How The HST Works

Like I said before, the HST is a Cassegrain reflector telescope. This means that light enters the telescope through the opening and bounces off the primary mirror to a secondary mirror. The size of the telescopes mirror determines its ability to gather light, and its ability to resolve two near objects from one another. The way these reflecting telescopes work is the more light it can collect and focus into a real or virtual image, the brighter the images. That is why the HST has a primary mirror of 7.9 feet (2.4 meters) in diameter, and a secondary mirror of 1.0 foot (.3 meters in diameter). These mirrors are coated with layers of aluminum measuring three-millionths of an inch thick and magnesium fluoride one-millionth of an inch thick. These layers make the HST reflect visible, infrared and ultraviolet light.

Image courtesy of hubblesite.org
The bigger the mirror the better the quality of picture. This is because when light passes through a narrow opening it diffracts and spreads out. The larger the mirror the less diffraction and spread. This is critical, because when lights is received from two stars through the HST you do not want these two light waves spreading and overlapping each other. Constructing large mirrors is extremely hard  to do. The HST mirror though is still not the largest and is small compared to some ground based telescopes that can be 400 inches (1000cm) and up. These large mirrors are not the only mirrors within the telescope though. There are many smaller, half reflective, half transparent mirrors at the focal point that reflect light to various instruments. Information above courtesy of hubblesite.org, nasa.gov, and How Everything Works.

Here is a picture courtesy of nasa.gov

A usually unknown fact about the HST is that it takes pictures in black and white, and the amazing colors seen are added from two or more black and white exposures made through colored filters. During image processing the colors matching the filters are added to the picture (www.armaghplanet.com).

Power Supply and Protection

The HST’s power comes from it’s solar panels, and uses only 2800 watts of power which is crazy knowing that a typical kitchen kettle is rated at 2200 watts. In the hostile environment of space the HST keeps safe with a blanket of multilayered insulation to shield to itself from the fluctuating temperatures. Beneath the insulation is a light aluminum shell providing protection to the crucial instruments.

Operating Hubble

The HST orbits the Earth every 97 minutes at a speed of 5 miles per second, and the Earth is orbiting the Sun at 67,000 mph. This makes focusing deep into the universe difficult when traveling at these speeds. To stay on target the HST uses a pair of guide stars that are located near the target. These stars are selected from a catalog with positions and brightness’s listed. The information given from guide stars is combined with precise observation instructions and is then sent to HST’s on-board computers. From there the computers send the data to the Fine Guidance Sensors, and they search for guide stars to lock onto. This method provides precise alignment for observing the universe.

 


Image courtesy of hubblesite.org

 

 



                        How To Operate The HST


Well if you want to operate the Hubble, you will need to become an astrophysicist with a massive amount of research done on what you might observe. Astronomers from around the world fight for just minutes to use this piece of art. To get on the schedule you must first send a proposal to the Space Telescope Science Institute (STScI). From there a review committee of experts go through the thousands of proposals to only select 200 that will use the HST to its full capabilities. Ground control though never goes off duty. There is a 24/7 crew monitoring the HST, so it stays safe and maintains its performance.

 



                                                     nasa.gov