The European Space Agency (ESA) nearly lost a veteran space telescope last month when a charged particle disabled one of the reaction wheels that keep its solar panels pointed at the sun.
The incident led to a race against time, as ground controllers had only three hours of battery life to find a solution before the spacecraft completely lost power, ESA revealed in a statement issued on Monday (October 18).
Since 2002, the Integral Gamma-ray Space Telescope has been scouring the sky for sources of high-energy X-rays and gamma rays – the most energetic type of radiation in the universe produced by dense and yet little-known objects such as pulsars and neutrons. . stars. But on September 22, ground controllers suddenly realized something was wrong when spotty data began to come in from the 4.4-ton (4-metric-ton) observatory. Soon after, the spacecraft automatically switched to so-called safe mode, during which all non-essential systems, including scientific instruments, are shut down.
“The data coming from Integral was choppy and coming in for short periods because it was spinning,” Richard Southworth, operations manager for Integral mission, said in the statement. “This made the analysis even more difficult.”
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The team soon determined that the spinning spacecraft’s choppy data delivery was due to the loss of one of Integral’s three reaction wheels. Reaction wheels control the attitude of a rotating satellite against the forces that affect the orbiting spacecraft: gravity, atmospheric resistance, solar wind pressure, and uneven cooling. With one of its three reaction wheels suddenly out of order, Integral began to spin and its solar panels lost illumination.
The 19-year-old Integral, ESA’s oldest space telescope, has already experienced some technical problems, which meant that the original backup systems designed to work in such circumstances did not work.
“The batteries were discharging as there were only short charging periods when the panels briefly looked at the sun,” Southworth added.
The ground crew attempted to restore function to the affected wheel, but the Integral spacecraft continued to wobble and spin every 21 minutes, five times faster than its operating maximum.
With the spacecraft’s battery quickly draining, the operators decided first to shut down additional systems to buy some time to resolve the gyro problem. Eventually, the team managed to find a way to reduce the turning speed by modifying the rotational speed of the reaction wheels.
“Everyone breathed a great sigh of relief,” Andreas Rudolph, head of the astronomical missions division of ESA’s Department of Mission Operations, said in the statement. “This was very close, and we were immensely relieved to pull the spacecraft out of this ‘near death’ experience.”
But what exactly brought down that reaction wheel? The space agency said the fault was caused by what engineers call a single-event disturbance, which occurs when a charged particle hits a sensitive electrical component. These incidents are usually caused by the solar wind, a stream of charged particles emanating from the sun. These accidents are frequently caused by solar flares and coronal mass ejections, powerful bursts of magnetized plasma from the sun’s upper atmosphere, the corona.
Interestingly, this incident occurred while the sun was fairly calm.
“This attack occurred on a day when no relevant space weather activity was observed,” Juha-Pekka Luntama, ESA’s chief of space meteorology, said in the statement. “Based on a discussion with our colleagues in the flight control team, it appears that the anomaly was caused by charged particles trapped in radiation belts around Earth.”
The Van Allen radiation belts are two donut-shaped regions around our planet where charged particles from the solar wind are trapped within the Earth’s magnetic field. Stretching between altitudes of 400 to 36,000 miles (640 to 58,000 kilometers), radiation belts are a known threat to orbiting satellites due to their high levels of charged particles.
In the days after the original emergency, the controllers of the Integral spacecraft had to repeat the stabilization procedure when the observatory began to rotate again.
ESA said in the statement that the secondary problem may have been caused by a star tracker that was temporarily blinded by Earth. Star trackers are cameras that help a satellite maintain its position by monitoring the position of the stars.
The spacecraft has been stable since September 27 and all systems were turned back on on October 1, ESA said in the statement. The spacecraft is now in the middle of an observing campaign focused on massive stars in the constellation Orion.
Follow Tereza Pultarova on Twitter @TerezaPultarova. Follow us on Twitter @Spacedotcom and on Facebook.
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