The Primary Mirror

The primary mirror of the Hubble telescope measures 2.4 m (8 ft) in diameter and weighs about 826 kg (1820 lbs). It is constructed of ultra-low expansion silica glass and coated with a thin layer of pure aluminum to reflect visible light. A thinner layer of magnesium fluoride is layered over the aluminum to prevent oxidation and to reflect ultraviolet light.

Final Preparations

Shortly after this image was taken, the Hubble telescope was shipped to Kennedy Space Center and loaded into the cargo bay of the shuttle Discovery. The telescope measures 13.1 m (43.5 ft) in length, 4.27 m (14.0 ft) in diameter, and weighs 11,000 kg (25,500 lb). Note the size of the workers standing near the base of the telescope. Also note the orange cylinder attached to the telescope; this is one of the two solar arrays that provide power to Hubble's batteries. Once unrolled in orbit, each array will be over 12 m (40 ft) long and provide 1200 watts of power.


The Hubble Space Telescope was first scheduled for launch in 1986. But due the tragic loss of the shuttle Challenger in late January of that year, the launch was delayed four years. In April 1990, the Hubble telescope was lifted into orbit aboard the shuttle Discovery.


Crew members aboard the shuttle Discovery shot this photograph April 25, 1990. It shows the deployment of the Hubble Space Telescope from the payload bay, guided by the shuttle's robotic arm. The giant spaceborne telescope was put into orbit to collect information about a large variety of astronomical objects, from neighboring planets and stars to the most distant galaxies and quasars.

Pointing the HST

This artist's concept is a view from near the Hubble telescope, looking back at the shuttle Discovery shortly after deployment. The telescope's tracking system is very accurate. The pointing system comprises reaction wheels that actually move the telescope, gyros that report its position, star trackers that provide reference points, and the onboard computer that controls the pointing process.

Relaying Data

The path by which Hubble data arrive on Earth is outlined here. Images received by the telescope are converted into digital code and radioed to Earth using high-gain antennas at a rate of one million bits per second. Once the digital code is received by ground stations, it is converted into photographs or spectrograph readings for use by scientists.