The Faint Object Spectrograph (fig. 2) is a versatile instrument that can obtain the spectra of extremely faint astronomical objects in the ultraviolet and visible wavebands. A spectrum is a distribution of colors, or wavelengths, created by passing a beam of light through a prism.

A spectrum reveals the nature of the source we are viewing. We can tell whether it is hot or cold, dense or rarified, and even its chemical composition. Analysis of the spectrum also yield the remoteness and relative velocity of the object being studied.

The spectrograph works by picking up the image of a star, galaxy, interstellar dust cloud or other object that appears on the telescope's focal plane as a point of light. Then, via a system of optical mirrors and gratings that work like prisms, the light beam is spread out, from ultraviolet through the visible.

The fanned-out beam is recorded on an imaging device called a digicon detector , which counts the photons of light in each region of the beam. The resulting spectrogram is then transmitted to Earth for study. spectrographic An extremely sensitive camera capable of pinpointing and electronically intensifying dim objects.

This instrument, being built by the European Space Agency , uses the spatial resolution of the telescope to capture images of very faint objects in the universe (fig. 1) .

It is expected to be able to detect stars as faint as the 28th magnitude and will easily pick out stars of magnitude 24, which is about the best a large ground observatory can now do. Magnitude is a designation of brightness - the lower the number, the brighter the object. The dimmest star the average person can see with the naked eye are magnitude 6. The planet Venus is magnitude -4.

The Faint Object Camera has a basic focal ratio of f/96 and is capable of observing faint objects or extended structures near bright sources. This device will have four filter wheels , each containing a variety of filters in 12 positions, which can be inserted in the optical path.

The system works by gathering and focusing incoming feeble starlight on an electronic image intensifier. The intensifier's output is scanned by a vidicon camera tube and an image consisting of 250,000 picture elements is obtained. Exposure times for very faint objects could run as long as ten hours.

An f/48 focal ratio camera system will permit the camera to operate in a spectrographic mode which is ideal for studying the structure and dynamics of the center regions of galaxies, the area where black holes are thought to occur. Thus the Faint Object Camera serves as a third, general-purpose spectrograph. This mode of operation will employ fourteen insertable filters. pointing stabilization control orientation fine guidance censors Instruments used to locate and lock on to a target object, maintaining position of the telescope relative to the target.

Because of the very high spatial reolution of the Space Telescope great pointing stability is required. Two of the fine guidance sensors will be used to locate and lock on to a target while the third is free to view and precisely measure the relative positions of other stars in the vicinity.

The three fine guidance sensors are expected to produce distance measurements ten times more accurate than those done from Earth . The sensors work through a complex system of mirrors and light detectors to locate the position of a star against a background of other stars. In measuring the distance to a star, ground controllers will focus the sensors on a foreground star to transmit its position relative to the stars in the background. Similar measurements are made about six months later. Changes will indicate the distance of the star from the earth .

The precise measurement of star positions is called astrometry. Information provided by the fine guidance sensors will assist in resolving the open-versus-closed universe question. filter wheels fig. 1 (fig. 1) A diagram of the Faint Object Camera with labeled components. optical mirrors gratings digicon detector fig. 2 (fig. 2) A diagram of the Faint Object Spectrograph with labeled components. goddard ground controllers Goddard Space Flight Center/STOCC NASA center in Greenbelt, MD which will operate the Hubble Space Telescope once it is in orbit.

Once the Space Shuttle carries the Hubble Space Telescope into orbit, project personnel at Goddard will operate the satellite through the Space Telescope Operations Control Center (STOCC), located at Goddard.

The STOCC is the largest and most complex control center for a scientific satellite to date, and will enable astronomers to utlilize the Hubble Space Telescope much like a ground observatory. The astronomers typically will work at the Space Telescope Science Institute in Baltimore. They will send their observing requests to the STOCC where the Hubble Space Telescope's controllers will program the observations. The data and images obtained by the Telescope's instruments then will be transmitted to the STOCC and on to the Space Telescope Science Institute , where astronomers will study the information and present their findings to the world community.

It is expected that the STOCC will operate 24 hours per day and provide a schedule of 3,500 hours of observing time annually. By comparison, ground observatories, which can operate only during the night, offer just 2000 hours of observing time per year. An instrument capable of obtaining the ultraviolet spectra of individual objects in crowded fields. The High Resolution Spectrograph (fig. 3) will be able to use the full resolving capability of the telescope to see much dimmer objects than previous space-born instruments. Although it performs in much the same way as the Faint Object Spectrograph , it will be much more accurate because it will be using more light and resolving it into much finer increments. The High Resolution Spectrograph will be looking at only the ultraviolet region of the spectrum, wavelengths that do not reach Earth. This ultraviolet region should provide the most detailed chemical composition information yet obtained on objects in space. The instrument's extremely fine resolution will enable it to pick out individual stars in crowded fields. In addition, binary stars that cannot be differentiated optically will be resolved so that each star can be studied separately. The spectrograph will be able to study such objects as supernovae, active galaxies, bright quasars, and even phenomena in our own solar system such as planetary atmospheres, auroral activity, and the presence of deuterium in comets. Deuterium, thought to have been manufactured during the Big Bang, occurs throughout the universe. If found in comets, it will reveal more about the relation of our solar system to the original cataclysmic explosion. Measures the brightness of an object, either within a particular wavelength or throughout the entire spectrum; detects fluctuations.

The High Speed Photometer (fig. 4) is designed to provide accurate observatons of the total light from an object in space, note any fluctuations in brightness on a time scale down to microseconds, and to detail any fine shapes or structures associated with the light source. These measurements are made over a wide spectral interval, including the ultraviolet.

It is the simplest instrument of the group, containing no moving parts, and relies entirely on the pinpoint accuracy of the spacecraft's fine guidance sensors to accomplish its work. After the light of a star or other source is received, a detector can measure either the total brightness or the intensity of light within a particular portion of the spectrum.

The High Speed Photometer, in addition, will transmit accurate information on fluctuation in brightness over time. Detection of rapidly spinning neutron or other compact stars will be possible, as well as detailed data on the shape and structure of the fine spikes or flares often associated with such compact objects.

The instrument will also be of special value to astronomers in establishing calibration standards for faint stellar objects. high resolution spectrograph fig. 3 (fig. 3) A diagram of the High Resolution Spectrograph with labeled components. high speed photometer detector fig. 4 (fig. 4) A diagram of the High Speed Photometer with components labeled. Introduction article A short description of the telescope and its purpose.

Imagine trying to see the clouds from the bottom of a muddy pond. That is how astronomers describe their view of the stars and planets through the Earth's atmosphere. As advanced as astronomical technology has become, our capabilities will be forever limited by the turbulence and brightness of our atmosphere. Even the finest ground observatories, such as the one at Mt. Palomar, California, are restricted by these conditions. In addition, the selective absorption of the atmosphere, which lets in visible light and radio waves emitted by stars and planets, but excludes most other forms of energy, limits our knowledge of celestial bodies.

To open the universe to observation in infrared, ultraviolet, x-ray, gamma-ray, and cosmic ray energies, NASA launched numerous satellites, each helping to explain different processes behind astronomical phenomena. But, to date, the value of these orbiting observatories has been limited by their relatively small size and limited spectral capability.

Now, for the first time, a ground-sized observatory will be placed in orbit to view the universe in visible and ultraviolet light unobscured by Earth's atmosphere.

Called the Edwin P. Hubble Space Telescope , the new observatory is a NASA-wide and international cooperative effort . Its name honors Edwin P. Hubble (1889-1953), who discovered that the universe extends far beyond the Milky Way galaxy.

The Hubble Space Telescope will weigh about 25,000 pounds (11,300 kg) and will have a length of 43 feet (13.1 m) and a diameter of 14 feet (4.26 m). Its major components are an optical telescope assembly , five scientific instruments , and a support systems module . !home An artist's conception of the space telescope in orbit.

- NASA's Office of Space Science and Applications, Washington, DC, is responsible for overall direction of the Hubble Space Telescope Program.

- Marshall Space Flight Center, Huntsville, AL, is the leading NASA center for the Hubble Space Telescope, providing day-to-day management of the project. Marshall also directs the construction and integration of the telescope and spacecraft systems.

- Goddard Space Flight Center in Greenbelt, MD, is responsible for development of the Telescope's four American-contributed scientific instruments , the development of the ground system, and Telescope operations once in orbit.

- European Space Agency (ESA), a consortium of eleven western European nations, is responsible for developing the Faint Object Camera , one of five scientific instruments aboard the Hubble Space Telescope. ESA is also developing the solar arrays which power the spacecraft and will provide a small resident staff to help operate the Space Telescope Science Institute in Baltimore.

The ESA's principal members include: Belgium, Denmark, France, West Germany, Ireland, Italy, the Netherlands, Spain, Sweden, Switzerland, and the United Kingdom. Associate members include Austria and Norway.

- Johnson Space Center in Houston, Texas, will launch the Hubble Space Telescope using the Space Shuttle.

- Kennedy Space Center, Florida, is also involved in Space Shuttle launch operations.

- The Association of Universities for Research in Astronomy (AURA) has responsibility for operating the Space Telescope Science Institute in Baltimore, MD, under contract to NASA's Goddard Space Flight Center . AURA includes: University of Arizona, California Institute of Technology, University of California at Berkeley, University of Chicago, University of Colorado, Harvard, University of Hawaii, University of Illinois, Indiana University, Johns Hopkins University, Massachusetts Institute of Technology, University of Michigan, Ohio State, Princeton, University of Texas at Austin, University of Wisconsin, and Yale. responsibilities fig. 6 (fig. 6) A chart illustrating the organizations working on the Hubble Space Telescope and their responsibilities. resp. - word support system resp. - word optical telescope assembly resp. - word fine guidance resp. - word faint object camera resp. - word goddard resp. - word Scientific instrument scientific instruments The wide field/planetary and faint object cameras, the faint object and high resolution spectrographs, and the high-speed photometer. The five scientific instruments, four American and one European, are located behind the primary mirror, at the focal plane, where they can pick up light reflected from the telescope. They are the wide field/planetary camera , the faint object spectrograph , the high resolution spectrograph , the high speed photometer , and the faint object camera , the latter provided by the European Space Agency . In addition, the fine guidance sensors , part of the support systems module , because of their ability to accurately locate stars, could be considered a sixth scientific instrument. Each instrument is housed in a separate module and will draw 110 to 150 watts of power. All are exchangeable during maintenance visits by the Space Shuttle. hubble space telescope space telescope edwin p. hubble space telescope main telescope A diagram of the telescope with major components labelled.

The module has four main sections: the light shield, the forward shell, the equipment section, and the aft shroud. These four pieces fit together like stacked cannisters to enclose the telescope assembly and scientific instruments.

The aperture door , which also serves as a light shield, is located at the front of the Support Systems Module. The telescope must be shielded from the Sun, Earth, and Moon so that the scientific instruments are not damaged by a flood of light. While in operation, the telescope will not be turned to within 50 degrees of the Sun, precluding observations of the planet Mercury. Internal baffles in the Support Systems Module door and just below the secondary mirror prevent scattered light from degrading the focal plane image.

Just behind the light shield and the forward shell is the equipment section of the spacecraft. This doughnut-shaped section is made up of 10 compartments that house the electronic and control modules. Access to many of these modules will be easy as most compartments open from the outside via a hatch or access door. An astronaut can open a hatch, disconnect a module from its plug-in compartment, and insert a new module, all without disturbing the other instruments in the spacecraft.

The aft shroud fits over the section containing the scientific instruments and the fine guidance sensors . Access covers on this shroud enable astronauts to get at the instruments and sensors for removal or maintenance.

Handrails and portable foot restraints are fixed on the external surface to permit astronauts to perform their maintenance and refurbishment tasks. Four magnetic torquers , also located on the shroud exterior, work with four reaction wheels within the Support Systems Module equipment section to control the spacecraft's orientation in space. The magnetic torquers are magnetized metal rods controlled by an onboard computer. A change in their position causes the spacecraft to re-align itself in relation to the Earth`s magnetic field.

Electrical power is supplied by onboard batteries, which are charged by the two solar arrays during the sunlit portion of the telescope's orbit. An average of 2.4 kw is needed to operate the spacecraft and its instruments. Wide Field Planetary Camera A camera that can take photographs either in "wide-field" or "planetary" mode. The resulting images are transmitted by radio to Earth.

This instrument (fig. 8) can operate in one of two modes. In "wide field" mode, its focal ratio of f/12.9 will permit examination of large areas of space, leading to more accurate plotting of the spatial relationships of distant objects such as galaxies and quasars. High-resolution images of planets within our solar system can be obtained by the planetary camera, which has a focal ratio of f/30.

Images telemetered to Earth by radio will be far better than pictures produced by ground-based cameras. Pictures of Jupiter, for example, will be comparable to those taken by the two Voyager spacecraft in 1979. Pictures of more distant planets will not be as clear as those taken by Voyager, but will be far superior to those taken from Earth.

The camera consists of a complex system of instruments and mirrors. The field of view is split by a pyramidal mirror into four separate areas which are focused onto four charge-coupled devices . These devices have been designed to receive light of low intensity at very high resolution. A portion of the image is received on each target plate and is subdivided into 640,000 picture elements (pixels). The light intensities of each pixel are transmitted to Earth via telemetry signals for assembly into images for study. Images can be created from different spectral bands by directing the light through any one of 50 spectral filters within the camera. !index Blinking Eyes
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