The major parts of the Space Telescope are labeled in this cut-away illustration. To learn more about a specific part, click on its label -- not on the part, itself. Other telescope components not shown in the diagram are listed after the illustration.
Users with Slow Modems: if you are not viewing the show with images, we highly recommend loading the following diagram (about 50KB). Though we have included text equivalents, it is interesting and useful to see this imagemap illustration of the Hubble Space Telescope's parts.
Radio antenna | Solar panels | Primary mirror | Secondary mirror | Aperture door | Light shield | Aft shroud | Baffle | Electronic boxes | Instrument module | Guidance sensors
Other Parts:
Focal plane |
Thermal insulation |
Computer systems |
Optical Telescope Assembly |
Forward shell |
Wide Field Planetary Camera 1 |
Wide Field Planetary Camera 2
It is crucial that the precise optical equipment in the HST (the fine guidance sensors and the instruments of the focal plane) is never exposed to space, where it could risk damage. The aft shroud protects these instruments, covering one end of the telescope. It is one of four insulated cylindrical pieces which make up the central "canister" portion of the HST.
Select a different part...The aperture door is an insulated cylinder located on one end of the telescope. It protects the technical instruments lying behind the primary mirror from contamination and small particles which could interfere with their operation. With the light shield, the aperture door is one of four main assemblies which together make up the HST.
Select a different part...Parts of Hubble's Optical Telescope Assembly, the telescope's two baffles are placed one in front of the primary mirror and one behind the secondary mirror. In processing light reflected off of the mirrors, it is vital that excess light be kept out of the telescope so that it does not drown out the image. The baffles prevent this light from even entering this imaging area.
Select a different part...One of four insulated cylinders which make up the HST, the electronic boxes are also known as the equipment section because they encase almost all of the controls for Hubble's systems. They house not only electronics, but also the telescope's power supply (see solar arrays), communications units (see radio antenna), and the instruments that control each precise movement of the HST (see computer systems).
Select a different part...Known more properly as Fine Guidance Sensors, the three Guidance Sensors are three of eight instruments which cover the focal plane. When the HST is positioned to focus in on a particular target, two of the sensors are used to locate the exact position of the target and to ensure that the target never moves in relation to the cameras. If the telescope were allowed to jiggle, images would be blurry and difficult to use; but the sensors allow the telescope to take crisp photographs with excellent resolution. The third sensor is most often used to accurately measure the distances to various stars near the target area -- a science called astrometry.
Select a different part...Covered by the aft shroud, the instrument module holds four of the eight instruments which share the focal plane. There are four long boxes, referred to as axial modules, stacked tightly in a square -- all scientific instruments which capture celestial sights seen in the HST's focal plane. The telescope's three Fine Guidance Sensors and the all important Wide Field Planetary Camera are also focal plane instruments, but they are attached separately from the other four.
Select a different part...The light shield works with the aperture door to guard the HST's vital scientific systems against damage. Since the telescope is above Earth's atmosphere, it is exposed to strong, direct sunlight when it passes by the sun. The light shield protects the instruments from the sun's light during the daytime portion of the telescope's orbit.
Select a different part...Just one and one-half inches shy of eight feet in diameter, the HST's primary mirror weighs 1825 pounds -- nearly one ton. Together with the secondary mirror, the primary mirror makes up the Optical Telescope Assembly, which reflects light between the two mirrors based on a principle which dates back to Isaac Newton and the 17th century.
The mirror is incredible for several reasons. First, it is made out of special glass that is designed not to warp and is covered by a layer of pure aluminum exactly three millionths of an inch thick. In addition, the mirror was sanded by a computer-run machine that was built specially to produce Hubble's primary mirror. The surface was so finely sanded that when a special coating just one millionth of an inch thick was applied, the primary mirror became the largest object in history to be made in such precise detail.
For all of the precision in its creation, the primary mirror was found to have a slightly improper curvature soon after the HST was launched. Though the mirror had been tested before the launch, poor analysis of conflicting test results led NASA scientists to miss a glitch in the sanding that was about the diameter of a human hair. Additional tests on the ground would have cost far less than fixing the problem after the launch. Unfortunately, the HST project became embroiled in controversy because of the faulty curvature. The problem was solved with the installation of COSTAR (Corrective Optics Space Telescope Axial Replacement), two mirrors that reflected the light properly onto the focal plane.
Select a different part...Programmed with instructions sent daily from the Goddard Space Flight Center, the HST communicates with the computers of Earth scientists via its two radio antennae. Hubble communicates over the radio waves at a rate of one megabyte of information per second, receiving program instructions and sending back data from which photographs are generated.
Select a different part...Exactly measured like the primary mirror, Hubble's secondary mirror is made of a special non-warping glass, a foot in diameter. This smaller mirror, too, is coated on its reflective surface with three millionths of an inch of aluminum and one millionth of an inch of a special compound which enables it to reflect ultraviolet light. Together with the primary mirror, the two reflecting surfaces make up the HST's Optical Telescope Assembly.
Select a different part...In full, the HST's scientific instruments and computer systems require a total of 2,400 watts of power -- enough to keep approximately 16 household light bulbs burning bright. The telescope's two solar arrays provide these all-important items with power. Made up of many individual solar panels, the arrays convert sunlight into power, which is stored in batteries and then sent on to the equipment. In sunlight, the arrays charge the six batteries, which supply power during the portion of the orbit when the craft is on Earth's night-time side.
Select a different part...The light reflected through Hubble's Optical Telescope Assembly is focused onto the instruments of the focal plane. Eight scientific instruments, located behind the primary mirror in the aft shroud, make up the focal plane, which is about the size and shape of a dinner plate.
Since the Hubble Space Telescope was designed to spend many years in space, each device dwells in its own independent module, which can be removed quickly and easily by astronauts. Thus, broken instruments can be repaired and outdated technology can be replaced with the latest equipment without disturbing the entire telescope's arrangement. This, together with a special latch on each module designed to make detachment and maintenance efficient, was perhaps one of the greatest design achievements.
The four instruments of the instrument module, each about the size of a telephone booth, are called axial modules because they are configured with their long sides along the telescope's axis. Since all of the focal plane's instruments can have access to the plane at the same time, each has other equipment in its module so that light can be filtered and reflected and so that data can be processed individually. The eight focal plane instruments are:
The WFPC can map vast expanses of the universe and can capture great galaxies billions of light-years away with ten times greater clarity than modern ground-based telescopes. It can also photograph the entire face of any planet in the Solar System (except Mercury) with just one exposure.
Hubble's Optical Telescope Assembly, incredibly, is based on principles that Isaac Newton first proposed and used in the 17th century. Light coming into the telescope is reflected first off of the primary mirror, which focuses it into the smaller secondary mirror, which in turn directs the light into the focal plane, where cameras and other instruments capture the image. The Optical Telescope Assembly is housed in the HST's forward shell component.
Diagram. A reflecting telescope operates based on Newtonian theory. Light comes in (from the left), and is reflected off of the large, concave primary mirror and onto the small, convex secondary mirror. Light is reflected off of the secondary mirror and focused in the focal plane, where instruments analyze it. Original diagram by The Online Planetarium Show.
One of four insulated cylindrical pieces of the Hubble Space Telescope, the forward shell protects the Optical Telescope Assembly. It houses the OTA's primary and secondary mirrors.
Select a different part...The HST is built like a stack of four small cylinders -- the aperture door, the forward shell, the equipment section and the aft shroud. Each section is protected by thermal insulation to protect against heat -- 200 degrees in sunlight -- and against cold -- -150 degrees during the nighttime portion of its orbit. In addition to this glittering, silver-colored insulation, the Telescope has special coatings of thermal protectants and electric heaters within the craft to better control internal temperature. Since one side of Hubble is hardly ever exposed to the heat of the sun -- facing Earth when the Telescope passes through the sunlight -- many computer and other electronic systems are placed on that side so they can be kept cooler.
Select a different part...To control the many instruments and complex systems on the HST, there is set of computer subsystems that process instructions, control motion and send back data. Programs and instructions for observation and positioning are sent daily to the Telescope from the Goddard Space Flight Center on Earth through radio antennae at a rate of one megabyte per second. Similarly, data from the Telescope's scientific instruments is sent back to Earth and used by scientists to generate images.
As a wide field camera, the WFPC will observe great realms in space and capture entire distant galaxies. It will collect the most data of any of the instruments because it photographs such large areas. Incredibly, the WFPC can view areas several billion light-years away at resolution that is ten times better than the best possible with Earth-bound telescopes.
In planetary mode, the WFPC can capture with a single exposure the face of any planet in the solar system, except Mercury, which is too close to the sun. Photographs of Jupiter and other planets closer to Earth will be similar to those from the two Voyager spacecraft, and the pictures of more distant planets will be a vast improvement over those taken on Earth.
The WFPC will have one great advantage over spacecraft like the Voyager and Galileo probes: it can regularly capture planetary images, showing changes over time. By no means, however, does this make spacecraft missions obsolete; in fact, the Cassini probe will be sent on its way to Saturn in 1997. In addition, these spacecraft can drop probes to send back data about a planet's atmosphere and conditions. Even so, the WFPC represents a significant step in planetary observation.
Wide Field Planetary Camera 2. When the HST was being serviced in 1993, the WFPC was replaced with a newer version. Though the camera's operation and function remained unchanged, the new WFPC could see objects some 11 billion light-years away, eight billion light-years farther away than those visible through the WFPC 1. The replacement of the WFPC was a perfect illustration of the genius of the HST's design: the compartment in which the WFPC is housed was taken out and replaced without having to fiddle with the Telescope's other parts. Though the operation was conducted on the same mission as the controversial repairs, the replacement of the WFPC was actually a triumph for the concept of the HST. A part had been upgraded so that the Telescope could continue operation with the newest technology, just as planned.
Select a different part...The following traces the development of the Space Telescope, from initial speculation to its final launch and repair. The stages into which we have divided this fascinating process are our own, not official NASA standards. Our story actually begins in 1609, when Galileo popularizes the telescope for observing the sky. After he trains a telescope on the sky, the world of astronomy quickly develops better and larger telescopes to exceed all expectations and to solve the great mysteries of space. It is based on these ideas that we begin our look at the development of the Hubble Space Telescope....
The notion of having an orbiting observatory is not a new one; in fact, as early as the 1920's scientists had speculated about the possibility. In the 1940's and 50's, scientists suggested the benefits of having a telescope in space that could escape from the restrictions of Earth's atmosphere. At this stage, the space telescope was only an astronomer's dream but it was a realistic one that offered intriguing new possibilities.
NASA was formed in 1958 fostering further interests in a project to put an astronomical observatory in space. Indeed by the early 60's, NASA was already developing plans for an Orbiting Astronomical Observatory to study ultraviolet light. Several study groups were formed to discuss the possibility of a space telescope yet when they issued their decisions there was disagreement over the telescope size, some favoring a much larger version and others proposing a smaller telescope which could be built and deployed much more quickly. In 1965 a scientific review board was formed and its findings recommended that NASA pursue the larger telescope design.
By the early 1970's, design had already begun in earnest and a series of feasibility studies were conducted in 1971 following the advice of the 1965 board to construct a large Space Telescope with a mirror approximately three meters (approximately ten feet) in diameter. Five years of preliminary design studies were undertaken in 1972 and by 1977 the size of the mirror had been reduced to 2.4 meters (approximately eight feet), where it would remain for the rest of the project. In 1975 the European Space Agency pledged partnership in the project and NASA secured Congressional approval just two years later.
Beginning in 1977 and for the next nine years, two "prime" contractors were assigned by NASA to work on the Hubble Space Telescope's support systems and Optical Telescope Assembly. In addition, many contractors were also assigned to construct the scientific instruments. At the same time, a group of scientists was gathered to devise and organize plans for how observation time was to be used once the telescope was launched. Such planning was essential if the project were to be run efficiently and successfully, for the new observatory would bring unprecedented opportunity and there would certainly be an unprecedented demand.
The Space Telescope was slated for launch in the late 1980's, but it was postponed in 1986, when Shuttle flights were put on hold after the Challenger exploded. Even after the Shuttle resumed service, several uncertain launch dates were further delayed so that thorough tests could be completed. Finally, on April 24, 1990, the Hubble Space Telescope, renamed in late 1983, was launched and forty years of dreaming turned into one great moment of reality. The HST had been deployed from the Space Shuttle Discovery -- appropriate, for the Telescope would help astronomers see spectacular celestial sights never before viewed in such detail.
In early December 1993, astronauts from the Space Shuttle Endeavor repaired the HST's optics and successfully replaced the Wide Field Planetary Camera with the WFPC 2, which could see billions of light-years farther than the original. In fact, the replacement of the WFPC had already been slated for this mission, and the repairs were added to the schedule only later. Though there had been controversy surrounding the testing of the flawed primary mirror, the repairs went quite smoothly and critics of the Telescope were all but silenced by the unparalleled clarity of its new pictures. The HST now sees farther back in time and with more clarity -- some 100 times better -- than any Earth-bound telescope in history.
The Hubble Space Telescope continues its operation today and will for many years to come, ever aiding astronomers in their quest to understand unknown realms and to find the age of the universe. According to NASA, Hubble is "the greatest scientific instrument of any kind, ever."
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