NASA’s highly successful Kepler space telescope has had more than its share of near fatal experiences.
The latest happened in April when the spacecraft went into “Emergency Mode” which among other things allows for priority access to ground-based communications via NASA’s Deep Space Network. NASA noted at the time that the spacecraft is nearly 75 million miles from Earth, making the communication slow. Even at the speed of light, it takes 13 minutes for a signal to travel to the spacecraft and back.
The spacecraft has since returned to normal function.
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While NASA hasn’t fully examined all the issues from that emergency it did say this week that “all the signs are pointing towards a single bit that changed state in the memory of an electronic chip that controls the internal command and data bus onboard the spacecraft.”
From NASA: “The memory was designed to be highly resistant to upset but if a high-energy cosmic ray hit in just the wrong place or at the wrong time in a write cycle an upset can occur. In this case, the upset caused a disruption in the internal data stream, passing invalid data sets to the flight computer, setting off several fault responses including the shutdown of critical heaters on the spacecraft. After a couple of hours, propellant froze in the propulsion system effectively disabling pointing control. Without pointing control, the spacecraft slowly drifted until the sun got too close to a “forbidden zone” around the optical axis of the telescope, causing the Emergency Mode to kick in and protect the telescope. While we have an excellent fault protection system onboard, no amount of pre-planning is going to work if we get multiple, random faults, which is why we have the Emergency Mode in the first place.”
You may recall that in May of 2013, Kepler was out of commission and thought to be kaput because of an equipment failure. But the space agency came up with a way to make use of the Sun and Kepler's orbit around it to stabilize the craft and let it start taking images of space again. The Kepler verified planet count currently stands at 2,327.
While Kepler has survived and thrived it will come to an end. NASA announced said this week that Kepler is to continue science operations through the end of the FY19, by which time the on-board fuel is expected to be depleted.
How many more planets will it spot by then?
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