Space Topics: Hubble Space Telescope
Science Instruments
Instruments Currently Installed on the Telescope
Advanced Camera for Surveys (ACS)
Installed March 2002 on the third Hubble servicing mission, ACS is able to
detect light with wavelengths from the ultraviolet to the near infrared. ACS
actually consists of three component cameras:
- The Wide Field Camera (WFC) searches for galaxies and galaxy clusters
in near-infrared wavelengths. It is the most-utilized channel of the
ACS. It has a three-mirror optical design, with a 250-1,050 nanometer
spectral response, a 202” x 202” field of view, and two CCDs
having 2,048 by 4,096 pixels.
- The High Resolution Camera (HRC) captures images of near, bright objects,
the centers of galaxies with black holes, and ordinary galaxies, star clusters
and gaseous nebulae. It has a three-mirror optical design, with a 200-1,050
nanometer spectral response, a 29.1” x 26.1” field of view,
and a CCD having 1,024 x 1,024 pixels. The CCD is enhanced to permit the
capture of near-ultraviolet light.
- The Solar Blind Camera (SBC) is used to detect faint and faraway objects,
including hot stars, quasars, and aurorae on Jupiter. It has a two-mirror
optical design, with a 115-180 nanometer spectral response, and a 14.58” x
30.8” field of view.
In addition, the ACS has 38 filters and dispersers on three wheels to permit
color imaging and photometry. Two wheels are shared by HRC and WFC.
Wide Field and Planetary Camera (WFPC2)
Installed during Hubble servicing mission 1, in 1993, WFPC2 is the most commonly
used camera on the HST. It responds to light from ultraviolet to near-infrared
wavelengths and is equipped with 48 filters for color imaging and photography.
Its sensor actually consists of four separate CCDs. Three of the CCDs are “wide-field
cameras,” and one is a “planetary camera” with a much smaller
field of view and higher resolution. This camera has taken Hubble's most beautiful
and famous photographs. WFPC2 images are often instantly recognizable because
they appear to have a "bite" taken out of the corner.
Near Infrared Camera and Multi-Object Spectrometer (NICMOS)
NICMOS was installed in 1997 during the second servicing mission. NICMOS
is especially sensitive to infrared light with wavelengths between 0.8 and
2.5 microns, making it useful for studying objects obscured by interstellar
gases, the formation of stars, and planetary atmospheric changes over time.
It is kept at a very low temperature of 77 kelvins (-196º Celsius, -321º Fahrenheit),
so that the instrument's own heat does not interfere with infrared light from
space. A 140-kilogram (230-pound) block of nitrogen ice cooled it until servicing
mission 3B in 2002, when it was replaced with a cyrocooler that refrigerates
it with liquid neon. NICMOS has three adjacent, independent cameras, each
with a dedicated array at a different magnification scale.
Space Telescope Imaging Spectrometer (STIS)
STIS was installed in 1997 during the second servicing mission and replaced
the GHRS spectrograph. It stopped science operations after an electronics
failure on August 3, 2004 and is now in “safe” mode. STIS was
used to measure light in ultraviolet, visible, and infrared wavelengths to
find the chemical composition, density, and motion of objects in space. It
captured the first spectral data from the atmosphere of an extrasolar planet.
Fine Guidance Sensors (FGS)
Two of these three sensors lock onto “guide” stars to keep Hubble
oriented correctly by measuring their positions and using them as guides.
The third one makes measurements of distances and movements of stars and tiny
moons. The FGS keep Hubble oriented within 0.01 arcseconds of its desired
position. The observation sensor can be used to determine if stars have planets
orbiting them by determining whether they have a slight “wobble,” find
double stars, and determine the angular diameter and distances of stars.
Past Instruments Removed from the Telescope
Faint Object Camera (FOC), replaced by the Advanced Camera
for Surveys in 2002
Faint Object Spectrograph (FOS), removed in 2002.
Goddard High-Resolution Spectrograph (GHRS), removed
in 1997.
High-Speed Photometer (HSP), removed in 1993.
Wide-Field
Planetary Camera 1 (WFPC1), replaced by the WFPC2
in 1993.
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