Something strange is killing off pixels at an alarming rate in the detectors of a multi-billion dollar space telescope scheduled to launch in 2014.

The problem is just the latest blow for NASA’s ultra-sensitive James Webb Space Telescope (JWST), which is expected to launch late and run over-budget.

JWST has a 6.5-metre mirror, which is nearly three times as wide as the mirror on the Hubble Space Telescope. The telescope could glimpse the universe’s first stars and galaxies.

But in December Marcia Rieke of the University of Arizona in Tucson and colleagues found that roughly 2 per cent of pixels in a detector destined for JWST’s Near Infrared Camera (NIRCam) were transmitting signals although no light was hitting them. That’s four times as many “hot pixels” as there were when the detector was analysed in 2008.


The researchers later found that the problem affects four of the camera’s five long-wavelength detector arrays. “We don’t know what is happening, and we don’t know if there’s a way to reverse it or slow it down,” says Rieke, principal investigator for the NIRCam. “Until we understand the root cause, I think we’re all going to be quite nervous.”

Latest setback

NASA allows no more than 5 per cent of a detector’s pixels to be hot by the end of the telescope’s five-year space mission. At this rate, the detectors may exceed this limit before the telescope even leaves the ground, says Rieke.

The pixel problem follows a series of setbacks for JWST. In November 2010, an independent review panel predicted that JWST is unlikely to launch before September 2015, more than a year later than planned, and will cost $1.5 billion more than expected.

NASA has set up a review board to analyse the detector problem and discuss solutions. “It’s too early to speculate on what the root cause is or what we’re going to do to fix it,” says JWST programme director Rick Howard. He says it may be a month or more before the expert board comes to a conclusion.