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Hubble Space Telescope Banner

The Hubble Space Telescope

diagram of science instruments

Bill Gutsch helped translate this information from more technical NASA documents.


The Hubble Space Telescope has a variety of scientific instruments. These include two cameras, two devices called spectrographs and additional instruments called fine guidance sensors. Because the HST orbits in outer space above the atmosphere, it can see more clearly than telescopes on the surface of the earth. When astronomers speak about how clearly a telescope sees, they talk about how fine a detail the telescope can see or how close together two objects like stars can be and still be seen as two distinct objects by the telescope.

The moon is about a half of a degree across. Since astronomers divide degrees up into 60 minutes of arc, the moon may also be said to be about 30 minutes of arc across. A circle, as you know, has 360 degrees. Each degree is sub-divided into 60 arc minutes, and each arc minute into 60 arc seconds. The best telescopes on the ground can rarely see detail that is less than 1 second of arc wide (or split two stars that are less that one second of arc apart in the sky) because turbulence in the earth's atmosphere causes the image to ripple and shimmer. By comparison, the HST can see detail down to less than 0.1 seconds of arc across or, in other words, more than 10 times clearer. This is one of the main reasons astronomers like to use the HST.


(called "Wiff-Pick") This instrument was not on the HST originally but replaced another camera when astronauts also went up to fix other things on the HST during the first servicing mission in December 1993. The Wide Field / Planetary Camera 2 has special optics that correct for the problem in the HST's main mirror and is actually four imaging regions (rather like four pieces of film) in one. However, these cameras do not use film like cameras you have at home that you use to take snapshots but instead take pictures electronically rather like a home camcorder. Three of the image taking regions are arranged in an "L" shape and can take pictures of fairly large things down to a certain level of detail. Together these three create what is called the Wide Field Camera. The fourth region can only see a tiny piece of the sky but produces images that show very fine detail. It is known as the Planetary Camera. The Live from observations of Neptune will use WF/PC 2.


During the 1993 Servicing Mission, the other instruments on board the HST also got special "eye glasses" to correct for the wrongly shaped main mirror. Together, these special lenses are called COSTAR and they now help HST see with wonderful clarity. The instruments COSTAR helps are:


This camera was developed for NASA by the European Space Agency and can see details better than any other device on board the HST. This camera is also very, very sensitive to light and helps astronomers study some of the most distant galaxies in the universe. Indeed the Faint Object Camera (FOC) must be used with special filters if the HST is pointed at anything less than 200 millions times fainter than the faintest star which can be seen with the unaided eye! The FOC will be used to image pluto during the Live from observations.


A spectrograph is an instrument which takes the light from planets, stars and galaxies and spreads it out into a rainbow or spectrum of colors (just like a prism). From the spectrum of an object, astronomers can determine an amazing amount of information including the object's temperature, what it's made of and whether it's moving toward or away from us and how fast. As its name suggests, the Faint Object Spectrograph can examine very faint objects such as distant or small galaxies. It can examine the visible part of an object's spectrum as well as some of the radiation the object gives off at both ends of the spectrum (infrared and ultraviolet) beyond what the human eye can see.


This instrument was named after the scientist who was the first to design and launch liquid fueled rockets in the US. This spectrograph looks totally within the ultraviolet part of the spectrum (that is, the part that is responsible for giving us a sun burn). It can't study objects in space as faint as the Faint Object Spectrograph but it can examine the spectrum of brighter objects in as much as 100,000 times greater detail. Astronomers use this instrument to get very detailed information on an object's chemical make up as well as motions within an object such as the way a star is blasted apart in a supernova or the way gas is swirling in a bright galaxy to help them find evidence for black holes.


When parents or teachers talk about your "attitude", they may be referring to how you feel about things or people around you. When scientists talk about the attitude of a spacecraft, however, they are referring to which way the spacecraft is pointing. Attitude control, in turn, refers to how accurately the spacecraft can be kept pointing in a particular direction.

The pointing of some spacecraft is done using little rockets attached to the spacecraft that gently turn it in different directions. But, that is not the way the Hubble Space Telescope is pointed. The HST is so sensitive and has to work for so many years in space, that scientists use a system of gyroscopes (little devices that look like and spin like toy tops) to measure the rate the HST is moving. Reaction wheels are used to turn the HST. The system applies Newton's laws of action and reaction in a very interesting way. This all happens very slowly. In the process of being re-aimed from one object to the next, the HST turns about as fast as the minute hand on a clock. Other gyroscopes keep the HST pointed steadily at its target just as gyroscopes help keep planes and rockets on course.


The HST runs on sunlight. Flanking the telescope's tube are two thin, blue panels containing solar cells. (They look like curtains being stretched out to dry). Each is about 7 and a half feet by 39 feet in size. They convert sunlight directly into electricity to run the telescope's scientific instruments, computers and radio transmitters. Some of the energy generated is also stored in on board batteries so the telescope can continue to have power even when it's in the earth's shadow (which is about 25 minutes out of each 96 minute orbit).

The solar panels, along with the FOC, were built by the European Space Agency. The Live From Broadcast on March14 will receive a videoconference uplink from The European Space Agency's facility at Garching, near Munich, Germany.


Scientists remain in contact with the HST by means of radio signals. In turn, the HST sends its images and other data to the ground by radio signals as well. These signals do not go directly from the Space Telescope Science Institute to HST and back. Instead, they follow a complicated "bounce around" route using different earth orbiting communications satellites and other relay stations on the ground.

Information for this description of the Hubble Telescope came from the National Space Science Data Center and the Space Telescope Science Institute.

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