Wide Field and Planetary Camera 2
Encyclopedia
The Wide Field and Planetary Camera 2 (WFPC2) is a baby grand piano sized camera
built by the Jet Propulsion Laboratory
and formerly installed on the Hubble Space Telescope
. It was installed by servicing mission 1 (STS-61
) in 1993, replacing the telescope's original Wide Field and Planetary Camera
(WFPC). WFPC2 was used to image the Hubble Deep Field
in 1995, the Hourglass Nebula
and Egg Nebula
in 1996, and the Hubble Deep Field South
in 1998. During STS-125
, WFPC2 was removed and replaced with the Wide Field Camera 3
as part of the mission's first spacewalk on May 14, 2009. After returning to Earth, the camera was displayed briefly at the Jet Propulsion Laboratory
, then at the Denver Museum of Nature and Science
before moving to its final home at the Smithsonian's National Air and Space Museum
.
's Jet Propulsion Laboratory
, which also built the predecessor
WFPC
("WFPC1") camera launched with Hubble in 1990. WFPC2 contains internal
corrective optics to fix the spherical aberration in the Hubble telescope's primary mirror.
The charge-coupled device
s (CCDs) in the WFPC2 detected electromagnetic radiation
in a range from 120 nm
to 1100 nm. This included the 380 nm to 780 nm of the visible spectrum, all of the near ultraviolet
(and a small part of the extreme ultraviolet band) and most of the near infrared
band. The sensitivity distribution of these CCDs is roughly normal, with a peak around 700 nm and concomitantly very poor sensitivity at the extremes of the CCDs' operating range. WFPC2 featured four identical CCD detectors, each 800x800 pixel
s. Three of these, arranged in an L-formation, comprise Hubble's Wide Field Camera (WFC). Adjacent to them is the Planetary Camera (PC), a fourth CCD with different (narrower-focused) optics. This afforded a more detailed view over a smaller region of the visual field. WFC and PC images are typically combined, producing the WFPC2's characteristic stairstep image. When distributed as non-scientific JPEG
files the PC portion of the image is shown with the same resolution as the WFC portions, but astronomers receive a raw scientific image package which presents the PC image in its native, higher detail.
To allow scientists to view specific parts of the electromagnetic spectrum the WFPC2 featured a rotating wheel which moves different optical filters into the lightpath (between the WFPC2's aperture and the CCD detectors). The 48 filter elements included:
closed a number of long exposures are taken, and pixels which differ significantly from near black are flagged. To avoid false positives caused by cosmic ray
s tripping a given pixel, the output of different calibration shots are compared. Pixels which are consistently "hot" are recorded, and astronomers who analyse raw WFPC2 images receive a list of these pixels. Typically astronomers adjust their photo-processing software to ignore these bad pixels.
WFPC2 was largely superseded for broad-band imaging by the Advanced Camera for Surveys
, installed during servicing mission 3B in 2002. However, the early 2007 failure of ACS resulted in WFPC2 returning to its role as Hubble's primary visible light camera. WFPC2 was removed from HST during Servicing Mission 4 in May 2009, for return to Earth and eventual museum display. It was replaced by Wide Field Camera 3
, which features two UV/visible detecting CCDs, each 2048x4096 pixels, and a separate IR CCD of 1024 x 1024, capable of receiving infrared radiation up to 1700 nm.
Camera
A camera is a device that records and stores images. These images may be still photographs or moving images such as videos or movies. The term camera comes from the camera obscura , an early mechanism for projecting images...
built by the Jet Propulsion Laboratory
Jet Propulsion Laboratory
Jet Propulsion Laboratory is a federally funded research and development center and NASA field center located in the San Gabriel Valley area of Los Angeles County, California, United States. The facility is headquartered in the city of Pasadena on the border of La Cañada Flintridge and Pasadena...
and formerly installed on the Hubble Space Telescope
Hubble Space Telescope
The Hubble Space Telescope is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4 meter aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared...
. It was installed by servicing mission 1 (STS-61
STS-61
STS-61 was the first Hubble Space Telescope servicing mission, and the fifth flight of the Space Shuttle Endeavour. The mission launched on 2 December 1993 from Kennedy Space Center in Florida. The mission restored the spaceborne observatory's vision, marred by spherical aberration, with the...
) in 1993, replacing the telescope's original Wide Field and Planetary Camera
Wide Field and Planetary Camera
The Wide Field/Planetary Camera was a camera installed on the Hubble Space Telescope until December 1993. It was one of the instruments on Hubble at launch, but its functionality was severely impaired by the defects of the main mirror optics which afflicted the telescope...
(WFPC). WFPC2 was used to image the Hubble Deep Field
Hubble Deep Field
The Hubble Deep Field is an image of a small region in the constellation Ursa Major, constructed from a series of observations by the Hubble Space Telescope. It covers an area 2.5 arcminutes across, two parts in a million of the whole sky, which is equivalent in angular size to a 65 mm tennis...
in 1995, the Hourglass Nebula
Hourglass Nebula
The Engraved Hourglass Nebula is a young planetary nebula situated in the southern constellation Musca about 8,000 light-years away from Earth. It was discovered by Annie Jump Cannon and Margaret W. Mayall during their work on an extended Henry Draper Catalogue...
and Egg Nebula
Egg Nebula
The Egg Nebula is a bipolar protoplanetary nebula approximately 3,000 light-years away from Earth. It was discovered by Raghvendra Sahai and John Trauger of NASA's Jet Propulsion Laboratory in Pasadena, California...
in 1996, and the Hubble Deep Field South
Hubble Deep Field South
The Hubble Deep Field South is a composite of several hundred individual images taken using the Hubble Space Telescope's Wide Field and Planetary Camera 2 over 10 days in September and October 1998. It followed the great success of the original Hubble Deep Field in facilitating the study of...
in 1998. During STS-125
STS-125
STS-125, or HST-SM4 , was the fifth and final space shuttle servicing mission to the Hubble Space Telescope .Launch occurred on 11 May 2009 at 2:01 pm EDT...
, WFPC2 was removed and replaced with the Wide Field Camera 3
Wide Field Camera 3
The Wide Field Camera 3 is the Hubble Space Telescope's last and most technologically advanced instrument to take images in the visible spectrum...
as part of the mission's first spacewalk on May 14, 2009. After returning to Earth, the camera was displayed briefly at the Jet Propulsion Laboratory
Jet Propulsion Laboratory
Jet Propulsion Laboratory is a federally funded research and development center and NASA field center located in the San Gabriel Valley area of Los Angeles County, California, United States. The facility is headquartered in the city of Pasadena on the border of La Cañada Flintridge and Pasadena...
, then at the Denver Museum of Nature and Science
Denver Museum of Nature and Science
The Denver Museum of Nature & Science is a municipal natural history and science museum in Denver, Colorado. It is a resource for informal science education in the Rocky Mountain region. A variety of exhibitions, programs, and activities help museum visitors learn about the natural history of...
before moving to its final home at the Smithsonian's National Air and Space Museum
National Air and Space Museum
The National Air and Space Museum of the Smithsonian Institution holds the largest collection of historic aircraft and spacecraft in the world. It was established in 1976. Located in Washington, D.C., United States, it is a center for research into the history and science of aviation and...
.
Design
WFPC2 was built by NASANASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
's Jet Propulsion Laboratory
Jet Propulsion Laboratory
Jet Propulsion Laboratory is a federally funded research and development center and NASA field center located in the San Gabriel Valley area of Los Angeles County, California, United States. The facility is headquartered in the city of Pasadena on the border of La Cañada Flintridge and Pasadena...
, which also built the predecessor
WFPC
Wide Field and Planetary Camera
The Wide Field/Planetary Camera was a camera installed on the Hubble Space Telescope until December 1993. It was one of the instruments on Hubble at launch, but its functionality was severely impaired by the defects of the main mirror optics which afflicted the telescope...
("WFPC1") camera launched with Hubble in 1990. WFPC2 contains internal
corrective optics to fix the spherical aberration in the Hubble telescope's primary mirror.
The charge-coupled device
Charge-coupled device
A charge-coupled device is a device for the movement of electrical charge, usually from within the device to an area where the charge can be manipulated, for example conversion into a digital value. This is achieved by "shifting" the signals between stages within the device one at a time...
s (CCDs) in the WFPC2 detected electromagnetic radiation
Electromagnetic radiation
Electromagnetic radiation is a form of energy that exhibits wave-like behavior as it travels through space...
in a range from 120 nm
Nanometre
A nanometre is a unit of length in the metric system, equal to one billionth of a metre. The name combines the SI prefix nano- with the parent unit name metre .The nanometre is often used to express dimensions on the atomic scale: the diameter...
to 1100 nm. This included the 380 nm to 780 nm of the visible spectrum, all of the near ultraviolet
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
(and a small part of the extreme ultraviolet band) and most of the near infrared
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
band. The sensitivity distribution of these CCDs is roughly normal, with a peak around 700 nm and concomitantly very poor sensitivity at the extremes of the CCDs' operating range. WFPC2 featured four identical CCD detectors, each 800x800 pixel
Pixel
In digital imaging, a pixel, or pel, is a single point in a raster image, or the smallest addressable screen element in a display device; it is the smallest unit of picture that can be represented or controlled....
s. Three of these, arranged in an L-formation, comprise Hubble's Wide Field Camera (WFC). Adjacent to them is the Planetary Camera (PC), a fourth CCD with different (narrower-focused) optics. This afforded a more detailed view over a smaller region of the visual field. WFC and PC images are typically combined, producing the WFPC2's characteristic stairstep image. When distributed as non-scientific JPEG
JPEG
In computing, JPEG . The degree of compression can be adjusted, allowing a selectable tradeoff between storage size and image quality. JPEG typically achieves 10:1 compression with little perceptible loss in image quality....
files the PC portion of the image is shown with the same resolution as the WFC portions, but astronomers receive a raw scientific image package which presents the PC image in its native, higher detail.
To allow scientists to view specific parts of the electromagnetic spectrum the WFPC2 featured a rotating wheel which moves different optical filters into the lightpath (between the WFPC2's aperture and the CCD detectors). The 48 filter elements included:
- A polarizing filter.
- A graduated filter, featuring a wide range of very narrowband filters. By positioning the target object at a precise part of the field, the operator can use an accurately picked narrowband filter (albeit over a very small part of the field).
- A number of different optical filters, allowing the operator to choose from a variety of different response characteristics.
Performance
As predicted, over the course of its mission the WFPC2 experienced degradation of the CCDs, resulting in defective ("hot") pixels. The telescope's operators perform monthly calibration tests to catalog these; with the WFPC's apertureAperture
In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture of an optical system is the opening that determines the cone angle of a bundle of rays that come to a focus in the image plane. The aperture determines how collimated the admitted rays are,...
closed a number of long exposures are taken, and pixels which differ significantly from near black are flagged. To avoid false positives caused by cosmic ray
Cosmic ray
Cosmic rays are energetic charged subatomic particles, originating from outer space. They may produce secondary particles that penetrate the Earth's atmosphere and surface. The term ray is historical as cosmic rays were thought to be electromagnetic radiation...
s tripping a given pixel, the output of different calibration shots are compared. Pixels which are consistently "hot" are recorded, and astronomers who analyse raw WFPC2 images receive a list of these pixels. Typically astronomers adjust their photo-processing software to ignore these bad pixels.
WFPC2 was largely superseded for broad-band imaging by the Advanced Camera for Surveys
Advanced Camera for Surveys
The Advanced Camera for Surveys is a third generation axial instrument aboard the Hubble Space Telescope . The initial design and scientific capabilities of ACS were defined by a team based at Johns Hopkins University. ACS was assembled and tested extensively at Ball Aerospace & Technologies Corp...
, installed during servicing mission 3B in 2002. However, the early 2007 failure of ACS resulted in WFPC2 returning to its role as Hubble's primary visible light camera. WFPC2 was removed from HST during Servicing Mission 4 in May 2009, for return to Earth and eventual museum display. It was replaced by Wide Field Camera 3
Wide Field Camera 3
The Wide Field Camera 3 is the Hubble Space Telescope's last and most technologically advanced instrument to take images in the visible spectrum...
, which features two UV/visible detecting CCDs, each 2048x4096 pixels, and a separate IR CCD of 1024 x 1024, capable of receiving infrared radiation up to 1700 nm.
See also
- Wide Field and Planetary CameraWide Field and Planetary CameraThe Wide Field/Planetary Camera was a camera installed on the Hubble Space Telescope until December 1993. It was one of the instruments on Hubble at launch, but its functionality was severely impaired by the defects of the main mirror optics which afflicted the telescope...
- Wide Field Camera 3Wide Field Camera 3The Wide Field Camera 3 is the Hubble Space Telescope's last and most technologically advanced instrument to take images in the visible spectrum...
- Cosmic Origins SpectrographCosmic Origins SpectrographThe Cosmic Origins Spectrograph is a science instrument that was installed on the Hubble Space Telescope during Servicing Mission 4 in May 2009. It is designed for ultraviolet spectroscopy of faint point sources with a resolving power of ≈1,550–24,000...
- Advanced Camera for SurveysAdvanced Camera for SurveysThe Advanced Camera for Surveys is a third generation axial instrument aboard the Hubble Space Telescope . The initial design and scientific capabilities of ACS were defined by a team based at Johns Hopkins University. ACS was assembled and tested extensively at Ball Aerospace & Technologies Corp...
- Near Infrared Camera and Multi-Object SpectrometerNear Infrared Camera and Multi-Object SpectrometerThe Near Infrared Camera and Multi-Object Spectrometer is a scientific instrument for infrared astronomy, installed on the Hubble Space Telescope , operating from 1997 to 1999, and from 2002 to 2008...
- Faint Object CameraFaint Object CameraThe Faint Object Camera was a camera installed on the Hubble Space Telescope from launch in 1990 until 2002. It was replaced by the Advanced Camera for Surveys.The camera was built by Dornier GmbH and was funded by the European Space Agency...