press-releases articles Astronomers call it "discovery efficiency." It is a measure of an observatory's potential to produce scientific results in a fixed amount of time: the faster you can take good pictures, the higher the discovery efficiency. The Advanced Camera for Surveys will increase the discovery efficiency of the Hubble Space Telescope by one full order of magnitude. Put another way, ACS is equivalent to launching nine more HSTs: now that's a lot of picture-taking.
ACS is designed to optimize Hubble, taking full advantage of HST's uniqueness as a space-based telescope with a wide field of view, superb image quality, and sensitivity in visible to far ultra-violet wavelengths. The Advanced Camera actually brings three cameras to HST: they are the Wide Field, High Resolution, and Solar Blind Cameras. As each of these is designed to perform a unique imaging role, ACS will be able to support many different types of astronomy.
It is possible to blur the image that the Hubble telescope transmits by using detector pixels that are too large: this is not the case in the design of the ACS High Resolution Camera charge coupled device detector. Its one-million pixels are sized perfectly to sample the HST image without losing any of the precious optical information. The coupled HST/ACS design allows the HRC to take extremely detailed pictures of astronomical objects such as the inner regions of galaxies and to search neighboring stars for planets and planets-to-be.
Particular features, such as emission lines that indicate the presence of certain molecules, become detectable only in the ultra-violet portion of the spectrum. The Solar Blind Channel blocks visible light and uses a highly sensitive photon-counting detector to enhance the visibility of these features. This channel will be used to study, among other subjects, weather on planets in our own solar system.
ACS's Wide Field Camera is designed to execute efficient surveys of the universe by collecting the most light in the shortest time possible. WFC does this by having high throughput and (you guessed it) a wide field of view. At 40,000 square arc sec, the ACS field of view will be the largest ever on Hubble and more than twice the size of current champion surveyor Wide Field Planetary Camera-2. ACS achieves high throughput in this camera with the use of highly reflective silver-coated mirrors and charge-coupled device detectors with 16-million pixels optimized for sensitivity to visible light. The design result is that 44% of the light that enters the WFC field is collected by ACS (and available to be featured on magazine covers everywhere). The ACS Science Team, led by Dr Holland Ford of Johns Hopkins University, plans to make extensive use of Wide Field Channel images to study the nature and distribution of galaxies in order to understand how they and our universe evolved.
The Advanced Camera for Surveys poses for its own picture. Servicing Mission-3 will leave HST a completely refurbished observatory as ACS replaces the Faint Object Camera, the last of the original instruments.
