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| Organization | NASA, ESA |
|---|---|
| Wavelength regime | optical |
| Orbit height | 600 km |
| Orbit period | 100 min |
| Launch date | 24 April 1990 |
| Deorbit date | circa 2010 |
| Mass | 11,000 kg |
| Other names | (none) |
| Webpage | http://hubble.nasa.gov |
| Physical Characteristics | |
| Telescope Style | reflector |
| Diameter | 4.2 m |
| Collecting Area | approx. 55 m2 |
| Focal Length | (m, ft) |
| Instruments | |
| NICMOS | camera and spectrometer |
| ACS | survey camera |
| WFPC2 | wide field camera |
| STIS | spectrometer and camera |
Data from the telescope is collected and analyzed by astronomers and scientists at the Space Telescope Institute, located at Johns Hopkins University in Baltimore, Maryland.
Working outside the atmosphere has advantages because the atmosphere obscures images and filters out electromagnetic radiation at certain wavelengths, mainly in the infrared.
| Table of contents |
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2 Discoveries 3 Launch and initial disappointment 4 Servicing Missions 5 Hubble's future and beyond 6 See also 7 External links |
Hubble weighs about 11,000 kilograms, is 13.2 meters long, has a maximum diameter of 4.2 meters and cost US 2 billion ($2,000,000,000).
The telescope is a reflector with two mirrors; the main mirror has a diameter of about 2.4 meters.
The light collected and focused by the telescope ends up in one of several instruments. The instruments have been
exchanged with different (and better) ones during the several maintenance missions.
The current (as of 2004) complement of instruments is:
Technical description
Each of which also has some capability as a spectrometer. Additionally, the telescope's Fine Guidance Sensors (FGS) can and have been used for science.
Two solar panels provide electricity, which is mainly used to power the cameras and the four large flywheels used to orient and stabilize the telescope. The telescope's infrared camera and multi object spectrometer also need to be cooled down to minus 180 degrees Celsius for operation.
Discoveries
Pictures taken by the Hubble Space Telescope: Clockwise from the upper left, the "Tadpole" galaxy, the "Cone Nebula", two colliding spiral galaxies dubbed "The Mice", and stellar birth in the Omega Nebula. (Images courtesy of NASA)
Additional Hubble Discoveries
The telescope was launched by Space Shuttle Discovery mission STS-31 on April 24, 1990. This had been postponed from a 1986 launch date by the Space Shuttle Challenger disaster in January that year.
The first images back from the telescope were generally regarded as a big disappointment for astronomers and all concerned in the project. They were blurred, and despite image processing could not match the predicted resolution. It was determined that the main mirror had been ground slightly too flat at the edges, a problem that could have been tested for on the ground if the funds had been available.
The telescope has been revisited several times by spacewalking astronauts in space shuttles in order to correct malfunctions, install new equipment, and boost the telescope back into a higher orbit (atmospheric drag causes Hubble to slowly fall out of orbit).
Servicing Mission 4, planned for February 2005, was due to be the last servicing mission, as Hubble reached the end of its life expectancy. After the Space Shuttle Columbia disaster, all future shuttles must be inspected externally on orbit before reentry, a task which NASA has decided is too expensive to be done without the facilities of the International Space Station (ISS). The shuttle is incapable of reaching both HST and ISS during the same mission. Therefore, this and all future service missions have been cancelled. There is also popular belief that this decision was motivated by the Bush administration's new manned space agenda.
Hubble uses gyroscopes to stabalize itself in orbit. Without them it will be unable to remain steady long enough to take meaningful pictures. The current gyroscopes are expected to have all failed by 2012, resulting in the end of Hubble's science mission (it may end earlier as, at the moment, three gyros are required. Work is underway to allow operation on two). The gyros also are what allow ground controllers to position the telescope. Without them, it will enter a gravity-gradient posture.
Hubble is currently (July 2003) in a 307 nm orbit. If it is not reboosted by a shuttle or other means, it will reenter the Earth's atmosphere sometime between 2013 and 2022. The exact date is dependant on how active the Sun is and its impact on the upper atmosphere, though it is likely to be earlier rather than later. The state of Hubble's gyros also impact the reentry date, as a controllable telescope can be made to minimize atmospheric drag.
Not all of the telescope will burn up on reentry. Parts of the main mirror and its support structure are expected to survive. NASA currently calculates a 1 in 700 chance of human fatality for a completely uncontrolled reentry. NASA originally intended to attach a propulsion module to the satellite in a future mission, which would provide a controlled reentry in 2010. At this time only Russia has the automatic docking capabilities to complete such a plan. Even this option is not simple, as Hubble has none of the active docking hardware required for the Russian automated docking systems to function.
Other options are:
Now the space agency and the astronomy community have to sit down and figure out what, if anything, should follow the Hubble. The James Webb Space Telescope (JWST, formerly known as the Next Generation Space Telescope, NGST) may replace the HST in 2012.
However, the JWST is an infrared telescope, while the Hubble covered the range from the near infrared through the visible into the near ultraviolet.
What complicates the question are the breathtaking advances in Earth-based astronomy since the Hubble was conceived. At that time, the conventional wisdom was that there was no way to make mirrors much bigger for ground-based telescopes, since they wouldn't be able to cool off and stabilize at night before the sun came up. Besides, continuously changing variations in atmospheric seeing would ensure that such bigger telescopes would return images no better than those obtained by smaller telescopes. Building a space telescope seemed to be the only way around these obstacles.
In fact, the obstacles fell more easily than anyone expected. All it required was a different mindset on how to make big telescopes. Instead of building one huge mirror that would take all night to stabilize, modern giant telescopes use smarter schemes. For example, the Keck telescope at Mauna Kea in Hawaii has a 10 meters segmented mirror, composed of a mosaic of separate mirrors arranged together and continuously adjusted by a bed of computer controlled actuators to ensure that they maintain their proper shape.
As far as the seeing problem goes, such a telescope can use an adaptive optics system, adjusting the mirrors continuously to compensate for changes in the atmosphere. Furthermore, astronomy organizations have been able to find and make very good use of high, dry sites with excellent seeing, such as Mauna Kea, and the high Atacama Desert in Chile.
This means that there may not really be any need to replace the Hubble to obtain better astronomical imagery in the visible range. The new ground-based telescopes can do the job, and even the most ambitious of them, like the Keck and the Very Large Telescope (VLT) in Chile, are much less expensive than the Hubble, and naturally much easier to service and update. For example, the VLT cost was roughly 1/7 of the HST cost, and gave the astronomic community four 8.2 meters telescopes, with a resolution almost as high as the Hubble (though, of course, not nearly as high as a Hubble replacement).
Space-based astronomy remains irreplaceable for those wavelengths that are blocked by the atmosphere, such as most of the infrared, and all the ultraviolet, X-ray and Gamma ray regions of the electromagnetic spectrum.
While NASA has long had a good relationship with the astronomy community, the agency's space-based astronomy programs have tended to operate on a parallel, independent track from ground-based astronomy efforts. Some observers believe that NASA and the National Science Foundation, which handles US government-funded ground-based astronomy, will soon be in discussions, and even that eventually both space and ground based astronomy will be directed under the same overall program.
On January 29, 2004, NASA's Administrator said that that he will review his decision to cancel the final servicing mission of the Hubble Space Telescope due to public outcry and requests from Congress for NASA to look for a way to save the Hubble Space Telescope. Adm. Hal Gehman, chairman of the NASA board that investigated the Space Shuttle Columbia incident will review and send his opinion to NASA according to a letter sent from NASA Administrator Sean O' Keefe to Maryland Senator Barbara Mikulski, Mikulski is the ranking Democrat on the Senate subcommitte that oversees NASA's budget. Websites have been set up dedicated to saving the Hubble Space Telescope. Federal lawmakers noted that NASA's next generation space telescope, named the James Webb Telescope is not scheduled for launch until 2010, many years after the Hubble Space Telescope is expected to cease functions, they also noted that about $200 million have already been spent on two new instruments designed for the Hubble Space Telescope and it might cost $300 million for a mission to return the Hubble Space Telescope safely to the Earth. Source: [1]
Launch and initial disappointment
Servicing Missions
The completion of this servicing mission, considerably enhanced Hubble's capabilities, some enthusiasts claiming that it is now effectively a "new instrument".Hubble's future and beyond
Hubble was designed for 15 years of operation, and it will end up serving for 22.See also
External links
Servicing cancellation links