CAPE CANAVERAL, Fla. - Future spacewalking construction workers at the International Space Station apparently have one less worry today: The remote possibility of being electrocuted while laboring outside the station.
Quick-look data from a new measuring device indicates that the station's two electrical grounding rods are working as advertised.
Known as Plasma Contactor Units, the devices are designed to neutralize dangerous electrostatic potential that can build up on metal surfaces of the station as it plows through electrically charged plasma in the space environment.
"We have already started collecting data, and we can see that the Plasma Contactor Units are clamping the voltage between the plasma and the station as was hoped and predicted," said NASA flight director Bill Reeves.
Shaped like suitcases and mounted on a girder-like station truss, the so-called PCUs emit a stream of xenon gas into the electrically charged environment around the station.The gas is intended to eliminate the possibility of an electrostatic discharge that could create a shock hazard for spacewalking astronauts working outside the station.
Recent NASA analyses, however, raised questions about whether the grounding rods would operate as expected once a massive new pair of solar wings was erected at the outpost.
Stretching 240 feet (73 meters) from tip to tip, the solar arrays are capable of generating 64 kilowatts of power -- or enough electricity to supply 30 average American homes (minus air conditioning).
Jutting out from a $600 million electric tower erected at the station by shuttle Endeavour's crew last Sunday, the giant arrays since have been unfurled and activated, quintupling the amount of electricity available to power outpost systems.
The mere presence of the high-voltage arrays, however, prompted deep concern among NASA's engineering community. In a worst-case scenario, NASA analyses showed that the wings could trigger a deadly electrostatic discharge similar to a lightning bolt.
Complicating matters was the fact that the grounding rods are not equipped to provide actual measurements of the electrical environment surrounding the station.
Consequently, Endeavour spacewalkers Carlos Noriega and Joe Tanner mounted a specially designed measuring device atop the station's new five-story electric tower during a sortie outside the station Wednesday.
The so-called Floating Potential Probe is designed to gauge electrical potential outside the outpost to determine if a shock hazard in fact exists. The device was activated Friday, and data so far shows that the grounding rods appear to be operating as originally expected.
The PCUs "are working perfectly," Reeves said. "We're seeing very low numbers."
That, of course, is good news to future spacewalking station construction workers.
More than 145 spacewalks still will be required to finish building the outpost, which eventually will weigh 480 tons and span an area the size of two football fields set side-by-side.
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