Hubble Mission Timeline

In 1923, Astronomer Edwin Powell Hubble spent months collecting data about the largest known spiral nebula at the Mt. Wilson Observatory in California, which led him to conclude that Andromeda is not a nebula, but a galaxy and, most importantly, that the Milky Way is only one of the galaxies in our universe. With these findings, he changed how we view our place in space.

He was able to make these calculations by measuring the variation of the luminosity (the length of time it takes a star to go from bright to dim and back again) of Cepheid variable stars in the Andromeda Galaxy based on a formula developed in 1912 by Harvard “computer” Henrietta Leavitt.

Hubble calculated that Andromeda is approximately 900,000 light-years away, more than eight times the distance to the farthest known stars in the Milky Way, which conclusively proved that Andromeda is a separate star system and the Milky Way is not the sum of the universe.

For this reason—and his many other accomplishments as an astronomer—NASA formally named the space telescope after him in 1983.

More than 40 years after it was conceived, NASA’s Hubble Space Telescope was launched into Earth orbit from the Kennedy Space Center in Cape Canaveral, Florida. A day later, astronauts guided the 43-foot, 12-ton telescope from the cargo bay of the space shuttle Discovery, out into orbit 332 miles above Earth’s surface.

In addition to its 92-inch primary mirror to collect light, fine guidance sensors to point and lock on to targets, and solar panels for power, Hubble's original configuration included four key scientific instruments:

• High Speed Photometer (HSP) to measure the brightness of celestial objects in ultraviolet, visible, and near-infrared light
• Wide Field/Planetary Camera (WFPC, later known as WFPC1), to photograph objects in ultraviolet, visible, and near-infrared light
• Faint Object Camera (FOC) to detect visible and ultraviolet light from extremely dim objects
• Goddard High Resolution Spectrograph (GHRS) to capture the ultraviolet spectra (individual wavelengths of light) of celestial objects

Nearly one month after launch, NASA Headquarters, NASA’s Goddard Space Flight Center, and the Space Telescope Science Institute released the long-awaited first-light image from the Hubble Space Telescope. Taken to assist in focusing the telescope and made using Hubble's Wide Field/Planetary Camera (WFPC), the image shows part of a star cluster about 1,300 light-years from Earth.

Though underwhelming compared to the spectacularly detailed and colorful images that we now associate with Hubble, the image was important because it was able to demonstrate that progress was being made in commissioning the telescope: Light was in fact being collected by the mirror, and passing through the optics to the detectors.

Placed beside a photograph of the same region taken with a slightly larger ground-based telescope, the relative clarity of the image also highlighted the key advantage of sending a telescope into space: a view of the universe unimpeded by Earth's atmosphere.

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After analyzing the Hubble Space Telescope’s first images, scientists realized the primary mirror had a flaw known as spherical aberration. An investigation revealed that during its manufacture, the outer edge of the mirror was ground too flat by a depth of 4 microns (roughly equal to one-50th the thickness of a human hair). The flaw scattered the light reflected by cosmic objects, resulting in fuzzy images.

STScI staff and their partners at NASA immediately began experimenting with algorithms to resolve and make use of Hubble’s data and imagery, pushing forward image processing technology. Less than two months later, STScI convened an expert workshop on the issue.

While Hubble was not returning the image quality expected, it was still providing results that were impossible for ground-based telescopes, with high resolution and spectra that led to new research. Year-one science presentations at STScI covered planets, hot stars, cool stars, chemically peculiar stars, stellar systems, gravitationally lensed quasars, and quasar absorption systems.

Dr. Tod R. Lauer of the National Optical Astronomy Observatory in Tucson, Arizona, and more than a dozen of his colleagues co-published an article in the Astrophysical Journal analyzing some of the first images delivered by the Hubble Space Telescope: observations of the core of galaxy NGC 7457.

“The appearance of the reduced images is striking—the sharp nucleus stands out clearly from the surrounding galaxy,” the authors commented. “It is immediately apparent that the center of NGC 7457 is extremely compact.” The team found that although the center remained unresolved, the images demonstrated that Hubble can “provide unique and astrophysically interesting information” about the central structure of galaxies.

NGC 7457 is 40 million light-years away. Before Hubble’s observation, distance limited study at the same resolution to  about two dozen galaxies within the Local Group—a small, gravitationally bound collection of roughly 40 nearby galaxies, approximately 5 million light-years from Earth.

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During five space walks totaling 35 hours and 28 minutes, astronauts completed the first servicing mission for the Hubble Space Telescope. Two teams of two astronauts installed or replaced 10 instruments, including the Corrective Optics Space Telescope Axial Replacement (COSTAR) and the Wide Field Planetary Camera 2 (WFPC2). COSTAR corrected the flatness of the mirror’s outer edge, and WFPC2 contained built-in corrective optics, significantly improving Hubble’s ultraviolet performance.

Additional upgrades included new solar arrays and solar array drive electronics, rate sensor units, two gyro electronic-control units, and eight electrical fuses. The team also installed two new magnetometers, two protective covers over original magnetometers, and a Goddard High Resolution Spectrograph (GHRS) kit.

The mission was a success, as shown by the images captured of M100, which demonstrated that the corrective optics incorporated within the WFPC2 compensated fully for the optical aberration in Hubble’s primary mirror.

Congress committed funding for four astronomical satellites, allowing scientists to collect and analyze data throughout the entire electromagnetic spectrum. NASA’s astrophysics director Charlie Pellerin conceived of the program, first presenting it in 1985.

The Great Observatories include the Hubble Space Telescope, which specializes primarily in the visible-light spectrum; the Compton Gamma Ray Observatory (CGRO), which gathered gamma rays; the Spitzer Space Telescope, which focuses on the infrared; and the Chandra X-ray Observatory, which observes X-rays. By spanning the electromagnetic spectrum, the four observatories continue to help scientists determine how stars and galaxies form, and provide insights into the origin and evolution of the universe.

STScI astronomer Holland Ford and Richard Harms of the Applied Research Corp. used the Hubble Space Telescope’s Wide Field Planetary Camera-2 (in planetary camera mode) to image a whirlpool of hot gas orbiting around the center of the giant elliptical galaxy M87. The astronomers used Hubble’s Faint Object Spectrograph to measure the speed of the swirling gas, and saw that there was not enough mass from stars to account for the tremendous gravitational field pulling the gas into a whirlpool shape—the powerful attraction had to be coming from something unseen.

Black holes by definition cannot be seen, as their gravity is so strong that even light cannot reach escape velocity, and so is not emitted or reflected. The supermassive black hole at the center of M87 was calculated to be as massive as five billion of our suns, concentrated into a space no larger than our solar system.

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On July 16, 1994, all eyes were trained on Jupiter as the first fragment of Comet Shoemaker-Levy 9 plunged through the atmosphere of the gas giant. The impacts continued for the next week, forming scars—more visible than Jupiter’s Great Red Spot—that lasted for months.

Carolyn Shoemaker, Gene Shoemaker, and David Levy, who were using the Schmidt Telescope at Palomar to search for near-Earth objects, discovered comet Shoemaker-Levy 9 in March 1993. Observations soon revealed that the comet was orbiting Jupiter and was on a course for collision the following year. With its corrective optics successfully installed in December 1993, Hubble was in position to give scientists a front row seat to a never-before-witnessed event.

With the comet broken into 21 fragments by the gravitational force between it and Jupiter, the collisions lasted for a full week. Hubble observed, documenting the impacts and the evolution of the impact sites, bringing new insight into our understanding of how objects in the Solar System change over time.

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Five years after its launch, the Hubble Space Telescope captured an image that quickly came to symbolize both the power of the telescope and the beauty of the universe. The “Pillars of Creation” are towers of gas and dust in the Eagle Nebula, some 6,500 light-years away. Illuminated by young, massive stars just above the field of view, the pillars protrude from the wall of a giant cavity that has been carved into the gas and dust by intense ultraviolet radiation emitted by these stars. Cocooned within the pillars, hidden from view, are newly forming stars.

The picture was taken on April 1, 1995, using Hubble’s Wide Field Planetary Camera 2 (WFPC2), which was installed by astronauts during the first servicing mission, in December 1993. The stepped shape of the image reflects the shape of the camera itself.

Like many Hubble images, this was constructed by combining data from different filters, and provides information about the make-up of space. Red represents light emitted from sulfur atoms, green from hydrogen, and blue from oxygen.

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In November 1995, astronomers released a color mosaic of the Orion Nebula, a glowing cloud of gas and dust just 1,500 light years from Earth. The panorama, spanning 2.5 light-years, reveals a turbulent region of glowing gas lit by hundreds of bright, young stars.

One might imagine that this region was chosen for its beauty, but it was actually the focus of important research on star and planet formation. Within the region, astronomers identified 153 glowing protoplanetary disks—regions of dust and gas surrounding young stars. Protoplanetary disks are embryonic solar systems: The dust in these disks may eventually come together to form planets and moons. The existence of so many protoplanetary disks was evidence that planet formation is probably common in the Milky Way. With its broad and detailed view of the Orion Nebula, Hubble had opened a new laboratory for the study of planet and star formation.

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The Hubble Space Telescope’s Deep Field image was released at the 187th American Astronomical Society meeting, amazing astronomers and the public. In the most detailed optical view of the universe to date, 276 long exposures collected faint light, so that what appeared to the naked eye to be empty space in the sky was revealed to be crowded with over 3,000 distant galaxies. Coupled with discoveries of exoplanets, the Hubble Deep Field’s revelation of a vast universe theoretically home to many other Earth-like planets altered perceptions of humanity’s place in the cosmos.

The 10 consecutive days needed to create the image were a controversial use of Hubble’s precious time, and were undertaken at the direction of STScI Director Robert Williams. His gamble paid off with amazing science, giving astronomers insight into the era of early galaxy formation after the big bang. This would impact astronomy for decades to come, with an increased focus on pushing observation back to the earliest days of the universe.

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Astronomers obtained clear pictures of Pluto’s surface for the first time with the Hubble Space Telescope, revealing nearly the entire surface as it rotated over 6.4 days. Pluto is two-thirds the size of Earth’s Moon and 1,200 times farther away.

The images revealed distinctive features, including a ragged northern polar cap bisected by a dark strip, a bright spot seen rotating with the planet, a cluster of dark spots, and a bright linear marking. The images confirmed the presence of icy-bright polar cap features, which had been inferred from indirect evidence in the 1980s. The research was led by Dr. Alan Stern of Southwest Research Institute’s Boulder, Colorado, research office.

Most of the surface features were likely produced by the complex distribution of frosts that migrate across Pluto’s surface, which allow gases to freeze and sublimate, thinning or thickening its atmosphere throughout its 248-year orbit. These observations helped pave the way for NASA’s New Horizons mission, which conducted a six-month flyby study of Pluto in 2015.

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Astronauts aboard space shuttle Discovery replaced two key Hubble instruments during the second servicing mission. The Goddard High Resolution Spectrograph (GHRS) was replaced with the Near Infrared Camera and Multi-Object Spectrometer (NICMOS) to allow Hubble to observe the universe in infrared wavelengths, and the Faint Object Spectrograph (FOS) was swapped with the Space Telescope Imaging Spectrograph (STIS) to take detailed pictures of celestial objects and hunt for black holes.

Throughout several spacewalks, astronauts also replaced a fine guidance sensor to allow ground-controlled alignment corrections; added an optical control electronics enhancement kit; and upgraded its suite of electronics.

The mission's success was proven by release of new data in the months that followed. Hubble went on to analyze the light in the glowing gas rings around supernova 1987A, see the Orion Nebula in infrared, and detect the signature of a supermassive black hole in M84.

Before 1997, astronomers assumed that the expansion rate of the universe must be decreasing. This made sense: The gravitational force exerted by the mass in the universe would be pulling on itself, slowing the expansion of space over time.

To measure this deceleration, two teams of astronomers embarked on studies to measure the brightness and redshift of distant supernovae. Brightness is directly related to a supernova’s distance, while redshift is a function of its apparent velocity. Combined with other studies, these data could be used to determine the change in the expansion rate of the universe over time.

But when they analyzed the data, the astronomers were astounded to discover that the universe is actually expanding at an increasing rate. They reasoned that the source of this unexpected acceleration, which they called dark energy, must oppose gravity. The result fundamentally changed our understanding of the universe, and astronomers now estimate that roughly 70% of the matter and energy in the universe is dark energy.

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In the mid-1920s, Edwin Hubble recognized that the farther a galaxy is from Earth, the faster it appears to be moving away from us. This correlation between distance and apparent velocity shows that the universe is expanding, and is primary evidence for the big bang theory.

However, because of the difficulty of measuring precise distances to galaxies, the exact rate of expansion—the Hubble constant (H₀)—remained uncertain. Without H₀, it is impossible to determine how long the universe has been expanding, and thus how old it is.

With its powerful optics and position above the blurring effects of the atmosphere, the Hubble Space Telescope was uniquely suited for determining galactic distances. By correlating the distances of 18 galaxies to their apparent speeds, astronomers successfully narrowed the expansion rate down to an uncertainty of just 10 percent. The new constant tightened the possible age of the universe from 10 to 20 billion to 12 to 14 billion years old. Based on further refinements, we now think the universe is about 13.8 billion years old.

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In November 1999, Hubble went into safe mode after four of its six gyroscopes failed. As a result, NASA prioritized this servicing mission, sending astronauts on the space shuttle Discovery to replace all six gyroscopes, which accurately point the telescope at celestial targets.

Six days and three six-hour spacewalks later, the crew successfully replaced worn or outdated equipment, and performed several critical maintenance upgrades. They installed a computer that was 20 times faster than its predecessor and a digital data recorder that stored 10 times as much data. The crew also added an electronics enhancement kit, battery improvement kits, and new outer layers of thermal protection. Hubble was practically new.

The telescope’s first images, which were released in January, proved Hubble had a crystal-clear view. Astronomers pointed Hubble at two targets, NGC 2392 and Abell 2218, which gave scientists a clear view of a planetary nebula, as well as the first detailed look at the internal structure of a cluster of galaxies.

In May and June of 2000, astronomers focused Hubble’s Space Telescope Imaging Spectrograph (STIS) on HD 209458 b, an exoplanet orbiting a Sun-like star 150 light-years from Earth. Their goal: analyzing the colors of light given off by the star and measuring slight changes in the brightness of each color as the planet passed in front of the star. Atoms and molecules in the planet's atmosphere should absorb specific colors, leaving gaps in the light spectrum and providing evidence for the composition of the atmosphere.

In November 2001, astronomers reported success: The spectrum of starlight passing through the atmosphere of HD showed clear evidence for sodium—the first direct measurement of an atmosphere outside our solar system.

The discovery showed that it is possible to detect extremely subtle differences in light, and analyze the atmospheres of planets in star systems hundreds of trillions of miles away.

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Astronauts aboard the space shuttle Columbia successfully installed a powerful new instrument—the Advanced Camera for Surveys (ACS)—as well as a power unit, solar arrays, and a cooling unit for the Near Infrared Camera and Multi-Object Spectrometer (NICMOS).

The first stunning ACS images were released in April. An unexpected benefit of the image of the Tadpole Galaxy was the enormous number of galaxies seen in the background, which gave it an appearance similar to the galaxy-filled Hubble Deep Field image taken in 1995. However, the ACS picture was taken in one-twelfth the time.

The new solar arrays generated 27 percent more electrical power than the previous arrays, which doubled the electrical power that can be allocated to the scientific instruments on Hubble. The cooling unit, which allowed NICMOS to resume operations after three years, enabled it to send images of galaxies in several stages of development, demonstrating its powerful new capability to make remarkable discoveries unique to space-based near-infrared astronomy.

On January 7, 2003, STScI released this Hubble image illustrating the effect of gravity warping space, and thus light, as predicted by Albert Einstein. Though Hubble had previously used the natural phenomena of massive bodies in space magnifying distant objects behind them—known as gravitational lensing—it had never been seen in such dramatic detail.

Astronomers pointed Hubble's Advanced Camera for Surveys (ACS) at Abell 1689, one of the most massive galaxy clusters known, for over 13 hours. The gravity of the supercluster's trillion stars—plus dark matter—act as a 2-million-light-year-wide “lens” in space, warping distant galaxies into clearly visible arcs amid the more distinct and bright foreground galaxies. The ACS is five times more sensitive than Hubble’s previous cameras; this image reveals 10 times more arcs than would be seen by a ground-based telescope.

The associated data from the observation provided material for the study of the age of the universe, its early eons, and the elusive nature of dark matter.

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On March 9, 2004, astronomers at STScI unveiled the deepest portrait of the visible universe ever achieved: the Hubble Ultra Deep Field (HUDF). A million-second-long exposure revealed the faint first galaxies that dispelled the “dark ages” after the big bang. Gone are the majestic spiral and elliptical galaxies we have come to recognize today, replaced with strange shapes of galaxies in a “toddler” stage of chaotic development, when order and structure were just beginning to emerge in the universe.

The ancient light seen in the HUDF cannot be viewed by ground-based telescopes, or even in Hubble’s previous faraway looks, called the Hubble Deep Fields. The HUDF field contains an estimated 10,000 galaxies and is actually two separate images taken by Hubble’s Advanced Camera for Surveys (ACS) and the Near Infrared Camera and Multi-object Spectrometer (NICMOS). The smallest, reddest galaxies may be among the most distant known, existing when the universe was just 800 million years old.

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In a meeting with the Hubble Team, including STScI Director Steven Beckwith, NASA Administrator Sean O’Keefe shared his decision to cancel Hubble Servicing Mission 4, because the scientific return did not outweigh the safety risks. Dr. Beckwith and STScI staff quickly took up Administrator O'Keefe's challenge to develop new methods of extending Hubble's scientific capacity without the servicing mission upgrades.

After an outcry from the public and astronomy community, Congress directed NASA to request a study from the National Research Council (NRC) of robotic and shuttle servicing options for extending the life of Hubble. In December 2004, the NRC committee announced its support for reinstating a shuttle servicing mission. NASA Administrator O’Keefe resigned shortly afterward.

Less than 20 percent of the matter in the universe is normal matter: protons, neutrons, and electrons that make up stars, gas, dust, and other materials. The remaining 80% is dark matter. Dark matter does not reflect or emit any type of light and can be detected based only on the gravitational influence it exerts on normal matter and on light.

In 2006, the Chandra X-Ray Observatory, working in collaboration with Hubble and other telescopes, revealed the most direct evidence yet that dark matter does exist. Observations of a galaxy cluster known as the Bullet Cluster showed that there is not enough mass in the normal matter to explain the motions of the galaxies in the cluster. Without dark matter holding them together, the galaxies and hot gas would have quickly flown apart. In addition, the distribution of mass in the cluster does not coincide with the distribution of normal matter. These observations helped rule out a competing idea that the effects attributed to dark matter could be the result of an incomplete understanding of gravity.

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The Hubble Space Telescope, which observed the Kuiper Belt object Xena in December 2005, revealed to astronomers that it is approximately 5 percent larger than Pluto. Hubble observations yielded a diameter of 1,490 miles (with an uncertainty of 60 miles), while it measured Pluto's diameter as 1,422 miles. Previous ground-based observations suggested that Xena was about 30 percent greater in diameter. Xena is located about 10 billion miles away and amounts to 1.5 pixels across in Hubble's view, which is enough to precisely make a size measurement.

The team, led by Dr. Mike Brown, planned to use Hubble and other telescopes to study additional Kuiper Belt objects that are almost as large as Pluto and Xena. Finding that the largest known Kuiper Belt object is a virtual twin to Pluto further complicated the debate about whether to categorize the large icy worlds that dwell in the Kuiper Belt as planets. If Pluto were considered to be the minimum size for a planet, Xena would also fulfill the criterion.

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Even a stubborn bolt, which initially refused to move, couldn’t stop the crew. Members of the space shuttle Atlantis went on to conduct five spacewalks, replacing the Wide Field Planetary Camera 2 (WFPC2) with the Wide Field Camera 3 (WFC3); removing the Corrective Optics Space Telescope Axial Replacement (COSTAR) and installing the Cosmic Origins Spectrograph (COS); and repairing its spectrograph and Advanced Camera for Surveys (ACS). They also replaced its gyroscopes, among a slew of additional repairs.

With WFC3, Hubble can view galaxies, star clusters, and other objects across a wide swath of the electromagnetic spectrum, from ultraviolet to near-infrared light. COS slices across billions of light-years to map the structure of the universe and trace the distribution of elements that are fundamental to life. Overall, these instruments are more sensitive and observe in ways that are significantly more efficient than previous instruments. The images released in September proved Hubble’s new capabilities.

With the eXtreme Deep Field, or XDF, astronomers improved on Hubble’s already-remarkable achievements in imaging the beginnings of the universe. The XDF was assembled by combining 10 years of NASA’s Hubble Space Telescope photographs taken of a patch of sky at the center of the original Hubble Ultra Deep Field (2004).

The XDF image reaches much fainter galaxies and includes very deep exposures in red light from Hubble’s recently installed infrared camera, enabling new studies of the earliest galaxies. More than 2,000 images of the same field were taken with Hubble’s two premier cameras—the Advanced Camera for Surveys and the Wide Field Camera 3, which extends Hubble’s vision into near-infrared light—and combined to make the XDF.

The universe is 13.7 billion years old, and the XDF revealed galaxies that span back 13.2 billion years. To put this achievement in perspective, before Hubble was launched in 1990, astronomers could barely see galaxies to 7 billion light-years away.

In celebration of its 25th anniversary, Hubble was once again pointed toward the Eagle Nebula, some 6,500 light-years away. Hubble's Wide Field Camera 3 (WFC3), which replaced the WFPC2 used for the original image released in 1995, revealed a sharper, wider view of the region. In the visible light image, bright, young stars just out of the field of view illuminate the iconic pillars of dense gas and dust. Streamers of gas are driven off the pillars by intense ultraviolet radiation from the hot stars.

The infrared image reveals details that are completely invisible in the original image: young stars forming deep within the pillars. While visible light from these stars cannot penetrate their thick cocoons of gas and dust, infrared light passes through it freely.

The images highlight the tremendous capabilities of the 25-year-old Hubble Space Telescope and the benefits of regular servicing missions. The WFC3 was installed during the fifth and final servicing mission in 2009.

STScI released the largest Hubble Space Telescope image ever assembled, a sweeping panoramic view of our closest galactic neighbor, Andromeda (M31). It is a dazzling display of Hubble’s imaging power, resolving individual stars in a galaxy over 2 million light-years away, covering a swath of its disk 61,000 light-years long.

Never before had astronomers been able to see individual stars over a major portion of an external spiral galaxy; in this image there are more than 100 million individual stars. This was the first data to reveal populations of stars in the context of their home galaxy.

The panoramic image is the product of the Panchromatic Hubble Andromeda Treasury (PHAT) program, showing the galaxy in its natural visible-light color, as photographed with Hubble’s Advanced Camera for Surveys in red and blue filters July 2010 through October 2013.

The nebula's intricate shape is caused by a complex interplay of the pulsar, a fast-moving wind of particles coming from the pulsar, and material originally ejected by the supernova explosion and by the star itself before the explosion.

This image combines data from five different telescopes: the VLA (radio) in red; Spitzer Space Telescope (infrared) in yellow; Hubble Space Telescope (visible) in green; XMM-Newton (ultraviolet) in blue; and Chandra X-ray Observatory (X-ray) in purple.

Researchers suggest this “outgassing” is one possible cause for `Oumuamua’s slight acceleration, as detected by several telescopes. The irregularly shaped object is now traveling away at about 70,000 miles per hour. The orbits of the major planets are included for scale. The box-shaped constellation Corvus is in the background near image center, and the bright blue star Spica is at upper left of center, in the constellation Virgo. The stars at bottom left belong to the constellation Hydra.

The planet and moon orbit the star Kepler-1625, located 8,000 light-years away in the constellation Cygnus. The parent star is similar to our Sun, and the planet and moon are located in its habitable zone where temperatures allow for liquid water to remain stable. However, both worlds are gaseous bodies and not suitable for life as we know it.