The following graph shows the projected Signal to Noise ratios for both MPP and non-MPP CCDs, at the start of the mission, and at the end of the mission (assuming a five year mission lifetime) showing the slight degradation in performance due to radiation damage.

A signal of 1 photon per pixel per second is assumed. The signal has been integrated for 100 seconds - yielding a total detected signal of 100 photons with a shot noise of 10 photons. At EIS wavelengths these values must be multiplied by the electron conversion factor, which is 15 at a wavelength of around 240 A.

An rms read out noise for the CCD of 8 electrons has been assumed (which may be slightly high for a readout of about 500,000 pixels per second).

The above graph shows the increase in the Signal to Noise ratio as the CCD temperature decreases (and hence dark current also decreases). The CCD approaches photon noise limited performance around -25 Centigrade for an MPP device and around -55 Centigrade for a non-MPP device.