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The Hubble Space Telescope is the world’s enormous eye in the sky, the purveyor of the depths of space and time, the bringer of beauty. For the past decade, Hubble has been bringing us unbelievable pictures of galaxies, nebulas, black holes, quasars and pulsars. It has redefined cosmology and brought incredible scientific finds to the astronomical community. But exactly what is it?
The Hubble Space Telescope is a 2.4-meter reflecting telescope in low-Earth orbit that was originally deployed by the Discovery space shuttle on April 25, 1990. The telescope is a cooperative program between the National Aeronautics and Space Administration (NASA) and the European Space Agency (ESA). It is managed by the Space Telescope Science Institute (STScI) at Johns Hopkins University in Baltimore, Maryland. STScI is operated for NASA by the Association of Universities for Research in Astronomy, Inc. (AURA). The telescope is 13.2 meters long (43.5 feet), 4.2 meters (14 feet) in diameter and weighs 24,000 pounds.
HST was planned for a very long time. In 1946 (before the first satellites), a brilliant theoretical astrophysicist named Lyman Spitzer proposed a space-based telescope that would be free of the distortions of Earth’s atmosphere. Through the 60s and the 70s he lobbied for it and was instrumental in its design and development.
Hubble was designed to be upgraded through servicing missions. Each new mission has upgraded Hubble’s scientific power by a factor of 10 or greater and parts with limited life spans are replaced. Each mission has turned Hubble into a new state-of-the-art observatory!
It was this design that saved the telescope when it was discovered that Hubble had a spherical aberration in its primary mirror. Hubble’s primary mirror was two microns too flat. The aberration was fixed in December 1993 during an Endeavor shuttle mission.
But Hubble may be doomed to an early death due to the cancellation of future servicing missions by NASA Administrator Sean O'Keefe.
The Current Situation
Hubble was to be serviced one last time, Servicing Mission 4, in 2006. The original mission for the telescope was 15 years and then it was stretched to 20, with a projected end date of 2010. Without another servicing mission, the telescope will probably not live that long.
What could cause Hubble to fail? The two areas of greatest concern are Hubble's gyroscopes and batteries.
Gyroscopes: Hubble depends on gyroscopes to point the telescope and keep it stable. If too many fail, it will become unusable. Hubble has a total of six gyroscopes, of which two are currently broken and were to have been replaced on Servicing Mission 4. It uses three to point. Scientists are developing software and techniques to allow Hubble to operate with just two gyroscopes and they will test them in the fall. Based on previous history, it is likely that Hubble will be down to two gyroscopes by 2006 and one in 2007.
Batteries: Hubble uses a set of rechargeable nickel-hydrogen batteries that are recharged by Hubble's solar panels. The batteries keep the telescope pointed during the night - if the batteries die it could only stay pointed for a single day. The batteries are original to Hubble (1990) and no one knows how long they will last. They are starting to deteriorate in performance.
Other: Other random parts may break, such as electronics, as the shielding material has been aging. Fortunately, Hubble has redundant systems.
When the telescope stops working, the plan is to build and launch an unmanned robotic device that will rendezvous with Hubble and attach a rocket to it. The rocket will alter Hubble's orbit after firing so that Hubble will crash in the ocean, away from shipping lanes.
Why did NASA decide not to perform Servicing Mission 4? The decision was made to cancel because of safety concerns with sending astronauts by space shuttle to service Hubble. They are currently reviewing that decision, and public outcry may make a difference. So sign the Save the Hubble petition and write your congressperson! Hubble must continue to live for us all!
Instruments
HST has four instruments. They are the Wide Field/Planetary Camera 2, the Space Telescope Imaging Spectrograph, the Near Infrared Camera and Multi-Object Spectrograph and the newest addition, the Advanced Camera for Surveys.
Wide Field/Planetary Camera 2 (WF/PC)
The WF/PC (wif-pic) is the replacement camera that compensates for Hubble’s flat mirror by its relay mirrors being 2 microns too tall. The “camera” is actually four cameras.
Space Telescope Imaging Spectrograph (STIS)
A spectrograph is a device that spreads out the light gathered by a telescope so it can be analyzed to determine the properties of celestial objects such as chemical composition, temperature, velocity and magnetic fields. The STIS can study objects across a broad spectral range from the UV (115 nanometers) through the visible red and the near-infrared (1000 nanometers).
The STIS is two dimensional, which means it can record the spectrum in many locations simultaneously, resulting in greater efficiency.
Near Infrared Camera and Multi-Object Spectrograph (NICMOS)
This device provides infrared imaging and spectroscopic observations of astronomical targets. NICMOS detects light with wavelengths between 0.8 and 2.5 micrometers – longer than the human-eye limit.
NICMOS is a cryogenic instrument. The infrared detectors must operate at very cold temperatures and are kept inside a cryogenic “dewar” containing nitrogen ice.
Advanced Camera for Surveys (ACS)
ACS is a camera designed to provide the telescope with a deep, wide-field survey capability from the visible to near infrared, imaging from the near-UV to the near-infrared. The camera is responsible for some of the most incredible images on Phlare.com including the Cone Nebula and the Tadpole Galaxy.
Operation of the Telescope
The Hubble Telescope operates around the clock, but does not spend all of its time observing. It orbits the earth every 95 minutes and must spend time switching antennas, receiving and downloading data, calibrating or turning to acquire a new target. The Space Telescope Science Institute manages the master observation plan, and it is to STScI that astronomers must go to request the telescope’s time. Astronomers may wait years to get an opportunity to utilize Hubble. Only one in ten proposals are accepted. The telescope is available to astronomers worldwide
The master observation plan is then submitted to Goddard’s Space Telescope Operations Control Center (STOCC) where it is merged with its “housekeeping” plan to create a detailed operations schedule. Each event is translated into commands that are uploaded to the telescope several times a day.
Uploaded commands and downloaded data from the telescope are transmitted through the Tracking Data Relay Satellite (TDRS) and its ground station at White Sands, NM.
The observer on the ground can examine the raw images and other data within a few minutes for a quick look. Within 24 hours the data is delivered to STScI. STScI is responsible for data processing.
Hubble’s Greatest Discoveries
Hubble has provided a wealth of scientific data that has electrified the astronomical world. Here are some of its key discoveries.
Galaxy Evolution – Peering through time, Hubble has discovered that early galaxies were much smaller and more irregularly shaped than they are now. They may have provided the building blocks for elliptical and spiral galaxies through collisions and mergers.
Age of the Universe – Hubble observations allowed astronomers to determine an age of the universe using two different methods. The universe is 12 to 14 billion years old.
Black Holes - Hubble provided decisive spectroscopic evidence that supermassive black holes exist. Prior to that discovery, black holes were theorized.
Planets – Hubble provided visual proof that raw material for planets, dust disks, are common around young stars. This reinforced the assumption that planetary systems are common in the universe. Hubble also enabled the detection of a planet orbiting a star outside of our solar system and provided the first information about the planet’s chemical composition.
How Does Hubble See?
Hubble provides us with extraordinary images bursting with color. But Hubble doesn’t actually take color pictures at all. Its cameras record light with special electronic detectors that produce a black and white image. The images are shot through filters that allow only a certain wavelength of light through. That light is then recorded. After the data is downloaded, the colors are assigned for a variety of reasons. Keep in mind that Hubble can see all of the visible light spectrum (what we see) and way beyond into the infrared and ultraviolet. Scientists use color as a tool – they may simulate what our eyes would see (natural color), what an object looks like in infrared or UV (representative color) or use color to bring out structural detail (enhanced color.) Most of Hubble’s most popular images are made by combining red, green & blue filters to simulate what the human eye sees. To get a visual representation of the spectrum click here! For more information on this fascinating subject (and to play with some filters), visit the Hubble Site: Meaning of Color
How did Hubble get its name?
The Hubble Telescope is named after Dr. Edwin Hubble, an astronomer who made some of the most important discoveries of modern astronomy. Working at Mt. Wilson in the 1920s, Dr. Hubble showed that the faint clouds of light in the distance were actually other galaxies. In 1929, he determined that the farther a galaxy was away from Earth, the faster it appears to move away. This was the theory of the expanding universe, from whence came the Big Bang theory.
The Future
If Hubble is not upgraded again, it will likely die by 2006 or 2007. The next generation of space telescope, the James Webb Telescope, will be launched in 2011. The James Webb will be outfitted to see in the infrared red, and will be built to observe faint objects 400 times greater than any ground-based infrared telescope or NICMOS, but see as sharply as Hubble. It will be studying the origins of the universe. Objects from the beginnings of the universe are red-shifted and can be observed in the infrared. (Red-shifted is the astronomical observation of the Doppler effect – as celestial bodies move away from the observer the waves get longer or redder). If Hubble dies in 2006, it will leave a gap of five years with no extremely powerful space-based scope.
If you are interested in learning more about the Hubble Space Telescope and the James Webb Telescope, visit our links page.
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