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THE HISTORY OF THE HUBBLE SPACE TELESKOPE
NASA's Hubble Space Telescope is the first major
infrared-optical-ultraviolet telescope to be placed into orbit around the
Earth. Located high above Earth's obscuring atmosphere, the telescope has
provided the clearest views of the universe yet obtained in optical
astronomy.
The telescope is named after the American astronomer Edwin P. Hubble, who in
the 1920's found galaxies beyond our Milky Way and discovered that the
universe is uniformly expanding. The heart of the telescope is the 94.5
inch-diameter (2.4-meter) primary mirror. It is the smoothest optical mirror
ever polished, with a surface tolerance of one-millionth of an inch. It is
made of fused silica glass and weighs about 1,800 pounds.
Outside the blurring effects of Earth's turbulent atmosphere, the telescope
can resolve astronomical objects with an angular size of 0.05 arc seconds,
which is like seeing a pair of fireflies in Tokyo from your home in
Maryland. This razor-sharp vision is 10 to 20 times better than typical
resolution with large ground-based telescopes (depending on atmospheric
observing conditions).
The space telescope can detect objects as faint as 31st magnitude, which is
slightly better than the sensitivity of much larger earth-based telescopes.
(The human eye can see celestial objects as dim as sixth magnitude.) Because
generally the fainter an object is the farther away it is, Hubble has been
used to probe the limits of the visible universe and uncover
never-before-seen objects near the horizon of the cosmos. Because it is
outside our atmosphere, the telescope can view astronomical objects across a
broad swath of the electromagnetic spectrum, from ultraviolet light, to
visible, to near-infrared wavelengths. The telescope can also see faint
objects near bright objects. This is an important requirement for studying
the environments around stars and the glowing nuclei of active galaxies.
Hubble's crystal-clear vision has triggered a revolution in optical
astronomy. It has revealed a whole new level of detail and complexity in a
variety of celestial phenomena, from nearby stars to galaxies near the
limits of the observable universe. This has provided key new insights into
the structure and evolution of our universe across a broad scale.
HISTORY
The Hubble Space Telescope was launched April 24, 1990 by the space shuttle
Discovery. Hubble was originally equipped with five science instruments: the
Wide-Field Planetary Camera, the Faint Object Camera, the Faint Object
Spectrograph, the Goddard High-Resolution Spectrograph, and the High Speed
Photometer. In addition, three fine guidance sensors were used for pointing
and for precision astrometry, the measure of angles on the sky.
After Hubble was launched, scientists discovered that its primary mirror was
misshapen due to a fabrication error. This resulted in spherical aberration:
the blurring of starlight because the telescope could not bring all the
light to a single focal point. Using image-processing techniques scientists
were able to do significant research with Hubble until an optical repair
could be developed.
In December 1993 the first Hubble servicing mission carried replacement
instruments and supplemental optics aboard the space shuttle Endeavor to
restore the telescope to full optical performance. A corrective optical
device, called the Corrective Optics Space Telescope Axial Replacement, was
installed (requiring removal of the High Speed Photometer) so that it could
improve the sharpness of the first generation instruments. The Wide-Field
and Planetary Camera was replaced with a second camera, which has a built-in
correction for the aberration in the primary mirror.
In February 1997 the space shuttle Discovery returned to Hubble for a second
servicing mission. Two advanced instruments: the Near Infrared Camera and
Multi-Object Spectrometer and the Space Telescope Imaging Spectrograph were
swapped out with the two first-generation spectrographs. The astronauts also
replaced or enhanced several electronic subsystems and patched unexpected
tears in the telescope's shiny, aluminized thermal insulation blankets,
which give the telescope its distinctive foil-wrapped appearance.
About the Hubble Telescope
In December 1999 the space shuttle Discovery rendezvoused with Hubble for a
third servicing mission. Astronauts replaced faulty gyroscopes, which had
suspended science observations for nearly a month. The telescope also got a
new high-tech computer and a data recorder. The astronauts left the
telescope in "better than new" condition.
Two more Hubble servicing missions are planned for 2001 and 2003. The
Advanced Camera for Surveys will be installed in 2001. It will yield even
sharper pictures and a wider field of view. The Wide Field Camera 3 and the
Cosmic Origins Spectrograph will be installed in 2003. The telescope's
science operations are expected to end in 2010.
HUBBLE OPERATIONS
Hubble is controlled at the Goddard Space Flight Center in Greenbelt, Md.
The science mission is directed by the Space Telescope Science Institute at
the Johns Hopkins University in Baltimore, Md. Hubble research and funding
engages a significant fraction of the worldwide professional astronomical
community.
Astronomers compete annually for observing time on Hubble. The
over-subscription is typically four to one. Observing proposals are
submitted to peer review committees of astronomer experts. The institute
director makes the final acceptance and can use his own discretionary time
for special programs.
Accepted proposals must be meticulously planned and scheduled by institute
experts to maximize the telescope's efficiency. The telescope is not pointed
by direct remote control, but instead automatically carries out a series of
preprogrammed commands over the course of a day. A data "pipeline" assembled
and maintained by the institute ensures that all observations are stored on
optical disk for archival research. The data are sent to research
astronomers for analysis and then made available to astronomers worldwide
one year after the observation.
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