What I Learned Today

The Space Shuttle program is coming to an end. The next flight, STS-134, is currently scheduled for April 29, 2011. The goals of this mission are to deliver the Alpha Magnetic Spectrometer (AMS) and some communication antennas and other parts to the International Space Station. The flight readiness review will be on April 19, at which point they’ll determine the final launch date for Space Shuttle Endeavor.

Not an astronaut? You can still send your face to space at (no joke) Face in Space. NASA wants to literally UP-LOAD your digital image, along with the Space Shuttle, to the Space Station. Sure, it’d be faster to just send it on the comm link, but hey! This is outreach. So far, 315,048 people have participated. Your face won’t actually go up with STS-134, but instead with STS-135 — the final Shuttle flight. Last chance!

If you’d like the latest news from NASA, consider subscribing to one of the NASA RSS feeds. As we near the end of the Shuttle era, it will be interesting to see what next steps the agency takes.

The Kepler mission has already reported a slew of fascinating discoveries, including new planets and new kinds of planetary systems, and there is every expectation that in the final two years of observations it will continue to reveal more and more planetary treasures. However, no mission or instrument functions exactly as expected, and Kepler has had its share of challenges in collecting and processing its data. “Overview of the Kepler Science Processing Pipeline” by Jenkins et al. (2010) provides a fascinating behind-the-scenes look at some of these obstacles and their solutions.

Kepler consists of a one-meter telescope that has been staring at the same patch of sky for two years. Its goal is to measure the brightness of 156,000 stars every 29.4 minutes (“long-cadence” observations) and a smaller set of 512 stars ever 58.85 seconds (“short-cadence”). Each star generates a light curve of its brightness as a function of time. Exoplanets are detected as slight drops in the brightness while the planet transits in front of the star. For this light curve to be usable for detecting planets, Kepler needs two things: 1) a stable pointing so that the stars don’t bounce around or smear, and 2) a stable sensitivity so that any perceived brightening is due to an actual change in the stars.

During the first few months of observations, the first requirement was challenged. Kepler uses a set of “guide stars” to help fine-tune its pointing, and unfortunately it turned out that one of the guide stars selected in advance was an eclipsing binary. Whenever it would eclipse (so one star hid the other one), its brightness dropped and Kepler lost lock on it. As a result, the pointing was slightly off for 8 hours every 1.7 days (!). Kepler only downlinks its data once a month, so it took a few months to notice and correct this. The eclipsing binary star was eliminated from the guide star list and this problem has gone away.

The telescope is very sensitive to thermal conditions, any changes in which can wreak havoc with its focus. One of Kepler’s RWAs (reaction wheel assemblies, used to point the spacecraft, e.g., to pivot it towards Earth for data downlink and back to resume looking at the stars) has a heater that inadvertently modifies the telescope’s focus by about 1 micron every 3.2 hours. There’s no way to fix this, so it just has to be modeled and removed from the data in processing. Likewise, the spacecraft has experienced two “safing” events in which most of its systems shut down, which cools the entire assembly; each time when operations resumed, it took five days for the thermal effects to disappear from the data.

Perhaps most challenging is an artifact that manifests as “Moiré patterns caused by an unstable circuit with an operational amplifier oscillating at ~1.5 GHz.” Luckily, the actual impact on the data values is very small, generally only perturbing them by a single increment, but it is virtually impossible to adequately model and remove, so no doubt a source of at least minor frustration:

“Given that the Moiré pattern noise exhibits both high spatial
frequencies and high temporal frequencies, the prospect of reconstructing a high-fidelity model of the effects at the pixel level with an accuracy sufficient to correct the affected data appears unlikely. We are developing algorithms that identify when these Moiré patterns are present and mark the affected CCD regions as suspect on each affected LC.”

And finally, there was a curious overall brightening (termed “argabrightening”) observed in early phases of the mission. About 15 times per month, the background brightness of the entire field increased dramatically for a short time. The current hypothesis is that this was caused by remnant dust particles coming loose from Kepler and floating off, then reflecting sunlight back into the telescope. Detecting and removing affected observations was crucial for yielding consistent light curves. Fortunately, the rate of these events has decreased over time (Kepler might be running out of dust).

I look forward to more fascinating news from this great mission! And I hope they keep sharing the interesting challenges and lessons learned from operating a telescope from so very far away.

On a tip from my officemate, today I checked out the live camera feed from the clean room next door where our next Mars rover, the Mars Science Laboratory (or MSL), is being tested. MSL doesn’t launch until next fall, but they’re busy putting it through its paces right now to ensure that all of the instruments work as expected. It’s in a clean room so that we can minimize the amount of terrestrial biota it picks up prior to launch. We’d hate to inadvertently inject our own life into the pristine Martian environment — especially if we then detected it and thought it could be Martian!

As I write this, at 10:30 p.m., a technician in his bunny suit is walking around the rover, tinkering with connections and still hard at work. The video is dubbed “Curiosity Cam” because it is alliterative and because MSL acquired the name “Curiosity” as the result of a naming competition (I prefer simple old MSL).

But earlier today when I tuned in, JPL was also offering a live chat to accompany the video. Two anonymous folks in our newsroom were fielding any and all questions posed by anyone who dropped in. At first glance it seemed a bit dull — but then I started reading the comments and quickly became sucked in. How can you help but want to answer the questions of the curious public? Here are some excerpts. (Note that people who connected but didn’t log in via twitter or facebook, including me, were assigned generic “ustreamer” ids.)

The most common question (which maybe you have as well) is what the flashing blue light means. I thought it was probably just a visual signal that testing was in progress… but learned from the chat that instead it means that power is flowing to the rover.

ustreamer-43285: i’ve had 2 questions answered by jpl…this is awesome.
ustreamer-61986: i want to work for NASA!!!
ustreamer-01212: me too
Giati: me 3
ustreamer-25131: me 4
ustreamer-59789: Hell yeah, just no way im as smart as these guys. Awesome]
ustreamer-75761: yep nasa beats all other space agencys by a mile

Not a kilometer?

The two JPLers officially answering questions were named NASAJPL and NASAJPL-1. I was repeatedly impressed with how they fielded all sorts of questions, with a polite and informative tone, no matter the question.

ustreamer-33518: i hope this rover doesnt get stuck do you have a system to stop that happening?
NASAJPL: 33518, the rover’s six 20-inch wheels are designed to help maneuver out of such a situation.

One individual, 59789, was really taken with speculations about the upcoming astrobiology-related press conference on Thursday. The link he/she posted certainly falls into the “speculation” genre. I couldn’t resist chiming in to help out.

ustreamer-59789: Not at all. Thursday meetng will put that to rest. Nasa revealing they found biological life on Titan
ustreamer-59789: http://current.com/technology/92832052_story-of-the-century-nasa-may-announce-thursday-to-have-found-life-on-saturns-moon-titan.htm
NASAJPL-1: There are a lot of rumors about the Thursday briefing. It will NOT be an announcment of finding extraterrestrial life.
ustreamer-69544 (Me): There is a lot more to the field of astrobiology than just finding current life — we want to know about conditions conducive to life, and all of the chemistry involved, too.
NASAJPL-1: Repeat: it will NOT announce the finding of life on Titan. It’s too bad people out there are trying to get attention by running false stories.
NASAJPL-1: 69544 That is correct!

Then the questions started getting more and more interesting:

ustreamer-75761: wish ion drives were being used it would be a whole lot faster then currnent tech
ustreamer-69544 (Me): 75761, ion drives accelerate much more slowly than chemical rockets. They are good for very long trips but not for trips to Mars.
ustreamer-49140: 69544 … I understand that. But it’s still bewildering, with all our tech we have to send a FLEET of probs to mars to find out if theres life there. Surely it can be done with a single probe ?
ustreamer-69544 (Me): 49140, no one knows how to search the whole planet with a single spacecraft. But we learn more from each one sent!
ustreamer-49140: 69544. I agree, but we shouldent have to travel ALL over mars in an effort to find life. Just as someone sending a probe to earth would find life no matter where the probe landed.
ustreamer-69544 (Me): 49140, if life were as prevalent on Mars as it is on the Earth, you’re right, we would already have found it!

… and even relevant to geology!

ustreamer-02837: is it believed the lanscape on mars was created by water?
ustreamer-69544 (Me): 02837, the Martian surface has been shaped by ancient water, and aeons of wind, and episodes of volcanism.

ustreamer-77218: Earth is much bigger than Mars, but about 70 % of the Earthen surface is covered by water. On Mars there is 0 % covered. How much land compared to earth is it on Mars?
ustreamer-69544 (Me): 77218, great question! In fact the land surface on Mars is quite close to the land (non-ocean) area of the Earth.
ustreamer-77218: Thank’s “US-69544”. =) And Moon? about half of Mars?
ustreamer-69544 (Me): 77218, it looks like the Moon’s surface area is about 1/5 that of Mars.

(Actually, my quick math was a bit off — it’s between 1/4 and 1/5 that of Mars.)

After a while I started to wonder if NASAJPL and NASAJPL-1 would realize that I too was at JPL… and then I decided to get back to some real work. But wouldn’t it be fun to be the JPL expert fielding these questions?

Tonight I was lucky enough to get to watch the International Space Station fly by: a bright unwinking point arcing upward and then, just past zenith, disappearing as it passed into the Earth’s shadow. This sight somehow never fails to stir something inside me. It is one thing to read news articles about spacecraft in orbit, and quite another to see them with your own eyes. Beyond that, the ISS marks our ability specifically to maintain a human presence in space—quite a bold and amazing feat, no matter how many years have passed since the Apollo missions.

One way that we get humans (and equipment, supplies, etc.) from the ground and up to the ISS is via the Space Shuttle. The Shuttle is a marvel of engineering—perhaps too much of a marvel, rendering it less reliable than we might hope—and it is in the sunset of its career. 2010 will see the final Shuttle flights (just five more are planned), and then the Shuttle will be retired while effort and funds are focused instead on developing its successor, the Orion spacecraft. During the 5+-year gap between the Shuttle’s retirement and the first crewed Orion flights, we will rely on the Russian Soyuz spacecraft to reach and resupply the ISS.

There are many fascinating engineering details about the Shuttle and how it works. I recently came across one that really surprised me. It turns out that when the Shuttle de-orbits and descends through the Earth’s atmosphere to land, it manages that whole long glide and deceleration without any engine power. Effectively, it aerobrakes (taking advantage of our thick atmosphere), and attitude control is maintained through thrusters and hydraulically actuated surfaces. This isn’t enough to slow it all the way down, so the Shuttle also executes several S-shaped swoops to the left and right, dissipating speed horizontally instead of vertically.

You can watch a Shuttle landing from the cockpit view (STS-98): fascinating, although I guess the video starts after the four swooping banks have already been done. The dramatic right turn you see in the video is the commander’s final lineup with the runway—a final turn that also reduces speed and altitude.

The next shuttle to launch will be Endeavor (STS-130), on February 7. It will be the 32nd shuttle mission to the ISS.

I recently discovered Google Squared, an interesting combination of web search and automated information extraction. Actually, it reminds me strongly of the strictly formatted report we had to write in 6th grade English class on frogs. You had to draw a square chart and then label the rows with different kinds of information about frogs, like how they reproduce, what kind of food they eat, and where they live. You then labeled the columns with different information sources, like “Encyclopedia Britannica”, and then you filled in each square with what source X reported about property Y. You then used this chart to write the report itself. This was supposed to teach you how to do research, in the “look up information” sense of the word.

With Google Squared, though, the system figures out what the rows should be (different examples of the category you searched on) and what the columns should be (different properties of each of the examples). It’s fascinating, although you immediately run up against the limitations of current state-of-the-art IE (Information Extraction) technology.

Exhibit A: mars spacecraft

This produces a nice collection of Mars spacecraft, with columns for “mass”, “launch vehicle”, and “launch date.” The first thing I wanted to do was sort by launch date. Unfortunately, the columns aren’t sortable. You can however add your own columns, so I tried “cost”. This looked mostly reasonable, except that “Phoenix” was cited as $350M, “Mars Phoenix Lander” was $420M, Mariner was $2.6 (dollars?), and the Spirit rover was $10,000 (if only!). However, a really neat feature is that each factoid reports its source if you hover over it, and you can click to see other candidate values as well as a confidence rating. All of the values under “cost” were rated low-confidence, even the ones that looked accurate to me.

Exhibit B: science fiction authors

This yielded a combination of books and authors, with the auto-chosen columns being “publisher”, “language”, and “Australia” (?!). Specifying “science fiction author” yields the same list of items, but with different columns: “publisher”, “ISBN”, and “language”.

Exhibit C: ballroom dance

This yielded an excellent list of ballroom dances. Unfortunately, the columns (“typical instrument”, “mainstream popular” (?), and “stylistic origins”) were almost entirely unpopulated with data. I tried to add “tempo”, but this yielded a result for tango only (33 mpm). That one could definitely use work!

In summary, I’d say it’s a very cool idea (and fun to play with), but still definitely at the beta level. Doing a good job of information extraction from unrestricted text (the Web) is a really hard task. Keep at it, Google!