The K2 Campaign 10, ongoing since July 6, has suffered a couple of unexpected reductions to the intended science.
The initial line of sight pointing of the spacecraft at the start of the campaign was offset from its intended target by 12 arcsec, sufficient to lose much of the expected target light from the assigned apertures. This error was compounded by a downlink issue that failed to provide the requisite focal plane data that is intended to catch such errors. These data were subsequently acquired and pointing corrected on July 13. Although the spacecraft was in fine point throughout, the pointing offset will compromise much of the data for the first week of observations, and is likely to more seriously affect those targets near the edge of the focal plane where roll is largest.
Then, on July 20, the photometers was turned off as an apparent response to a failure of a module on the focal plane. The spacecraft otherwise continued to operate normally, and the anomaly was not discovered until a scheduled data downlink on July 28.
With extremely poor communication geometry at science attitude, spacecraft health checks consume significant DSN resources, requiring a 70-meter antenna. Such health checks are therefore performed infrequently during the K2 mission, roughly every two weeks.
While the cause of this is yet to be confirmed, the observables are in family with those seen in conjunction with the failure of science CCD Modules 3 and 7 in 2010 and 2014. Further, thermal data retrieved from the spacecraft are strongly suggestive of a drop in power dissipated by Module 4 that is again in family with a similar drop when Modules 3 and 7 failed. Thus there is a strong likelihood that Module 4 is no longer functioning. If this is indeed the case, this would leave us with 18 remaining science modules of the initial 21.
We undertook a recovery which involved reorienting the spacecraft to attain higher data rate communications with Earth and carefully powering on the various components that had been switched off, and science observations resumed on August 3.
Based on the thermal data, the Campaign 11 target apertures located on Module 4 are being reassigned to targets on other modules. We anticipate being able to confirm the health of the suspect module at the next planned health check on August 11 and further updates will be provide thereafter.
Events like this module failure are things that happen with an aging spacecraft. For future campaigns we will reallocate pixels to active modules as needed.