The most important spacecraft since the Hubble Space Telescope has been felled by a couple of reaction wheels that stubbornly held to their predicted useful lives, NASA reports.
If distant planets and their stars were this obvious, Kepler wouldn't have needed remotely the same pointing accuracy.
Something about Kepler, despite its stubborn refusal to return pretty pictures for our screen savers, prompts those with a taste for science and any literary pulse to wax poetic.
I have been guilty of this, though for good reason. I mean, scientists using the spacecraft have found planets roughly the size and mass of Earth in roughly an orbit that allows water to be water and not steam or ice (about the only precondition for life scientists seem to have been able to establish). Before Kepler, we knew of a few vulcan Jupiters, boiling balls of gas skimming their stars. Now it’s clear that star formation comes part and parcel with planet formation. Meaning that about every star you see hosts orbiting rocks. Not to Carl Sagan out you, but there are billions of billions of stars in our galaxy, and billions and billions of galaxies. So do the math.
Kepler tells us definitively: we’re not alone.
It also tells us we’re not unique, and if uniqueness is a proxy for importance, we’re not all that important. At least not remotely as important as many of us have come to believe.
I felt a particular connection to this spacecraft because I watched it being built, its 15-foot-long telescope standing erect in a Ball Aerospace high-bay clean room in Boulder. At its base was a $6 million, 95-megapixel sensor. Many of the team that build the Deep Impact spacecraft I detailed in the book moved on to Kepler. About 200 Ball Aerospace engineers and techs worked on Kepler.
The mission, for which NASA Ames Research Center scientist Bill Borucki fought for literally decades, devolved into an over-budget mess. It was yet another example of intelligent human beings grossly underestimating the difficulty of doing something new and different. Monte Henderson, a key source for the book and now a friend, was the project manager for a while, only to be sacrificed at NASA’s altar a year or so into his tenure.
Part of what made Kepler tough was aiming it. Kepler’s had to maintain a pointing accuracy within about a millionth of a degree for more or less four years (the need to reorient to send data back to Earth on occasion complicated this). Imagine being able to hold a laser steadily enough to a penny 700 miles away. Imagine doing that for months on end. That’s essentially what Kepler did, because that’s what it took to detect a planet occluding the dim the light of one of the 150,000 distant stars it stared at.
“The stability requirements on Kepler are extreme compared to any other space-based mission,” Henderson told me back in 2007.
The reaction wheels, four of them, were among the the fonts of that stability — they subtly adjusted Kepler’s aim. What used to be Goodrich made them. Others had since had problems with them.
Reaction wheels are moving components, which tend to be the great bugaboos of space engineering. These spun up and down at 1,000 to 4,000 RPMs. Two still do. Two now don’t. When you’re trying to drill a penny from 700 miles, you need three reaction wheels. So Kepler will hunt planets, at least in the sense that it did (NASA is open to the idea of other applications demanding lesser pointing accuracy for the spacecraft), no more.
But this spacecraft changed the world — or at least should have changed the world — like few human creations have.
