Hubble Space Telescope
The Hubble Space Telescope is a joint project between NASA and the European Space Agency. The telescope was launched into low Earth orbit in late 1990, and remains into operation. (1)Since its operation, the telescope has provided scientists and the public with spectacular images of deep space. It is one of the most technologically advanced pieces of equipment humans have put into orbit. Until now, the Hubble Space Telescope has helped researchers make countless discoveries about the universe, ranging from planets and stars to galaxies and cosmology.(2)
The Design of the Hubble Space Telescope
Although the telescope was launched into the orbit in late 1990, the origin date of the project is far before that. In 1946, Lyman Spitzer, a professor and researcher at Yale University, explained that the Earth's atmosphere not only blurs and distorts light coming from stars, but also blocks X-rays emitted from high-temperature phenomena in stars and other objects in his paper Astronomical Advantages of an Extra-Terrestrial Observatory.(2) He argued that a space telescope would offer great advantages over ground-based observations and allow scientists to accurately measure these X-rays as well. While teaching at Princeton University, Spitzer was asked to head a National Academy of Science Ad Hoc Committee on the Large Space Telescope. In 1969, the committee published Scientific Uses of the Large Space Telescope, in which the National Academy of Science urged the construction of Space Telescope.(2) At that time, the only agency likely to execute the National Academy's recommendation was NASA, and the main block of implementing the Large Space Telescope program is how to obtain the federal fund. The total cost of the large space telescope was roughly estimated at $400 to $500 and the motion of funding was rejected by the House Appropriations Subcommittee in 1975.(2) However, due to a large-scale lobbying effort by NASA and the European Space Agency's participation, the cost of the project down to about $200 million. The proposal was accepted by Congress, which granted the Large Space Telescope program funding in 1977. (2) The Large Space Telescope was renamed the Hubble Space Telescope in honour of Edwin Hubble, an American astronomer who determined that the universe extended beyond the borders of Milky Way.(1)
NASA orginally planned to launch the telescope in 1983, but the program experienced a considerable delay. Because the construction of mirror and optical assembly was handed over to Perkin-Elmer Corporation, the construction of the spacecraft and its support systems belonged to the Lockheed Missiles and Space Company. The mirror was completed in 1981, but the entire optical assembly was not put together until 1984. Subsequent final assembly of the spacecraft did not take place until 1985.(2) With all the pieces in place by December 1985, NASA planned the launch on October 1986. However, on January 28, 1986, when the Space Shuffle Challenger lifted off into the sky, in what appeared to be a routine launch, the vehicle exploded into a ball of smoke and flame. The accident stops the shuffle flights until 1988 and delayed the launch of the Hubble Space Telescope to April 24, 1990.(2)
Fuzzy Photos and Spectacular Repair
Hubble was finally launched aboard Discovery on April 24, 1990. The telescope's original equipment package included the Wide Field/Planetary Camera, Goddard High Resolution Spectograph, Faint Object Camera, Faint Object Spectograph and High Speed Photometer. (2) After a few weeks of operation, scientists noticed that the images being sent back by Hubble were fuzzy- close to useless. An investigation finally revealed Hubble's main mirror had a major defect, a spherical aberration caused by a manufacturing error. The flaw was just 1/50th the thickness of a sheet of paper.(1) In December 1993, the crew of STS-61 embarked on a service mission to replace a number of Hubble's parts. Two teams of astronauts completed repairs during a record five back-to-back spacewalks. During the repair, COSTAR was installed and the Wide Field/Planetary Camera was replaced with the Wide Field/Planetary Camera 2, which was designed to compensate for the mirror problem. The first new images from Hubble reached Earth were breathtaking.(1)
Hubble Space Telescope had already been serviced 5 times, in 1993, 1997, 1999, 2002, 2009 respectively. After its final serving mission took place in 2009, the telescope is expected to continue working until 2014. NASA plans to replace it with the James Webb Telescope, scheduled to launch in 2018.(2)
Three Astronomy Discoveries Using the Hubble Space Telescope
Firstly, the Hubble Space Telescope helped astronomers discover dark energy, which prevades our universe. Dark energy comprise about 70% of the universe's energy, yet scientists know almost nothing about it. This mysterious energy exerts a repulsive force that works against gravity. The telescope also provided evidence that dark energy has been engaged in a tug of war with gravity for billions of years, which means dark energy pushing galaxies away from each other at an increasing speed, making our universe expand at an accerlerating pace. Hubble also traced dark energy back 9 billion years ago. During that epoch, dark energy was struggling with gravity for control of cosmos. Dark energy finally won the struggle with gravity about 5 billion years ago.((3) page 2)
Secondly, Hubble help astronomers determine a precise age for the universe. Before Hubble was launched, astronomers used the expansion rate of universe to pin down the universe's age, the rate is named the Hubble constant. However, their values for the Hubble constant were highly uncertain, making their calculations for the universe's age ranged from 10 to 20 billion years. With the Hubble Space Telescope, astronomers used the telescope's keen vision to accomplish that goal. Astronomers measured the brightness of dozens of pulsating stars called Cepheid variables, they then calculated the stars' distance from earth. From this study and other related analyses, astronomers determined the Hubble constant and the universe's age to an accuracy of "about 5 percent"((3) page 2). By their calculation, the universe is about 13.75 billion years old.((3) page 2)
Thirdly, astronomers used Hubble to make the first three-dimensional map of dark matter, an invisible form of matter that makes up most of the universe's mass and forms its underlying structure. The gravity of dark matter allows normal matter in the form of gas and dust to collect and build up into stars and galaxies.((3), page 3) Although dark matter is invisible, astronomers detect its influence in galaxy clusters by observing how dark matter's gravity bonds and distorts the light of more distant background galaxies, a phenomenon called gravitational lensing. According to Hubble's observation, astronomers using gravitational lensing to construct the three-dimensional map by studying the warped images of half a million faraway galaxies. The new map provides the best evidence to date normal matter accumulates along the densest concentration of dark matter. The map stretches halfway back to the beginning of the universe and reveals a loose network of dark-matter filaments. Astronomers also used Hubble to observe the dark matter's distribution in the titanic collision of clusters of galaxies. Astronomers used Hubble to discover that a ghostly ring of dark matter that formed long ago during a clash between two groups of massive galaxies((3) page3)
NASA orginally planned to launch the telescope in 1983, but the program experienced a considerable delay. Because the construction of mirror and optical assembly was handed over to Perkin-Elmer Corporation, the construction of the spacecraft and its support systems belonged to the Lockheed Missiles and Space Company. The mirror was completed in 1981, but the entire optical assembly was not put together until 1984. Subsequent final assembly of the spacecraft did not take place until 1985.(2) With all the pieces in place by December 1985, NASA planned the launch on October 1986. However, on January 28, 1986, when the Space Shuffle Challenger lifted off into the sky, in what appeared to be a routine launch, the vehicle exploded into a ball of smoke and flame. The accident stops the shuffle flights until 1988 and delayed the launch of the Hubble Space Telescope to April 24, 1990.(2)
Fuzzy Photos and Spectacular Repair
Hubble was finally launched aboard Discovery on April 24, 1990. The telescope's original equipment package included the Wide Field/Planetary Camera, Goddard High Resolution Spectograph, Faint Object Camera, Faint Object Spectograph and High Speed Photometer. (2) After a few weeks of operation, scientists noticed that the images being sent back by Hubble were fuzzy- close to useless. An investigation finally revealed Hubble's main mirror had a major defect, a spherical aberration caused by a manufacturing error. The flaw was just 1/50th the thickness of a sheet of paper.(1) In December 1993, the crew of STS-61 embarked on a service mission to replace a number of Hubble's parts. Two teams of astronauts completed repairs during a record five back-to-back spacewalks. During the repair, COSTAR was installed and the Wide Field/Planetary Camera was replaced with the Wide Field/Planetary Camera 2, which was designed to compensate for the mirror problem. The first new images from Hubble reached Earth were breathtaking.(1)
Hubble Space Telescope had already been serviced 5 times, in 1993, 1997, 1999, 2002, 2009 respectively. After its final serving mission took place in 2009, the telescope is expected to continue working until 2014. NASA plans to replace it with the James Webb Telescope, scheduled to launch in 2018.(2)
"Pillars of Creation", took by Hubble in 1995
Firstly, the Hubble Space Telescope helped astronomers discover dark energy, which prevades our universe. Dark energy comprise about 70% of the universe's energy, yet scientists know almost nothing about it. This mysterious energy exerts a repulsive force that works against gravity. The telescope also provided evidence that dark energy has been engaged in a tug of war with gravity for billions of years, which means dark energy pushing galaxies away from each other at an increasing speed, making our universe expand at an accerlerating pace. Hubble also traced dark energy back 9 billion years ago. During that epoch, dark energy was struggling with gravity for control of cosmos. Dark energy finally won the struggle with gravity about 5 billion years ago.((3) page 2)
"Distant Supernova"
Secondly, Hubble help astronomers determine a precise age for the universe. Before Hubble was launched, astronomers used the expansion rate of universe to pin down the universe's age, the rate is named the Hubble constant. However, their values for the Hubble constant were highly uncertain, making their calculations for the universe's age ranged from 10 to 20 billion years. With the Hubble Space Telescope, astronomers used the telescope's keen vision to accomplish that goal. Astronomers measured the brightness of dozens of pulsating stars called Cepheid variables, they then calculated the stars' distance from earth. From this study and other related analyses, astronomers determined the Hubble constant and the universe's age to an accuracy of "about 5 percent"((3) page 2). By their calculation, the universe is about 13.75 billion years old.((3) page 2)
Thirdly, astronomers used Hubble to make the first three-dimensional map of dark matter, an invisible form of matter that makes up most of the universe's mass and forms its underlying structure. The gravity of dark matter allows normal matter in the form of gas and dust to collect and build up into stars and galaxies.((3), page 3) Although dark matter is invisible, astronomers detect its influence in galaxy clusters by observing how dark matter's gravity bonds and distorts the light of more distant background galaxies, a phenomenon called gravitational lensing. According to Hubble's observation, astronomers using gravitational lensing to construct the three-dimensional map by studying the warped images of half a million faraway galaxies. The new map provides the best evidence to date normal matter accumulates along the densest concentration of dark matter. The map stretches halfway back to the beginning of the universe and reveals a loose network of dark-matter filaments. Astronomers also used Hubble to observe the dark matter's distribution in the titanic collision of clusters of galaxies. Astronomers used Hubble to discover that a ghostly ring of dark matter that formed long ago during a clash between two groups of massive galaxies((3) page3)
Reference
1. Nola Taylor Redd, "Hubble Space Telescope: Pictures, Facts & History", April 23, 2014, space.com, http://www.space.com/15892-hubble-space-telescope.html
2. Okolski, Gabriel. "A Brief History of the Hubble Space Telescope." A Brief History of the Hubble Space Telescope. National Aeronatautics and Space Administration. Web. 28 Mar. 2015. http://history.nasa.gov/hubble
3. Hubble Space Telscope Top Science Findings, .http://hubblesite.org/hubble_20/downloads/hubble_topscience_lo-res.pdf
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