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Imagine a stack of cylinders the size of a school bus. Add a pair of rectangular wings of almost the same length. Now attach these wings the long way, with rods at the midway point of the stack. The result would be a rough sketch of the Hubble Space Telescope, also known as the Space Telescope, or HST for short. Regardless of what it is called, it is a 12-ton observatory that orbits the earth every 97 minutes as it looks out into space. Named for Edwin Hubble, the father of extragalactic astronomy and originator of the expanding universe theory, the HST has opened our view of the Universe far beyond what is possible from earth.
Compared to earthbound telescopes, the HST is an average sized telescope, yet its capabilities for revealing distant objects in space are much greater than its larger earth bound counterparts. Earth bound telescopes must look through the Earth’s atmosphere, which distorts the view of celestial objects -- rather like looking at an object through water. Viewing a sharp and accurate picture is not possible. For instance, stars don’t actually twinkle. The atmosphere makes it appear that they twinkle. While twinkling stars make for a pretty night sky, they don’t help astronomers learn about the universe. Fortunately, the HST sits above that problem as it orbits 380 miles above the earth, just barely above the Earth’s atmosphere!
Astronomers had long dreamed of the day they could look at the Universe with an unobstructed view. The idea for an Earth orbiting telescope was first put forth in the 1940’s. It was not until 1977, when the United States Congress approved funding for the Hubble Space Telescope, that it went from wishful thinking to an actual work in progress. It was designed and built during the 70’s and 80’s at a cost of $1.5 billion. It was and continues to be, a joint effort between NASA and the European Space Agency. NASA is responsible for the lion’s share of the funding and work, which represents about 85% of the total. On April 25, 1990 the space shuttle Discovery delivered the HST to its destination above the Earth.
Originally, the design called for a “Space Telescope” that could be returned to earth for repairs and maintenance every five years with on site checks every 2-½ years. However, by 1985, it was determined that bringing the telescope back to earth would pose problems with contamination, as well as load problems for the shuttle, which made it an unworkable plan. It was decided that the telescope would be designed to remain in orbit for the duration of its life span. Space shuttles rendezvous with it every three years thus enabling astronauts to carry out maintenance and repair.
The HST carries an impressive array of instruments that are contained in modular units, which can be removed for repairs and then replaced. NASA likens it to a set of dresser drawers. Equipment such as focusing mirrors, imaging instruments, computers, and pointing/control mechanisms are contained in the modular units. The body of the HST is approximately 43 feet long and 14 feet in diameter at its widest point. Forty-foot-long by eight-foot-wide solar panels are attached to each side of the telescope. They provide the necessary electricity to power the computers and other instruments. Antennas provide the means of communication between the telescope and astronomers on earth. Along the outside of the telescope, there are 76 handholds and special grapple fixtures, which aid astronauts sent to carry out repairs and maintenance.
HST is a reflecting telescope with one large mirror and one small. The large curved eight-foot diameter mirror is housed in a long tube. As with any telescope, the purpose of the mirrors is to gather starlight, thus making it possible to observe and study celestial objects. In this case, the information is fed to cameras and spectrographs instead of a human eye. This information is sent back to earth each day. The amount of information sent is staggering. According to NASA, the information retrieved each day would fill an encyclopedia. Time needed to review and analyze this mountain of information will keep scientists busy well into the future.
On June 25, 1990, two months after the HST was placed in its orbit, a defect in the mirror was discovered. During the first servicing mission of the telescope in December of 1993, astronauts installed corrective optics. The repair was successful and the resulting clear view was astounding. Over the years older instruments have been and continue to be upgraded or replaced with newer versions, which keep the HST on the cutting edge of astronomy.
The Near Infrared Camera & Multi-Object Spectrometer (NICMOS) and the Space Telescope Imaging Spectrograph (STIS) which astronauts installed in 1997 are two examples of the improvements technology has provided to make the HST more efficient. NICMOS has the ability to look into space at near-infrared wavelengths, longer than that possible with the human eye. For example, it is capable of looking at celestial objects so far back in time that they were created near the beginning of the Universe. It can also present a much better look into the clouds of dust where stars are formed. The Space Telescope Imaging Spectrograph (STIS) is a versatile tool. Its camera can span wavelengths from the visible to the ultraviolet. STIS also has a coronagraph that can block out the bright light from an object to allow the study of faint objects that would otherwise be lost in the brighter light.
The Hubble Space Telescope has expanded human understanding and knowledge of our own Solar System and beyond into the vast reaches of the Universe. HST gave us our first look at the surface of Pluto, the most distant planet in our Solar System. Astronomers were surprised to find a wide variety of surface features on the rocky planet. Hubble has also provided clearer pictures of a brown dwarf first discovered by earth-based telescopes. Great columns of gas and dust where stars are being born are revealed in the HST photos of the Eagle Nebula (M16). Astronomers can better study the birth and the death of stars thanks to the images provided by Hubble. It has found evidence to support the theory of Black Holes and provided clues to the age of the Universe, which is now thought to be younger than previous estimates.
HST has not only lived up to expectations, but has surpassed them. As a result, NASA has extended its life expectancy from fifteen years to twenty years. According to the latest plans, the Hubble Space Telescope will be brought back to Earth in the 2010 – approximately three years after it has been operating concurrently with its successor, the Next Generation Space Telescope (NGST), tentatively scheduled for launch in 2007!
Sources:
NASA Websites
European Space Agency Websites
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