The Hubble Space Telescope

The Hubble Space Telescope
The Hubble Space Telescope (HST), is a space-based telescope, and has made some of the most dramatic discoveries in the history of astronomy. From nearly 600km above the Earth's surface, the HST has expanded our understanding of star birth, star death, and galaxy evolution, and has helped move black holes from theory to fact. It has recorded over 100,000 images in the past eight years. Hubble generates around 120GB of data every week and has captured some of the most breathtaking images of the universe.

Sadly after the Columbia tragedy, servicing missions of Hubble has been cancelled. It is hoped that if no failures occurs, Hubble will continue operating until 2010, when funding will be moved to the James Webb Space Telescope (JWST). The JWST, Hubble's successor, will be launched in 2011.

History

Long before space flight was possible astronomers have dreamed of being able to place a telescope in orbit around the Earth. By orbiting above the atmosphere the telescope could observe stars, galaxies, and other objects without the light being absorbed or distorted by the Earth's atmosphere. This would provide for sharper images than any land-based telescope could offer and also make the telescope more sensitive to faint objects.

The development of the Space Shuttle made the possibility of a space based telescope a reality. In the 1970s NASA and the European Space Agency (ESA) proposed the development of a space telescope. It was decided to name the telescope after Edwin Powell Hubble who had discovered the expansion of the Universe in the 1920s.

Construction and assembly of the space telescope was a painstaking process which spanned almost a decade. The precision-ground mirror was completed in 1981, and the optical assembly was delivered for integration into the satellite in 1984. The science instruments were delivered for testing at NASA in 1983. Assembly of the entire spacecraft was completed in 1985.

Originally the Hubble Space Telescope (HST) was scheduled for launch in 1986, but it was delayed during the redesign of the Space Shuttle following the Challenger accident. On April 24, 1990 it was launched aboard the STS-31 mission of the Space Shuttle Discovery.

Within a few months of functioning, a flaw was discovered in Hubble's main mirror which significantly reduced the telescope's ability to focus. This defect was due to spherical aberration caused by an incorrectly shaped mirror and caused the images of stars planets and galaxies to be blurred. These optical errors were corrected in 1993 during a servicing mission. In 1994 Hubble began sending back high-quality images that changed the way we view the universe.

How are Hubble Images Created?

Hubble doesn't use film at all, but rather, more or less, the same technology used in digital cameras today. Its cameras record light from the universe with special electronic detectors (CCD's). These detectors produce images of the cosmos not in color, but in shades of black and white.

Hubble images are combinations of three separate exposures - one each taken in red, green, and blue light. When mixed together, these three colors of light can simulate almost any color Finished color images are actually combinations of two or more black-and-white exposures to which color has been added during image processing. The colors in Hubble images, which are assigned for various reasons, aren't always as the image would appear if viewed by the human eye. The colors are often used as a tool, whether it is to enhance an object's detail or to visualize what ordinarily could never be seen by the human eye.

Light from astronomical objects comes in a wide range of colors, each corresponding to a particular kind of electromagnetic wave. Hubble can detect all the visible wavelengths of light plus many more that are invisible to human eyes, such as ultraviolet and infrared light.

Astronomical objects often look different in these different wavelengths of light. To record what an object looks like at a certain wavelength, Hubble uses special filters that allow only a certain range of light wavelengths through. Once the unwanted light has been filtered out, the remaining light is recorded.

Hubble's many filters allow it to record images in a variety of wavelengths of light. Since the cameras can detect light outside the visible light spectrum, the use of filters allows scientists to study "invisible" features of objects - those only visible in ultraviolet and infrared wavelengths.

Many full-color Hubble images are combinations of three separate exposures - one each taken in red, green, and blue light. When mixed together, these three colors of light can simulate almost any color of light that is visible to human eyes. This provides for the often breathtaking images that Hubble offers us.

Hubble: Facts & Figures

  • Dimensions: Length: 15.9 m, diameter: 4.2 m. In addition two solar panels each 2.6 x 7.1 m.
  • Mass: 11,110 kg (at the time of launch).
  • Instruments:
    The Advanced Camera for Surveys (ACS)
    The Wide Field and Planetary Camera 2 (WFPC2)
    The Space Telescope Imaging Spectrograph (STIS)
    The Near Infrared Camera and Multi-Object Spectrometer (NICMOS)
    Fine Guidance Sensors (FGS'es)
  • Cost at launch: $1.5 billion
  • Orbit: At an altitude of 569 km (353 miles), inclined 28.5 degrees to the equator (low-Earth orbit)
  • Time to Complete One Orbit: 97 minutes
  • Speed: 17,500 mph (28,000 kph)
  • Sensitivity to Light: Ultraviolet through infrared (115-2500 nanometers)
  • First Image: May 20, 1990: Star Cluster NGC 3532
  • Energy source: the Sun
  • Mechanism: two 25-foot solar panels
  • Power usage: 2,800 watts
  • Primary Mirror: Diameter: 94.5 in (2.4 m) Weight: 1,825 lb (828 kg)
  • Secondary Mirror: Diameter: 12 in (0.3 m) Weight: 27.4 lb (12.3 kg)
  • Hubble Can't Observe: The Sun or Mercury, which is too close to the Sun

Sources: NASA & Hubblesite.org