There surely will be an inquiry into the apparent demise of the epochally successful Kepler spacecraft's ability to look fixedly at one place in the sky. For nearly four years it has examined a specific spangle of stars. Its gargantuan data stream revealed peculiar, slight dimmings that fit what should happen when planets have crossed their disks as seen from our vantage point. It's already hit pay dirt with the best seeming to come and now, pffffft. More on the inevitable post-mortem in a moment. First a summary and a roundup of media accounts.
News started circulating about a week ago that the 1.1-ton spacecraft had put itself into safe mode. It has had a recent history of doing that but this one looks a lot worse. One of three operating reaction wheels had already given up the ghost. The craft started with four of them spinning like tops, including a backup. Now down to two of them, the Kepler planet-finding factory cannot point the big Schmidt telescope in its belly precisely and continuously at anything.
( TECHNICAL-ish ASIDE: Reaction wheels are simple. They convey torque here and there, altering the motivation of some things to turn relative to others while conserving angular momentum. Imagine you have an electric drill in your hand with a big broad grinding wheel attached. If you pull the trigger to speed it up, even if the grinder is grinding nothing but air the handle of the drill twists strongly in the opposite direction from the wheel's spin-up. The motor goosed the wheel while braced by your grip. The torque flowed into your arm and through your feet into the floor, a fandango of conserved momentum. Same deal with spacecraft. By exerting torque on three, spinning reaction wheels in different planes and getting a compensating, pivoting push in return and delivered to the rest of the craft through the bolts holding the reaction wheel in place, one can tilt, nod and nudge the Kepler telescope this way and that or more important, by compensating for whatever perturbs it, gently and precisely keep it steadily pointed while not rolling on its axis.)
This marvelous instrument required more than half a billion dollars to build and put into orbit. It reflects decades of bullheaded insistence by William Borucki, the scientist who cajoled NASA into building it. After already finding oodles of huge planets, and now with it just recently apparently on the cusp of finding a load of Earth-massed ones, it looks to be dying or at best, headed for a second-rate second career looking around somewhat randomly. An improved generation of such instruments is in the works but is several years off. There is a backlog of data but nonetheless a lot of grad students and post-docs in exo-planetology are going to be wondering how they're going to get a real job any time soon without some Kepler planetary amazements on their CVs.
Media do a generally good job descibing what went wrong. More recent ones are starting to get deeply into hypotheses on the slim chances the mission may be able to continue at a useful level. Best, we have started to read about why NASA put failure-prone reaction wheels on Kepler in the first place.
Just to set the scene, you might read a situation report filed on line early this month from Kepler Project Manager Roger Hunter of NASA's Ames Research Ctr north of San Jose, CA. At the time, minor problems with the machine and its balky #4 reaction wheel were cropping up. It did not appear to be a crisis.. The immediate worry then was that sequestration would prevent the center from putting on a scheduled science conference. But Hunter also wrote in an earlier report, April 29, that "While the wheel may still continue to operate for some time yet, the engineering team has now turned its attention to the development of contingency actions should the wheel fail sooner, rather than later."
At least one outlet perked up and ran with that grim possibility:
- Wired – Kadhim Shubber (May 1): Nasa's planet-hunting Kepler mission may be on its last legs.
Sooner indeed. The problems' depth came clear to mission controllers on Sunday May 11. It took a few days for a media briefing to get the news flow started. Going through a few examples more or less in chronological order:
An admittedly incomplete list of stories (the last one listed here is, so far, the savviest):
May 15
- Christian Science Monitor – Pete Spotts: Kepler, a prolific hunter for other Earths, is suddenly in trouble ; Nice job, has lots of maybes. The essential narrative and followup to the speculations in this story have essentially held up since.
- Washington Post – Joel Achenbach: NASA's Kepler space telescope malfunction may end hunt for planets ; No, hunt will go on, but we know what it means. Achenbach, as did several reports, describes the inaccessibility of Kepler to wrench-wielding astronauts by quoting one such astronaut's frustration. That makes memorably that its path around the sun, while similar to that of Earth, has it drifting farther and farther from Earth – now 40 millions miles away in a so-called trailing orbit.
- Wall Street Journal – Robert Lee Hotz: NASA Telscope Imperiled by Glitch ; Brisk and to the point and a quote in keeping with the general tone from the start. The best that NASA's science operation can say is, "We are not ready to call the mission over."
- Space.com – Mike Wall: Planet-Hunting Kepler Spacecraft Suffers Major Failure, NASA Says ; Could be new missions, he writes, if they make sense while the telescope's gaze wanders a bit. But the tone is that of an obituary. Wall writes, "whatever the future holds for Kepler, the mission will go down in history as an incredible success."
May 16
- Astronomy Magazine – Sarah Scoles: Exoplanet-hunting Kepler space telescope experiences mechanical failure ;
- NY Times – Dennis Overbye: Breakdown Imperils NASA's Hunt for Other Earths ;
May 17
- IEEE Spectrum – Samuel K. Moore: How Kepler's Pointing system Might Have Failed; A deeper dig into the mechanics of reaction wheels, and their vulnerabilities – especially by the bearings to the shuddering g-forces of launch.
May 20
- NYTimes – Henry Fountain: Flywheel ; A primer on flywheels and reaction wheels. I liked the part about using thrusters to achieve a momentum dump. I was wondering how one handles a long-term perturbation that keeps trying to twise Kepler one way. One can't just keep speeding up a flywheel forever.
May 21-22
- Popular Mechanics – Sarah Fecht: Can Kepler, NASA's Planet-Hunter, Be Saved? ; Good roundup, including reference to forewarning that these wheels are not overwhelmingly reliable.
- SPECIAL KUDOS to this one — Nature News – Ron Cowen: The wheels come off Kepler / Space telescope's mission to find planets outside the Solar System is probably over ; Great hed, better content with an inquisitor's tone. First however, it's gotta be a tad weird being an American writer for Nature. One wonders if Ron, or one of the editors, made sure that the phrase familiar in American English as "checkered history" was rendered into the Brit-speak (ie real English) "chequered history." But one or the other is what these reaction wheels have, he reports, and attributes it to Borucki who surely wasn't thinking of the ..'qu..' version when he said it. This should be the kick-off point for the upcoming and inevitable inquiry and search for lessons learned that may be underway already. Cowen's list of missions whose engineers went without this kind of reaction wheel, deeming them too unreliable, is long enough to make one wonder. What were they thinking? The answer, to translate Cowen, is that they were thinking they'd better keep their fingers crossed. By the time they recognized the risks the spacecraft was already buttoned up and nearly ready for transport to the launch site.
SPEAKING OF TECHNICAL AND OTHER SNAFU INQUIRIES Dept:
I am going off on an editorial jag here with baldly politically partisan motivation. But here are two accounts of inquiries now underway with some elements parallel to what is transpiring with Kepler. One is sort of how the priorities should go at NASA. The other… not.
- San Francisco Chronicle (May 21) Jaxon Van Derbenken: Expert: Replace at-risk Bay Bridge rods ; For many weeks a scandal in the SF Bay Area has grown around revelation that the nearly-complete, new eastern span of the famed Bay Bridge has a bunch of long and broken bolts. Embedded in concrete, they stiffen the signature piece, a tall tower of the suspension bridge portion. The bolts are among many more that have not (yet) broken. Van Debenken is the Chron's ace investigative journalist and he has a bent for mega-failures of civil and infrastructure engineering such as PG&E's famous exploding natural gas main of a few years ago. This is just the latest of his Bay Bridge screwed-up-bolt accounts (today he has another: Bay Bridge bolts used on Richmond Bridge). This is fine reporting. Rather than focus on how long it took for the bridge owner, the state's Cal Trans, to describe publically exactly what is wrong with the bridge Van Derbenken and presumably official investigators are trying to learn how bolts with specs unsuited to the job got approved in the first place. That's the fundamental issue here.
- CBS News – Lindsey Boerma: Boehner: More Benghazi hearings on the way ; You all know what the House hearings on the murderous terrorist attack on the Benghazi US consulate are about. I could have linked to any of scores of news acounts. But media have really dropped the ball. They have let the loyal(?) opposition frame the issue. The result is exactly as though a farmer screamed all day long at his foreman for not figuring out and telling him immediately whether a missing horse was stolen, or ran off on its own. And then all the neighbors think that's important to know and join the chorus. Who cares exactly how long that took to figure out and share? The real question is why the barn door was left open in the first place. It is not whether it took three hours or three days for the administration to get its ducks in a row on the Benghazi attack's origin and blow by blow events. It's why the place with the big American flag (I presume it had one) on it was so poorly defended. Maybe it was because security-boost funding requests stalled in Congress? Anyway and back on point, no sensible Kepler inquiry is going to waste taxpayer money with screeching focussed solely on any initial mumbling at Kepler headquarters after the first reaction wheel crapped out and a second one started to act up. It's why after this many years into the space age those gadgets are not more reliable or why some alternative was not sought.
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