The problem was noticed in recent tests when the cameras were chilled to approximately –75 degrees Celsius.
"Recent tests show the cameras on TESS are slightly out of focus when placed in the cold temperatures of space where it will be operating," NASA spokesperson Felicia Chou said in response to a SpaceNews inquiry. "After a thorough engineering evaluation, NASA has concluded TESS can fully accomplish its science mission with the cameras as they are, and will proceed with current integration activities."
The problem with the TESS cameras came up during a July 24 meeting of the NASA Advisory Council science committee in Hampton, Virginia. Alan Boss, an astronomer with the Carnegie Institution, brought up the issue in a summary of a meeting last week of the Astrophysics Advisory Committee, of which he is a member.
"That could have some big effects on the photometry," he said of the focus problem. "This is certainly a concern for the folks who know a lot about photometry."