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James Webb Space Telescope

James Webb Space Telescope

The James Webb Space Telescope (JWST) is a planned orbital infrared observatory, intended (in part) to replace the aging Hubble Space Telescope. It will be jointly constructed and operated by CSA, ESA and NASA. Formerly called the Next Generation Space Telescope (or NGST), it was renamed after NASA's second administrator, James E. Webb, in 2002. The telescope's launch is planned for no earlier than June 2013.

Mission

The JWST's primary mission is to examine the infrared remnants of the big bang, and thus to make observations of an earlier state of the universe than is possible today. To achieve this, sensors of unparalleled sensitivity will be used, which in turn requires that the entire Observatory be particularly cold, and that major sources of IR interference (notably the Sun, the Earth, and the Moon) be blocked. To this end, JWST will be accompanied by a large metalized fanfold sunshield, which will unravel to block infrared radiation from these sources. The telescope's lagrangian orbit (see below) ensures that the Earth and Sun occupy the same relative position in the telescope's view, and thus make the operation of this shield possible. It is due no earlier than June 2013. After a commissioning period of approximately 6 months, the Observatory will begin the science mission, which required to last a minimum of 5 years. The potential for extension of the science mission beyond this period exists, and the Observatory is being designed accordingly.

Optics

Although JWST has a planned weight half that of the Hubble, its primary mirror (a 6.5 meter beryllium reflector) is more than 5 times larger. As this diameter is much larger than any current launch vehicle, the mirror is composed of 18 segments, which will unfold after the telescope is launched. Sensitive micromotors and wavefront sensor will position the mirror segments in the correct location, but subsequent to this initial configuration they will only rarely be moved; unlike terrestrial telescopes like the Keck which continually adjust their mirror segments using active optics to overcome the effects of gravitational loading and wind loading.

Current Status

The JWST program is in its detailed design phase. In January 2007 the program is scheduled to undergo a non-advocate review in order to determine if the proposed designs and technologies are sufficiently mature to begin the major construction phase. Prior to that major milestone in April 2006 the program will be reviewed following a replanning phase begun in August 2005. That replanning was necessitated by the cost growth revealed in Spring 2005. The primary outcomes of the replanning are significant changes in the integration and test plans, a 22-month launch delay (from 2011 to 2013), and elimination of system level testing for observatory modes at wavelength shorter than 1.7 micrometres. Other major features of the observatory are unchanged following the replanning efforts.

Construction & Engineering

Northrop Grumman Space Technology serves as the primary contractor for the development and integration of the Observatory. They are responsible for developing and building the Spacecraft, which includes both the spacecraft bus and sunshield. Ball Aerospace has been subcontracted to develop and build the Optical Telescope Element (OTE). Goddard Space Flight Center is responsible for providing the Integrated Science Instrument Module (ISIM). For the present architecture, the ISIM contains four science instruments and a fine guidance sensor. The primary science instrument of the Observatory is the NIRCam (Near InfraRed Camera), which will have a spectral coverage ranging from the edge of the visible (0.6 micrometres) through the near IR (5 micrometres). The NIRCam will also serve as the Observatory's wavefront sensor, which is required for wavefront sensing and control activities. The NIRCam is being built by a team led by the University of Arizona, with Principal Investigator Dr. Marcia Rieke. The industrial partner is Lockheed-Martin's Advanced Technology Center located in Palo Alto, California. In addition to the near IR imaging capabilities of the NIRCam, the Observatory will also perform spectrography over this range with the NIRSpec (Near InfraRed Spectrograph). The mid IR will be measured by the MIRI (Mid InfraRed Instrument), which contains both a mid IR camera and spectrometer that has a spectral range extending through 27 micrometres. The FGS (Fine Guidance Sensor) is the (non-science) instrument used to stabilize the line-of-sight of the Observatory during science observations.

External links

General Project Links
- [http://www.jwst.nasa.gov/ JWST homepage at NASA]
- [http://www.stsci.edu/jwst/ JWST homepage at STScI]
- [http://www.newscientist.com/article.ns?id=dn7423 Cost overruns put squeeze on Hubble’s successor] Science Instrument Teams
- [http://ircamera.as.arizona.edu/nircam/ NIRCam homepage at Arizona]
- [http://ircamera.as.arizona.edu/MIRI/page2.htm MIRI homepage at Arizona] Category:Space telescopes Category:Proposed spacecraft ja:ジェイムズ・ウェッブ宇宙望遠鏡

Infrared

Infrared (IR) radiation is electromagnetic radiation of a wavelength longer than that of visible light, but shorter than that of microwave radiation. The name means "below red" (from the Latin infra, "below"), red being the color of visible light of longest wavelength. Infrared radiation spans three orders of magnitude and has wavelengths between 700 nm and 1 mm.

Different regions in the infrared

IR is often subdivided into:
- near infrared NIR, IR-A DIN, 0.7–1.4 µm in wavelength, defined by the water absorption, and commonly used in fiber optic telecommunication because of low attenuation losses in the SiO₂ glass (silica) medium.
- short wavelength IR SWIR, IR-B DIN, 1.4–3 µm, water absorption increases significantly at 1450 nm
- mid wavelength IR MWIR, IR-C DIN, also intermediate-IR (IIR), 3–8 µm
- long wavelength IR LWIR, IR-C DIN, 8–15 µm)
- far infrared FIR, 15–1000 µm However, these terms are not precise, and are used differently in various studies i.e. near (0.7–5 µm) / mid (5–30 µm) / long (30–1000 µm). Especially at the telecom-wavelengths the spectrum is further subdivided into individual bands, due to limitations of detectors, amplifiers and sources. Infrared radiation is often linked to heat, since objects at room temperature or above will emit radiation mostly concentrated in the mid-infrared band (see black body). black body The common nomenclature is justified by the different human response to this radiation (near infrared = the red you just cannot see, far IR = thermal radiation), other definitions follow different physical mechanisms (emission peaks, vs. bands, water absorption) and the newest follow technical reasons (The common silicon detectors are sensitive to about 1050 nm, while InGaAs sensitivity starts around 950 nm and ends between 1700 and 2200 nm, depending on the specific configuration). Unfortunately the international standards for these specifications are not currently available.

Telecommunication bands in the infrared

Optical telecommunication in the near infrared is technically often separated to different frequency bands because of availability of light sources, transmitting /absorbing materials (fibers) and detectors.
- O-band 1260–1360 nm
- E-band 1360–1460 nm
- S-band 1460–1530 nm
- C-band 1530–1565 nm
- L-band 1565–1625 nm
- U-band 1625–1675 nm

The Earth as an infrared emitter

The Earth's surface absorbs visible radiation from the sun and re-emits much of the energy as infrared back to the atmosphere. Certain gases in the atmosphere, chiefly water vapor, but also carbon dioxide, methane, nitrous oxide, sulfur hexafluoride, and chlorofluorocarbons, absorb this infrared, and re-radiate it in all directions including back to Earth. Thus, the greenhouse effect, keeps the atmosphere and surface much warmer than if the infrared absorbers were absent from the atmosphere.

Applications

Night vision

Infrared is used in night-vision equipment, when there is insufficient visible light to see an object. The radiation is detected and turned into an image on a screen, hotter objects showing up brighter, enabling the police and military to acquire thermally significant targets, such as human beings and automobiles. Also see Forward looking infrared. Smoke is more transparent to infrared than to visible light, so firefighters use infrared imaging equipment when working in smoke-filled areas.

Other imaging

In infrared photography, infrared filters are used to capture only the infrared spectrum. Digital cameras often use infrared blockers. Cheaper digital cameras and some camera phones which do not have appropriate filters can "see" infrared, appearing as a bright white colour (try pointing a TV remote at your digital camera). This is especially pronounced when taking pictures of subjects near bright areas (such as near a lamp), where the resulting infrared interference can wash out the image.

Thermography

Infrared radiation can be used to remotely determine the temperature of objects (if the emissivity is known). This is termed thermography, or in the case of very hot objects in the NIR or visible it is termed pyrometry. Thermography (thermal imaging) is mainly used in military and industrial applications but the technology is reaching the public market in the form of infrared cameras on cars due to the massively reduced production costs.

Heating

Infrared radiation is used in Infrared saunas to heat the sauna's occupants and to remove ice from the wings of aircraft (de-icing).

Communications

IR data transmission is also employed in short-range communication among computer peripherals and personal digital assistants. These devices usually conform to standards published by IrDA, the Infrared Data Association. Remote controls and IrDA devices use infrared light-emitting diodes (LEDs) to emit infrared radiation which is focused by a plastic lens into a narrow beam. The beam is modulated, i.e. switched on and off, to encode the data. The receiver uses a silicon photodiode to convert the infrared radiation to an electric current. It responds only to the rapidly pulsing signal created by the transmitter, and filters out slowly changing infrared radiation from ambient light. Infrared communications are useful for indoor use in areas of high population density. IR does not penetrate walls and so does not interfere with other devices in adjoining rooms. Free space optical communication using infrared lasers can be a relatively inexpensive way to install a Gigabit/s communications link in urban areas, compared to the cost of burying fibre optic cable. Infrared lasers are used to provide the light for optical fibre communications systems. Infrared light with a wavelength around 1330 nm (best transmission) or 1550 nm (least dispersion) are the best choices for standard silica fibres.

Spectroscopy

Infrared radiation spectroscopy is the study of the composition of (usually) organic compounds, finding out a compound's structure and composition based on the percentage transmittance of IR radiation through a sample. Different frequencies are absorbed by different stretches and bends in the molecular bonds occurring inside the sample. Carbon dioxide, for example, has a strong absorption band at 4.2µm.

History

The discovery of infrared radiation is commonly ascribed to William Herschel, the astronomer, in the early 19th century. Herschel used a prism to refract light from the sun and detected the infrared, beyond the red part of the spectrum, through an increase in the temperature recorded on a thermometer. Simple infrared sensors were used by British, American and German forces in the Second World War as night vision aids for snipers.

External links

Journals

- [http://www.sciencedirect.com/science/journal/13504495 Infrared Physics and Technology] (Elsevier) (last access June 2005).

Web sites

- [http://scienceofspectroscopy.info/wiki/index.php?title=Infrared_Spectroscopy Infrared Spectroscopy] NASA Open Spectrum wiki site.
- [http://www.irda.org/ IrDA]Organization that creates low cost infrared data interconnection standards. Category:Electromagnetic spectrum ja:赤外線

Hubble Space Telescope

The Hubble Space Telescope is a telescope in orbit around the Earth. Its position outside the Earth's atmosphere allows it to take extremely sharp images, and since its launch in 1990, it has become one of the most important telescopes in the history of astronomy. It has been responsible for many ground-breaking observations and has helped astronomers achieve a better understanding of many fundamental problems in astrophysics. From its original conception in 1946 until its launch, the project to build a space telescope was beset by delays and budget problems. Immediately after its launch, it was found that the main mirror suffered from spherical aberration, severely compromising the telescope's capabilities. However, after a servicing mission in 1993, the telescope was restored to its planned quality and became a vital research tool as well as a public relations boon for astronomy. The future of Hubble is currently uncertain. Though the United States Congress has appropriated funds to repair the telescope in July 2005, it is possible that a servicing mission may be cancelled again. Without intervention it will re-enter the Earth's atmosphere some time after 2010. Its successor telescope, the James Webb Space Telescope, is due to be launched in 2013.

Conception, design and aims

Proposals and precursors

2013 The history of the Hubble Space Telescope can be traced back as far as 1946, when astronomer Lyman Spitzer wrote a paper entitled Astronomical advantages of an extra-terrestrial observatory. In it, he discussed the two main advantages that a space-based observatory would have over ground-based telescopes: First, the angular resolution (smallest separation at which objects can be clearly distinguished) would be limited only by diffraction, rather than by the turbulence in the atmosphere which causes stars to twinkle and is known to astronomers as seeing. Ground-based telescopes are typically limited to resolutions of 0.5–1.0 arcseconds, compared to a theoretical diffraction-limited resolution of about 0.1 arcsec for a telescope with a mirror 2.5 m in diameter. The second major advantage would be that a space-based telescope could observe infrared and ultraviolet light, which are strongly absorbed by the atmosphere. Spitzer devoted much of his career to pushing for a space telescope to be developed. In 1962 a report by the US National Academy of Sciences recommended the development of a space telescope as part of the space program, and in 1965, Spitzer was appointed as head of a committee given the task of defining the scientific objectives for a large space telescope. Space-based astronomy had begun on a very small scale following World War II, as scientists made use of the developments in rocket technology that had taken place. The first ultraviolet spectrum of the Sun was obtained in 1946. An orbiting solar telescope was launched in 1962 by the UK as part of the Ariel space program, and 1966 saw NASA's launch of the first Orbiting Astronomical Observatory (OAO) mission. OAO-1's battery failed after three days, terminating the mission, but OAO-2 carried out ultraviolet observations of stars and galaxies from its launch in 1968 until 1972, well beyond its original planned lifetime of one year. The OAO missions demonstrated the important role space-based observations could play in astronomy, and 1968 saw the development by NASA of firm plans for a space-based reflecting telescope with a mirror 3 m in diameter, known provisionally as the Large Orbiting Telescope or Large Space Telescope, with a launch slated for 1979. These plans emphasised the need for manned maintenance missions to the telescope to ensure such a costly program had a lengthy working life, and the concurrent development of plans for the reusable Space Shuttle indicated that the technology to allow this was soon to become available .

The quest for funding

The continuing success of the OAO program encouraged increasingly strong consensus within the astronomical community that the LST (Large Space Telescope, the original name) should be a major goal. In 1970 NASA established two committees, one to plan the engineering side of the space telescope project, and the other to determine the science goals of the mission. Once these had been established, the next hurdle for NASA was to obtain funding for the instrument, which would be far more costly than any Earth-based telescope. The US Congress questioned many aspects of the proposed budget for the telescope and forced cuts in the budget for the planning stages, which at the time consisted of very detailed studies of potential instruments and hardware for the telescope. In 1974, public spending cuts instigated by Gerald Ford led to Congress cutting all funding for the telescope project. In response to this, a nationwide lobbying effort was co-ordinated among astronomers. Many astronomers met congressmen and senators in person, and large scale letter-writing campaigns were organised. The National Academy of Sciences published a report emphasising the need for a space telescope, and eventually the Senate agreed to a budget half that originally refused by Congress. The funding issues led to something of a reduction in the scale of the project, with the proposed mirror diameter reduced from 3 m to 2.4 m, both to cut costs and to allow a more compact and effective configuration for the telescope hardware. A proposed precursor 1.5m space telescope to test the systems to be used on the main satellite was dropped, and budgetary concerns also prompted collaboration with the European Space Agency. ESA agreed to supply some of the instruments for the telescope as well as the solar cells which would power it and contribute approximately 15% of the costs, in return for European astronomers being guaranteed at least 15% of observing time on the telescope. Congress eventually approved funding of US$36,000,000 for 1978, and the design of the LST began in earnest, aiming for a launch date of 1983. During the early 1980s, the telescope was named after Edwin Hubble, who made one of the greatest scientific breakthroughs of the 20th century when he discovered that the universe was expanding.

Construction and engineering

universe 1979]] Once the Space Telescope project had been given the go-ahead, work on the program was divided between many institutions. Marshall Space Flight Center was given responsibility for the design, development and construction of the telescope, while the Goddard Space Flight Center was given overall control of the scientific instruments and ground control centre for the mission. Marshall commissioned optics company Perkin-Elmer to design and build the Optical Telescope Assembly (OTA) and Fine Guidance Sensors for the space telescope. Lockheed were commissioned to construct the spacecraft in which the telescope would be housed.

Optical Telescope Assembly (OTA)

The mirror and optical systems of the telescope were the most crucial part, and were designed to exacting specifications. Telescopes typically have mirrors polished to an accuracy of about a tenth of the wavelength of visible light, but because the Space Telescope was to be used for observations ranging from ultraviolet to near-infrared with ten times better resolution than the best previous telescopes, its mirror needed to be polished to an accuracy of 1/20 of the wavelength of visible light, or about 30 nanometres. Perkin-Elmer intended to use extremely sophisticated computer-controlled polishing machines to grind the mirror to the required shape, but in case their cutting-edge technology ran into difficulties, Kodak was commissioned to construct a back-up mirror using traditional mirror-polishing techniques. Construction of the mirror began in 1979, using ultra-low expansion glass. To keep the mirror's weight to a minimum it consisted of inch-thick top and bottom plates sandwiching a honeycomb lattice. Mirror polishing began in 1979 and continued until May 1981. NASA reports at the time questioned Perkin-Elmer's managerial structure, and the polishing began to slip behind schedule and over budget. To save money, NASA halted work on the back-up mirror and put the launch date of the telescope back to October 1984. The mirror was completed by the end of 1981 with the addition of a reflective coating of aluminum 75 nm thick and a protective coating of magnesium fluoride 25 nm thick, which increased the mirror's reflectivity in ultraviolet light. However, doubts continued to be expressed about Perkin-Elmer's competence on a project of this importance as their budget and timescale for producing the rest of the OTA continued to inflate. In response to a schedule described as "unsettled and changing daily," NASA postponed the launch date of the telescope until April 1985. Perkin-Elmer's schedules continued to slip at a rate of about one month per quarter, and at times delays reached one day for each day of work. NASA was forced to postpone the launch date until first March and then September 1986. By this time the total project budget had risen to $1.175 billion .

Spacecraft systems

$ The spacecraft in which the telescope and instruments were to be housed was another major engineering challenge. It would have to adequately withstand frequent passages from direct sunlight into the darkness of Earth's shadow which would generate major changes in temperature, while being stable enough to allow the extremely accurate pointing of the telescope that would be required. A shroud of multi-layered insulation keeps the temperature within the telescope stable, and surrounds a light aluminium shell in which the telescope and instruments sit. Within the shell, a graphite-epoxy frame keeps the working parts of the telescope firmly aligned. While construction of the spacecraft in which the telescope and instruments would be housed proceeded somewhat more smoothly than the construction of the OTA, Lockheed still experienced some budget and schedule slippage, and by the summer of 1985, construction of the spacecraft was 30% over budget and three months behind schedule. An MSFC report said that Lockheed tended to rely on NASA directions rather than take their own initiative in the construction .

Ground support

In 1983, the Space Telescope Science Institute (STScI) was established after something of a power struggle between NASA and the scientific community at large. STScI is operated by the Association of Universities for Research in Astronomy (AURA) and is physically located on the Homewood campus of Johns Hopkins University in Baltimore, which is one of the 32 U.S. universities and 7 international affiliates that comprise the AURA consortium. STScI is responsible for the scientific operation of the telescope and delivery of data products to astronomers, a function which NASA had wanted to keep 'in-house', but which scientists were keen to see based in an academic establishment. Engineering support is provided by NASA and contractor personnel at the Goddard Space Flight Center in Greenbelt, Maryland, 30 miles south of the STScI. Hubble's operation is monitored 24 hours per day by four teams of flight controllers who make up Hubble's Flight Operations Team. The Space Telescope European Coordinating Facility was established at Garching bei München near Munich in 1984 to provide similar support primarily for European astronomers.

Challenger disaster

In early 1986, the planned launch date of October that year looked feasible, but the Challenger disaster brought the US space program to a halt, grounding the Space Shuttle fleet and forcing the launch of Hubble to be postponed for several years. All telescope parts had to be kept in clean rooms until a launch could be rescheduled, a costly situation which pushed the overall costs of the project still higher. Eventually, following the resumption of Shuttle flights in 1988, the launch of the telescope was scheduled for 1990. In preparation for its final launch, dust which had accumulated on the mirror since its completion had to be removed with jets of nitrogen, and all systems were tested extensively to ensure they were fully functional. Finally, on 24 April 1990, shuttle mission STS-31 saw Atlantis launch the telescope successfully into its planned orbit. From its original total cost estimate of 435 million dollars (in FY77 funds), the telescope had by now cost over US$2.5 billion to construct. Hubble's cumulative costs to-date are approximately 14 billion dollars (inflation adjusted to the buying power of FY2005).

Instruments

Atlantis When launched, the HST carried five scientific instruments: the Wide Field and Planetary Camera (WF/PC), Goddard High Resolution Spectrograph (GHRS), High Speed Photometer (HSP), Faint Object Camera (FOC) and the Faint Object Spectrograph (FOS). WF/PC was a high-resolution imaging device primarily intended for optical observations. It was built by NASA's Jet Propulsion Laboratory, and incorporated a set of 48 filters isolating spectral lines of particular astrophysical interest. The instrument contained four CCD chips, three of which were 'wide field' chips while the fourth was the 'planetary camera' (PC). The PC took images at a longer effective focal length than the WF chips, giving it a greater magnification. The GHRS was a spectrograph designed to operate in the ultraviolet. It was built by the Goddard Space Flight Center in conjunction with Ball Aerospace, and could achieve a spectral resolution of 90,000 . Also optimised for ultraviolet observations were the FOC and FOS, both of which were also capable of the highest spatial resolution of any instrument on Hubble. Rather than CCDs these three instruments used photon-counting digicons as their detectors. FOC was constructed by ESA, while the Martin Marietta corporation built the FOS. The final instrument was the HSP, designed and built at the University of Wisconsin. It was optimised for visible and ultraviolet light observations of variable stars and other astronomical objects varying in brightness. It could take up to 100,000 measurements per second with a photometric accuracy of about 2% or better .

Flawed mirror

Within weeks of the launch of the telescope, the images returned showed that there was a serious problem with the optical system. Although the first images appeared to be sharper than ground-based images, the telescope failed to achieve a final sharp focus, and the best image quality obtained was drastically lower than expected. Images of point sources spread out over a radius of more than one arcsecond, instead of having a point spread function concentrated within a circle 0.1 arcsec in diameter as had been specified in the design criteria . Analysis of the flawed images showed that the cause of the problem must be that the primary mirror had been ground to the wrong shape. Although it was probably the most accurately figured mirror ever made, with variations from the prescribed curve of no more than 1/20 of the wavelength of light, it was too flat at the edges. The mirror was barely 2 micrometres out from the required shape, but the difference was catastrophic, introducing severe spherical aberration, a flaw in which light reflecting off the edges of a mirror reaches a different focus to the light reflecting off the centre. The aberration meant that images from the Space Telescope were only marginally better than the best images obtainable from the ground.

Origin of the problem

focus Working backwards from images of point sources, astronomers determined that the conic constant of the mirror was −1.0139, instead of the intended −1.00229. The same number was also derived by analysing the null correctors (instruments which accurately measure the curvature of a polished surface) used by Perkin-Elmer to figure the mirror, as well as by analysing interferograms obtained during ground testing of the mirror. A commission was established to determine how the error could have arisen and was headed by Lew Allen, director of the Jet Propulsion Laboratory. The Allen Commission found that the null corrector used by Perkin-Elmer had been incorrectly calibrated, as a spot on a metering scale where an end cap had worn away was wrongly believed to be a valid scale. The null corrector had then been wrongly spaced by 1.3 mm. During the polishing of the mirror, Perkin-Elmer had analysed its surface with two other null correctors, both of which (correctly) indicated that the mirror was suffering from spherical aberration. These tests were specifically designed to eliminate the possibility of major optical aberrations. Against written quality guidelines the company ignored these test results as it believed that the two null correctors were less accurate than the primary device which was reporting that the mirror was perfectly figured. The commission blamed the failings primarily on Perkin-Elmer. Relations between NASA and the optics company had been severely strained during the telescope construction due to frequent schedule slippage and cost overruns. NASA found that Perkin-Elmer had not regarded the telescope mirror as a crucial part of their business and were also secure in the knowledge that NASA could not take its business elsewhere once the polishing had begun. While the commission heavily criticised Perkin-Elmer for these managerial failings, NASA was also criticised for not picking up on the quality control shortcomings such as relying totally on test results from a single instrument.

Design of a solution

The flaw meant that Hubble could obtain data about as good as that achievable with a large ground-based telescope on a night of good seeing, but at a vastly greater cost. NASA and the telescope became the butt of many jokes, and the project was popularly regarded as a white elephant. However, the design of the telescope had always incorporated servicing missions, and astronomers immediately began to seek potential solutions to the problem which could be applied at the first servicing mission, scheduled for 1993. While Kodak had ground a back-up mirror for Hubble, it would have been impossible to replace the mirror in orbit, or bring the telescope temporarily back to Earth for a refit. Instead, the fact that the mirror had been ground so precisely to the wrong shape led to the design of new optical components with exactly the same error but in the opposite sense, to be added to the telescope at the servicing mission, effectively acting as 'spectacles' to correct the spherical aberration. Because of the way the instruments were designed, two different sets of correctors were required. The design of the Wide Field and Planetary Camera (WFPC) included four relay mirrors to direct light onto the four separate charge-coupled device (CCD) chips making up the camera, and so the relay mirrors on the replacement Wide Field and Planetary Camera 2 could be figured to correct the aberration. However, the other instruments lacked any intermediate surfaces which could be figured in this way, and so required an external correction device.

COSTAR

The system designed to correct the spherical aberration for light focussed at the FOC, FOS and GHRS was called the "Corrective Optics Space Telescope Axial Replacement" (COSTAR) and consisted essentially of two mirrors in the light path, one of which would be figured to correct the aberration . To fit the COSTAR system onto the telescope, one of the other instruments had to be removed, and astronomers selected the High Speed Photometer to be sacrificed. During the first three years of the Hubble mission, before the optical corrections could be fitted, the telescope still carried out a large number of observations. Spectroscopic observations in particular were not too badly affected by the aberration, but many imaging projects were cancelled as the space telescope no longer gave decisive advantages over ground-based observations. Despite the setbacks, the first three years saw numerous scientific advances as astronomers worked to optimise the results obtained using sophisticated image processing techniques.

Servicing missions and new instruments

image processing

Servicing mission 1

The telescope had always been designed so that it could be regularly serviced, but after the problems with the mirror came to light, the first servicing mission assumed a much greater importance, as the astronauts would have to carry out extensive work on the telescope to install the corrective optics. The seven astronauts selected for the mission were trained intensively in the use of the hundred or so specialised tools which would need to be used. The mission (STS-61) took place in December 1993, and involved installation of several instruments and other equipment over a total of 10 days. Most importantly, the High Speed Photometer was replaced with the COSTAR corrective optics package, and WFPC was replaced with the Wide Field and Planetary Camera 2 (WFPC2), with its internal optical correction system. In addition, the solar arrays and their drive electronics were replaced, as well as four of the gyroscopes used in the telescope pointing system, two electrical control units and other electrical components, and two magnetometers. The onboard computers were upgraded, and finally, the telescope's orbit was boosted, having been slowly decaying for three years due to drag in the tenuous upper atmosphere. drag On January 13, 1994, NASA declared the mission a complete success and showed the first of many much sharper images . The mission had been one of the most complex ever undertaken, involving five lengthy periods of extravehicular activity, and its resounding success was an enormous boon for NASA, as well as for the astronomers who now had a fully capable space telescope.

Subsequent servicing missions

Subsequent servicing missions were less dramatic, but each gave the space telescope new capabilities. Servicing Mission 2 (STS-82) in February 1997 replaced the GHRS and the FOS with the Space Telescope Imaging Spectrograph (STIS) and the Near Infrared Camera and Multi-Object Spectrometer (NICMOS), replaced an Engineering and Science Tape Recorder with a new Solid State Recorder, repaired thermal insulation and again boosted Hubble's orbit. NICMOS contained a heat sink of solid nitrogen to reduce the thermal noise from the instrument, but shortly after it was installed, an unexpected thermal expansion resulted in part of the heat sink coming into contact with an optical baffle. This led to an increased warming rate for the instrument and reduced its original expected lifetime of 4.5 years to about 2 years. Servicing Mission 3A (STS-103) took place in December 1999, replaced all six gyroscopes (one had failed and rendered the telescope unusable just weeks before the mission), replaced a Fine Guidance Sensor and the computer, installed a Voltage/temperature Improvement Kit (VIK) to prevent battery overcharging, and replaced thermal insulation blankets. The new computer was based on a space-qualified Intel 486 and permits some computing tasks that were previously performed by computers on the ground to be handled on board the spacecraft. Servicing Mission 3B (STS-109) in March 2002 saw the installation of a new instrument, with the FOC being replaced with the Advanced Camera for Surveys (ACS), and also saw the revival of NICMOS, which had run out of coolant in 1999. A new cooling system was installed which reduced the instrument's temperature enough for it to be usable again, although it was not as cold as its original design called for. The mission replaced the solar arrays for a third time, with the new arrays being smaller but generating more power. The new arrays were derived from those built for the Iridium comsat system and were only two-thirds the size of the old arrays, resulting in less drag against the tenuous reaches of the upper atmosphere, while providing 30% more power. The additional power allowed all instruments on board the Hubble to be run simultaneously, and reduced a vibration problem that occurred when the old, less rigid arrays entered and left direct sunlight. Hubble's Power Distribution Unit was also replaced in order to correct a problem with sticky relays, a procedure that required the complete electrical power down of the spacecraft for the first time since it was launched. The completion of this servicing mission considerably enhanced Hubble's capabilities. The two instruments primarily affected by the mission, ACS and NICMOS, together imaged the Hubble Ultra Deep Field in 2003 to 2004.

Scientific results

Important discoveries

Hubble Ultra Deep Field] Hubble has helped to resolve some long-standing problems in astronomy, as well as turning up results that have required whole new theories to explain them. Among its primary mission targets was to measure distances to Cepheid variable stars more accurately than ever before, and thus constrain the value of the Hubble constant, the measure of the rate at which the universe is expanding, which is also related to its age. Before the launch of Hubble, estimates of the Hubble constant typically had errors of up to 50%, but Hubble measurements of Cepheid variables in the Virgo cluster and other distant galaxy clusters provided a measured value with an accuracy of 10%, which is consistent with other accurate measurements made since Hubble's launch using other techniques. While Hubble helped to refine the age of the universe, it also threw doubt on its future. Astronomers using the telescope to observe distant supernovae uncovered evidence that far from decelerating under the influence of gravity, the universe may in fact be accelerating. This acceleration was later confirmed by other ground-based and space-based telescopes, but the cause of this acceleration is currently very poorly understood. The collision of Comet Shoemaker-Levy 9 with Jupiter in 1994 was very fortuitously timed for astronomers, coming just a few months after Servicing Mission 1 had restored Hubble's optical performance. Hubble images of the planet were sharper than any taken since the passage of Voyager 2 in 1979, and were crucial in studying the dynamics of the collision of a comet with Jupiter, an event believed to occur once every few centuries. Other major discoveries made using Hubble data include proto-planetary disks (proplyds) in the Orion Nebula; evidence for the presence of extrasolar planets around sun-like stars; and the optical counterparts of the still-mysterious gamma-ray bursts.

Impact on astronomy

gamma-ray burst Many objective measures show the enormous impact of Hubble data on astronomy. Over 4,000 papers based on Hubble data have been published in peer-reviewed journals, and countless more have appeared in conference proceedings. Looking at papers several years after their publication, about one-third of all astronomy papers have no citations, while only 2% of papers based on Hubble data have no citations. On average, a paper based on Hubble data receives about twice as many citations as papers based on non-Hubble data. Of the 200 papers published each year which receive the most citations, about 10% are based on Hubble data . Although the HST has clearly had a significant impact on astronomical research, the financial cost of this impact has been very large. A study on the relative impacts on astronomy of different sizes of telescopes found that while papers based on HST data generate 15 times as many citations as a 4 m ground-based telescope such as the William Herschel Telescope, the HST cost about 100 times as much to build and maintain . The development of adaptive optics in recent years means that ground-based telescopes can take images approaching the sharpness of Hubble images, at much lower cost, and this has been a key consideration in the debate about the future of space telescopes (see below).

Using the telescope

Anyone can apply for time on the telescope; there are no restrictions on nationality or academic affiliation. Competition for time on the telescope is extremely intense, and the ratio of time requested to time available (the oversubscription ratio) typically ranges between 6 and 9. Calls for proposals are issued roughly annually, with time allocated for a 'cycle' lasting approximately one year. Proposals are divided into several categories; 'general observer' proposals are the most common, covering routine observations. 'Snapshot observations' are those in which targets require only 45 minutes or less of telescope time, including the overheads of acquiring the target and so on; snapshot observations are used to fill in gaps in the telescope schedule which cannot be filled by regular GO programs. Astronomers may make 'Target of Opportunity' proposals, in which observations are scheduled if a transient event covered by the proposal occurs during the scheduling cycle. In addition, up to 10% of the telescope time is designated Director's Discretionary (DD) Time. Astronomers can apply to use DD time at any time of year, and it is typically awarded for study of unexpected transient phenomena such as supernovae. Other uses of DD time have included the observations that led to the production of the Hubble Deep Field and Hubble Ultra Deep Field, and in the first four cycles of telescope time, observations carried out by amateur astronomers (discussed below).

Observation scheduling

Hubble Ultra Deep Field Scheduling observations for Hubble is not a simple matter. It is situated in a low-Earth orbit so that it can be reached by the Space Shuttle for servicing missions, but this means that most astronomical targets are occulted by the Earth for slightly less than half of each orbit. Observations cannot take place when the telescope passes through the South Atlantic Anomaly due to elevated radiation levels, and there is a also a sizable exclusion zone around the Sun, and for some instruments around the Moon and Earth, which cannot be observed. However, there is a so-called continuous viewing zone (CVZ), at roughly 90 degrees to the plane of Hubble's orbit, in which targets are not occulted for long periods. Due to the precession of the orbit, the location of the CVZ moves slowly over a period of eight weeks. Because the limb of the Earth is always within about 30° of regions within the CVZ, the brightness of scattered earthshine may be elevated for long periods during CVZ observations. Because Hubble orbits in the upper atmosphere, its orbit changes over time in a way that is not accurately predictable. The density of the upper atmosphere varies according to many factors, and this means that Hubble's predicted position for six week's time could be in error by up to 4,000 km. Observation schedules are typically finalised only a few days in advance, as a longer lead time would mean there was a chance that the target would be unobservable by the time it was due to be observed .

Amateur observations

The first director of the STScI, Riccardo Giacconi, announced in 1986 that he intended to devote some of his DD time to allowing amateur astronomers to use the telescope. The total time to be allocated was only a few hours per cycle, but excited great interest among amateur astronomers. Proposals for amateur time were stringently peer reviewed by a committee of leading amateur astronomers, and time was awarded only to proposals with genuine scientific merit which did not duplicate proposals made by professionals and which required the unique capabilities of the space telescope. In total, 13 amateur astronomers were awarded time on the telescope, with observations being carried out between 1990 and 1997. After that time, however, budget reductions at STScI made the support of work by amateur astronomers untenable, and no further amateur programs have been carried out .

Hubble data

Transmission to Earth

Hubble data is initially stored on the spacecraft. When launched, the storage facilities were old-fashioned reel-to-reel tape recorders, but these were replaced by solid state data storage facilities during servicing missions 2 and 3A. From the onboard storage facilities, data is transferred to the ground via the Tracking and Data Relay Satellite System, a system of satellites designed so that satellites in low-Earth orbit can communicate with their mission control facilities during about 85% of their orbit. Data is transmitted to the TDRSS ground station and then on to the Goddard Space Flight Center for archiving.

Pipeline reduction

Astronomical data taken with CCDs must undergo several calibration steps before it is suitable for astronomical analysis. STScI has developed sophisticated software which automatically calibrates data when it is requested from the archive using the best calibration files available. This 'on-the-fly' processing means that large data requests can take a day or more to be processed and returned. The process by which data is calibrated automatically is known as 'pipeline reduction', and is increasingly common at major observatories. Astronomers may if they wish retrieve the calibration files themselves and run the pipeline reduction software locally. This may be desirable when calibration files other than those selected automatically need to be used.

Data analysis

Hubble data can be analysed using many different packages, but STScI develops the custom-made STSDAS (Space Telescope Science Data Analysis System) software. The software contains all the programs needed to run pipeline reduction on raw data files, as well as many other astronomical image processing tools, tailored to the requirements of Hubble data. The software runs as a module of IRAF, a popular astronomical data reduction program, which runs only under various flavours of Linux and Mac OS X.

Outreach activities

Mac OS X It has always been important for the Space Telescope to capture the public's imagination, given the considerable contribution of taxpayers to its construction and operational costs. After the difficult early years when the faulty mirror severely dented Hubble's reputation with the public, the first servicing mission allowed its rehabilitation as the corrected optics produced numerous remarkable images. Several initiatives have helped to keep the public informed about Hubble activities. The Hubble Heritage Project was established to produce high-quality images for public consumption of the most interesting and striking objects observed. The Heritage Team is composed of amateur as well as professional astronomers as well as people with backgrounds outside astronomy and emphasises the artistic nature of Hubble images. Hubble has also been used to photograph the Apollo 15 and 17 landing sites in the hope that parts of the lunar landing modules would be visible. In addition, STScI maintains several comprehensive websites for the general public containing Hubble images and information about the observatory. The outreach efforts are coordinated by the Office for Public Outreach, which was established in 2000 to ensure that US taxpayers saw the benefits of their investment in the space telescope program. The Heritage Project is granted a small amount of time to observe objects which, for scientific reasons, may not have images taken at enough wavelengths to construct a full colour image. In 2001, to celebrate the 11th anniversary of the launch of Hubble, NASA polled internet users to find out what they would most like Hubble to observe, and they overwhelmingly selected the Horsehead Nebula [http://heritage.stsci.edu/2001/12/caption.html]. A Heritage Project image of the nebula was released on 24 April 2001, the 11th anniversary of the launch.

Future

Equipment failure

2001]] Past servicing missions have exchanged old instruments for new ones, both avoiding failure and making possible new types of science. Without servicing missions, all of the instruments will eventually fail. On August 3, 2004, the power system of the Space Telescope Imaging Spectrograph (STIS) failed, rendering the instrument inoperable. The electronics had originally been fully redundant, but the first set of electronics failed in May 2001. It seems unlikely that any science functionality can be salvaged without a servicing mission. Hubble uses gyroscopes to stabilize itself in orbit and point accurately and steadily at astronomical targets. Normally, three gyroscopes are required for operation; observations are still possible with two gyros, but the area of sky that can be viewed would be somewhat restricted, and observations requiring very accurate pointing would be more difficult. In 2005, it was decided to switch to two-gyroscope mode for regular telescope operations as a means of extending the lifetime of the mission. The switch to this mode was made on August 31, 2005, leaving Hubble with two gyroscopes in use and two on backup. Estimates of the failure rate of the gyros indicate that Hubble may be down to one gyro by 2008, after which the telescope would be rendered unusable. In addition to predicted gyroscope failure, Hubble will eventually require a change of batteries. A robotic servicing mission including this would be tricky, as it requires many operations, and a failure in any might result in irreparable damage to Hubble. However, the observatory was designed so that during Shuttle servicing missions it would receive power from a connection to the Space Shuttle, and this fact may be utilized by adding an external power source (an additional battery) rather than changing the internal ones [http://news.bbc.co.uk/2/hi/science/nature/3652627.stm].

Orbital decay

Hubble orbits the Earth in the extremely tenuous upper atmosphere, and over time its orbit decays due to drag. If it is not re-boosted by a shuttle or other means, it will re-enter the Earth's atmosphere sometime between 2010 and 2032, with the exact date depending on how active the Sun is and its impact on the upper atmosphere. The state of Hubble's gyros also impacts the re-entry date, as a controllable telescope can be made to minimize atmospheric drag. Not all of the telescope would burn up on re-entry. Parts of the main mirror and its support structure would probably survive, leaving the potential for damage or even human fatalities (estimated at up to a 1 in 700 chance of human fatality for a completely uncontrolled re-entry). Addition of an external propulsion module to allow controlled re-entry is currently being investigated by NASA. It would not have to be executed until the expected natural re-entry date, after Hubble has completed its operational lifetime. One potential model involves a Pac-Man shaped unit entirely enclosing the satellite. Alternatively, instead of being used to control re-entry, the propulsion module could boost the telescope into a much higher orbit, in which it could remain indefinitely. Another possibility for safely de-orbiting Hubble is retrieval by a space shuttle. The Hubble telescope would then most likely be displayed in the Smithsonian Institution. The problems with this method are the cost of a shuttle flight (about US$500 million by some estimates) and risk to a shuttle's crew. In the wake of the Space Shuttle Columbia disaster, NASA's astronaut office is wary of risking a shuttle crew simply to retrieve a museum-bound telescope [http://www.space.com/businesstechnology/technology/hubble_grunsfeld_0306731.html]. Also, this mission would require a rebuild of the cargo space of the space shuttle sent to retrieve Hubble, since the only space shuttle unmodified since Hubble's launch (and therefore able to hold it in its cargo space) was the destroyed Columbia shuttle.

Debate over final servicing mission

The Space Shuttle was originally scheduled to visit Hubble again in February 2005. The tasks of this servicing mission would include adding fresh gyroscopes and replacing the Wide Field and Planetary Camera 2 with a new Wide Field Camera 3. However, then-NASA Administrator Sean O'Keefe decided that, in order to prevent a repeat of the Columbia disaster, all future shuttles must be inspected externally on orbit before re-entry, a task which cannot 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, and so future manned service missions were cancelled. This decision was assailed by numerous astronomers, who felt that the Hubble telescope was valuable enough to merit the risk. In particular, Hubble is one of the few telescopes currently operating which can image in the ultraviolet, and its successor telescope will not be launched until possibly several years after Hubble's demise. However, many astronomers feel strongly that the servicing of Hubble should not take place if the costs of the servicing come from the budget of its more important successor telescope, the JWST, as that could well cripple future space astronomy. The break in space observing capabilities between the decommissioning of Hubble and the commissioning of a successor is of major concern to some astronomers, given the great scientific impact of many space telescope observations. On 29 January 2004, Sean O'Keefe said that that he would 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. On 13 July 2004, an official panel from the National Academy of Sciences made the recommendation that the Hubble telescope be preserved despite the apparent risks. Their report urged "NASA should take no actions that would preclude a space shuttle servicing mission to the Hubble Space Telescope". On August 11, 2004, Sean O'Keefe requested the Goddard Space Flight Center to prepare a detailed proposal for a robotic service mission. It is expected that the proposal will take 12 months to produce—any such mission, likely to cost in excess of $1 billion, will not take place before 2007. The arrival, in April 2005, of the new NASA Administrator, Mike Griffin, has changed the status of both of the manned and unmanned rescue missions. Griffin has stated that he will reconsider the possibility of a manned servicing mission. Soon after his appointment, he authorized NASA's Goddard Space Flight Center to proceed with preparing for a manned Hubble maintenance flight, saying he would make the final decision on this flight after the next two shuttle missions. At the same time, Griffin decided to cancel the plans for a robotic rescue mission, calling it "not feasible." [http://www.washingtonpost.com/wp-dyn/content/article/2005/04/12/AR2005041201646.html]

Solutions

NASA and the ESA are currently investigating building a follow on to the Hubble Space Telescope called the Hubble Origins Probe http://www.pha.jhu.edu/hop/. If approved, it would not be ready for launch until 2010. The probe would very likely use an Atlas V rocket for its ride to orbit. It would also incorporate new technology into its design to reduce its weight in respect to the original. The mission would be a one time five year run and would receive no servicing from the Space Shuttle. The mission is still being debated and is still absent of any funding. Critics argue that the money would be better spent on a modern cost-effective space telescope design like the JWST rather than re-using the outdated design of Hubble. It may never be built.

References

- Benn C.R., Sánchez S.F. (2001), Scientific Impact of Large Telescopes, Publications of the Astronomical Society of the Pacific, v. 113, p.385
- Bless R.C., Walter L.E., White R.L. (1992), High Speed Photometer Instrument Handbook, v 3.0, STSci
- Brandt J.C. et al (1994), The Goddard High Resolution Spectrograph: Instrument, goals, and science results, Publications of the Astronomical Society of the Pacific, v. 106, p. 890-908
- Burrows C.J. et al (1991), The imaging performance of the Hubble Space Telescope, Astrophysical Journal, v.369, p.21
- Dunar A.J., Waring S.P. (1999), Power To Explore -- History of Marshall Space Flight Center 1960-1990, US Government Printing Office, ISBN 0160589924 (Chapter 12, Hubble Space telescope: [http://history.msfc.nasa.gov/book/chpttwelve.pdf]{{{{{{{{{{

CSA

CSA has these meanings:
- Canadian Sablefish Association
- Canadian Soccer Association
- Canadian Space Agency
- Canadian Standards Association
- Casting Society of America
- Central simple algebra
- Child Support Agency
- Chinese Students Association
- Clinical Skills Assessment
- Common Scrambling Algorithm
- Common Support Aircraft
- communications streaming architecture
- Community-supported agriculture
- Confederate States Army
- Confederate States of America
- Conseil Supérieur de l'Audiovisuel, French state organism which monitors the content of television and radio networks)
- Content Sharing Agreement
- Controlled Substances Act
- Corporación Scouts de Antioquia (Antioquias' Boy Scouts), organization of Boy Scouts of the Colombian province of Antioquia
- Corporate Sector Authority
- The Covenant, The Sword, and The Arm of the Lord, Arkansan white supremacist group prolific in the '70s and early '80s
- Crime Syndicate of America
- Cub Scouts of America
- Czech Airlines
- Cross Sectional Area

Esa

:This article is about the European Space Agency. For other meanings of ESA, see ESA (disambiguation). The European Space Agency (ESA), established in 1975,is an inter-governmental organisation dedicated to exploration of space with currently 17 member states. Its headquarters are in Paris, France. ESA has a staff (excluding sub-contractors and national space agencies) of about 1900 with a budget of 3 billion euros in 2005. ESA's spaceport is the Guiana Space Centre in Kourou, French Guiana, a site chosen because it is close to the equator from which commercially important orbits are easier to access. During the era of Ariane 4 ESA gained the position of market leader in commercial space launches and in recent years ESA has established itself as the major competitor of NASA in space exploration. ESA science missions are based at ESTEC in Noordwijk, Netherlands, Earth Observation missions at ESRIN in Frascati, Italy, ESA Mission Control (ESOC) is in Darmstadt, Germany, and the European Astronauts Centre (EAC), that trains astronauts for future missions is situated in Cologne, Germany.

History and goals

- [http://www.esa.int/esapub/sp/sp1235/sp1235v1web.pdf European Space Agency History 1958-1987 Volume I 458 pages PDF]
- [http://www.esa.int/esapub/sp/sp1235/sp1235v2web.pdf European Space Agency History 1958-1987 Volume II 691 pages PDF]

ESA's mission

Since the Cold War ended with the fall of the Soviet Union's "iron curtain," space agencies around the world had to refocus and revise their visions and goals. In an interview with JAXA, the Japanese Space Agency, Jean-Jacques Dordain ESA's Director General (since 2003) outlined briefly the European Space agency's mission:

Today space activities are pursued for the benefit of citizens, and citizens are asking for a better quality of life on earth. They want greater security and economic wealth, but they also want to pursue their dreams, to increase their knowledge, and they want younger people to be attracted to the pursuit of science and technology.

I think that space can do all of this: it can produce a higher quality of life, better security, more economic wealth, and also fulfil our citizens' dreams and thirst for knowledge, and attract the young generation. This is the reason space exploration is an integral part of overall space activities. It has always been so, and it will be even more important in the future.

History of ESA's foundation

Jean-Jacques Dordain After the Second World War many European scientists had left Europe in order to work either in the US or the Soviet Union. Although the booming recovering process of the 50s made it possible for European countries to invest into research and specifically into space related activities, European scientists realised solely national projects would not be able to compete with the two major superpowers. In 1958, only months after the Sputnik shock, Eduardo Amaldi and Pierre Auger, two prominent members of the European scientific community at that time, met to discuss the foundation of a common European space agency. The European nations decided to have two different agencies, one concerned to develop a launch system ELDO (European Launch Development Organisation) and the precursor of the European Space Agency, ESRO (European Space Research Organisation) that was established on March 20, 1964 per an agreement signed on June 14, 1962. From 1968 to 1972 ESRO could celebrate its first successes. Seven research satellites were brought into orbit, all by US launch systems. The ESRO's successor organisation ESTEC (European Space Research and Technology Centre, based in Noordwijk, the Netherlands) is still a part of ESA, though ESA itself is a much bigger organisation today. ESA in its current form was founded in 1974, when ESRO was merged with ELDO. ESA was constituted of 11 founding members including not only then EU-members (correctly stated: EC-members) but also Switzerland and Norway. ESA launched its first major scientific mission in 1975, Cos-B a space probe monitoring gamma-ray emissions in the universe.

From its beginnings to a leading institution

Cos-B Beginning in the 1970s, when the space race between the US and the Soviet Union had tuned down and space budgets were cut dramatically in both superpowers, ESA established itself as a forerunner in space exploration. ESA joined NASA and the UK in the IUE, the world's first high-orbit telescope, which was launched in 1978 and operated very successfully for 18 years. A number of successful Earth-orbit projects followed, and in 1986 ESA began Giotto, its first deep-space mission, to study the Comets Halley and Grigg-Skejllerup. Hipparcos, a star-mapping mission, was launched in 1989 and in the 1990s SOHO, Ulysses and the Hubble Space Telescope were all jointly carried out with NASA. Recent scientific missions in cooperation with NASA include the Cassini-Huygens space probe, to which ESA contributed by building the Titan landing module Huygens. As the successor of the ELDO, ESA has also constructed rockets for unmanned scientific and commercial payloads. Ariane 1, launched in 1979, brought mostly-commercial payloads into orbit from 1984 onward. The next two developments of the Ariane rocket were intermediate stages in the development of a more advanced launch system, the Ariane 4, which operated between 1988 and 2003 and would have established ESA as the world leader in commercial space launches. However its successor, the currently used Ariane 5 rocket, had starting problems. The first launch of the lightest variation of Ariane 5 in 1996 failed as did the first flight of the Ariane 5 ECA, a heavy modification of Ariane, in 2002. Despite these failures the Ariane 5 rocket has established itself within the heavily competitive commercial space launch market since its first successful flight in 1997 and prospectively will reach 25 successful launches by 2006. The beginning of the new millennium saw ESA become NASA's main competitor in scientific space research. While ESA had relied on cooperation with NASA in previous decades, especially the 1990s, changed circumstances (such as tough legal restrictions on information sharing by the American military) led to decisions to rely more on itself and on cooperation with Russia. A recent press issue thus stated:

Russia is ESA's first partner in its efforts to ensure long-term access to space. There is a framework agreement between ESA and the government of the Russian Federation on cooperation and partnership in the exploration and use of outer space for peaceful purposes, and cooperation is already under way in two different areas of launcher activity that will bring benefits to both partners.

Most notable for its new self-confidence are ESA's own recent successful missions Smart-1, a probe testing cutting-edge new space propulsion technology, the Mars Express mission as well as the development of the Ariane 5 rocket.

ESA's further goals and aims

Ariane 5]] ESA has ambitious space plans that may be divided into three large categories. First, ESA will maintain its scientific and research projects (e.g. tests and developments of new propulsion systems), try to find ways to reduce costs for their rocket fleet while enhancing their capacities, honour its commitments regarding the ISS and engage in further space exploration like the Venus Express mission that was launched in late 2005. The second category has many parallels to NASA's plans and constitutes of astronomy-space missions such as the Planck probe studying the cosmic microwave background (2007), the Herschel space observatory (2006), Corot that will be a milestone in the search for exoplanets and is due to launch in June 2006 or the Darwin interferometer. Darwin will mark the last step in the ultimate goal of discovering more exoplanets and the first Earth-size planet outside our solar system. While the projects described above are more or less similar in their structure and aim as NASA's and other space agencies' plans, the ESA's Mars project is different. The Aurora Programme lays out a time table for future missions to Mars, however in contrast to NASA's plans there is no emphasis on manned or unmanned lunar missions, it rather includes several flagship missions designed to develop and test technology needed for a manned European Mars mission currently planned for 2030. Among these flagship missions is ExoMars, a mission involving a Mars rover. Until 2005 ExoMars was planned to be a joint mission between NASA and ESA, however obstacles such as American technology law that prohibits sharing of classified space technology information led to ESA deciding to go for it alone. The mission is currently planned to launch in 2011. An even more ambitious Mars project is the Mars Sample Return Mission, that is planned as a follow-up mission to ExoMars. It will involve the first time a probe will return of samples from another planet, making it necessary to construct an ascent module that is capable of starting into Mars orbit and dock with the original probe.

Member countries, budget and organisations

Member countries and strategic partners

ExoMars ESA comprises the national space organisations and other entities of these seventeen countries: Austria, Belgium, Denmark, Finland, France, Germany, Greece, Ireland, Italy, Luxembourg, the Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and the United Kingdom. Many countries are likely to join ESA in the coming years, especially the countries who were part of the EU-enlargement in 2004. In addition ESA entered into important partnership agreements with non-member countries:
- Hungary and the Czech Republic signed the five-year Plan for European Cooperating State (PECS), that is aimed at preparing the states for full membership. Their firms can bid for and receive contracts to work on programmes. The countries can participate in almost all programmes, except for the Basic Technology Research Programme. The membership fees are much lower than with full membership.
- Poland and Romania are likely to be the next to sign PECS documents.
- Since January 1, 1979, Canada has the special status of cooperating state with the ESA. By virtue of this accord, Canada takes part in ESA's deliberative bodies and decision-making and also in ESA's programmes and activities. Canadian firms can bid for and receive contracts to work on programmes. The accord has a provision ensuring a fair industrial return to Canada. See also: Canadian Space Agency
- ESA has entered into a major joint venture with Russia (see below).
- Since China started to invest more money into space activities, the Chinese Space Agency has sought international partnerships. ESA is, beside the Russian Space Agency, one of its most important partners. Recently the two space agencies cooperated in the development of the Double Star Mission.

Relationship with the EU

Currently, ESA is not within the structures of the European Union (EU) — note that its membership contains non-EU countries such as Switzerland and Norway. There are ties between the organisations, with various agreements in place and being worked on, to establish the legal status of ESA with regard to the EU . There are common goals between ESA and the EU, and ESA has an EU liaison office in Brussels. The EU in particular wishes to secure political control of Europe's space access, an issue of vital importance for Europe's political and economic role in the world.

Budget

European Union beginning in 2007]] The budget of ESA was announced as €2.977 billion for 2005. This constitutes a ten per cent increase in the budget in comparison with 2004. The increase will be largely invested in ESA's launch vehicles that are currently the most expensive part of ESA's activities (Twenty-two per cent of the budget goes into launch vehicles; human space flight is second in budget expenditures). In 2005, the three largest contributors, together funding two thirds of ESA's budget, are France (29.3%), Germany (22.7%) and Italy (14.2%). In comparison with NASA's budget of sixteen thousand million dollars (€13 thousand million), ESA's budget of €3 thousand million superficially looks considerably less. However in order to make a true comparison more factors have to be considered: # Unlike the US, Europe maintains both ESA and national space agencies (see below). These national space agencies do have considerable budgets provided for scientific research and joint projects with ESA. For instance, the German Aerospace Center (German acronym DLR) has a budget for 2005 of €760 million and the French CNES had a budget of €1.3 thousand million in 2004. Taking the budgets of all national space agencies together and adding them to ESA's figures would at least double the amount spent by Europe for space related activities. # Considerable costs are incurred by NASA in maintaining the ageing Space Shuttle. A single Space Shuttle launch costs more than $600 million and during the last decades up to one third of NASA's budget had to be invested in the Shuttle to keep it flying (for 2005, $5 thousand million are allocated for the Space Shuttle constituting 30% of the budget ). Although ESA had plans for an own manned spacecraft such as Hermes, it has never actually developed or maintained a manned launch system, rather it has paid for seats on the American and Russian spacecrafts, and therefore was and is not burdened with the costs of human space flights. In the last years ESA has become interested in the Russian built but jointly owned Soyuz (controlled by Starsem it is owned by EADS, ESA and the Russian Space Agency) that is capable of human space flight and will further decrease costs for European manned missions (see below). One Soyuz launch costs approximately $30 million # While NASA's funding of many research projects has been cut in the recent years and months in order to free money for the development of the Crew Exploration Vehicle and for the retirement of the Space Shuttle, ESA's investment in research and development projects has increased steadily in the last years. With the joining of new ESA member states the budget is likely to increase further by a large rate in the next years. # After the space race activities of the 1960s and early '70s, NASA has maintained a huge administration and bureaucracy that still burdens both current projects and NASA budgets. ESA was never involved in large-scale political activity such as the space race, it therefore has always had a small and efficient structure and agency level comparable to a private company. In terms of absolute Euros (Dollars), ESA has the second largest budget after NASA in the World, with the Japanese JAXA having annual funds of €1.6 thousand million at its disposal taking the third place, followed by the ambitious Chinese Space Agency with around €1 billion. However, this comparison has to be tempered with the fact that the actual purchasing power parity cost is a more meaningful measure of the sizes of various space programs. Since space programs are by their very nature extremely hi-tech labor intensive, the cost of the labor dominates the expenditure costs in developed countries. With a purchasing power parity of 5.5 for India and 4.5 for China, their Space programs are actually worth 3 thousand million and 9 thousand million Euros approximately, thus making them larger than both ESA and Japanese space programs. Although the Russian Space Agency is still considered as one of the most experienced space agencies, its budget is dramatically low reaching not more than $800-900 million per year approximately the same amount the Indian Space Agency can rely on. One point in favor of the Russian Space Agency is that just like the Chinese and the Indian space programs, it's budget is growing rapidly largely stemming from the high growth rates of the Russian economy, which leads to increasing amounts of money available with the government.

Notable national space agencies

- The Centre National d'Études Spatiales (CNES) (National Centre for Space Study) is the French government space agency (administratively, a "public establishment of industrial and commercial character"). Its headquarters are in central Paris.
- The Italian Space Agency (Agenzia Spaziale Italiana or ASI) was founded in 1988 to promote, coordinate and conduct space activities in Italy. Operating under the Ministry of the Universities and of Scientific and Technological Research, the agency cooperates with numerous entities active in space technology and with the president of the Council of Ministers. Internationally, the ASI provides Italy's delegation to the Council of the European Space Agency and to its subordinate bodies.
- The German Aerospace Center (DLR) (German: Deutsches Zentrum für Luft- und Raumfahrt e.V.) is the national research centre for aviation and space flight of the Federal Republic of Germany and of other member states in the Helmholtz Association. Its extensive research and development projects are included in national and international cooperative programmes. In addition to its research projects, the centre is the assigned space agency of Germany bestowing headquarters of German space flight activities and its associates.
- The British National Space Centre (BNSC) is a partnership of the UK government departments which are active in space. Through the BNSC the partners provide delegates to represent the UK on the various ESA governing bodies. Each partner funds its own programme.

Launch vehicle fleet

British National Space Centre in March 2004.]] ESA has made great progress towards its goal of having a complete fleet of launch vehicles in service, competing in all sectors of the launch market. ESA's fleet will soon consist of three major rocket designs, Ariane 5, Soyuz and Vega. Rocket launches are carried out by Arianespace, an ESA subsidiary (a minority share is held by EADS as well), at ESA's spaceport in French Guiana. Because many communication satellites have equatorial orbits, launches from French Guiana are able to take larger payloads into space than from other northern spaceports.

Ariane 5

The Ariane 5 rocket is the primary launcher of the ESA. Its maximum estimated payload is 6-10 metric tons to GTO and up to 21 metric tons to LEO. The launch craft has been in service since 1997 and replaced the Ariane 4. The Ariane rocket exists in several specifications, the heaviest one of these is the Ariane 5 ECA that has been successfully launched in February 2005 for the first time, after it failed during its first test flight in 2002. ESA's Ariane 1, 2, 3 and 4 launchers (the latter of which was ESA's long time workhorse) have been retired.

Soyuz launch vehicle

Soyuz is a Russian medium payload (ca. 3 metric tons to GTO) launcher to be brought into ESA service in 2007 .ESA has entered into a 340 million euro joint venture with the Russian Federal Space Agency over the use of the Soyuz launcher . Under the agreement, the Russian agency will manufacture Soyuz rocket parts for ESA, which will then be shipped to French Guiana for assembly. ESA benefits because it gains a medium payloads launcher, complementing its fleet while saving on development costs. In addition, the Soyuz rocket — which has been the Russian's space launch workhorse for some 40 years — is proven technology with a good safety record, which ESA might be happy to use for launching humans into space. Russia also benefits in that it will get access to the Kourou launch site. Launching from Kourou rather than Baikonur will allow the Russians to almost double the Soyuz payload (3.0 tonnes vs. 1.7 tonnes), because of Kourou's closer proximity to the equator. Both sides benefit from the long term strategic cooperation that in addition will be used to jointly develop future technology. It is perhaps worth noting that France (ESA's largest contributor) has historically had good relations with Russia, which contributed to reaching the agreement. (See [http://stream1.euronews.net:8080/ramgen/mag/space-soyouz-en.rm?usehostname EuroNews report about the joint venture] (Real video stream).)

Vega

Vega is ESA's small payload (ca. 1.5 metric tons to 700 km orbit) launcher; its first launch is planned for 2007 . The leading ESA's member state for the Vega Programme is Italy contributing 65 % of the costs. Vega itself has been designed to be a body launcher with three solid propulsion stages and an additional liquid propulsion upper module to place the cargo into the exact orbit intended. For a small-cargo rocket it is remarkable that Vega will be able to place multiple payloads into orbit. See also: [http://esamultimedia.esa.int/docs/VEGAbrochure.pdf ESA's Vega Brochure]

Human space flight

History

Italy At the time ESA was formed its main goals did not encompass human space flight, rather it considered itself to be primarily a scientific research organisation for unmanned space exploration in contrast to its American and Soviet counterparts. It is therefore not surprising that the first non-Soviet European in space was not an ESA astronaut on a European space craft: It was Czechoslovakian Vladimir Remek who in 1978 became the first European in space - on a Soviet Soyuz spacecraft, followed by the Pole Miros%C5%82aw_Hermaszewski and East German Sigmund Jähn in the same year. This Soviet cooperation programme named Intercosmos primarily involved the participation of Eastern bloc countries, however in 1982 Jean-Loup Chrétien became the first western European cosmonaut on a flight to the Soviet Salyut 7 space station. Because Chrétien did not officially fly into space as an ESA astronaut, but rather as a member of the French CNES astronaut corps, the German Ulf Merbold is considered the first ESA astronaut ever to fly into space. He participated in the STS-9 space shuttle mission that included the first use of the European built Spacelab in 1983. STS-9 marked the beginning of an intensive ESA/NASA joint partnership that included dozens of space flights of ESA astronauts in the following years. Beside paying for seats on the Space Shuttle ESA continued its human space flight cooperation with the Soviet Union and later Russia, including numerous visits to Mir. During the latter half of the 1980s European human space flights changed from being the exception to rather constituting a routine and therefore in 1990 the European Astronaut Centre that is situated in Cologne, Germany was established. It selects and trains prospective astronauts and is responsible for the coordination with international partners especially with regards to the International Space Station. As of 2005 the ESA corps officially counts 18 members, including nationals from all big European countries except the United Kingdom.

ESA Astronaut Corps

United Kingdom Pedro Duque (E), Gerhard Thiele (D), Jean-François Clervoy (F), Umberto Guidoni (I), Léopold Eyharts (F), Reinhold Ewald (D), Roberto Vittori (I), Claude Nicollier (CH). Paolo Nespoli (I), Thomas Reiter (D), Christer Fuglesang (S), Frank De Winne (B), Michel Tognini (F), Hans Schlegel (D), Philippe Perrin (F), André Kuipers (NL). ESA astronauts to have visited the ISS are:
- U. Guidoni (I), ESA, 9th ISS flight (6A) Raffaello MPLM, STS-100/ISS, 19/04/01 - 01/05/01
- C. Haigneré (F), CNES Andromède, Soyuz/ISS, 21/10/01 - 31/10/01
- R. Vittori (I), ASI Marco Polo, Soyuz/ISS, 25/04/02 - 05/05/02
- Ph. Perrin (F), NASA/ESA, ISS assembly flight UF-2, STS-111/ISS, 05/06/02 - 19/06/02
- F. De Winne (B), ESA, Odissea, Soyuz/ISS, 30/10/02 - 10/11/02
- P. Duque (E), ESA, Cervantes, Soyuz/ISS 18/10/03 - 28/10/03
- A. Kuipers (NL), ESA, DELTA Mission, 8S/ISS, 19/04/04 - 30/04/04
- R. Vittori (I), ASI Eneide, Soyuz/ISS, 15/04/05 - 25/04/05

ESA's own manned launch vehicles

In the 1980s France pressed for an independent European manned launch vehicle. Around 1985 it was decided to pursue a reusable spacecraft model and starting in November 1987 a project to create a mini-shuttle by the name of Hermes was introduced. The craft itself was modelled comparable to the first proposals of the Space Shuttle and should constitute a small reusable spaceship that would carry 3 to 5 astronauts and 3 to 4 metric tons of payload for scientific experiments. With a total maximum weight of 21 metric tons it would have started from the parallely developed Ariane 5 rocket. It was planned solely for use in LEO space flights. The planning and pre-development phase concluded in 1991, however the production phase was never fully implemented because at that time the political landscape had changed significantly. With the fall of the Soviet Union ESA looked forward to a cooperation with Russia to built a next-generation human space vehicle. Thus the Hermes programme was cancelled in 1995 after about 3 billion dollars had been invested. In the 21st century ESA started new programmes in order to create an own manned spacecraft, most notably among its various projects and proposal is Hopper where a prototype built by EADS called Phoenix has already been tested. While projects such as Hopper are neither concrete nor to be realised within the next decade, a more interesting possibility has emerged recently. After talks with the Russian Space Agency in 2004 and June 2005 a cooperation between ESA and the Russian Space Agency was announced to jointly work on the Russian designed Kliper shuttle, a reusable spacecraft that would be available for space travel beyond mere LEO (e.g. the moon or even Mars). Kliper constitutes the Russian counterpart to the American Crew Exploration Vehicle proposal and is currently in a more advanced stage of development. It is speculated that Europe will finance the bulk of the development costs of an estimated 3 thousand million euros (Europe's contribution may amount to 1.8 thousand million euros over the next years) and that Kliper will be jointly built and later be able to take off both from French Guiana and Baikonur. With ESA's participation expected to be approved in December 2005, Kliper may see its first launch as early as 2011. With regard to the rocket that will be used for its launch, the Ariane 5 as a heavy lifter, looks to be more than capable of launching the 13ton Kliper into LEO, however as with the American CEV questions remain how it will be launched to destinations beyond LEO. Today the only viable rocket that would be able to launch either the CEV or Kliper into a lunar trajectory or to Mars is the Russian built Energia rocket that was successfully launched two times in late 1980s, but has been suspended in the wake of the fall of the Soviet Union. A modular approach putting several modules (Kliper, a propulsion module, a mission module, a lunar lander module...) into lower Earth orbit and dock them is thus planned for flights to the Moon and further.

James Webb Space Telescope

Mission

Optics

Current Status

Construction & Engineering

See also

External links

Infrared

Different regions in the infrared

Telecommunication bands in the infrared

The Earth as an infrared emitter

Applications

Night vision

Other imaging

Thermography

Heating

Communications

Spectroscopy

History

See also

External links

Journals

Web sites

Hubble Space Telescope

Conception, design and aims

Proposals and precursors

The quest for funding

Construction and engineering

Optical Telescope Assembly (OTA)

Spacecraft systems

Ground support

Challenger disaster

Instruments

Flawed mirror

Origin of the problem

Design of a solution

COSTAR

Servicing missions and new instruments

Servicing mission 1

Subsequent servicing missions

Scientific results

Important discoveries

Impact on astronomy

Using the telescope

Observation scheduling

Amateur observations

Hubble data

Transmission to Earth

Archive

Pipeline reduction

Data analysis

Outreach activities

Future

Equipment failure

Orbital decay

Debate over final servicing mission

Solutions

References

CSA

Esa

History and goals

ESA's mission

History of ESA's foundation

From its beginnings to a leading institution

ESA's further goals and aims

Member countries, budget and organisations

Member countries and strategic partners

Relationship with the EU

Budget

Notable national space agencies

Launch vehicle fleet

Ariane 5

Soyuz launch vehicle

Vega

Human space flight

History

ESA Astronaut Corps

ESA's own manned launch vehicles

ESA projects

International Space Station