be detected at all. Even more impressive, these discoveries were made with a 2.1-m telescope on the ground, not in space. You might be wondering how exactly they were detected if it’s so hard even to find Earth-sized planets. That’s because these comets aren’t being detected directly, e.g., by the brief drop in stellar brightness when a planet transits in front of it. Instead, what’s actually being detected are slight perturbations (lasting about 5 days) to the star’s spectrum across multiple wavelengths, which indicates a compositional difference. Since we don’t expect the star to briefly change its composition and then revert back, this is interpreted as seeing gases boiling off the comet as it passes close to the sun.

If so, I’d expect that the particular changes would serve as a kind of “fingerprint” for that particular comet, and be somewhat repeatable the next time it approaches its star. But comet periods can be a lot longer than planet periods (at least in our solar system) so it might take a while to get any repeat signals.

The scientific reason this is interesting is that it can serve to fill in a gap in our knowledge. We’ve seen systems with dusty disks surrounding the star (before planets form), and we’ve seen more mature systems with their planets already formed. We haven’t yet explored the in-between stage in which a lot of material (comets, asteroids) is moving around in the process of forming into large planetesimals. For that reason, astronomers targeted young (type A) stars for the exocomet hunt.

Further, turns out that the technique used wouldn’t work with older/cooler stars. In discoverer Barry Welsh’s talk today at the AAS meeting (he’s giving a press conference tomorrow), he noted that the spectral absorption features they think come from comet outgassing get “narrower and harder to detect in older stars.” I’m not sure of the specifics on this, but it suggests we won’t be able to find exocomets in all of the stars we’ve been studying… at least this way. Astronomers’ innovations will continue to push the envelope!

I get asked that question a lot. I end up giving two answers: my own wishful dreams, and the less inspiring view of what I think might actually happen.

I recently came across a thoughtful article that agrees with my complicated views on the subject very well. It’s titled “Mission to Mars: Will America Lose the Next Frontier?” After noting the merits of the MSL rover, the article points out the downside of the project: by going almost $1B over its initial cost estimate, MSL has forced the delay or cancellation of other Mars endeavors. (I believe that the article’s note about the cancellation of the Mars 2016 mission is a reference to the 2018 MAX-C mission, a step on the path to sample return, which was canceled. We do have a mission slated for 2016, announced after the article’s publication: the Mars Insight lander.) Similarly, the article notes the terrible impact that the James Webb Space Telescope has had on NASA’s astrophysics program. JWST is NASA’s poster child for mind-blowing cost overruns. Initially estimated at $500M, it’s grown by leaps and bounds and is now estimated at $8B. Both MSL and JWST are sure to deliver rich scientific gains in their respective missions. However, I think this article is correct and fair to note the other efforts that have fallen by the wayside to ensure that these projects are complete.

The main message of the article, however, is the bigger view on what this means in terms of larger, longer-term goals:

“But today, thanks to a combination of budgetary stress, regulatory overkill, and an unfortunate lack of political skill at the highest levels of NASA, the Mars exploration program is in deep trouble. It may be a very long time before the U.S. space agency launches another significant Mars mission.”

Put simply, NASA doesn’t have the budget to send humans to Mars. “Regulatory overkill” refers to a strict intolerance of any NASA failure, no matter how large or small, which necessitates over-engineering (and ballooning costs). Unless something dramatic changes in NASA leadership, political weight, or budgetary windfall, it’s unlikely that our space agency is going to get us there. But all is not lost; Elon Musk is on the job.