Hubble Space
Telescope
NASA’s Hubble Space Telescope, the first of the great observatories, was deployed from the Space Shuttle Discovery into Earth orbit in April 1990. It is a product of two decades of research and development by 10,000 scientists and engineers at various NASA Centers, private companies, universities, and the European Space Agency. The purpose of the Hubble, the most complex and sensitive optical telescope ever made, is to study the cosmos from low-Earth orbit for 15 years or more.
Scientific Objectives
Scientists designed the Hubble Space Telescope to provide fine detail imaging, produce ultraviolet images and spectra, and detect very faint objects. The Hubble is meeting these three objectives, even though the spacecraft experienced a shaky start.
Two months after its deployment in space, scientists detected a 2-micron spherical aberration in the primary mirror that affected the telescope’s ability to focus faint light sources into a precise point. This imperfection was very slight, one-fiftieth the width of ahuman hair.
Computer processing overcame much of the defect, but a scheduled Space Shuttle servicing mission in 1993 permitted scientists to correct the problem. During four spacewalks, new instruments were installed into the Hubble that had optical corrections. A second servicing mission in 1997 further upgraded the instruments on the telescope.
Key Features
The Hubble Space Telescope is approximately the size of a railroad car, with two cylinders joined together and wrapped in a silvery reflective heat shield blanket. Wing-like solar arrays extend horizontally from each side of these cylinders, and dish-shaped antennas extend above and below the body of the telescope. The design is modular so the Space Shuttle can easily replace malfunctioning units.
The telescope has three major sections: the support systems module, the optical telescope assembly, and the scientific instruments. The support systems module holds the optical telescope assembly and scientific instruments in place and insulates them from extreme temperature highs and lows, when the satellite is in full light or darkness.
The support system includes the European Space Agency’s solar arrays, which consist of two "wings" containing 48,000 solar cells. The pointing control system aims the telescope to a desired position and locks it in place within 0.01 arc second through a series of gyroscopes, star trackers, momentum wheels, electromagnets, and fine guidance sensors. In addition, computers, high-gain antennas, and an electrical power system allow the Hubble to receive commands and transmit data back to scientists on Earth.
The optical telescope assembly contains two secondary and one larger primary mirror (2.36 meters) to collect and focus light from selected celestial objects. The mirrors are housed near the center of the telescope. Light hits the primary mirror and bounces to the secondary mirror—to a focal plane where the scientific instruments are located.
The scientific instruments include the Wide Field/Planetary Camera, the Faint Object Camera, the Goddard High Resolution Spectrograph, the Faint Object Spectrograph, and the High Speed Photometer. The find guidance system also performs scientific measurements. The instruments are positioned about 1.5 meters behind the primary mirror. The goals of these five instruments are as follows:
- The Wide Field/Planetary Camera 2 is designed to investigate the age of the universe and to search for new planetary systems around young stars. It takes pictures of large numbers of galaxies and of closeups of planets in our solar system.
- The Space Telescope Imaging Spectograph will spread out light into its component colors so that the properties of celestial objects, such as chemical composition, radial velocity, rational velocity, and magnetic fields, can be measured. The spectograph is able to record the spectrum of many locations in a galaxy simultaneously.
- The Near Infrared Camera and Multi-Object Spectrometer is a cryogenically cooled instrument that provides the capability of infrared imaging and spectroscopic observations of astronomical targets. The instrument detects light with wavelengths longer than the human eye limit.
- The Faint Object Camera, a contribution of the European Space Agency, focuses on smaller areas than the other camera and is used for producing sharp images at great distances. The data produced from this camera will help determine the distance scale of the universe and peer into centers of globular star clusters, binary stars, and other faint phenomena.
