19 Mar 2009
Forty two individual sensors form the largest CCD array ever launched by NASA.
The Kepler spacecraft launched earlier this month will use imaging sensors from e2v to spot Earth-like planets orbiting other stars. "This is groundbreaking," Paul Jorden, Technical Specialist at e2v explained to optics.org. "Kepler's focal plane array of 42 e2v CCDs forms the largest array of CCDs ever built for a spacecraft."
The sensor array will spot the distant worlds by detecting minute changes in brightness as they orbit in front of their parent stars. "Kepler will be the pre-eminent instrument in this task, and at present it is unique," said Jorden.
Designing a sensor array on such a scale presented substantial technical challenges, and almost every aspect of the packaging and operation of the detector had to be specially designed, according to Jorden.
"The chips need a high dynamic range and must be very linear," he said. "Repeatable performance is critical, as Kepler will have to make measurements of a star's brightness and then return to it perhaps a year later to take another brightness measurement."
Packaging of the chips was a crucial consideration. "The individual detectors had to be packed together as closely as possible to make the instrument efficient," noted Jorden. "A high degree of mechanical stability and precision was essential, since they directly affect the photometric precision that the device is capable of."
The resulting focal plane array features an image size of 28 x 55 mm and 2200 x 1044 active pixels, an effective resolution of more than 95 megapixels.
Supplying the sensors to NASA is a notable success for the UK-based company. "The original intention was for a dual-supply arrangement, along with a US company, to ensure security of supply," commented Jorden. "But the client was so pleased with our work that in the end they ordered them all from us."
Like all such missions, patience is needed before the success of the detector can be assessed. "It will be another month or so before the instrument is opened up fully," said Jorden. "We hope to start getting results back in about six months. After that, the expectation is that Kepler will detect hundreds of Earth-like planets over its three to five year lifetime."
Future missions will also benefit, according to Jorden. "This has been one detector in an evolution," he said. "We have learned things from making it and can design even better ones for other missions. This was a stepping stone."