142-418: IUE may refer to: International Ultraviolet Explorer Indiana University East Niue International Airport ( IATA code ) International Union of Electrical Workers Topics referred to by the same term [REDACTED] This disambiguation page lists articles associated with the title IUE . If an internal link led you here, you may wish to change
284-558: A Hubble sphere . Some disputed estimates for the total size of the universe, if finite, reach as high as 10 10 10 122 {\displaystyle 10^{10^{10^{122}}}} megaparsecs, as implied by a suggested resolution of the No-Boundary Proposal . Assuming that the Lambda-CDM model is correct, the measurements of the parameters using a variety of techniques by numerous experiments yield
426-477: A blue supergiant , where theory had strongly expected a red supergiant . Hubble Space Telescope images revealed a nebula surrounding the progenitor star which consisted of mass lost by the star long before it exploded; IUE studies of this material showed that it was rich in nitrogen , which is formed in the CNO cycle – a chain of nuclear reactions which produces most of the energy emitted by stars much more massive than
568-577: A geosynchronous orbit – that is, one with a period equal to one sidereal day of 23 h 56 m. A satellite in such an orbit remains visible from a given point on the Earth's surface for many hours at a time, and can thus transmit to a single ground station for a long period of time. Most space observatories in Earth orbit, such as the Hubble Space Telescope , are in a low Earth orbit in which they spend most of their time operating autonomously because only
710-511: A 2.4 m (7 ft 10 in) mirror. The largest ground-based telescope, the Gran Telescopio Canarias , has a primary mirror 10.4 m (34 ft) across. A smaller mirror means less light-gathering power, and less spatial resolution, compared to a larger mirror. The stated aims of the telescope at the start of the mission were: The telescope was constructed as a joint project between NASA, ESRO (which became ESA in 1975) and
852-462: A best value of the age of the universe at 13.799 ± 0.021 billion years, as of 2015. Over time, the universe and its contents have evolved. For example, the relative population of quasars and galaxies has changed and the universe has expanded . This expansion is inferred from the observation that the light from distant galaxies has been redshifted , which implies that the galaxies are receding from us. Analyses of Type Ia supernovae indicate that
994-445: A common shutter, but the 3-arcsecond aperture was always open. As a result, two aperture configurations were possible: (1) both 3-arcsecond apertures open and both 10- by 20-arcsecond slots closed, or (2) all four apertures open. With this instrumentation, the observational options open to an observer were long-wavelength and/or short-wavelength spectrograph, high or low resolution, and large or small apertures. Exposures could be made with
1136-484: A flat mirror in front of the echelle grating so that the only dispersion was provided by the spherical grating. As the SEC Vidicons could integrate the signal for up to many hours, data with a signal-to-noise ratio of 50 could be obtained for B0 stars of 9th and 14th magnitudes in the high- and low-resolution modes, respectively. The distinguishing characteristic of the units was their wavelength coverage. One unit covered
1278-402: A galaxy have planets . At the largest scale , galaxies are distributed uniformly and the same in all directions, meaning that the universe has neither an edge nor a center. At smaller scales, galaxies are distributed in clusters and superclusters which form immense filaments and voids in space, creating a vast foam-like structure. Discoveries in the early 20th century have suggested that
1420-509: A large amount during the 1980s. The reason for this decline is not yet fully understood, but one hypothesis is that a large volcanic eruption had injected sulfur compounds into the atmosphere, and that they were declining following the end of the eruption. Halley's Comet reached perihelion in 1986, and was observed intensively with the IUE, as well as with a large number of other ground-based and satellite missions. UV spectra were used to estimate
1562-589: A large amount of information is being lost. The vast majority of all stars are cooler than the Sun, but the fraction that is hotter includes massive, highly luminous stars which shed enormous quantities of matter into interstellar space, and also white dwarf stars, which are the end stage of stellar evolution for the vast majority of all stars and which have temperatures as high as 100,000 K when they first form. The IUE discovered many instances of white dwarf companions to main sequence stars. An example of this kind of system
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#17328525885781704-436: A lower bandwidth , but consumed less power, and also transmitted in all directions. The VHF transmitters were used when the spacecraft was in the Earth's shadow and thus reliant on battery power instead of solar power. In normal operations, observers could hold the telescope in position and wait approximately 20 minutes for the data to be transmitted, if they wanted the option of repeating the observation, or they could slew to
1846-539: A reasonably good account of various observations about the universe. The initial hot, dense state is called the Planck epoch , a brief period extending from time zero to one Planck time unit of approximately 10 seconds. During the Planck epoch, all types of matter and all types of energy were concentrated into a dense state, and gravity —currently the weakest by far of the four known forces —is believed to have been as strong as
1988-442: A set of four coordinates: ( x , y , z , t ) . On average, space is observed to be very nearly flat (with a curvature close to zero), meaning that Euclidean geometry is empirically true with high accuracy throughout most of the universe. Spacetime also appears to have a simply connected topology , in analogy with a sphere, at least on the length scale of the observable universe. However, present observations cannot exclude
2130-423: A small fraction of the Earth's surface can see them at a given time. Hubble, for example, orbits the Earth at an altitude of approximately 600 km (370 mi), while a geosynchronous orbit has an average altitude of 36,000 km (22,000 mi). As well as allowing continuous communications with ground stations, a geosynchronous orbit also allows a larger portion of the sky to be viewed continuously. Because
2272-403: A time could dial in and would be able to retrieve an observation in 10–30 seconds. As the mission entered its second decade, plans were made for its final archive. Throughout the mission, calibration techniques were improved, and the final software for data reduction yielded significant improvements over earlier calibrations. Eventually, the entire set of available raw data was recalibrated using
2414-464: Is Sirius , and at visible wavelengths, the main sequence star is far brighter than the white dwarf. However, in the UV, the white dwarf can be as bright or brighter, as its higher temperature means it emits most of its radiation at these shorter wavelengths. In these systems, the white dwarf was originally the heavier star but has shed most of its mass during the later stages of its evolution. Binary stars provide
2556-445: Is a composite particle made of quarks held together by the strong force . Hadrons are categorized into two families: baryons (such as protons and neutrons ) made of three quarks, and mesons (such as pions ) made of one quark and one antiquark . Of the hadrons, protons are stable, and neutrons bound within atomic nuclei are stable. Other hadrons are unstable under ordinary conditions and are thus insignificant constituents of
2698-442: Is affected by dust along the line of sight. Almost all astronomical observations are affected by this interstellar extinction , and correcting for it is the first step in most analyses of astronomical spectra and images. IUE data was used to show that within the galaxy, interstellar extinction can be well described by a few simple equations. The relative variation of extinction with wavelength shows little variation with direction; only
2840-417: Is called the observable universe . The proper distance (measured at a fixed time) between Earth and the edge of the observable universe is 46 billion light-years (14 billion parsecs ), making the diameter of the observable universe about 93 billion light-years (28 billion parsecs). Although the distance traveled by light from the edge of the observable universe is close to the age of the universe times
2982-411: Is composed almost completely of dark energy, dark matter, and ordinary matter . Other contents are electromagnetic radiation (estimated to constitute from 0.005% to close to 0.01% of the total mass–energy of the universe) and antimatter . The proportions of all types of matter and energy have changed over the history of the universe. The total amount of electromagnetic radiation generated within
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#17328525885783124-405: Is composed of two types of elementary particles : quarks and leptons . For example, the proton is formed of two up quarks and one down quark ; the neutron is formed of two down quarks and one up quark; and the electron is a kind of lepton. An atom consists of an atomic nucleus , made up of protons and neutrons (both of which are baryons ), and electrons that orbit the nucleus. Soon after
3266-646: Is equal to, less than, or greater than 1. These are called, respectively, the flat, open and closed universes. Observations, including the Cosmic Background Explorer (COBE), Wilkinson Microwave Anisotropy Probe (WMAP), and Planck maps of the CMB, suggest that the universe is infinite in extent with a finite age, as described by the Friedmann–Lemaître–Robertson–Walker (FLRW) models. These FLRW models thus support inflationary models and
3408-597: Is in the Local Group of galaxies, which in turn is in the Laniakea Supercluster . This supercluster spans over 500 million light-years, while the Local Group spans over 10 million light-years. The universe also has vast regions of relative emptiness; the largest known void measures 1.8 billion ly (550 Mpc) across. The observable universe is isotropic on scales significantly larger than superclusters, meaning that
3550-523: Is known as dark matter . In the widely accepted ΛCDM cosmological model, dark matter accounts for about 25.8% ± 1.1% of the mass and energy in the universe while about 69.2% ± 1.2% is dark energy , a mysterious form of energy responsible for the acceleration of the expansion of the universe . Ordinary (' baryonic ') matter therefore composes only 4.84% ± 0.1% of the universe. Stars, planets, and visible gas clouds only form about 6% of this ordinary matter. There are many competing hypotheses about
3692-782: Is subject to the Pauli exclusion principle ; no two leptons of the same species can be in exactly the same state at the same time. Two main classes of leptons exist: charged leptons (also known as the electron-like leptons), and neutral leptons (better known as neutrinos ). Electrons are stable and the most common charged lepton in the universe, whereas muons and taus are unstable particles that quickly decay after being produced in high energy collisions, such as those involving cosmic rays or carried out in particle accelerators . Charged leptons can combine with other particles to form various composite particles such as atoms and positronium . The electron governs nearly all of chemistry , as it
3834-480: Is the Standard Model , a theory that is concerned with electromagnetic interactions and the weak and strong nuclear interactions. The Standard Model is supported by the experimental confirmation of the existence of particles that compose matter: quarks and leptons , and their corresponding " antimatter " duals, as well as the force particles that mediate interactions : the photon , the W and Z bosons , and
3976-430: Is unknown whether or not they are composed of smaller and even more fundamental particles. In most contemporary models they are thought of as points in space. All elementary particles are currently best explained by quantum mechanics and exhibit wave–particle duality : their behavior has both particle-like and wave -like aspects, with different features dominating under different circumstances. Of central importance
4118-869: Is unknown. Dark matter, a mysterious form of matter that has not yet been identified, accounts for 26.8% of the cosmic contents. Dark energy, which is the energy of empty space and is causing the expansion of the universe to accelerate, accounts for the remaining 68.3% of the contents. Matter, dark matter, and dark energy are distributed homogeneously throughout the universe over length scales longer than 300 million light-years (ly) or so. However, over shorter length-scales, matter tends to clump hierarchically; many atoms are condensed into stars , most stars into galaxies, most galaxies into clusters, superclusters and, finally, large-scale galactic filaments . The observable universe contains as many as an estimated 2 trillion galaxies and, overall, as many as an estimated 10 stars – more stars (and earth-like planets) than all
4260-576: The Big Bang , primordial protons and neutrons formed from the quark–gluon plasma of the early universe as it cooled below two trillion degrees. A few minutes later, in a process known as Big Bang nucleosynthesis , nuclei formed from the primordial protons and neutrons. This nucleosynthesis formed lighter elements, those with small atomic numbers up to lithium and beryllium , but the abundance of heavier elements dropped off sharply with increasing atomic number. Some boron may have been formed at this time, but
4402-418: The Big Bang , would have completely annihilated each other and left only photons as a result of their interaction. These laws are Gauss's law and the non-divergence of the stress–energy–momentum pseudotensor . Due to the finite speed of light , there is a limit (known as the particle horizon ) to how far light can travel over the age of the universe . The spatial region from which we can receive light
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4544-532: The German words Das All , Weltall , and Natur for universe . The same synonyms are found in English, such as everything (as in the theory of everything ), the cosmos (as in cosmology ), the world (as in the many-worlds interpretation ), and nature (as in natural laws or natural philosophy ). The prevailing model for the evolution of the universe is the Big Bang theory. The Big Bang model states that
4686-587: The Goddard Space Flight Center (GSFC). According to the agreement setting up the project the observing time would be divided between the contributing agencies with 2/3 to NASA, 1/6 to ESA and 1/6 to the UK's SERC. The telescope mirror was a reflector of the Ritchey–Chrétien telescope type, which has hyperbolic primary and secondary mirrors. The primary was 45 cm (18 in) across. The telescope
4828-562: The International Astronomical Union (IAU) were devoted to discussions of IUE results. All the planets in the Solar System except Mercury were observed; the telescope could not point at any part of the sky within 45° of the Sun, and Mercury's greatest angular distance from the Sun is only about 28°. IUE observations of Venus showed that the amount of sulfur monoxide and sulfur dioxide in its atmosphere declined by
4970-617: The Milky Way is roughly 100,000–180,000 light-years in diameter, and the nearest sister galaxy to the Milky Way, the Andromeda Galaxy , is located roughly 2.5 million light-years away. Because humans cannot observe space beyond the edge of the observable universe, it is unknown whether the size of the universe in its totality is finite or infinite. Estimates suggest that the whole universe, if finite, must be more than 250 times larger than
5112-463: The expansion is accelerating . The more matter there is in the universe, the stronger the mutual gravitational pull of the matter. If the universe were too dense then it would re-collapse into a gravitational singularity . However, if the universe contained too little matter then the self-gravity would be too weak for astronomical structures, like galaxies or planets, to form. Since the Big Bang,
5254-404: The general theory of relativity , explains gravity by recognizing that spacetime is not fixed but instead dynamical. In general relativity, gravitational force is reimagined as curvature of spacetime . A curved path like an orbit is not the result of a force deflecting a body from an ideal straight-line path, but rather the body's attempt to fall freely through a background that is itself curved by
5396-553: The gluon . The Standard Model predicted the existence of the recently discovered Higgs boson , a particle that is a manifestation of a field within the universe that can endow particles with mass. Because of its success in explaining a wide variety of experimental results, the Standard Model is sometimes regarded as a "theory of almost everything". The Standard Model does not, however, accommodate gravity. A true force–particle "theory of everything" has not been attained. A hadron
5538-483: The grains of beach sand on planet Earth ; but less than the total number of atoms estimated in the universe as 10 ; and the estimated total number of stars in an inflationary universe (observed and unobserved), as 10 . Typical galaxies range from dwarfs with as few as ten million (10 ) stars up to giants with one trillion (10 ) stars. Between the larger structures are voids , which are typically 10–150 Mpc (33 million–490 million ly) in diameter. The Milky Way
5680-441: The hadron epoch , and the lepton epoch . Together, these epochs encompassed less than 10 seconds of time following the Big Bang. These elementary particles associated stably into ever larger combinations, including stable protons and neutrons , which then formed more complex atomic nuclei through nuclear fusion . This process, known as Big Bang nucleosynthesis , lasted for about 17 minutes and ended about 20 minutes after
5822-506: The interstellar medium provides a powerful tool for studying its composition. Ultraviolet astronomy was impossible before the Space Age , and some of the first space telescopes were UV telescopes designed to observe this previously inaccessible region of the electromagnetic spectrum . One particular success was the second Orbiting Astronomical Observatory ( OAO-2 ), which had a number of 20 cm (7.9 in) UV telescopes on board. It
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5964-404: The large-scale structure of the universe. Other than neutrinos , a form of hot dark matter , dark matter has not been detected directly, making it one of the greatest mysteries in modern astrophysics . Dark matter neither emits nor absorbs light or any other electromagnetic radiation at any significant level. Dark matter is estimated to constitute 26.8% of the total mass–energy and 84.5% of
6106-399: The law of universal gravitation , Isaac Newton built upon Copernicus's work as well as Johannes Kepler 's laws of planetary motion and observations by Tycho Brahe . Further observational improvements led to the realization that the Sun is one of a few hundred billion stars in the Milky Way , which is one of a few hundred billion galaxies in the observable universe. Many of the stars in
6248-421: The naked eye , since Kepler's star in 1604 – before the invention of the telescope . The opportunity to study a supernova so much more closely than had ever been possible before triggered intense observing campaigns at all major astronomical facilities, and the first IUE observations were made about 14 hours after the discovery of the supernova. IUE data were used to determine that the progenitor star had been
6390-421: The observable universe and global geometry . Cosmologists often work with a given space-like slice of spacetime called the comoving coordinates . The section of spacetime which can be observed is the backward light cone , which delimits the cosmological horizon . The cosmological horizon, also called the particle horizon or the light horizon, is the maximum distance from which particles can have traveled to
6532-442: The observer in the age of the universe . This horizon represents the boundary between the observable and the unobservable regions of the universe. An important parameter determining the future evolution of the universe theory is the density parameter , Omega (Ω), defined as the average matter density of the universe divided by a critical value of that density. This selects one of three possible geometries depending on whether Ω
6674-624: The ultimate fate of the universe and about what, if anything, preceded the Big Bang, while other physicists and philosophers refuse to speculate, doubting that information about prior states will ever be accessible. Some physicists have suggested various multiverse hypotheses, in which the universe might be one among many. The physical universe is defined as all of space and time (collectively referred to as spacetime ) and their contents. Such contents comprise all of energy in its various forms, including electromagnetic radiation and matter , and therefore planets, moons , stars, galaxies, and
6816-477: The weak and strong nuclear forces , decline very rapidly with distance; their effects are confined mainly to sub-atomic length scales. The universe appears to have much more matter than antimatter , an asymmetry possibly related to the CP violation . This imbalance between matter and antimatter is partially responsible for the existence of all matter existing today, since matter and antimatter, if equally produced at
6958-468: The 1960s, but the IUE allowed astronomers to observe a very large number of stars, allowing the first proper studies of how stellar mass loss is related to mass and luminosity. In 1987, a star in the Large Magellanic Cloud exploded as a supernova . Designated SN 1987A , this event was of enormous importance to astronomy, as it was the closest known supernova to Earth, and the first visible to
7100-421: The Big Bang, so only the fastest and simplest reactions occurred. About 25% of the protons and all the neutrons in the universe, by mass, were converted to helium , with small amounts of deuterium (a form of hydrogen ) and traces of lithium . Any other element was only formed in very tiny quantities. The other 75% of the protons remained unaffected, as hydrogen nuclei. After nucleosynthesis ended,
7242-657: The ESA ground station at Villanueva de la Cañada near Madrid . Because of its elliptical orbit, the spacecraft spent part of each day in the Van Allen radiation belts , during which time science observations suffered from higher background noise. This time occurred during the second U.S. shift each day and was generally used for calibration observations and spacecraft "housekeeping", as well as for science observations that could be done with short exposure times. The twice-daily transatlantic handovers required telephone contact between Spain and
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#17328525885787384-449: The Earth in its geosynchronous orbit and will continue to do so more or less indefinitely as it is far above the upper reaches of the atmosphere of Earth . Anomalies in the Earth's gravity due to its non-spherical shape meant that the telescope tended to drift West from its original location at approximately 70° West longitude towards approximately 110° West. During the mission, this drift was corrected by occasional rocket firings, but since
7526-480: The GSFC 8 hours was used only for maintenance. In February 1996, further budget cuts led ESA to decide that it would no longer maintain the satellite. Operations ceased on 30 September 1996, and all the remaining hydrazine was discharged, the batteries were drained and switched off, and at 18:44 UTC on 30 September 1996, the radio transmitter was shut down and all contact with the spacecraft was lost. It continues to orbit
7668-399: The Sun. Astronomers inferred that the star had been a red supergiant, and had shed a large amount of matter into space, before evolving into a blue supergiant and exploding. The IUE was used extensively to investigate the interstellar medium (ISM). The ISM is normally observed by looking at background sources such as hot stars or quasars; interstellar material absorbs some of the light from
7810-634: The United Kingdom's SERC. SERC provided the Vidicon cameras for the spectrographs as well as software for the scientific instruments. ESA provided the solar arrays to power the spacecraft as well as a ground observing facility in Villafranca del Castillo , Spain . NASA contributed the telescope, spectrograph, and spacecraft as well as launching facilities and a second ground observatory in Greenbelt, Maryland at
7952-463: The United Kingdom, and was launched on 26 January 1978, 17:36:00 UTC aboard a NASA Thor-Delta 2914 launch vehicle . The mission lifetime was initially set for 3 years, but in the end, it lasted 18 years, with the satellite being shut down in 1996. The switch-off occurred for financial reasons, while the telescope was still functioning at near original efficiency. It was the first space observatory to be operated in real-time by astronomers who visited
8094-488: The United States to coordinate the switch. Observations were not coordinated between the stations so that the astronomers taking over after the handover would not know where the telescope would be pointing when their shift started. This sometimes meant that observing shifts started with a lengthy pointing maneuver, but allowed maximum flexibility in scheduling of observing blocks. Data was transmitted to Earth in real-time at
8236-422: The absolute amount of absorption changes. Interstellar absorption in other galaxies can similarly be described by fairly simple "laws". The IUE vastly increased astronomers' understanding of active galactic nuclei (AGN). Before its launch, 3C 273 , the first known quasar, was the only AGN that had ever been observed at UV wavelengths. With IUE, UV spectra of AGN became widely available. One particular target
8378-453: The archive required a visit in person to one of two Regional Data Analysis Facilities (RDAFs), one at the University of Colorado and the other at GSFC . In 1987, it became possible to access the archive electronically, by dialing into a computer at Goddard Space Flight Center. The archive, then totaling 23 Gb of data, was connected to the computer on a mass storage device. A single user at
8520-522: The astronomical community for its aims and design. Wilson headed a British team which proposed an ultraviolet spectrograph , and their design was recommended for acceptance in 1966. However, management problems and cost overruns led to the cancellation of the LAS program in 1968. Wilson's team scaled down their plans and submitted a more modest proposal to ESRO, but this was not selected as the Cosmic Ray satellite
8662-417: The background source and so its composition and velocity can be studied. One of IUE's early discoveries was that the Milky Way is surrounded by a vast halo of hot gas, known as a galactic corona . The hot gas, heated by cosmic rays and supernova , extends several thousand light years above and below the plane of the Milky Way. IUE data was also crucial in determining how the light from distant sources
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#17328525885788804-411: The clouds and the quasar are all at different distances from Earth, and moving at different velocities due to the expansion of the universe , the quasar spectrum has a "forest" of absorption features at wavelengths shorter than its own Lyman alpha emission. Before IUE, observations of this so-called Lyman-alpha forest were limited to very distant quasars, for which the redshift caused by the expansion of
8946-476: The contents of intergalactic space . The universe also includes the physical laws that influence energy and matter, such as conservation laws , classical mechanics , and relativity . The universe is often defined as "the totality of existence", or everything that exists, everything that has existed, and everything that will exist. In fact, some philosophers and scientists support the inclusion of ideas and abstract concepts—such as mathematics and logic—in
9088-434: The data. After six months, it became public. The IUE allowed astronomers their first view of the ultraviolet light from many celestial objects and was used to study objects ranging from Solar System planets to distant quasars. During its lifetime, hundreds of astronomers observed with IUE, and during its first decade of operations, over 1500 peer reviewed scientific articles based on IUE data were published. Nine symposia of
9230-500: The definition of the universe. The word universe may also refer to concepts such as the cosmos , the world , and nature . The word universe derives from the Old French word univers , which in turn derives from the Latin word universus , meaning 'combined into one'. The Latin word 'universum' was used by Cicero and later Latin authors in many of the same senses as
9372-546: The density of matter was less than the density of dark energy, marking the beginning of the present dark-energy-dominated era . In this era, the expansion of the universe is accelerating due to dark energy. Of the four fundamental interactions , gravitation is the dominant at astronomical length scales. Gravity's effects are cumulative; by contrast, the effects of positive and negative charges tend to cancel one another, making electromagnetism relatively insignificant on astronomical length scales. The remaining two interactions,
9514-488: The distance from Earth is greater, the Earth occupies a much smaller portion of the sky as seen from the satellite than it does from low Earth orbit. A launch into a geosynchronous orbit requires much more energy for a given weight of payload than a launch into a low Earth orbit. This meant that the telescope had to be relatively small, with a 45 cm (18 in) primary mirror, and a total weight of 312 kg (688 lb). Hubble, in comparison, weighs 11.1 tonnes and has
9656-407: The earliest state of the universe was an extremely hot and dense one, and that the universe subsequently expanded and cooled. The model is based on general relativity and on simplifying assumptions such as the homogeneity and isotropy of space. A version of the model with a cosmological constant (Lambda) and cold dark matter , known as the Lambda-CDM model , is the simplest model that provides
9798-485: The end of each science observation. The camera read-out formed an image of 768 × 768 pixels , and the analogue-to-digital converter resulted in a dynamic range of 8 bits . The data was then transmitted to Earth via one of six transmitters on the spacecraft; four were S-band transmitters, placed at points around the spacecraft such that no matter what its attitude, one could transmit to the ground, and two were Very high frequency (VHF) transmitters, which could sustain
9940-519: The end of the exposure. The IUE was launched from Kennedy Space Center , Florida on a Thor-Delta launch vehicle, on 26 January 1978. It was launched into a transfer orbit , from which its onboard launch vehicle fired it into its planned geosynchronous orbit. The orbit was inclined by 28.6° to the Earth's equator and had an orbital eccentricity of 0.24, meaning that the satellite's distance from Earth varied between 25,669 km (15,950 mi) and 45,887 km (28,513 mi). The ground track
10082-534: The end of the mission the satellite has drifted uncontrolled to the West of its former location. The IUE archive is one of the most heavily used astronomical archives. Data were archived from the start of the mission, and access to the archive was free to anyone who wished to use it. However, in the early years of the mission, long before the advent of the World Wide Web and fast global data transmission links, access to
10224-411: The energy of each photon decreases as it is cosmologically redshifted . At around 47,000 years, the energy density of matter became larger than that of photons and neutrinos , and began to dominate the large scale behavior of the universe. This marked the end of the radiation-dominated era and the start of the matter-dominated era . In the earliest stages of the universe, tiny fluctuations within
10366-620: The final version of the data reduction software, creating a uniform high-quality archive. Today, the archive is hosted at the Mikulski Archive for Space Telescopes at Space Telescope Science Institute and is available via the World Wide Web and APIs. Universe The universe is all of space and time and their contents. It comprises all of existence , any fundamental interaction , physical process and physical constant , and therefore all forms of matter and energy , and
10508-399: The first 10 seconds. This initial period of inflation would explain why space appears to be very flat . Within the first fraction of a second of the universe's existence, the four fundamental forces had separated. As the universe continued to cool from its inconceivably hot state, various types of subatomic particles were able to form in short periods of time known as the quark epoch ,
10650-476: The first subatomic particles and simple atoms to form. Giant clouds of hydrogen and helium were gradually drawn to the places where matter was most dense , forming the first galaxies, stars, and everything else seen today. From studying the effects of gravity on both matter and light, it has been discovered that the universe contains much more matter than is accounted for by visible objects; stars, galaxies, nebulas and interstellar gas. This unseen matter
10792-430: The first time. Unlike plasma, neutral atoms are transparent to many wavelengths of light, so for the first time the universe also became transparent. The photons released (" decoupled ") when these atoms formed can still be seen today; they form the cosmic microwave background (CMB). As the universe expands, the energy density of electromagnetic radiation decreases more quickly than does that of matter because
10934-425: The galaxy, with its mass being estimated at between 50 and 100 million times that of the Sun. The UV emission varied on timescales of a few days, implying that the region of emission was only a few light days across. Quasar observations were used to probe intergalactic space. Clouds of hydrogen gas in between the Earth and a given quasar will absorb some of its emission at the wavelength of Lyman alpha . Because
11076-427: The gradual reionization of the universe between about 200–500 million years and 1 billion years, and also for seeding the universe with elements heavier than helium, through stellar nucleosynthesis . The universe also contains a mysterious energy—possibly a scalar field —called dark energy , the density of which does not change over time. After about 9.8 billion years, the universe had expanded sufficiently so that
11218-482: The ground stations in the United States and Spain. Astronomers made over 104,000 observations using the IUE, of objects ranging from Solar System bodies to distant quasars . Among the significant scientific results from IUE data were the first large-scale studies of stellar winds , accurate measurements of the way interstellar dust absorbs light, and measurements of the supernova SN 1987A which showed that it defied stellar evolution theories as they then stood. When
11360-426: The ground. Many types of objects emit copious quantities of UV radiation, though: the hottest and most massive stars in the universe can have surface temperatures high enough that the vast majority of their light is emitted in the UV. Active Galactic Nuclei , accretion disks , and supernovae all emit UV radiation strongly, and many chemical elements have strong absorption lines in the UV so that UV absorption by
11502-457: The link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=IUE&oldid=932896027 " Category : Disambiguation pages Hidden categories: Short description is different from Wikidata All article disambiguation pages All disambiguation pages International Ultraviolet Explorer International Ultraviolet Explorer ( IUE or Explorer 57 , formerly SAS-D),
11644-432: The massive stars can lose as much as a billion times more material each year in winds traveling at several thousand kilometers per second. These stars exist for a few million years, and during this time the stellar wind carries away a significant fraction of their mass and plays a crucial role in determining whether they explode as supernova or not. This stellar mass loss was first discovered using rocket-borne telescopes in
11786-435: The mission ended, it was considered the most successful astronomical satellite ever. The human eye can perceive light with wavelengths between roughly 350 (violet) and 700 (red) nanometres . Ultraviolet light has wavelengths between roughly 10 nm and 350 nm. UV light can be harmful to human beings and is strongly absorbed by the ozone layer . This makes it impossible to observe UV emission from astronomical objects from
11928-544: The modern English word is used. A term for universe among the ancient Greek philosophers from Pythagoras onwards was τὸ πᾶν ( tò pân ) 'the all', defined as all matter and all space, and τὸ ὅλον ( tò hólon ) 'all things', which did not necessarily include the void. Another synonym was ὁ κόσμος ( ho kósmos ) meaning 'the world , the cosmos '. Synonyms are also found in Latin authors ( totum , mundus , natura ) and survive in modern languages, e.g.,
12070-448: The modern universe. From approximately 10 seconds after the Big Bang , during a period known as the hadron epoch , the temperature of the universe had fallen sufficiently to allow quarks to bind together into hadrons, and the mass of the universe was dominated by hadrons . Initially, the temperature was high enough to allow the formation of hadron–anti-hadron pairs, which kept matter and antimatter in thermal equilibrium . However, as
12212-541: The next heavier element, carbon , was not formed in significant amounts. Big Bang nucleosynthesis shut down after about 20 minutes due to the rapid drop in temperature and density of the expanding universe. Subsequent formation of heavier elements resulted from stellar nucleosynthesis and supernova nucleosynthesis . Ordinary matter and the forces that act on matter can be described in terms of elementary particles . These particles are sometimes described as being fundamental, since they have an unknown substructure, and it
12354-431: The next target and then start the data transmission to Earth while observing the next target. The data transmitted were used for "quick look" purposes only, and full calibration was carried out by IUE staff later. Astronomers were then sent their data on magnetic tape by post, about a week after processing. From the date of the observation, the observers had a six-month proprietary period during which only they had access to
12496-518: The observed rate of expansion. Contributions from scalar fields that are constant in space are usually also included in the cosmological constant. The cosmological constant can be formulated to be equivalent to vacuum energy . Dark matter is a hypothetical kind of matter that is invisible to the entire electromagnetic spectrum , but which accounts for most of the matter in the universe. The existence and properties of dark matter are inferred from its gravitational effects on visible matter, radiation, and
12638-462: The observer would verify that the telescope was pointing at the correct field, and then acquire the exact object to be observed. If the object to be observed was fainter than 14th magnitude, the observer would point the telescope at a star that could be seen, and then apply "blind" offsets, determined from the coordinates of the objects. The accuracy of the pointing was generally better than 2 arcsecond for blind offsets The FES acquisition images were
12780-524: The only direct way to measure the mass of stars, from observations of their orbital motions. Thus, observations of binary stars where the two components are at such different stages of stellar evolution can be used to determine the relationship between the mass of stars and how they evolve. Stars with masses of around ten times that of the Sun or higher have powerful stellar winds . The Sun loses about 10 solar masses per year in its solar wind , which travels at up to around 750 km/s (470 mi/s), but
12922-428: The other fundamental forces, and all the forces may have been unified . The physics controlling this very early period (including quantum gravity in the Planck epoch) is not understood, so we cannot say what, if anything, happened before time zero . Since the Planck epoch, the universe has been expanding to its present scale, with a very short but intense period of cosmic inflation speculated to have occurred within
13064-442: The possibilities that the universe has more dimensions (which is postulated by theories such as string theory) and that its spacetime may have a multiply connected global topology, in analogy with the cylindrical or toroidal topologies of two-dimensional spaces . General relativity describes how spacetime is curved and bent by mass and energy (gravity). The topology or geometry of the universe includes both local geometry in
13206-458: The presence of other masses. A remark by John Archibald Wheeler that has become proverbial among physicists summarizes the theory: "Spacetime tells matter how to move; matter tells spacetime how to curve", and therefore there is no point in considering one without the other. The Newtonian theory of gravity is a good approximation to the predictions of general relativity when gravitational effects are weak and objects are moving slowly compared to
13348-408: The present dark-energy era, it dominates the mass–energy of the universe because it is uniform across space. Two proposed forms for dark energy are the cosmological constant , a constant energy density filling space homogeneously, and scalar fields such as quintessence or moduli , dynamic quantities whose energy density can vary in time and space while still permeating them enough to cause
13490-437: The rate at which the comet lost dust and gas, and the IUE observations allowed astronomers to estimate that a total of 3×10 tons of water evaporated from the comet during its passage through the inner Solar System. Some of the most significant results from IUE came in the studies of hot stars. A star that is hotter than about 10,000 K emits most of its radiation in the UV, and thus if it can only be studied in visible light,
13632-456: The same from all vantage points and has no center. An explanation for why the expansion of the universe is accelerating remains elusive. It is often attributed to the gravitational influence of "dark energy", an unknown form of energy that is hypothesized to permeate space. On a mass–energy equivalence basis, the density of dark energy (~ 7 × 10 g/cm ) is much less than the density of ordinary matter or dark matter within galaxies. However, in
13774-456: The same time, a second observer who is moving relative to the first will see those events happening at different times. The two observers will disagree on the time T {\displaystyle T} between the events, and they will disagree about the distance D {\displaystyle D} separating the events, but they will agree on the speed of light c {\displaystyle c} , and they will measure
13916-477: The same value for the combination c 2 T 2 − D 2 {\displaystyle c^{2}T^{2}-D^{2}} . The square root of the absolute value of this quantity is called the interval between the two events. The interval expresses how widely separated events are, not just in space or in time, but in the combined setting of spacetime. The special theory of relativity cannot account for gravity . Its successor,
14058-401: The second derivative of the cosmic scale factor a ¨ {\displaystyle {\ddot {a}}} has been positive in the last 5–6 billion years. Modern physics regards events as being organized into spacetime . This idea originated with the special theory of relativity , which predicts that if one observer sees two events happening in different places at
14200-400: The single remaining gyroscope. Most other parts of the telescope systems remained fully functional throughout the mission. In 1995, budget concerns at NASA almost led to the termination of the mission, but instead the operations responsibilities were redivided, with ESA taking control for 16 hours a day, and GSFC for the remaining 8 only. The ESA 16 hours was used for science operations, while
14342-464: The slewing and guiding performance of the telescope was evaluated and optimized Finally, image quality and spectral resolution were studied and characterized, and the performance of the telescope, spectrographs and cameras were calibrated using observations of well-known stars . After these three phases were completed, the "routine phase" of operations began on 3 April 1978. Optimization, evaluation and calibration operations were far from complete, but
14484-483: The smaller aperture was only used when the larger field of view would have contained unwanted emission from other objects. There were two cameras for each spectrograph, one designated the primary and the second being redundant in case of failure of the first. The cameras were named LWP, LWR, SWP and SWR where P stands for prime, R for redundant and LW/SW for long/short wavelength . The cameras were television cameras , sensitive only to visible light, and light gathered by
14626-461: The spacecraft. Successive failures of these in 1979, 1982, 1983, 1985 and 1996 ultimately left the spacecraft with a single functional gyroscope. Telescope control was maintained with two gyros by using the telescope's Sun sensor to determine the spacecraft's attitude, and stabilization in three axes proved possible even after the fifth failure, by using the Sun sensor, the Fine Error Sensors and
14768-414: The speed of light, 13.8 billion light-years (4.2 × 10 ^ pc), the proper distance is larger because the edge of the observable universe and the Earth have since moved further apart. For comparison, the diameter of a typical galaxy is 30,000 light-years (9,198 parsecs ), and the typical distance between two neighboring galaxies is 3 million light-years (919.8 kiloparsecs). As an example,
14910-449: The speed of light. The relation between matter distribution and spacetime curvature is given by the Einstein field equations , which require tensor calculus to express. The universe appears to be a smooth spacetime continuum consisting of three spatial dimensions and one temporal ( time ) dimension. Therefore, an event in the spacetime of the physical universe can be identified by
15052-483: The standard model of cosmology, describing a flat , homogeneous universe presently dominated by dark matter and dark energy . The fine-tuned universe hypothesis is the proposition that the conditions that allow the existence of observable life in the universe can only occur when certain universal fundamental physical constants lie within a very narrow range of values. According to this hypothesis, if any of several fundamental constants were only slightly different,
15194-433: The statistical properties of the universe are the same in all directions as observed from Earth. The universe is bathed in highly isotropic microwave radiation that corresponds to a thermal equilibrium blackbody spectrum of roughly 2.72548 kelvins . The hypothesis that the large-scale universe is homogeneous and isotropic is known as the cosmological principle . A universe that is both homogeneous and isotropic looks
15336-421: The structures they form, from sub-atomic particles to entire galactic filaments . Since the early 20th century, the field of cosmology establishes that space and time emerged together at the Big Bang 13.787 ± 0.020 billion years ago and that the universe has been expanding since then. The portion of the universe that we can see is approximately 93 billion light-years in diameter at present, but
15478-444: The telescope and spectrographs first fell on a UV-to-visible converter. This was a caesium - tellurium cathode , which was inert when exposed to visible light, but which gave off electrons when struck by UV photons due to the photoelectric effect . The electrons were then detected by the TV cameras. The signal could be integrated for up to many hours, before being transmitted to Earth at
15620-428: The telescope was understood well enough for routine science observations to begin. Use of the telescope was divided between NASA, ESA and United Kingdom in approximate proportion to their relative contributions to the satellite construction: two-thirds of the time was available to NASA, and one-sixth each to ESA and United Kingdom. Telescope time was obtained by submitting proposals, which were reviewed annually. Each of
15762-675: The telescope's only imaging capability; for UV observations, it only recorded spectrum . For this, it was equipped with two spectrographs. They were called the Short Wavelength Spectrograph (SWS) and the Long Wavelength Spectrograph (LWS) and covered wavelength ranges of 115 to 200 nanometres and 185 to 330 nm respectively. Each spectrograph had both high and low-resolution modes, with spectral resolutions of 0.02 and 0.60-nm respectively. The spectrographs could be used with either of two apertures. The larger aperture
15904-402: The telescope, a high-resolution and a low-resolution spectrograph, and four detectors. There were two Fine Error Sensors (FES), and their first purpose was to image the field of view of the telescope in visible light . They could detect stars down to 14th magnitude , about 1500 times fainter than can be seen with the naked eye from Earth . The image was transmitted to the ground station, where
16046-404: The temperature of the universe continued to fall, hadron–anti-hadron pairs were no longer produced. Most of the hadrons and anti-hadrons were then eliminated in particle–antiparticle annihilation reactions, leaving a small residual of hadrons by the time the universe was about one second old. A lepton is an elementary , half-integer spin particle that does not undergo strong interactions but
16188-409: The three agencies considered applications separately for its allocated observing time. Astronomers of any nationality could apply for telescope time, choosing whichever agency they preferred to apply to. If an astronomer was awarded time, then when their observations were scheduled, they would travel to the ground stations which operated the satellite, so that they could see and evaluate their data as it
16330-476: The total matter in the universe. The remaining 4.9% of the mass–energy of the universe is ordinary matter, that is, atoms , ions , electrons and the objects they form. This matter includes stars , which produce nearly all of the light we see from galaxies, as well as interstellar gas in the interstellar and intergalactic media, planets , and all the objects from everyday life that we can bump into, touch or squeeze. The great majority of ordinary matter in
16472-452: The total size of the universe is not known. Some of the earliest cosmological models of the universe were developed by ancient Greek and Indian philosophers and were geocentric , placing Earth at the center. Over the centuries, more precise astronomical observations led Nicolaus Copernicus to develop the heliocentric model with the Sun at the center of the Solar System . In developing
16614-436: The two spectrographs simultaneously, but the entrance apertures for each were distinct and separated in the sky by about 1 arcminute. An additional restriction was that data could be read out from only one camera at a time. However, one camera could be exposed while the other camera was being read out. The choice of high or low resolution could be made independently for the two spectrographs. The particle flux monitor experiment
16756-523: The universe brought it into optical wavelengths. IUE allowed nearer quasars to be studied, and astronomers used this data to determine that there are fewer hydrogen clouds in the nearby universe than there are in the distant universe. The implication is that over time, these clouds have formed into galaxies. This experiment included the ultraviolet spectrograph package carried by the IUE, consisting of two physically distinct echelle-spectrograph/camera units capable of astronomical observations. Each spectrograph
16898-488: The universe entered a period known as the photon epoch . During this period, the universe was still far too hot for matter to form neutral atoms , so it contained a hot, dense, foggy plasma of negatively charged electrons , neutral neutrinos and positive nuclei. After about 377,000 years, the universe had cooled enough that electrons and nuclei could form the first stable atoms . This is known as recombination for historical reasons; electrons and nuclei were combining for
17040-406: The universe had a beginning and has been expanding since then. According to the Big Bang theory, the energy and matter initially present have become less dense as the universe expanded. After an initial accelerated expansion called the inflationary epoch at around 10 seconds, and the separation of the four known fundamental forces , the universe gradually cooled and continued to expand, allowing
17182-454: The universe has decreased by 1/2 in the past 2 billion years. Today, ordinary matter, which includes atoms, stars, galaxies, and life , accounts for only 4.9% of the contents of the universe. The present overall density of this type of matter is very low, roughly 4.5 × 10 grams per cubic centimeter, corresponding to a density of the order of only one proton for every four cubic meters of volume. The nature of both dark energy and dark matter
17324-406: The universe has expanded monotonically . Perhaps unsurprisingly , our universe has just the right mass–energy density , equivalent to about 5 protons per cubic meter, which has allowed it to expand for the last 13.8 billion years, giving time to form the universe as observed today. There are dynamical forces acting on the particles in the universe which affect the expansion rate. Before 1998, it
17466-482: The universe is unseen, since visible stars and gas inside galaxies and clusters account for less than 10 percent of the ordinary matter contribution to the mass–energy density of the universe. Ordinary matter commonly exists in four states (or phases ): solid , liquid , gas , and plasma . However, advances in experimental techniques have revealed other previously theoretical phases, such as Bose–Einstein condensates and fermionic condensates . Ordinary matter
17608-422: The universe would have been unlikely to be conducive to the establishment and development of matter , astronomical structures, elemental diversity, or life as it is understood. Whether this is true, and whether that question is even logically meaningful to ask, are subjects of much debate. The proposition is discussed among philosophers , scientists , theologians , and proponents of creationism . The universe
17750-467: The universe's density led to concentrations of dark matter gradually forming. Ordinary matter, attracted to these by gravity , formed large gas clouds and eventually, stars and galaxies, where the dark matter was most dense, and voids where it was least dense. After around 100–300 million years, the first stars formed, known as Population III stars. These were probably very massive, luminous, non metallic and short-lived. They were responsible for
17892-407: The wavelength range from 1192 to 1924 A in the high-resolution mode and 1135 to 2085 A in the low-resolution mode. For the other unit, the ranges were from 1893 to 3031 A and 1800 to 3255 A for the high-and low-resolution modes, respectively. Each unit also had its own choice of entrance apertures: either a 3-arcsecond hole or a 10- by 20-arcsecond slot. The 10- by 20-arcsecond slots could be blocked by
18034-399: Was NGC 4151 , the brightest Seyfert galaxy . Starting soon after IUE's launch, a group of European astronomers pooled their observing time to repeatedly observe the galaxy, to measure variations over time of its UV emission. They found that the UV variation was much greater than that seen at optical and infrared wavelengths. IUE observations were used to study the black hole at the centre of
18176-489: Was 1.3 MeV . The experiment was also sensitive to protons with energies greater than 15 MeV. The instrument was used as an operational tool to aid in determining background radiation and acceptable camera exposure time. The data were also useful as a monitor of the trapped radiation fluxes. The instrument was provided by Dr. C. Bostrom of the Applied Physics Laboratory of Johns Hopkins University . The instrument
18318-422: Was a slot with a field of view roughly 10 × 20 arcseconds; the smaller aperture was a circle about 3 arcseconds in diameter. The quality of the telescope optics was such that point sources appeared about 3 arcseconds across, so the use of the smaller aperture required very accurate pointing, and it did not necessarily capture all of the light from the object. The larger aperture was therefore most commonly used, and
18460-454: Was a three-element echelle system composed of an off-axis paraboloidal collimator, an echelle grating, and a spherical first-order grating that was used to separate the echelle orders and focus the spectral display on an image converter plus SEC Vidicon camera. There was a spare camera for each unit. The camera units were able to integrate the signal. The readout/preparation cycle for the cameras took approximately 20 minutes. Wavelength calibration
18602-411: Was designed to give high-quality images over a 16 arcminute field of view (about half the apparent diameter of the Sun or Moon ). The primary mirror was made of beryllium , and the secondary of fused silica – materials chosen for their light weight, moderate cost, and optical quality. The instrumentation on board consisted of the Fine Error Sensors (FES), which were used for pointing and guiding
18744-485: Was expected that the expansion rate would be decreasing as time went on due to the influence of gravitational interactions in the universe; and thus there is an additional observable quantity in the universe called the deceleration parameter , which most cosmologists expected to be positive and related to the matter density of the universe. In 1998, the deceleration parameter was measured by two different groups to be negative, approximately −0.55, which technically implies that
18886-549: Was focused, and the prime and redundant cameras in both channels were tested. It was found that the SWR camera did not work properly, and so the SWP camera was used throughout the mission. Initially, this camera suffered from significant electronic noise, but this was traced to a sensor used to align the telescope after launch. Once this sensor was switched off, the camera performed as expected. The cameras were then adjusted for best performance, and
19028-488: Was given precedence. Rather than give up on the idea of an orbiting UV telescope, they instead sent their plans to NASA astronomer Leo Goldberg , and in 1973 the plans were approved. The proposed telescope was renamed the International Ultraviolet Explorer . The telescope was designed from the start to be operated in real-time, rather than by remote control. This required that it would be launched into
19170-424: Was initially centered at a longitude of approximately 70° West. The first 60 days of the mission were designated as the commissioning period. This was divided into three main stages. Firstly, as soon as its instruments were switched on, the IUE observed a small number of high-priority objects, to ensure that some data had been taken in the event of an early failure. The first spectrum, of the star Eta Ursae Majoris ,
19312-436: Was launched in 1968 and took the first UV observations of 1200 objects, mostly stars. The success of OAO-2 motivated astronomers to consider larger missions. The orbiting ultraviolet satellite which ultimately became the IUE mission was first proposed in 1964 by British astronomer Robert Wilson . The European Space Research Organisation (ESRO) was planning a Large Astronomical Satellite (LAS), and had sought proposals from
19454-478: Was placed in IUE to monitor the trapped electron fluxes that affected the sensitivity of the ultraviolet sensor in the IUE spectrograph package experiment, NSSDC ID 1978-012A-01. The particle flux monitor was a lithium-drifted silicon detector with a half-angle conical field of view of 16°. It had an aluminum absorber of 0.357 g/cm in front of the collimator and a brass shield with a minimum thickness of 2.31 g/cm . The effective energy threshold for electron measurements
19596-409: Was provided by the use of a hollow cathode comparison lamp. The photometric calibration was accomplished by observing standard stars whose spectral fluxes had previously been calibrated by other means. Both echelle-spectrograph/camera units were capable of high-resolution (0.1 Angstrom (A)) or low-resolution (6 A) performance. The dual high/low-resolution capability was implemented by the insertion of
19738-478: Was taken for calibration purposes three days after launch. The first science observations targeted objects including the Moon , the planets from Mars to Uranus , hot stars including Eta Carinae , cool giant stars including Epsilon Eridani , the black hole candidate Cygnus X-1 , and galaxies including Messier 81 (M81) and Messier 87 (M87). Then, the spacecraft systems were tested and optimized. The telescope
19880-457: Was taken. This mode of operation was very different from most space facilities, for which data is taken with no real-time input from the astronomer concerned, and instead resembled the use of ground-based telescopes. For most of its lifetime, the telescope was operated in three eight-hour shifts each day, two from the U.S. ground station at the Goddard Space Flight Center in Maryland , and one from
20022-542: Was the first space observatory primarily designed to take ultraviolet (UV) electromagnetic spectrum . The satellite was a collaborative project between NASA , the United Kingdom 's Science and Engineering Research Council (SERC, formerly UKSRC) and the European Space Agency (ESA), formerly European Space Research Organisation (ESRO). The mission was first proposed in early 1964, by a group of scientists in
20164-444: Was turned off on 4 October 1991 because it was giving erroneous information. The IUE was designed to have a minimum lifetime of three years and carried consumables sufficient for a five-year mission. However, it lasted far longer than its design called for. Occasional hardware failures caused difficulties, but innovative techniques were devised to overcome them. For example, the spacecraft was equipped with six gyroscopes to stabilize
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