The Advanced Camera for Surveys (ACS) is a third-generation axial instrument aboard the

Hubble Space Telescope The Hubble Space Telescope (often referred to as HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most versa ...

(HST). The initial design and scientific capabilities of ACS were defined by a team based at

Johns Hopkins University Johns Hopkins University (Johns Hopkins, Hopkins, or JHU) is a private university, private research university in Baltimore, Maryland. Founded in 1876, Johns Hopkins is the oldest research university in the United States and in the western hem ...

. ACS was assembled and tested extensively at Ball Aerospace & Technologies Corp. and the

Goddard Space Flight Center The Goddard Space Flight Center (GSFC) is a major NASA space research laboratory located approximately northeast of Washington, D.C. in Greenbelt, Maryland, United States. Established on May 1, 1959 as NASA's first space flight center, GSFC empl ...

and underwent a final flight-ready verification at the

Kennedy Space Center The John F. Kennedy Space Center (KSC, originally known as the NASA Launch Operations Center), located on Merritt Island, Florida, is one of the National Aeronautics and Space Administration's (NASA) ten field centers. Since December 1968 ...

before integration in the cargo bay of the Columbia orbiter. It was launched on March 1, 2002, as part of Servicing Mission 3B (

STS-109 STS-109 (SM3B) was a Space Shuttle mission that launched from the Kennedy Space Center on 1 March 2002. It was the 108th mission of the Space Shuttle program, the 27th flight of the orbiter '' Columbia'' and the fourth servicing of the Hubble ...

) and installed in HST on March 7, replacing the

Faint Object Camera The Faint Object Camera (FOC) was a camera installed on the Hubble Space Telescope from launch in 1990 until 2002. It was replaced by the Advanced Camera for Surveys. In December 1993, Hubble's vision was corrected on STS-61 by installing COST ...

(FOC), the last original instrument. ACS cost US$86 million at that time. ACS is a highly versatile instrument that became the primary imaging instrument aboard HST. It offered several important advantages over other HST instruments: three independent, high-resolution channels covering the

ultraviolet Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nanometer, nm (with a corresponding frequency around 30 Hertz, PHz) to 400 nm (750 Hertz, THz), shorter than that of visible light, but longer than ...

to the

near-infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of Light, visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from ...

regions of the

spectrum A spectrum (plural ''spectra'' or ''spectrums'') is a condition that is not limited to a specific set of values but can vary, without gaps, across a continuum. The word was first used scientifically in optics to describe the rainbow of colors i ...

, a large detector area and

quantum efficiency The term quantum efficiency (QE) may apply to incident photon to converted electron (IPCE) ratio of a photosensitive device, or it may refer to the TMR effect of a Magnetic Tunnel Junction. This article deals with the term as a measurement of ...

, resulting in an increase in HST's discovery efficiency by a factor of ten, a rich complement of

filter Filter, filtering or filters may refer to: Science and technology Computing * Filter (higher-order function), in functional programming * Filter (software), a computer program to process a data stream * Filter (video), a software component tha ...

s, and coronagraphic,

polarimetric Polarimetry is the measurement and interpretation of the polarization of transverse waves, most notably electromagnetic waves, such as radio or light waves. Typically polarimetry is done on electromagnetic waves that have traveled through or ...

, and grism capabilities. The observations undertaken with ACS provided astronomers with a view of the Universe with uniquely high sensitivity, as exemplified by the

Hubble Ultra-Deep Field The Hubble Ultra-Deep Field (HUDF) is a deep-field image of a small region of space in the constellation Fornax, containing an estimated 10,000 galaxies. The original data for the image was collected by the Hubble Space Telescope from Septemb ...

, and encompass a wide range of astronomical phenomena, from comets and planets in the

Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar S ...

to the most distant

quasars A quasar is an extremely luminous active galactic nucleus (AGN). It is pronounced , and sometimes known as a quasi-stellar object, abbreviated QSO. This emission from a galaxy nucleus is powered by a supermassive black hole with a mass ranging ...

known.

Channels and detectors

ACS includes three independent channels (one now disabled), each optimized for specific scientific tasks:

Wide Field Channel (WFC)

The WFC is the most utilized channel of ACS. Its detector consists of two butted 2048x4096, 15 µm/pixel

charge-coupled device A charge-coupled device (CCD) is an integrated circuit containing an array of linked, or coupled, capacitors. Under the control of an external circuit, each capacitor can transfer its electric charge to a neighboring capacitor. CCD sensors are a ...

s (CCDs) for a total of 16

megapixel In digital imaging, a pixel (abbreviated px), pel, or picture element is the smallest addressable element in a raster image, or the smallest point in an all points addressable display device. In most digital display devices, pixels are the smal ...

s manufactured by Scientific Imaging Technologies (SITe). The WFC plate scale is 0.05″ per pixel and it has an effective field-of-view of 202″×202″. The spectral range of the WFC detector is 350–1100 nm. An example of a use of this channel was

SWEEPS Nielsen Media Research (NMR) is an American firm that measures media audiences, including television, radio, theatre, films (via the AMC Theatres MAP program), and newspapers. Headquartered in New York City, it is best known for the Nielsen rat ...

, which found 16 candidate exoplanets in the Galactic core.

High-Resolution Channel (HRC)

Mars close encounter (captured by the Hubble Space Telescope)

The HRC, which has been permanently disabled since 2007 due to an electrical fault, provided ultra-sharp views over a smaller field-of-view. The HRC detector was a 1024×1024 SITe CCD which had a smaller field-of-view (26"×29") than the WFC but twice the spatial sampling (0.025" per pixel). This detector was also significantly more sensitive than the WFC at near-ultraviolet wavelengths (<350 nm). The channel used two light suppression options for imaging faint objects around bright stars, improving the contrast of targets close to bright sources by tenfold. The first was a commandable coronagraphic mask that included two occulting spots, one of diameter 1.8" at the center of the field and the other of diameter 3.0" nearer to a corner. The first spot was the most popular of the two, for example, for imaging circumstellar disks around nearby bright stars or the host galaxies of luminous quasars. The second was the so-called Fastie Finger, 0.8" in width and 5" in length, located at the entrance of the HRC dewar window.

Solar Blind Channel (SBC)

The Multi Anode Microchannel Array (MAMA) of the SBC is a low-background photon-counting device optimized for the ultraviolet in the wavelength range of 115–170 nm. It consists of a photocathode, a microchannel plate, and an anode array. Its spatial sampling is 0.034"x0.030" per pixel and its field-of-view is 34.6"×30.0". The ACS SBC is in fact a flight spare from the

Space Telescope Imaging Spectrograph The Space Telescope Imaging Spectrograph (STIS) is a spectrograph, also with a camera mode, installed on the Hubble Space Telescope. Aerospace engineer Bruce Woodgate of the Goddard Space Flight Center was the principal investigator and creat ...

(STIS).

ACS problems and fixes 2006–2009

On 25 June 2006 ACS suffered an electronic failure. It was powered up successfully on its redundant (side-2) electronics. The instrument subsystems, including the CCD detectors, proved to be working after engineering tests, and ACS resumed science operations on July 4, 2006. On 23 September 2006, the ACS again failed, though by 9 October the problem had been diagnosed and resolved. On January 27, 2007, the ACS failed due to a short circuit in its backup power supply. The instrument's Solar Blind Channel (SBC) was returned to operation on 19 February 2007 using the side-1 electronics. The Wide Field Channel (WFC) was returned to service by

STS-125 STS-125, or HST-SM4 (Hubble Space Telescope Servicing Mission 4), was the fifth and final Space Shuttle mission to the Hubble Space Telescope (HST) and the last solo flight of the Space Shuttle Atlantis, Space Shuttle ''Atlantis''. The launch of ...

in May 2009. The High Resolution Channel (HRC), however, remains offline.

Gallery

File:Advanced Camera for Surveys.jpg, The ACS during assembly. File:NGC 3370 Hi.jpg, ACS Wide Field Channel (ACS/WFC) image of

NGC 3370 NGC 3370 (also known as ''UGC 5887'' or ''Silverado Galaxy'' ) is a spiral galaxy about 98 million light-years away in the constellation Leo. It is comparable to our Milky Way both in diameter (100,000 light years) and mass (1011 solar masse ...

from 2002. File:Ceres optimized.jpg, ACS High-Resolution Channel (ACS/HRC) image of

Ceres Ceres most commonly refers to: * Ceres (dwarf planet), the largest asteroid * Ceres (mythology), the Roman goddess of agriculture Ceres may also refer to: Places Brazil * Ceres, Goiás, Brazil * Ceres Microregion, in north-central Goiás ...

from 2005.

Filters and dispersers

ACS possesses a set of 38 filters and dispersers distributed among three wheels. Two of these wheels are shared by the HRC and WFC light paths while the third is dedicated to the SBC. The HRC and WFC elements consist of eleven broad-band filters, one medium-band filter, five narrow-band filters, three visible and three ultraviolet polarizers, one prism for the HRC, and one grism (580–1100 nm). Four of the filters have bandpasses in the near-ultraviolet and so can be used with the HRC only. The primary broad-band filters are equivalent to the ''u'', ''g'', ''r'', ''i'', and ''z'' filters of the ground-based

Sloan Digital Sky Survey The Sloan Digital Sky Survey or SDSS is a major multi-spectral imaging and spectroscopic redshift survey using a dedicated 2.5-m wide-angle optical telescope at Apache Point Observatory in New Mexico, United States. The project began in 2000 a ...

(SDSS). Five linear ramp filters divided into three individual segments each provide continuous imaging capability from 380 nm to 1070 nm and so ensure adequate sampling of

emission lines A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from emission or absorption of light in a narrow frequency range, compared with the nearby frequencies. Spectral lines are often used to iden ...

over a large range in redshift. Only the middle segment is accessible to the HRC. The SBC wheel is populated with one medium-band filter (Lyα), five long-pass filters, and two objective prisms.

Timeline

Hubble solar arrays after Servicing Mission 3B

*March 7, 2002, ACS installed in the Hubble Space Telescope (

) *June 19, 2006; ACS/WFC and HRC go offline due to problem with Low Voltage Power Supply *July 4, 2006 ACS resumed science operations by switching to back-up electronics *23 September 23, 2006, the ACS goes offline again *October 9, 2006 ACS problem diagnosed and resolved. *January 27, 2007 the ACS failed due to a short circuit in its backup power supply. *2009, ACS/WFC repaired (

)

References

External links

* * th
ACS Web site
at

, which includes a complete description of the instrument, the ground calibration campaigns, the detectors, and the filters. * th
ACS Web site
at th
Space Telescope Science Institute
(STScI)
All Publicly released ACS images
* a collection of HST images, including ACS, at th
Gallery
of the Hubble Site

{{Hubble Space Telescope Hubble Space Telescope instruments Space imagers