HOUSTON – A glitch in the International Space Station's (ISS) U.S.-built attitude control system may have its root in a massive solar flare that erupted from the Sun this week, a NASA flight director said Friday.
"The leading theory right now is that the additional solar activity has taken the normal density of the [Earth's] atmosphere and it's about two and a half times more than it normally is," ISS flight director Joel Montalbano said during a morning update here at the Johnson Space Center. "So we're seeing some problems with our software converging on a nice stable attitude for attitude control."
The space station typically relies on four large gyroscopes — one of which is currently offline — that spin to maintain attitude control without consuming precious propellant. Only two gyroscopes are required to maintain ISS orientation with the system.
[Attitude, as opposed to altitude, refers to the position, orientation and direction of the space station relative to the Earth.]
The station is also equipped with Russian thrusters and can be oriented by docked spacecraft, such as Russian Soyuz and Progress vehicles, as well as NASA shuttles.
NASA flight controllers opted to use the space shuttle Discovery's thrusters to orient the ISS on Thursday until the non-propellant mode is reactivated, Montalbano said.
"So what we'll do is that solar activity is dying down and were going to try again to go to a non-propulsion mode later today," Montalbano said, adding that Discovery is well stocked with propellant to help control ISS attitudes through the two spacecraft's docked STS-116 mission operations. "We think we understand the problem."
To date, solar activity has not endangered the astronauts and their ISS counterparts in any way, though they did take precautions earlier this week to be safe.
Spacewalking astronauts mentioned the solar flare may have led to some stunning auroras they spotted while working outside the ISS on Thursday.
Flight controllers mentioned the solar flare's effects in the morning mail to Discovery's STS-116 crew.
"Isn't it interesting that solar winds appear to be affecting your flight!" flight controllers relayed up to the shuttle astronauts. "We hope that all of you take a little time today to catch your breath and to look out the window in order to store future memories."
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