OPTICAL TELESCOPES

HUBBLE SPACE TELESCOPE

 The Best Telescope for astronomers seeking pin – sharp views of the depths of the Universe is the Hubble Space Telescope. Launched in 1990 after decades of planning, Hubble is an unmanned observatory in orbit far above the clouds and atmospheric dust that block the view of Earth – based telescopes. Astronomers from dozens of countries use Hubble , functioning it by remote control. The human observer at the light detectors, while electronic cameras document excellent images of the cosmos.

 HOW HUBBLE WORKS

The heart of Hubble is a reflecting telescope – much like telescopes on Earth. In space, however, it must operate without mains electricity , a mounting to swivel it around, or cables linking it to control computers. Instead , Hubble carries the type of equipment found on many satellites: solar panels to provide power, reaction wheels for pointing, and radio antennas for communicating with Earth.

 GROUND CONTROL

Mission control for Hubble is at NASA’s Gordard Space Flight Center, in Maryland, USA. All signals to and from Hubble pass through this center, where engineers constantly monitor the spacecraft’s health. The engineers act as a link between the orbiting telescope and the Hubble astronomers, working at the nearby Space Telescope Science Institute in Baltimore, who control the telescope’s observing schedule.

 DEFECTIVE MIRROR

The first pictures astronomers received from Hubble were out of focus, though still better than any ground-based telescope. NASA realized that the mirror had been made in slightly the wrong shape, 0.002 mm too shallow at the outer edge.

 SERVICING MISSIONS

With Hubble firmly in the grip of Space Shuttle Discovery, astronauts Steven Smith and Mark Lee service the orbiting telescope. Like any other vehicle, Hubble needs regular servicing. Shuttle astronauts replace equipment such as computers and tape recorders and update the telescope by installing new cameras and detectors for light and infrared radiation. On the first servicing mission in 1993, they installed"contact lenses"to correct the focus because of a fault on the main mirror that blurred Hubble’s view.

 ADVANTAGES OF HUBBLE

Telescopes viewing the Universe from Earth must look upwards through our turbulent atmosphere, which constantly shifts and distorts the light from stars and galaxies – rather like looking through the swirling water in a busy swimming pool. That’s why stars seem to twinkle. From its perch above the atmosphere, Hubble has a clear view of everything in the Universe, from planets to quasars billions of light years away.