Overview of the advanced camera for surveys on-orbit performance

We present an overview of the ACS on-orbit performance based on the calibration observations taken during the first three months of ACS operations. The ACS meets or exceeds all of its important performance specifications. The WFC and HRC FWHM and 50% encircled energy diameters at 555 run are 0.088" and 0.14", and 0.050" and 0.10". The average rms WFC and HRC read noises are 5.0 e(-) and 4.7 e(-). The WFC and HRC average dark currents are similar to 7.5 and similar to 9.1 e(-)/pixel/hour at their operating temperatures of - 76 degreesC and - 80 degreesC. The SBC + HST throughput is 0.0476 and 0.0292 through the F125LP and F150LP filters. The lower than expected SBC operating temperature of 15 to 27 degreesC gives a dark current of 0.038 e(-)/pix/hour. The SBC just misses its image specification with an observed 50% encircled energy diameter of 0.24" at 121.6 nm. The ACS HRC coronagraph provides a 6 to 16 direct reduction of a stellar PSF, and a similar to1000 to similar to9000 PSF-subtracted reduction, depending on the size of the coronagraphic spot and the wavelength. The ACS grism has a position dependent dispersion with an average value of 3.95 nm/pixel. The average resolution lambda/Deltalambda for stellar sources is 65, 87, and 78 at wavelengths of 594 mn, 802 nm, and 978 nm.