Hubble Space Telescope

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The Hubble Space Telescope ( HST ) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. Though not the first space telescope, Hubble is one of the largest and most versatile, and is well known as an important research tool and public relations award for astronomy. The HST is named after astronomer Edwin Hubble, and is one of NASA's Great Observatories, along with the Compton Sinar Gamma Observatory, the Chandra X-ray Observatory, and the Spitzer Space Telescope.

With a 2.4-foot (7.9 feet) mirror, Hubble's four main instruments observe in close, visible, and near-infrared ultraviolet spectra. Hubble's orbit beyond Earth's atmospheric distortion allows it to take extremely high-resolution images, with a much lower backlight than ground-based telescopes. Hubble has recorded some of the most detailed visible light images ever, allowing a deep view into space and time. Many Hubble observations have produced breakthroughs in astrophysics, such as accurately determining the extent of the universe's expansion.

HST was built by the US space agency NASA, with contributions from the European Space Agency. The Space Telescope Science Institute (STScI) selected Hubble's target and processed the resulting data, while Goddard Space Flight Center controls the spacecraft.

The space telescope was proposed in early 1923. Hubble was funded in the 1970s, with a proposed launch in 1983, but the project was struck by technical delays, budget problems, and Challenger disaster (1986). When it was finally launched in 1990, Hubble's main mirror was found not working properly, sacrificing telescope capability. Optics were corrected to the quality desired by the service mission in 1993.

Hubble is the only telescope designed to be served in space by astronauts. After being launched by Space Shuttle in 1990, the next five Space Shuttle missions were repaired, upgraded, and replaced on the telescope system, including all five major instruments. The fifth mission was initially canceled for security reasons after the Columbia disaster (2003). However, after a lively public discussion, NASA administrator Mike Griffin approved a fifth service mission, completed in 2009. The telescope operates in 2018, and can last until 2030-2040. His scientific successor, James Webb Space Telescope (JWST), is scheduled for launch in May 2020.

Video Hubble Space Telescope

Conception, design, and purpose

Proposals and precursors

In 1923, Hermann Oberth - regarded as the father of modern rocketry, along with Robert H. Goddard and Konstantin Tsiolkovsky - published German Diet Rakete zu den PlanetenrÃÆ'¤ umen ("The Rocket into Planetary Space"), which mentions how the telescope could be pushed into Earth's orbit by a rocket.

The history of the Hubble Space Telescope can be traced back as far back as 1946, to Lyman Spitzer's astronomer paper "The astronomical advantage of an observatory of outer space". In it, he discusses two key advantages that a space-based observatory will have ground-based telescopes. First, the angular resolution (the smallest separation in which the object can be clearly distinguished) will be limited only by diffraction, rather than by turbulence in the atmosphere, causing the twinkling stars, known to astronomers as sight. At that time the ground-based telescope was limited to a resolution of 0.5-1.0 seconds, compared with a limited theoretical diffraction resolution of about 0.05 arksec for telescopes with a mirror of 2.5 m (8.2 m) in diameter. Second, space-based telescopes can observe infrared and ultraviolet light, which is highly absorbed by the atmosphere.

Spitzer devoted most of his career to encouraging the development of the space telescope. In 1962, a report by the US National Academy of Sciences recommended the development of space telescopes as part of the space program, and in 1965, Spitzer was appointed head of a committee tasked with defining scientific goals for large space telescopes.

Space-based astronomy began on a very small scale after World War II, when scientists harnessed developments in rocket technology. The first ultraviolet spectrum of the Sun was obtained in 1946, and the National Aeronautics and Space Administration (NASA) launched the Orbiting Solar Observatory (OSO) to obtain the UV, X-ray and gamma-ray spectra in 1962. An orbiting solar telescope was launched in 1962 by the United Kingdom as part of the Ariel space program, and in 1966 NASA launched the first Orbiting Astronomical Observatory (OAO) mission. Battery OAO-1 failed after three days, ending the mission. This was followed by OAO-2, which performed ultraviolet observations of stars and galaxies from its launch in 1968 to 1972, well beyond its original plan for one year.

The mission of OSO and OAO demonstrates the important role that space-based observations can play in astronomy, and in 1968, NASA developed a corporate plan for a space-based reflecting telescope with a 3 m (9.8 ft) mirror diameter, known temporarily as Large Orbiting Telescope or Large Space Telescope (LST), with a launch scheduled for 1979. The plan emphasizes the need for manned maintenance missions to telescopes to ensure such expensive programs have a long lifetime, and the development of shared plans for reusable spacecraft shows that technology to allow this immediately available.

Quest for funding

The continued success of the OAO program has prompted a growing consensus in the astronomy community that LST should be the ultimate goal. In 1970, NASA set up two committees, one to plan the engineering side of the space telescope project, and the other to determine the scientific objectives of the mission. Once this has been established, the next hurdle for NASA is getting funding for the instrument, which will be much more expensive than Earth-based telescopes. The US Congress questioned many aspects of the proposed budget for telescopes and forcible cuts in the budget for the planning stage, which at the time consisted of very detailed studies of instruments and potential hardware for telescopes. In 1974, public spending cuts caused Congress to remove all funds for the telescope project.

In response, the national lobbying effort is coordinated among astronomers. Many astronomers meet congressmen and senators personally, and large-scale letter-writing campaigns are held. The National Academy of Sciences published a report emphasizing the need for a space telescope, and finally the Senate approved half of the budget originally approved by Congress.

The funding issue led to a project scale reduction, with the proposed mirror diameter reduced from 3 m to 2.4 m, both to cut costs and to allow for a more compact and effective configuration for telescope hardware. A 1.5m (4.9 feet) space telescope precursor proposed to test the system to be used on the main satellite was dropped, and budget concerns also encouraged collaboration with the European Space Agency. ESA agreed to provide funding and supply one of the first generation instruments for the telescope, as well as the solar cells that will empower it, and staff to work on telescopes in the United States, in exchange for European astronomers guaranteed at least 15% of telescope observation time. Congress finally approved funding of US $ 36 million for 1978, and the LST design began in earnest, aiming for the launch date of 1983. In 1983 the telescope was named after Edwin Hubble, who made a mistake one of the greatest scientific breakthroughs of the 20th century when he discovered that the universe was expanding.

Construction and engineering

After the Space Telescope project has been given a green light, the work on the program is shared among many institutions. The Marshall Space Flight Center (MSFC) is responsible for the design, development and construction of telescopes, while Goddard Space Flight Center is given complete control over scientific instruments and ground-control centers for the mission. MSFC commissioned Perkin-Elmer optical companies to design and build Optical Telescope Assembly (OTA) and Fine Guidance Sensors for space telescopes. Lockheed was assigned to build and integrate the spacecraft in which the telescope would be placed.

Optical Telescope Assembly (OTA)

Optically, HST is a Cassegrain reflector of Ritchey-ChrÃÆ' Â © tien design, like the largest professional telescope. This design, with two hyperbolic mirrors, is known for good imaging performance over a wide field of view, with the disadvantage that the mirror has a form that is difficult to fabricate and test. Mirrors and telescope optical systems determine the ultimate performance, and they are designed to exact specifications. Optical telescopes typically have polished mirrors up to an accuracy of about a tenth of the wavelength of visible light, but the Space Telescope is used for observations from being seen through ultraviolet (shorter wavelengths) and defined as limited diffraction to take full advantage of the space environment. Therefore, a mirror is required to be polished to an accuracy of 10 nanometers (0.4 microinches), or about 1/65 of the red light wavelength. At the end of the long wavelength, the OTA is not designed with optimal IR performance - for example, the mirror is kept at a stable temperature (and warm, about 15 Â ° C) by the heater. This limits Hubble's performance as an infrared telescope.

Perkin-Elmer intends to use a computer-controlled, highly-polished machine to grind the mirror to the desired shape. However, if their latest technology is in trouble, NASA is demanding a sub-contract of PE to Kodak to make a backup mirror using traditional polishing techniques. (The Kodak and Itek teams are also bidding on the original mirror reflective job.They offer both companies to reexamine each other's work, which almost certainly catches the polishing mistakes that then cause such problems.) Kodak mirror is now on a permanent screen in National Air and Space Museum. The Itek mirror built as part of the effort is now used in the 2.4 m telescope at the Magdalena Ridge Observatory.

Perkin-Elmer mirror construction began in 1979, beginning with blanks produced by Corning from their ultra-low expansion glass. To keep the minimum mirror weight consisting of the top and bottom plates, each one inch (25 mm) thick, flanking the honeycomb lattice. Perkin-Elmer simulates microgravity by supporting a rear mirror with 130 bars using a variety of styles. This ensures that the final shape of the mirror will be correct and to specification when it is finally deployed. Mirror polishing continued until May 1981. The NASA report at the time questioned the Perkin-Elmer managerial structure, and polishing began to slip behind schedule and budget. To save money, NASA stopped working on the backup mirror and put the telescope's launch date back to October 1984. The mirror was completed in late 1981; it was washed using 2,400 US gallons (9.100Ã, L) of hot water, deionized and then received a reflective coating of 65Ã, thick (2.6Ã,  ° in) aluminum and a protective layer as thick as 25Ã, nm (0.98Ã, ) magnesium fluoride.

Doubts continue to be expressed about Perkin-Elmer's competence on this important project, as the budget and time scale for producing the remaining OTAs continue to expand. Responding to a schedule described as "uneasy and changing daily," NASA postponed the launch date of the telescope until April 1985. Perkin-Elmer's schedule continued to decline at a rate of about one month per quarter, and sometimes the delay reached one day for each business day. NASA was forced to postpone the launch date until March and then September 1986. At this time, the total project budget has increased to US $ 1.175 billion .

Spacecraft System Spacecraft

The spacecraft in which telescopes and instruments have to be placed is another major engineering challenge. It should withstand the frequent part of direct sunlight into the darkness of the Earth's shadow, which will cause major changes in temperature, while stable enough to allow a very accurate telescope pointer. The multi-layer insulation sheath keeps the temperature inside the telescope stable and surrounds the lightweight aluminum shell where the telescope and instrument sit. Inside the shell, a frame of graphite-epoxy keeps the telescope's working parts straight. Since the graphite composite is hygroscopic, there is a risk that the water vapor is absorbed by the truss while in the Lockheed clean room it will later be expressed in a vacuum; so that the instrument telescope is covered with ice. To reduce that risk, nitrogen gas cleaning is done before launching the telescope into space.

While the construction of spacecraft in which telescopes and instruments would be placed somewhat more smoothly than OTA development, Lockheed still experienced some budgets and slippage schedules, and by the summer of 1985, the construction of spacecraft was 30% above budget and three months late from schedule. An MSFC report says that Lockheed tends to rely on NASA guidance rather than taking their own initiative into development.

Computer systems and data processing

The first two primary computers on the HST were the 1.25 MHz DF-224 system, built by Rockwell Autonetics, containing three redundant CPUs, and two NSSC-1 (NASA Standard Spacecraft Computer, Model 1) systems developed by Westinghouse. and GSFC uses diode-transistor logic (DTL). A co-processor for the DF-224 was added during Servicing Mission 1 in 1993, consisting of two strings of redundancy from Intel 80386 processor with 80387 math co-processor. The DF-224 and 386 co-processors were replaced by a 251 MHz Intel-based 80486 processor system during the 3A Mission Service in 1999.

In addition, some science instruments and components have self-embedded microprocessor-based control systems. The MATS (Multiple Access Transponder) components, MAT-1 and MAT-2, utilize the Hughes Aircraft CDP1802CD microprocessor. The Wide Field and Planetary Camera (WFPC) also use RCA 1802 microprocessors (or possibly the older 1801 version). WFPC-1 was replaced by WFPC-2 during Service Mission 1 in 1993, which was subsequently replaced by Wide Field Camera 3 (WFC3) during Mission Service 4 in 2009.

Initial instrument

When launched, HST brings five scientific instruments: Wide Field and Planetary Camera (WF/PC), Goddard High Resolution Spectrograph (GHRS), High Speed ​​Photometer (HSP), Camera Faint Object (FOC) and Faint Spectrograph Object (FOS). ). WF/PC is a high resolution imaging device primarily intended for optical observation. It was built by NASA's Jet Propulsion Laboratory, and incorporates a set of 48 filters that isolate the spectrum lines of certain astrophysical interests. The instrument contains eight charge-coupled device (CCD) chips that are shared between two cameras, each using four CCDs. Each CCD has a resolution of 0.64 megapixels. "Wide field cameras" (WFC) cover large angular areas at the expense of resolution, while "planetary cameras" (PCs) take pictures at longer effective focal lengths than WF chips, giving them greater magnification.

GHRS is a spectrograph designed to operate in ultraviolet. It was built by the Goddard Space Flight Center and can achieve 90,000 spectral resolutions. Also optimized for ultraviolet observations are FOC and FOS, which are capable of the highest spatial resolution of any instrument in Hubble. Instead of CCD these three instruments use photon-counting digicons as their detector. FOC was built by ESA, while University of California, San Diego, and Martin Marietta Corporation built FOS.

The final instrument is HSP, designed and built at the University of Wisconsin-Madison. It is optimized for observations of visible light and ultraviolet variable stars and other astronomical objects that vary in brightness. It takes up to 100,000 measurements per second with a photometric accuracy of about 2% or better.

The HST guidance system can also be used as a scientific instrument. Its three Fine Guidance Sensors (FGS) are primarily used to keep telescopes accurately pointed during observation, but can also be used to perform highly accurate astrometry; accurate measurements for in 0.0003 arcseconds have been achieved.

Ground Support

The Space Telescope Science Institute (STScI) is responsible for the scientific operation of telescopes and the delivery of data products to astronomers. STScI is operated by the University Association for Research in Astronomy (AURA) and is physically located in Baltimore, Maryland on the Homewood campus of Johns Hopkins University, one of 39 US universities and seven international affiliates who formed the AURA consortium. STScI was founded in 1981 after something of a power struggle between NASA and the scientific community in general. NASA wants to keep this function in-house, but scientists want it to be based on academic formation. The Space Telescope European Coordinating Facility (ST-ECF), founded in Garching bei MÃÆ'¼nchen near Munich in 1984, provided similar support to European astronomers through 2011, when it was transferred to the European Space Center for Astronomy.

One rather complex task that falls onto STScI is the scheduling of observations for the telescope. Hubble is in low Earth orbit to allow service missions, but this means that most astronomical targets are occult by the Earth for slightly less than half of each orbit. Observations can not be made when the telescope passes the South Atlantic Anomaly because of high radiation levels, and there is also a considerable exception zone around the Sun (which blocks the observations of Mercury), the Moon and Earth. The angle of sun avoidance is about 50 °, to keep the sun from illuminating any part of the OTA. Avoidance of Earth and Moon keep the bright light from FGS, and keep spreading light from entering instrument. If FGS is turned off, however, the Moon and Earth can be observed. Earth observations were used very early in the program to produce a flat field for the WFPC1 instrument. There is a so-called continuous view zone (CVZ), about 90 ° to the orbital plane of Hubble, where the target is not touched on for a long time. Due to orbital precession, the CVZ location moves slowly for eight weeks. Since the limbs of the Earth are always located in about 30 ° of the region in CVZ, the scattered lightness of the earth's light may increase for long periods during CVZ's observation.

Hubble orbits in low Earth orbit at an altitude of about 540 kilometers (340 mi) and a slope of 28.5 Â °. Positions along their orbits change over time in ways that can not be predicted accurately. The density of the upper atmosphere varies according to many factors, and this means that Hubble's prediction of a six-week position could be an error of up to 4,000 km (2,500 mi). The observation schedule is usually completed only a few days in advance, because longer waiting times mean there is a possibility that the target will be not observable at that time as it will be observed.

Technical support for HST is provided by NASA and contractor personnel at Goddard Space Flight Center in Greenbelt, Maryland, 48 km (30 mi) south of STScI. Hubble's operations are monitored 24 hours per day by four flight control teams that make up the Hubble Flight Operations Team.

Challenger disaster, delay, and eventual launch

At the start of 1986, the planned launch date of October of that year seemed viable, but Challenger's accident brought the US space program to a standstill, grounded the Space Shuttle fleet and forced the launch of Hubble to be postponed for several years. Telescopes should be kept in a clean room, switched on and cleaned with nitrogen, until the launch can be rescheduled. This expensive situation (about US $ 6 million per month) drives the overall cost of the project higher. This delay allows time for engineers to conduct extensive testing, replace batteries that are likely to fail, and make other improvements. In addition, the ground software required to control Hubble was not ready in 1986, and was barely ready for the 1990 launch.

Finally, after the resumption of the shuttle flight in 1988, the launch of the telescope was scheduled for 1990. On April 24, 1990, Space Shuttle successfully launched the telescope into a planned orbit during the STS-31 mission.

From an estimated total initial cost of approximately $ 400 million, the cost of the telescope was approximately $ 4.7 billion at the time of its release. Hubble's cumulative cost is estimated to be approximately US $ 10 billion in 2010, twenty years after its launch.

Maps Hubble Space Telescope

List of Hubble instruments

Hubble accommodates five science instruments at a given time, plus Fine Guidance Sensors, which are primarily used for aiming telescopes but sometimes used for science (astrometry). The initial instrument was replaced with more advanced instruments during the Shuttle service mission. COSTAR is a strictly corrective optical device rather than an actual science instrument, but it occupies one of five instrument spaces.

Since last service mission in 2009, four active instruments have been ACS, COS, STIS and WFC3. NICMOS is stored in hibernation, but can be restarted if WFC3 fails in the future.

• Advanced Camera for Surveys (ACS; 2002-present)
• Cosmic Origins Spectrograph (COS; 2009-present)
• Substitute a Corrective Optical Space Telescope (COSTAR; 1993-2009)
• Camera Faint Object (FOC; 1990-2002)
• Faint Object Spectrograph (FOS; 1990-1997)
• Fine Guidance Sensor (FGS; 1990-present)
• Goddard High Resolution Spectrograph (GHRS/HRS; 1990-1997)
• High Speed ​​Photometer (HSP; 1990-1993)
• Near Infrared Cameras and Multi-Object Spectrometers (NICMOS; 1997-present, hibernation since 2008)
• Space Telescope Imaging Spectrograph (STIS; 1997-present (not working 2004-2009))
• Wide Field and Planetary Camera (WFPC; 1990-1993)
• Wide Field and Planetary Camera 2 (WFPC2; 1993-2009)
• Wide Field Camera 3 (WFC3; 2009-current)

Of the previous instruments, three (COSTAR, FOS and WFPC2) were featured at the Smithsonian National Air and Space Museum. FOC is in the museum Dornier, Germany. HSP is in Space at the University of Wisconsin-Madison. WFPC was first dismantled, and some components were then reused in WFC3. The current location of GHRS is unclear.

src: cdn.spacetelescope.org

Flawed mirror

Within weeks of launching the telescope, the returned images showed serious problems with the optical system. Although the first image looks sharper than ground-based telescopes, Hubble failed to achieve the last sharp focus and the best image quality obtained is much lower than expected. The point source image is spread over a radius of more than one arc second, instead of having a point distribution function (PSF) concentrated in a 0.1 arkec diameter circle as defined in the design criteria.

The defect image analysis shows that the cause of the problem is that the main mirror has been polished to the wrong shape. Although it may be the most precise optical mirror ever made, smooth to about 10m (0.4 inches), the perimeter is too flat about 2,200 nanometers (2.2 micrometers; 87 microinches). This distinction is disastrous, introduces severe spherical aberrations, defects in which the light reflecting off the edge of the mirror focuses on a different point from the light that bounces from its center.

The effect of a mirror defect on scientific observation depends on a particular observation - the core of the PSF being violated is sharp enough to allow high-resolution observations of bright objects, and point source spectroscopy is only affected through loss of sensitivity. However, the loss of light to a large halo, beyond focus greatly reduces the usefulness of telescopes for faded objects or high contrast imaging. This means that almost all cosmological programs are basically impossible, because they require observation of very dim objects. NASA and the telescope were subjected to many jokes, and the project was popularly regarded as a white elephant. For example, in the 1991 comedy The Naked Gun 2Ã,½: The Smell of Fear , Hubble is depicted with Lusitania , Hindenburg , and Edsel. Nevertheless, during the first three years of Hubble's mission, prior to optical correction, the telescope still performs a large number of productive observations of less demanding targets. These errors are well characterized and stable, allowing astronomers to partially compensate for damaged mirrors using sophisticated image processing techniques such as deconvolution.

The origin of the problem

A commission headed by Lew Allen, director of the Jet Propulsion Laboratory, was established to determine how the error could arise. The Allen Commission finds that the reflective null corrector, the test device used to achieve a true non-spherical mirror, has been incorrectly assembled - one lens out of position with 1.3 mm (0.051 in). During the early grinding and polishing of the mirrors, Perkin-Elmer analyzed its surface with two conventional null biasing correction. However, for the final processing steps, they switch to specially crafted null reflectors, which are explicitly designed to meet very strict tolerances. The incorrect device assembly causes the mirror to be very precise but to the wrong shape. Several recent tests, using conventional null correction, reported true ball disorders. But this result is dismissed, thus missing the chance to catch the error, because the reflective null corrector is considered more accurate.

The commission blamed the failure especially on Perkin-Elmer. The relationship between NASA and optical companies has been very tense during telescope construction, due to frequent slip schedules and cost swelling. NASA found that Perkin-Elmer did not adequately review or supervise mirror construction, did not assign the best optical scientist to the project (as it did for prototypes), and in particular did not involve optical designers in glass construction and verification. While the commission strongly condemns Perkin-Elmer for these managerial failures, NASA has also been criticized for not grasping the lack of quality control, such as relying solely on test results from a single instrument.

Design solution

The telescope design always incorporated the mission of serving, and astronomers immediately began looking for potential solutions to problems that could be applied to the first service mission, which was scheduled for 1993. While Kodak had installed a backup mirror for Hubble, it would have been impossible to replace the mirror in orbit; too expensive and time-consuming to bring telescopes back to Earth for repairs. In contrast, the fact that the mirror has been milled in such a way that the wrong shape causes the design of new optical components with exactly the same faults but in the opposite sense, to be added to the telescope on a ministry mission, effectively acting as a "goggle" to correct the spherical aberrations.

The first step is the exact characterization of the error in the main mirror. Working backwards from the point source image, astronomers determined that the conical cone of the mirror as constructed is -1.01390 Ã, Â ± 0.0002 , instead of the intended -1 , 00230 . The same number is also obtained by analyzing the null corrector used by Perkin-Elmer to look for mirrors, as well as by analyzing the interferogram obtained during the test of the mirror soil.

Because of the way the HST instrument is designed, two different correction devices are required. Wide Field and Planetary Camera 2 designs have been planned to replace existing WF/PCs, including relay mirrors to direct light to four separate charge-coupled device (CCD) chips that make up two cameras. Inverted inversion errors on the surface can completely undo the major deviations. However, other instruments do not have intermediate surfaces that can be found in this way, and therefore external correction devices are required.

The Space Corrective Space Space Space Shuttle Replacement (COSTAR) Replacement System is designed to improve spherical aberration for focusing light on FOC, FOS, and GHRS. It consists of two mirrors in the path of light with one ground to correct the aberration. In order to fit the COSTAR system into the telescope, one of the other instruments must be removed, and astronomers choose a High Speed ​​Photometer to sacrifice. In 2002, all original instruments requiring COSTAR have been replaced by instruments with their own corrective optics. COSTAR was removed and returned to Earth in 2009 where it is on display at the National Air and Space Museum. The area previously used by COSTAR is now occupied by the Spectrograph Origian Cosmic.

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Serve new missions and instruments

Hubble is designed to accommodate servicing and equipment repairs regularly while in orbit. Limited instruments and life objects are designed as orbital replacement units. Five service missions (SM 1, 2, 3A, 3B, and 4) were flown by the NASA space shuttle, the first in December 1993 and the last in May 2009. The service mission is a complex operation that begins with maneuvers to intercept telescopes in orbit and carefully picked it up with the shuttle's mechanic arm. The work required is then performed in several spacewalks moored over a period of four to five days. After the visual inspection of the telescope, astronauts make repairs, replace damaged or damaged components, improve equipment, and install new instruments. Once the work is done, the telescope is reinstated, usually after upgrading to a higher orbit to overcome the orbital damage caused by atmospheric uptake.

Service Mission 1

Once problems with Hubble's mirrors are found, the first service mission is assumed to be more important, because astronauts need to do extensive work to install corrective optics. The seven astronauts for the mission are trained to use around a hundred specialized tools. SM1 flew aboard the Endeavor in December 1993, and involved the installation of several instruments and other equipment for ten days.

Most importantly, High Speed ​​Photometer is replaced with COSTAR corrective optical package, and WFPC is replaced with Wide Field and Planetary Camera 2 (WFPC2) with an internal optical correction system. Their solar arrays and electronic drives are also replaced, as well as four gyroscopes in a pointing telescope system, two electric control units and other electrical components, and two magnetometers. The onboard computer is enhanced with an additional processor, and the Hubble orbit is enhanced.

On January 13, 1994, NASA stated that the mission was fully successful and showed sharper images. This mission is one of the most complex to be done up to that date, which involves five periods of extra-long vehicle activity. Its success is a boon for NASA, as well as for astronomers who now have more capable telescopes of space.

Service Mission 2

Mission Service 2, flown by Discovery in February 1997, replacing GHRS and FOS with Space Telescope Imaging Spectrograph (STIS) and Near Infrared Camera and Multi-Object Spectrometer (NICMOS), replacing Engineering and Scientific Tape Recorder with a new Solid State Recorder, and improved thermal insulation. NICMOS contains solid nitrogen heat sinks to reduce the thermal noise of the instrument, but shortly after installation, unexpected thermal expansion causes parts of the heat sink to come into contact with the optical baffle. This causes an increased heating rate for the instrument and reduces the initial expectation of 4.5 years to about 2 years.

Service Mission 3A

Mission Service 3A, flown by Discovery , occurred in December 1999, and was a breakup from Mission 3 after three of the six onboard gyroscopes had failed. The fourth failed several weeks before the mission, making the telescope incapable of making scientific observations. The mission replaces all six gyroscopes, replaces the Fine Guidance Sensor and computer, installs the Voltage/temperature Improvement Kit (VIK) to prevent overcharging, and replaces the thermal insulation blanket. The new computer is 20 times faster, with six times more memory, than the replaced DF-224. This increases throughput by moving some computing tasks from the ground to the spacecraft and saving money by allowing the use of modern programming languages.

Service Mission 3B

The 3B Mission Service flown by Columbia in March 2002 saw the installation of a new instrument, with the FOC (which, except for the Fine Guidance Sensors when used for astrometry, was the last of the original instrument) was replaced by Advanced Camera for Surveys (ACS). This means that COSTAR is no longer needed, since all new instruments have built-in correction for main mirror deviations. The mission also revives the NICMOS by installing a closed cycle refrigerant and replacing the solar array for the second time, providing 30 percent more power.

Service Mission 4

The plan called for Hubble to be served in February 2005, but the Columbia disaster in 2003, where the orbiter was destroyed while reentering the atmosphere, had a profound effect on the Hubble program. NASA administrator Sean O'Keefe decides that all future space shuttle missions should be able to reach the International Space Station's secure place if flight problems develop. Since no transport is capable of reaching both HST and ISS during the same mission, the mission of the future crew service is canceled. This decision was attacked by many astronomers, who felt that Hubble was valuable enough to risk people. The planned successor of HST, James Webb Telescope (JWST), is not expected to be launched until at least 2018. The gap in the ability to observe space between Hubble's decommissioning and replacement commissioning is a major concern for many astronomers, given the significant scientific impact of HST. Consideration that JWST will not be placed in low Earth orbit, and therefore can not be easily upgraded or repaired in the event of initial failure, only makes this concern more acute. On the other hand, many astronomers feel that Hubble's service should not happen if the cost comes from the JWST budget.

In January 2004, O'Keefe said he would review his decision to cancel his final service mission to HST due to public protests and a request from Congress to NASA to find a way to save him. The National Academy of Sciences held an official panel, recommended in July 2004 that HST should be preserved despite risks. Their report urged "NASA should not take action that would preclude the mission of sending the shuttle to the Hubble Space Telescope". In August 2004, O'Keefe asked Goddard Space Flight Center to prepare a detailed proposal for the robotic service mission. The plan was later canceled, the robot mission described as "unworthy". At the end of 2004, several members of Congress, led by Senator Barbara Mikulski, held public hearings and fought with public support (including thousands of letters from schoolchildren across the country) to get the Bush Administration and NASA to reconsider the decision to cancel plans for the Hubble rescue mission.

The nomination in April 2005 of the new NASA Administrator with a technique rather than an accounting background, Michael D. Griffin, changed the situation, as Griffin stated he would consider a manned service mission. Immediately after his appointment, Griffin authorized Goddard to continue preparations for Manned Hubble maintenance flights, saying he would make the final decision after the next two shuttle missions. In October 2006 Griffin gave the green light, and the 11-day mission by Atlantis is scheduled for October 2008. Hubble's main data handling unit failed in September 2008, stopping all scientific data reporting until its backups were brought online on 25 October 2008. Due to the failure of the backup unit will make the HST powerless, the service mission is delayed to include a replacement for the main unit.

Mission Service 4, flown by Atlantis in May 2009, is the last shuttle mission scheduled for HST. SM4 installed a replacement data handling unit, improved the ACS and STIS systems, installed an improved nickel hydrogen battery, and replaced other components. SM4 also installed two new observation instruments - Wide Field Camera 3 (WFC3) and Cosmic Origins Spectrograph (COS) - and Soft Capture and Rendezvous System, which will allow future rendezvous, capture and disposal of Hubble. crew or robot missions. Except for the ACS High Resolution Channels that can not be fixed and disabled, work done during SM4 makes the telescope fully functional, and remains as of 2018.

src: www.nasa.gov

Main project

Since the beginning of the program, a number of research projects have been conducted, some of which are almost entirely with Hubble, other coordinated facilities such as the Chandra X-ray Observatory and ESO Very Large Telescope. Although the Hubble observatory is nearing the end of its lifetime, there are still major projects scheduled for it. One example is the upcoming Frontier Fields program, which was inspired by Hubble's in-depth observation of the Abell 1689 galaxy cluster.

Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey

In a press release in August 2013, CANDELS is referred to as "the biggest project in Hubble history". The survey "aims to explore the evolution of galaxies in the early universe, and the first seed of the cosmic structure is less than a billion years after the Big Bang." The CANDELS project site describes the following survey objectives:

The Near-IR Cosmic Assembly Deep Extragalactic Legacy Survey is designed to document the first third of galaxy evolution from z = 8 to 1.5 through deep imaging of over 250,000 galaxies with WFC3/IR and ACS. It will also find the First Type of SNe outside z & gt; 1.5 and specify their accuracy as standard candles for cosmology. Five major multi-wavelength sky regions are selected; each of which has multi-wavelength data from Spitzer and other facilities, and has a wide spectroscopy of a brighter galaxy. The use of five widely separated fields reduces cosmic variance and produces statistically strong and complete statistical samples up to 10 ⁹ solar masses up to z ~ 8.

Frontier Fields Program

The program, officially named "Hubble Deep Fields Initiative 2012", aims to advance knowledge of early galaxy formation by studying high redshift galaxies in the blank fields with the aid of gravitational lenses to see "the faintest galaxies in the distant universe". The Frontier Fields web page describes the purpose of the current program:

• to reveal an inaccessible population of z = 5-10 galaxies that are 10 to 50 times dimmer intrinsically than currently known
• to establish our understanding of star mass and the star formation history of the galactic sub-L * at the earliest time
• to provide a statistically significant first morphological characterization of galaxy star formation at z & gt; 5
• to find the z & gt; 8 galaxies are quite stretched by grouping clusters to see internal structures and/or simply enlarged by lens groupings for follow-up spectroscopy.

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Public use

Anyone can apply for time on the telescope; there are no restrictions on citizenship or academic affiliation, but funding for analysis is only available to US agencies. Competition time on the telescope is very tight, with about one fifth of the proposals submitted in each cycle produce time on schedule.

Calls for proposals are issued approximately every year, with time allocated to cycles lasting approximately one year. Proposals are divided into categories; The "general observer" proposal is the most common, encompassing routine observations. "Snapshot Observations" are those where the target takes only 45 minutes or less of telescope time, including overhead such as obtaining a target. Snapshot observations are used to fill gaps in telescope schedules that can not be filled by regular GO programs.

Astronomers can create a "Target Opportunity" proposal, where observations are scheduled if the provisional event covered by the proposal occurs during the scheduling cycle. In addition, up to 10% of telescope time is defined as "discretionary director" (DD) time. Astronomers may apply to use DD time at any time of the year, and are usually given to study unexpected temporary phenomena such as supernovae.

Another use of DD time has included observations leading to the views of Hubble Deep Field and Hubble Ultra Deep Field, and in the first four cycles of telescope time, observations made by amateur astronomers.

The public image processing of Hubble data is encouraged because most of the data in the archive has not been processed into a color image.

Amateur observation

STScI's first director, Riccardo Giacconi, announced in 1986 that he intended to devote a portion of his director's discretionary time to allow amateur astronomers to use telescopes. Total time allocated for only a few hours per cycle but is very attractive to amateur astronomers.

Proposals for amateur time are strictly reviewed by amateur astronomer committees, and time is awarded only for proposals deemed to have genuine scientific rewards, not duplicate proposals made by professionals, and require the unique capabilities of the space telescope. Thirteen amateur astronomers were given time on the telescope, with observations made between 1990 and 1997. One such study was "Comet Transition - UV Search for OH". The first proposal, "The Hubble Space Telescope Study of Posteclipse Brightening and Albedo Changes on Io", is published in Icarus , a journal devoted to the study of the solar system. A second study of other amateur groups was also published in Icarus . After that time, however, budget reductions at STScI made working support by amateur astronomers untenable, and no additional amateur programs have been performed.

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Scientific results

Primary project

In the early 1980s, NASA and STScI assembled four panels to discuss key projects. This is a scientifically important project and will require significant telescope time, which will be explicitly dedicated to each project. This ensures that these special projects will be completed early, in case the telescope fails faster than expected. The panel identifies three such projects: 1) studies of nearby intergalactic media using quasar absorption channels to determine the nature of intergalactic media and gas content from galaxies and galaxy clusters; 2) In-depth secondary survey using Wide Field Camera to retrieve data whenever one of the other instruments is used and 3) a project to determine Hubble's constant in ten percent by reducing errors, both external and internal, in distance-scale calibrations.

Important discovery

Hubble has helped solve some old problems in astronomy, while also raising new questions. Some results require a new theory to explain it. Among its main mission targets is to measure the distance to a Cepheid variable star more accurately than before, and thus limit the value of the Hubble constant, the measure of the rate at which the universe expands, which is also related to its age. Prior to the launch of HST, the estimated Hubble constant typically has errors of up to 50%, but Hubble's measurements of the Cepheid variables in Virgo Clusters and other distant galaxy clusters provide measured values ​​with Ã, Â ± 10% accuracy, consistent with other more accurate measurements made since the launch of Hubble using other techniques. It is estimated that the present age is about 13.7 billion years old, but before Hubble Telescope scientists estimate ages ranging from 10 to 20 billion years.

While Hubble helped refine the age estimate of the universe, it also doubts theories about its future. Astronomers from High-z Supernova Search Team and Cosmology Project Supernova use ground-based telescopes and HST to observe distant supernovae and find evidence that, far from slowing under the influence of gravity, the expansion of the universe may actually accelerate. Three members of both groups have been awarded the Nobel Prize for their discovery. The cause of this acceleration is still poorly understood; the most common cause associated is dark energy.

The spectra and high-resolution images provided by HST have been particularly well suited to establish the prevalence of black holes in nearby galactic nuclei. While it has been hypothesized in the early 1960s that black holes will be found in the centers of several galaxies, and astronomers in the 1980s identified a number of good black hole candidates, the work done with Hubble suggests that black holes may be common to centrally- the center. of all galaxies. The Hubble program further establishes that the mass of nuclear black holes and galactic properties are closely related. The legacy of Hubble's program on black holes in galaxies is to show a deep connection between galaxies and their central black holes.

The collision of Comet Shoemaker-Levy 9 with Jupiter in 1994 by chance for astronomers came just months after Mission 1 had restored Hubble's optical performance. Hubble's image of the planet is sharper than that taken since Voyager 2's journey in 1979, and is very important in studying the dynamics of comet collisions with Jupiter, an event believed to occur every few centuries.

Other inventions made with Hubble data include proto-planetary disks (proplyds) in the Orion Nebula; evidence of the existence of extrasolar planets around a Sun-like star; and an optical colleague of gamma ray bursts that are still mysterious. HST has also been used to study objects on the outside of the Solar System, including Pluto and Eris dwarf planets.

A Hubble's unique Hubble-enabled window is Hubble's Deep Field, Hubble Ultra-Deep Field, and Hubble Extreme Deep Field images, which use unmatched Hubble sensitivity at visible wavelengths to create images from the deepest patches of the sky that ever gotten. at optical wavelength. The images reveal galaxies billions of light years away, and have produced many scientific papers, giving new windows to the early universe. Wide Field Camera 3 enhances the look of these fields in infrared and ultraviolet, supporting the discovery of some of the farthest objects ever found, such as MACS0647-JD.

The non-standard SCP 06F6 object was discovered by the Hubble Space Telescope in February 2006. During June and July 2012, US astronomers using Hubble discovered the fifth month moving around the icy Pluto ice.

In March 2015, the researchers announced that the aurora measurements around Ganymede revealed that the moon had the sea below the surface. Using Hubble to study its auroral movements, the researchers determined that a large saltwater ocean helps suppress the interaction between Jupiter and Ganymede magnetic fields. The oceans are estimated to reach 100 km (60 mi) deep, trapped under a crust of 150 km (90 mi).

On December 11, 2015, Hubble captured a picture of the reappearance of a supernova for the first time, dubbed "Refsdal", which was calculated using a different mass model of galaxy clusters whose gravity deflected supernovae light. Supernova was previously seen in November 2014 behind the galactic cluster MACS J1149.5 2223 as part of the Hubble Frontier Fields program. The astronomer finds four separate images of the supernova in a setting known as Einstein Cross. The light from this cluster has taken about five billion years to reach Earth, although the supernova exploded about 10 billion years ago. The detection of Refsdal's reappearance serves as a unique opportunity for astronomers to test their model of how mass, especially dark matter, is distributed in this cluster of galaxies.

On March 3, 2016, researchers using Hubble data announced the discovery of the farthest galaxies known to date: GN-z11. Hubble's observations took place on February 11, 2015, and April 3, 2015, as part of the CANDELS/GOODS-North survey.

Impact on astronomy

Many objective measures show the positive impact of Hubble data on astronomy. Over 15,000 papers based on Hubble's data have been published in peer-reviewed journals, and many more have appeared in the conference proceedings. Looking at the paper several years after their publication, about a third of all astronomy papers have no quotes, while only 2% of the papers based on Hubble's data have no quotes. On average, a Hubble-based paper receives about twice as many citations as papers based on non-Hubble data. Of the 200 papers published each year that receive many quotes, about 10% are based on Hubble data.

Although HST certainly helps with astronomical research, the financial costs are enormous. A study of the relative astronomical merits of various telescope sizes found that while papers based on HST data yielded 15 times as many citation as a ground-based telescope 4 m (13 ft) like Telescope William Herschel, the HST costs about 100-fold. more times to build and maintain.

Deciding between building a ground-based telescope telescope is very complex. Even before Hubble was launched, special ground-based techniques such as interferometry masking aperture had obtained high-resolution optical and infrared images than Hubble would have achieved, albeit limited to a target of approximately 10 ⁸ times brighter than the most dim targets. observed by Hubble. Since then, advances in adaptive optics have expanded the capability of high-resolution ground-based telescope imaging to cryptic infrared object imaging. The versatility of adaptive versus HST observation depends largely on the specific details of the research question in question. In the visible band, adaptive optics can only improve the field of view is relatively small, while the HST can perform high-resolution optical imaging over a wide field. Only a small portion of astronomical objects are accessible for high resolution, ground-based imagery; In contrast Hubble can perform high-resolution observations of any part of the night sky, and on objects that are highly unconscious.

Aerospace Engineering

In addition to its scientific results, Hubble has also made significant contributions to aerospace engineering, particularly the performance of systems in low Earth orbit. This insight results from the longevity of Hubble in orbit, extensive instrumentation, and the return of assemblies to Earth where they can be studied in detail. In particular, Hubble has contributed to studying the behavior of graphite composite structures in vacuum, optical contamination of residual gas and human services, radiation damage to electronics and sensors, and long-term behavior of multi-layer insulation. One lesson learned is that gyros that are assembled using pressurized oxygen to produce suspension fluids are susceptible to failure due to electric wire corrosion. Gyros are now assembled using pressurized nitrogen.

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Hubble Data

Transmission to Earth

Hubble data originally stored on spacecraft. When launched, storage facilities are ancient roll-to-roll tape recorders, but these are replaced with solid state data storage facilities while serving missions 2 and 3A. Around twice a day, the Hubble Space Telescope telescope data into satellites in the Satellite Tracking System and Geosynchronous Data Relay (TDRSS), which then downlink science data to one of two high-income 60-foot (18-meter) high-efficiency microwave antennas. located at the White Sands Test Facility in White Sands, New Mexico. From there they were sent to the Space Telescope Operations Control Center at Goddard Space Flight Center, and finally to the Space Telescope Science Institute for archiving. Every week, HST links about 140 gigabits of data.

Color image

All images from Hubble are a monochromatic gray scale, taken through various filters, each passing by a certain wavelength of light, and incorporated in each camera. Color images are created by combining separate monochrome images captured through different filters. This process can also create versions of fake colored images including infrared and ultraviolet channels, where infrared is usually given as deep red and ultraviolet is given as dark blue.

Archive

All Hubble data is finally available through the Mikulski Archive for the Space Telescope at STScI, CADC and ESA/ESAC. The data are usually exclusive - only available to the principal investigator (PI) and astronomer designated by the PI - for six months after it is taken. PIs may apply to STScI directors to extend or reduce ownership periods in some circumstances.

Observations made on the Discretionary Administrator Time are exempt from the ownership period, and immediately released to the public. Calibration data such as flat plane and dark frame are also available to the public directly. All data in the archive is in FITS format, which is suitable for astronomical analysis but not for public use. The Hubble Heritage Project processes and releases to the public a small selection of the most striking images in JPEG and TIFF formats.

Pipeline Reduction

Astronomical data taken with CCDs must undergo several calibration steps before they are suitable for astronomical analysis. STScI has developed sophisticated software that automatically calibrates the data when they are requested from the archive using the best available calibration files. On-the-fly processing means that a large data request can take a day or more to process and return. The process by which calibrated data is automatically known as 'pipeline reduction', and is increasingly common in the main observatories. Astronomers may if they want to take their own calibration files and run pipeline reduction software locally. This may be desirable when a calibration file other than the one selected automatically needs to be used.

Data analysis

Hubble data can be analyzed using many different packages. STScI manages tailor-made Space Data Analysis (STSDAS) software, which contains all the programs needed to run pipe reductions in raw data files, as well as many other astronomical image processing tools, tailored to Hubble's data needs. The software runs as an IRAF module, a popular astronomical data reduction program.

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Outreach Activities

It is always important for the Space Telescope to capture the public's imagination, given the large contribution of taxpayers to its construction and operational costs. After difficult early years when damaged mirrors greatly damaged Hubble's reputation with the public, the first service mission allowed rehabilitation as the corrected optics produced many outstanding images.

Several initiatives have helped keep people informed about Hubble's activities. In the United States, outreach efforts are coordinated by the Office for Public Outreach Space Station (STScI) Office, established in 2000 to ensure that US taxpayers see the benefits of their investment in the space telescope program. To that end, STScI operates the HubbleSite.org website. The Hubble Heritage Project, which operates outside STScI, provides the public with high-quality images of the most interesting and striking objects observed. The Heritage team consists of amateur and professional astronomers, as well as people with a background outside of astronomy, and emphasizes the aesthetic nature of Hubble images. The Inheritance Project is given a small amount of time to observe objects that, for scientific reasons, may not have images taken at sufficient wavelengths to build a colorful image.

Since 1999, the leading Hubble outreach group in Europe has become the Hubble Europe Space Information Center (HEIC). The office was established at the European Space Telescope Coordination Facility in Munich, Germany. HEIC's mission is to fulfill HST's outreach and education assignment for the European Space Agency. This work centered on the production of news and photo releases highlighting interesting Hubble results and images. It often comes from Europe, and therefore raises awareness of ESA's Hubble share (15%) and contributions of European scientists to the observatory. ESA produced educational material, including a videocast series called Hubblecast designed to share world-class scientific news with the public.

Hubble Space Telescope has won two Space Achievement Awards from the Space Foundation, for its outreach activities, in 2001 and 2010.

There is a replica of the Hubble Space Telescope at the courthouse courtyard in Marshfield, Missouri, the hometown of Edwin P. Hubble.

Picture of the celebration

The Hubble Space Telescope celebrates its 20th anniversary in space on April 24, 2010. To commemorate the occasion, NASA, ESA, and the Space Science Institute of Science (STScI) released images of the Carina Nebula.

To commemorate the 25th anniversary of Hubble in space on April 24, 2015, STScI released a Westerlund 2 cluster image, located about 20,000 light years (6,100 pc) in the constellation Carina, via its Hubble 25 site. The European Space Agency creates a dedicated 25th birthday page on its website. In April 2016, a special celebration image of the Bubble Nebula was released for Hubble's "26th birthday".

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Equipment failure

Past service missions have exchanged old instruments for new ones, both avoiding failures and allowing new types of science. Without serving missions, all instruments will ultimately fail. In August 2004, the power system of the Telescope Imaging Spectrograph (STIS) failed, leaving the instrument inoperable. The electronics were completely redundant, but the first electronic device failed in May 2001. This power supply was fixed during Mission 4 in May 2009.

Similarly, main camera software for the main Main Survey (ACS) failed in June 2006, and the backup power supply for backup failed on January 27, 2007. Only Solar Blind Channel (SBC) instruments can be operated using the electronic-1 side. A new power supply for wide angle channels is added during SM 4, but a quick test reveals this does not help high-resolution channels. The Wide Field Channel (WFC) was returned to service by STS-125 in May 2009 but the High Resolution Channel (HRC) remains offline.

HST uses gyroscopes to detect and measure rotations so as to stabilize itself in orbit and pinpoint accurately and steadily on astronomical targets. Usually, three gyroscopes are required un

Source of the article : Wikipedia