Tool time for Hubble
Posted: Tuesday, September 09, 2008 6:15 PM by Alan Boyle
NASA
Atlantis astronaut Mike Massimino practices using the Mini Power Tool to remove
screws from a circuit box for the Space Telescope Imaging Spectrometer. The
screws will be retained in the color-coded, see-through capture plate - a device that is attached over the box and keeps the tiny fasteners from floating away in space.
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Overhauling the Hubble Space Telescope requires much more than astronaut elbow grease in zero-G: More than 60 new tools had to be created in a multimillion-dollar effort that involved trips to the hardware store - and to the toy box.
The tools took their share of the spotlight during this week's briefings on NASA's final Hubble servicing mission, conducted at Goddard Space Flight Center in Maryland as well as Johnson Space Center in Houston.
"We had to develop a whole new class of tools for spacewalking," said astronaut John Grunsfeld, who will be making his third service call on the Hubble during next month's mission.
At Goddard, we got an up-close look at the gizmos in action from the engineers who developed them for Grunsfeld and the Atlantis mission's other spacewalkers.
One of the indispensible items for Hubble's handymen will be the Mini Power Tool, a shiny pistol-shaped screwdriver/drill that has an LED light at the tip to illuminate the space telescope's innards.
For the first time, astronauts will actually be swapping out bad circuitry on two out-of-commission instruments inside the 18-year-old telescope. The instruments' circuit boxes "were basically never designed to be accessed," said Tomas Gonzalez-Torres, lead spacewalk officer for the mission. But they'll have to be accessed next month if NASA hopes to revive Hubble's Advanced Camera for Surveys and the Space Telescope Imaging Spectrograph.
The electronics box for the camera equipment has a protective mesh and 36 fasteners that have to be removed. The spectrograph's circuit box has a cover held in place by even more fasteners: 117, to be exact.
Imagine trying to twist out more than 100 tiny hex-head screws in zero-G, with your head buried inside the Hubble itself, and you get a sense of how devilish the job could be. One loose screw could ruin a billion-dollar telescope.
To do the job, the Goddard team fashioned ingenious boards that are designed to be clamped onto the box covers, leaving color-coded, see-through receptacles for each screw. They're called capture plates, but they look more like the "busy boards" that parents buy to keep their toddlers occupied.
The holes on top of each board are big enough for the power tool's screwdriver bits to go through, but not big enough for the loosened screw to float out into space. When all the screws are removed, each cover will be stowed with the screws trapped inside. The circuit cards will be replaced, and then the astronauts will clamp on brand-new covers with an easy-on, easy-off design.
Tools and toys
That's just one example of the tool team's ingenuity. Matt Ashmore, the lead engineer for the Mini Power Tool, said that he designed the device's pistol grip after going to the hardware store with an astronaut glove.
"We held every single power tool they had in the store, to see what kind of handle felt really good with an astronaut glove," Ashmore told me.
Even the astronauts got into the act: Grunsfeld and his Atlantis crewmate, rookie spaceflier Drew Feustel, came up with the idea of using a reach extender (nicknamed the "PikStik," after the commercial product) to push Hubble's new gyroscopes into place.
Feustel said he was inspired by a play version of the reacher that he pulled out of his children's toy box. "That was the first thing that I had envisioned using on Hubble," he said. It turned out that Grunsfeld had a similar idea - and they worked with Goddard's team to develop an industrial-strength version with a locking trigger mechanism.
Pit crew in space
Both Ashmore and Feustel said they've put in a lot of tool time working on cars in their garage. Feustel was an auto mechanic long before he was an astronaut, and Ashmore spends his off time tinkering with a '69 Dodge Polara. "That's my baby," he said.
That experience came in handy during the tool development effort. "We wanted to be able to do this pit-crew-style," Ashmore said of the power-tool job.
In such matters, practice makes perfect: When the astronauts started training for the Hubble spacewalks, it took two hours to unscrew the fasteners on the STIS electronics cover. Now Ashmore says they can do the job like an Indy pit crew, in less than a half-hour. That translates to one loose screw roughly every 15 seconds.
Even a simple unscrewing job doesn't always go smoothly - so NASA's spacewalk planners are ready with backup plans: Some of the screws on the Advanced Camera for Surveys will have to be loosened manually, due to the weird angle of attack inside the telescope. If a screw doesn't come out easily, it'll be OK to break the screw head off with the bit and leave the threads behind. And if a screw won't budge at all, there's always the option of drilling the darn head right off.
Not your typical tools
Such scenarios may sound familiar to anyone who's had to do some home fix-up, but this is not your typical worksite. So the tools can't be typical, either. They have to be custom-made, with materials and lubricants that can stand up to the rigors of space.
And that means they have to be expensive. E. Michael Kienlen Jr., deputy project manager for Goddard's HST Development Office, said the cost of Hubble tool development hasn't been broken out for this mission. He noted that an earlier effort to develop a bigger pistol-grip power tool for use with Hubble and the international space station costed out to about $10 million, or roughly $1.5 million each for seven of the tools.
Common sense tells you that developing more than 60 tools for the upcoming Hubble mission probably carries an eight-figure price tag as well - which means you won't be seeing the Mini Power Tool at Home Depot anytime soon. But if the tools produce new dividends from a mission that NASA estimates has cost about $10 billion so far, the price will be well worth it.
