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30 years into the Void: A History of the Hubble Space Telescope
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30 years into the Void: A History of the Hubble Space Telescope by Joe Renzetti
On August 24, 1990 the Space Shuttle Discovery embarked on mission STS-31 which deployed a very special payload into orbit: a $1.5 billion Ritchey–Chrétien astrograph known as the Hubble Space Telescope (HST). It was equipped with a 2.4m primary mirror and 57600mm of focal length.
HST was the first of its kind, a visual light reflector telescope operating outside of the Earth’s atmosphere giving it a clear, undistorted view of the Universe.
43.5 feet in length, the telescope is about the size of a school bus. Hubble gathers energy from the sun using two 25-foot solar panels. It requires much less power than one might think, averaging 2,100 watts of power usage. A hair dryer requires about 1,800 watts.
As anyone who has tried to keep a steady view on their telescope mount knows how difficult it can be to track the sidereal rate of the Earth’s rotation. Hubble had an even more daunting task of holding steady while imaging, and orbiting at 17,000 miles per hour. This is done with an array of six highly sensitive gyroscopes that measure the speed that the 11 metric ton telescope is moving and then turn and lock it onto targets.
When first launched, the instruments on Hubble included the Wide Field Planetary Camera (WFPC), the Goddard High Resolution Spectrograph (GHRS), the Faint Object Camera (FOC), the Faint Object Spectrograph (FOS) and the High Speed Photometer. The original WFPC had a “wide” field of view of 2.6 arcminutes at f/12.9 and a planetary view of 66 arcseconds at f/30.
It had 4 CCD sensors with a resolution of a mere 800 x 800 pixels each. It contained 48 filters mounted in 12 wheels of the Selectable Optical Filter Assembly (SOFA). They cover a wide range of broadband and narrowband visible light spectrums, as well as Ultraviolet and Infrared wavelengths. The WFPC, and its successors WFPC2 and WFPC3, are the size of a baby grand piano.
The Hubble Space Telescope was almost a catastrophic failure due to a flaw in the mirror design caused by a miscalibration error in the equipment during the mirror’s manufacture. The result was a mirror with a spherical aberration of 2.2 microns, or one-50th the thickness of a human hair. This meant the instruments could not reach proper focus and returned blurry images back the Earth.
Since installing a replacement mirror was not an option, the Hubble engineers came up with COSTAR - the Corrective Optics Space Telescope Axial Replacement.
COSTAR corrected the aberration by placing small and carefully designed mirrors in front of the original Hubble instruments. This was installed during the 1993 service mission and was subsequently replaced in the final 2009 service mission with new instruments that were designed with their own corrective optics. COSTAR is now on display in the Smithsonian’s National Air and Space Museum.
Hubble’s data has been key in several significant discoveries made from its observations. It was able to pin down the age of the Universe at 13.8 billion years. The rate of expansion of the Universe was found to be accelerating due to dark energy, which makes up 74 percent of the combined mass-energy in the Universe. Hubble analyzed the distortions caused by dark matter’s gravity on light from distant galaxies and helped construct 3-D maps of where dark matter is distributed in the universe. Two new moons of Pluto were discovered, dubbed Nix and Hydra.
Observations of star forming regions in the Orion nebula showed that protoplanetary disks of gas and dust are ubiquitous around many young stars.
Hubble was able to observe comet Shoemaker-Levy 9 colliding spectacularly with Jupiter in 1994. In that same year Hubble took the world’s first images of the surface of Saturn’s moon Titan, using its infrared filters to pentrate its thick haze.
Observations of galaxies produced strong evidence that supermassive black holes are at the core of most galaxies. Hubble’s programs further established that the masses of the nuclear black holes and properties of the galaxies are closely related.
Hubble was also used to make the first measurements of the atmospheric composition of extrasolar planets, identifying atmospheres that contain sodium, oxygen, carbon, hydrogen, carbon dioxide, methane and even water vapor.
One of the most awe inspiring discoveries made by Hubble came from a chance experiment known as the Hubble Deep Field. Astronomers were curious what would happen if they pointed the Hubble Space Telescope at a random blank spot in space where no galaxies were present in photos at the time. The region was in the constellation Ursa Major and covered an area about 2.6 arcminutes arcross. The image was assembled from 342 separate exposures taken with the Hubble’s WFPC2 camera over ten consecutive days between December 18 and 28, 1995. This observation revealed 3,000 galaxies in this tiny patch of sky- some of which are among the youngest and most distant known. By revealing such large numbers of very young galaxies, the Hubble Deep Field has become a landmark image in the study of the early universe.
Three years after the Hubble Deep Field observations were taken, a region in the south celestial hemisphere was imaged in a similar way and named the Hubble Deep Field South. In 2004 a deeper image, known as the Hubble Ultra-Deep Field (HUDF), was constructed from a few months of light exposure. This was followed by the Hubble eXtreme Deep Field (XDF) in 2012.
Outreach activities have also been an important part of Hubble’s service to capture the public’s imagination, given the considerable contribution by taxpayers to its construction and operational costs. As a result, the Space Telescope Science Institute created the Hubble Heritage Project. Founded in 1998 it is a project of a group of astronomers and image processing specialists who create visually aesthetic public images from Hubble’s data archives, which are usually only shared within the astronomical community. The team is even granted observation time with Hubble Space Telescope to fill in the gaps in the images they process.
The Hubble Heritage Project has been recognized for its contribution to public inspiration by producing some of the most aesthetically pleasing images ever produced in astronomy.
In 2001, NASA polled internet users to find out what they would most like Hubble to observe. They overwhelmingly selected the Horsehead Nebula.
A select few amateur astronomers were even awarded time on the telescope, with observations being carried out between 1990 and 1997. The total time allocated was only a few hours per cycle and was awarded only to proposals that had genuine scientific merit, did not duplicate proposals made by professionals, and required the unique capabilities of the space telescope.
The Hubble Legacy Archive was created to allow public access to Hubble’s raw image data online. It has been a popular archive for amateurs to process visual images, as well as professionals analyzing the scientific data.
The Hubble Space Telescope was designed with a life expectancy of only 10 years. It has greatly exceeded that lifespan thanks to five Space Shuttle service missions that replaced various equipment on the telescope. These missions were carried out in 1993, 1997, 1999, 2002, and 2009. The upgrades and replaced equipment included the aforementioned COSTAR, the solar arrays, various sensors, gyros, batteries, and new upgraded cameras.
There is currently no set date for Hubble’s retirement. It is predicted that it will continue to be in service for quite a few years still. Hubble’s successor the James Webb Space Telescope (JWST) will be capable of probing much deeper into the early Universe, but will not duplicate Hubble’s wavelength coverage of visible light. instead it will concentrate on the further infrared bands. But, since its design and deployment 30 years ago, Hubble’s broadband spectrum and resolution can now be achieved on larger ground-based telescopes. This is mainly due to the invention and perfection of Adaptive Optics that can compensate for the distorting effect of the Earth’s atmospheric seeing conditions.
When the Hubble Space Telescope is finally retired it will re-enter the Earth’s atmosphere by orbital decay and a controlled re-entry, which will destroy the telescope over the Pacific Ocean. The legacy of Hubble’s influence will last well past its lifespan thanks to the efforts of amateurs and professionals alike, who worked to promote its awe inspiring views of the cosmos. The technological breakthroughs implemented on the Hubble Space Telescope have been used to greatly advance the image quality captured by amateur astrophotographers by used of thermally controlled CCD sensors and narrowband filters.
Perhaps no other scientific instrument has captured the imagination and wonder of the public the way the Hubble Space Telescope has. It inspired students of all ages to ponder new science questions and to seek answers about the mysteries of the Universe.
- Chopin, zjc26138, Mark9473 and 18 others like this