Edwin Hubble transformed our view of the cosmos by publishing a paper in the Proceedings of the National Academy of Sciences that provided evidence that the universe is constantly expanding. By collecting data at the Mt. Wilson Observatory in California, Hubble determined distances to galaxies outside the Milky Way, which led him to find a linear relationship between an object’s velocity and its distance from us. His work followed that of French astronomer Georges Lemaître, who published observational and theoretical evidence reaching the same conclusion in 1927. The findings, now known as the Hubble–Lemaître Law, indicate that galaxies are moving away from one another at speeds proportional to their distance.

Although astronomers have used telescopes since the 1600s, the Earth’s atmosphere limits the data we can observe by distorting light. In 1946, Lyman Spitzer proposed designing, building, and launching an “extra-terrestrial observatory” into Earth’s orbit—but his paper was printed as an appendix of a long, detailed document prepared for the Project RAND (an organization formed after World War II to connect military planning with research and development decisions) of the Douglas Aircraft Company.

Although his paper did not appear in a peer-reviewed astronomical journal and was not widely distributed, writing the proposal had an influential effect on the author, convincing him that a large space telescope would revolutionize astronomy—and that this observatory could be launched in his lifetime. When he became the director of the Princeton University Observatory in 1947, he began a program to work toward this significant, long-term goal. The paper was reprinted with a postscript in Astronomy Quarterly in 1990 after the Hubble Space Telescope launched.

After the launch of Sputnik in 1957, the U.S. accelerated its space program and launched its first satellite, Explorer 1, in 1958. Its orbit ranged from 220 miles (354 kilometers) to 1,563 miles (2,515 kilometers) off the Earth’s surface, making just under 13 orbits each day. Explorer 1 made its final transmission almost five months later on May 23. It entered Earth’s atmosphere and burned up in March of 1970, after more than 58,000 orbits.

Its primary science instrument was a cosmic-ray detector—designed to measure the radiation environment in Earth orbit—that revealed a much lower cosmic-ray count than expected. This finding led to the discovery two months later, by another U.S. satellite, of radiation belts of charged particles trapped in space by Earth’s magnetic field.

In 1958, President Dwight D. Eisenhower signed the National Aeronautics and Space Act (commonly known as the Space Act) into law, creating the National Aeronautics and Space Administration (NASA). Although the Space Act has been amended many times, the objectives set for NASA have largely remained the same. In part, its objectives are to support:

• The expansion of human knowledge of phenomena in the atmosphere and space;
• The development and operation of vehicles capable of carrying instruments, equipment, supplies, and living organisms through space; and
• The establishment of long-range studies of the potential benefits to be gained from, the opportunities for, and the problems involved in the utilization of aeronautical and space activities for peaceful and scientific purposes.

NASA began operations on October 1, with 8,000 employees, an annual budget of $100 million, three major research laboratories, and two smaller test facilities. Today, NASA has 20 locations around the country.

Dr. Nancy Grace Roman joined NASA as its first chief of astronomy and relativity programs in the Office of Space Science when the agency was in its first year of operations. She quickly became a champion for the Large Space Telescope, now known as the Hubble Space Telescope, which astronomers proposed be the first space-based observatory capable of observing in ultraviolet and visible light.

In 1960, Roman brought together astronomers from all over the U.S. to meet with NASA engineers to revise the telescope’s designs, ensure that it met engineering requirements, and confirm it would be capable of capturing and returning data from a low-Earth orbit.

The team went on to develop charge coupled devices (CCDs) that included a chloramine coating to guarantee the telescope would not only be sensitive to visible light, but also to ultraviolet light, and could be operated remotely.

During her time at NASA, she oversaw the development of three orbiting solar observatories and several astronomical observatories, including the Copernicus satellite, which observed ultraviolet and X-ray light, and the International Ultraviolet Explorer (IUE), which observed in ultraviolet light.

Dr. Roman retired in 1979, but continued to contribute to astronomy through other roles at NASA, universities, and as a volunteer, sharing her knowledge of astronomy with the public until her death in 2018.

NASA’s Nancy Grace Roman Space Telescope, formerly known as the Wide Field Infrared Survey Telescope (WIFRST), is named in honor of Dr. Roman.

When President John F. Kennedy addressed a special joint session of the U.S. Congress, he made a strong argument for the country to commit to a lunar landing before 1970. In his speech, Kennedy stated, “First, I believe that this nation should commit itself to achieving the goal, before this decade is out, of landing a man on the Moon and returning him safely to the Earth. No single space project in this period will be more impressive to mankind, or more important for the long-range exploration of space; and none will be so difficult or expensive to accomplish.”

He acknowledged the difficulties ahead, including the development of new technologies that would allow the U.S. to accomplish this goal. When Apollo 11 touched down on the Moon July 20, 1969, President Kennedy’s mission was realized.

Astronomers first put forth the idea to construct and launch a Large Space Telescope (LST) during a Space Science Board meeting in Woods Hole, Massachusetts, in the summer of 1965. Around the same time, NASA conducted studies to determine the feasibility of a project like this. It wasn’t until a series of scientific reports came out in the following years that the concept was translated into a substantial report published by the National Academy of Sciences, titled “Scientific Uses of the Large Space Telescope.”

This report arrived at several significant conclusions. First, the LST would make a major contribution to our knowledge of cosmology, particularly our understanding of the structure, scale, and evolution of the universe. And, notably, that the telescope should work in concert with other, smaller space-based telescopes, as well as a number of ground-based instruments.

More than a billion people watched as astronaut Neil Armstrong climbed down the Apollo 11’s Eagle lunar lander ladder and proclaimed, “That’s one small step for a man, one giant leap for mankind.” The U.S. had succeeded in putting men on the Moon. Astronaut Edwin “Buzz” Aldrin joined him, declaring the Moon’s surface to be “magnificent desolation.”

The pair of astronauts explored the surface 300 feet from the Eagle, deploying scientific experiments and reporting on lunar surface samples. The astronauts also planted an American flag to honor the fallen Apollo 1 crew, and a plaque to commemorate the accomplishment before blasting off to dock with the Columbia, where astronaut Michael Collins waited. The crew safely reentered the Earth’s atmosphere, landing on July 24 in the Pacific Ocean near Hawaii. Over the next three years, 10 astronauts also landed on the Moon.

To ensure the health and longevity of the ambitious Space Telescope project, NASA requested that the National Academy of Sciences organize a committee to study and report on the type of institution that should support it.

The study participants—led by Dr. Donald F. Hornig and made up of astronomers who operated ground-based observatories, conducted space-based experiments, and processed digital data—recommended founding an independent organization known as the Space Telescope Science Institute to provide not only long-term guidance and support for the telescope, but also to engage astronomers around the world.

Specifically, they recommended designing an institute operated by a broad-based consortium of universities and nonprofit institutions to encourage collaboration, and recommended employing sufficient staff to allocate time to use the telescope, carry out its science operations, generate new capabilities for the telescope, and reduce and broadly disseminate its data.

“No one can predict what new kinds of objects, what new concepts, what new enigmas [the Space Telescope] will yield, nor what particular combination of ground-based observations and [Space Telescope] observations may yield them,” the study participants reasoned. “Astronomers not yet born may provide its crowning discoveries.”

NASA's Marshall Space Flight Center in Huntsville, Alabama, is selected to oversee the overall design, development, and construction of the space telescope. It contracted Perkin-Elmer Corporation in Danbury, Connecticut, to develop the optical system and guidance sensors, and Lockheed Missiles and Space Company in Sunnyvale, California, to produce the protective outer shroud and the support systems for the telescope, and to assemble the finished product.

NASA's Goddard Space Flight Center in Greenbelt, Maryland, led the development of the scientific instruments, including the Goddard High Resolution Spectrograph, and the ground control center. The European Space Agency furnished the solar arrays and the Faint Object Camera. Three more instruments, the Wide Field/Planetary Camera, the Faint Object Spectrograph, and the High Speed Photometer, were designed and created by scientists at major universities.

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.

At 11:39 a.m. in Cape Canaveral, Florida, NASA’s space shuttle Challenger exploded over the Atlantic, killing all seven crew members on board. The disaster was caused by the aft field joint on the right solid rocket booster, which wasn’t completely sealed due to the cold weather. Vaporized material streamed from the joint, forming a flame plume and transforming into an enveloping burn 73 seconds after liftoff. The crew included Teacher-in-Space Sharon Christa McAuliffe, and astronauts Gregory Jarvis, Judith A. Resnik, Francis R. (Dick) Scobee, Ronald E. McNair, Mike J. Smith, and Ellison S. Onizuka.

The Hubble Space Telescope was originally scheduled to launch that October, but was delayed when all NASA shuttle flights were grounded. The space shuttle program resumed with the successful launch of space shuttle Discovery in 1988.

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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Before NASA’s Compton Gamma Ray Observatory (CGRO) launched, it was not known if gamma rays only resulted from local, modest energy events. CGRO found that gamma-ray bursts are scattered evenly throughout the sky, proving that the bursts came from various cosmological distances.

The observatory made many other significant observations, including evidence of supermassive black holes, quasars, and supernova remnants. It also discovered blazars, a class of quasars that shine brightest in the gamma-ray range.

In 1999, the instrument cued a computer-controlled telescope at Las Alamos National Laboratory in New Mexico within 20 seconds of registering a burst. This experiment proved that its newly automated process worked, and CGRO sent regular gamma-ray burst alerts to inform the Hubble Space Telescope, the Chandra X-ray Observatory, and ground-based observatories around the world.

After one of CGRO’s gyroscopes failed in November 1999, NASA deorbited the satellite. It reentered Earth’s atmosphere June 4, 2000.

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.

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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.

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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In 1993, just three years into the Hubble mission, the Association of Universities for Research in Astronomy (AURA) established the HST & Beyond Committee to consider the scientific goals and technological needs of the astronomical community following the planned decommissioning of Hubble in the early 21st century.

The conclusions of the study, published in what came to be known informally as the Dressler Report, included recommendations that Hubble be kept in operation past 2005, and that NASA develop a new general-purpose space telescope with a mirror at least 4 meters in diameter and a wavelength range in the near-infrared.

The authors proposed that the “Next Generation Space Telescope” be powerful and sensitive enough to see beyond Hubble’s range, back into the “dark zone” of the first billion years of the universe to gather the faint infrared light of newly forming galaxies.

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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.

With the success of the Hubble Deep Field, which revealed thousands of extremely distant, previously unknown galaxies in a tiny patch of sky, astronomers began to consider a telescope that could see even farther—to a time when galaxies were first forming.

In the summer of 1996, shortly after publication of the “HST & Beyond” report recommending that NASA construct a large near-infrared observatory to accomplish this goal, the Association of Universities for Research in Astronomy (AURA) brought together three teams to study the technical and financial feasibility of such an endeavor.

All three teams concluded that design and construction of a large near-infrared telescope—with a 6- or 8-meter mirror, the ability to maintain the extremely low temperatures required for high sensitivity, and a clear observation post beyond the Earth and Moon—while ambitious, was in fact possible.

The study report, written by H. S. Peter Stockman and published in 1997, served as a guide for further research and development of the Next Generation Space Telescope.

Components of the International Space Station (ISS) were launched piece by piece and assembled in-orbit 240 miles above the Earth, beginning in 1998 with the Russian module Zarya, meaning sunrise, and the American module named Unity. The construction took an unprecedented international collaboration of five space agencies representing 16 countries: NASA; Russia’s Roscosmos State Corporation for Space Activities; the European Space Agency; the Canadian Space Agency; and the Japan Aerospace Exploration Agency.

The ISS orbits Earth every 90 minutes, and is second only to the Moon as the brightest object in the night sky visible without a telescope, thanks to more than an acre of solar arrays.

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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After its successful deployment by space shuttle Columbia, NASA’s Chandra X-ray Observatory used a built-in propulsion system to boost itself to a high-Earth orbit. Chandra passes more than a third of the way to the Moon before returning approximately 9,942 miles (16,000 kilometers) away from Earth, allowing it to observe up to 55 hours.

Chandra was first proposed to NASA in 1976 by STScI’s founding director Dr. Riccardo Giacconi and Dr. Harvey Tananbaum of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts. Funding and definition studies began in 1977 by NASA’s Marshall Space Flight Center.

Designed to detect X-ray emission from hot and energetic regions of the universe, Chandra has observed planets and comets, quasars, supernova remnants, and, most notably, discovered black holes. The observatory also made a major advance in the study of dark matter by tracing the separation of dark matter from normal matter in collisions between galaxy clusters. It also contributes to research on the nature of dark energy.

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.

As originally intended, the International Space Station has been continuously crewed ever since U.S. astronaut Bill Shepherd and Russian cosmonauts Yuri Gidzenko and Sergei Krikalev first stayed for several months. Crew members are not only responsible for conducting scientific experiments, but also for maintaining the station inside and out.

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.

The Next Generation Space Telescope was renamed in honor of former NASA Administrator James E. Webb to recognize him as a champion for science. Although President John Kennedy had committed to landing a man on the moon before the end of the 1970s, Webb believed that NASA had to balance its efforts between human space flight and science.

James Webb was also a champion of a large space-based telescope mission, which would eventually become the Hubble Space Telescope. By the time he retired, NASA had launched more than 75 space-based science missions to study stars and galaxies, the Sun, and the environment of space above the Earth’s atmosphere.

Around the same time the Webb telescope was renamed, NASA selected the TRW corporation of Redondo Beach, California, (now Northrop Grumman Aerospace Systems) to build the Webb telescope. NASA also formed the Science Working Group to define and publish a rationale for the science requirements that will guide the Webb telescope’s formulation, design, and operation.

When seen with our eyes or viewed with telescopes that are designed to see only visible light, the space between distant stars and galaxies looks completely dark. But in fact, the entire sky is lit with a faint glow of very low-frequency light, a relic of the energy left over from the big bang that formed the universe some 13.8 billion years ago.

This glow, known as the cosmic microwave background radiation (CMB), was first detected in 1964. Between 1989 and 1993, the Cosmic Background Explorer satellite (COBE) mapped the radiation across the entire sky, revealing slight variations, or anisotropies, which reflect slight differences in temperature from place to place. In 2001, the Wilkinson Microwave Anisotropy Probe (WMAP) began mapping the CMB in even greater detail and in February 2003 NASA released the first WMAP map of the universe. The map was updated regularly until 2012, and details of the CMB were further refined with data from the Planck Space Telescope between 2009 and 2013.

After launching on a Delta II rocket from Florida, NASA’s Spitzer Space Telescope, named for astrophysicist Dr. Lyman Spitzer, settled into an Earth-trailing orbit. The observatory was purposefully designed to have two missions: one cool and one warm. The first used cryogenically cooled instruments to efficiently map large areas of the sky. After it depleted its liquid helium more than five year later, it switched to its second mission. Spitzer currently uses two IRAC channels to measure the near- to mid-infrared portion of the spectrum to study comets and asteroids in our solar system, planets orbiting other stars, and distant galaxies.

In 2017, the telescope discovered the first known system of seven Earth-size planets around a single star, TRAPPIST-1. Three of the planets are located in the habitable zone, the area around the parent star where a rocky planet is most likely to have liquid water. The finding set a new record for greatest number of habitable-zone planets found around a single star outside our solar system.

In January 2020, the spacecraft was decommissioned, ending more than 16 years of discovery. The Spitzer mission's complete data archive is publicly available through STScI's Mikulski Archive for Space Telescopes and will continue to be mined for decades to come.

The Mars Rover Spirit was the first to land on the Red Planet on January 3, after a journey of almost seven months, with Opportunity following on January 24. They landed on opposite sides of the planet and began their missions of photography and on-site analysis of Martian rocks and soil. Less than two months after landing, NASA announced that Opportunity had found evidence of past-flowing liquid water.

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.

NASA announced the discovery of the first Solar System object larger than Pluto, which immediately brought the classification of Pluto and the definition of a planet into question. The object was nicknamed Xena by the discovery team, and later became officially known as Eris, even as its size relative to Pluto was debated when new data from the distant Solar System was collected. A year after its discovery was announced, the decision was made to classify Eris not as the tenth Solar System planet, but as a dwarf planet, alongside many similarly sized objects in the Kuiper Belt.

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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NASA’s first planet-hunting spacecraft continuously monitored a patch of space that contains 150,000 stars like the Sun for indications of Earth-sized planets from 2009 to 2013. Kepler, which observed infrared light, explored the structure and diversity of planetary systems, determined the percentage of terrestrial and larger planets that are in or near the habitable zone of a variety of stars, and defined the distribution of sizes and shapes of the orbits of these planets.

When its second reaction wheel stopped functioning in 2013, the mission was transformed and renamed K2. It continued operating from 2014 to 2018, still using the transit method—measuring the detection of a planet when it passes in front of a star—to make observations in an ecliptic plane with a limited duration of 80 days for each observation.

The Kepler mission detected over 4,700 candidate exoplanets, with more than 2,300 confirmed. By 2018, K2 detected more than 500 candidates and confirmed over 350.

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.

Following Hubble’s upgrade in May 2009, a new category of observation programs was initiated to make the most of the telescope’s improved capabilities. Multi-cycle Treasury Programs invite astronomers to propose large, ambitious observation programs that require hundreds of Hubble orbits over multiple years. The Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey, known as CANDELS, was one of three initial programs chosen.

The CANDELS survey involved imaging more than 250,000 distant galaxies to allow researchers to map the distribution of tiny, young galaxies in the ancient universe, test theories of galaxy formation and evolution, and understand the early stages of formation of supermassive black holes.

The survey was also designed to detect distant supernovas that can be used as “standard candles” for measuring distances to distant galaxies, and gain more insight into the nature of dark energy and the expansion of the universe.

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The crew of Atlantis completed a mission to resupply the International Space Station with thousands of pounds of supplies and equipment during the NASA’s final space shuttle mission. The program began in 1981 and included 135 missions. The program allowed astronauts to recover and repair satellites, including the Hubble Space Telescope, conduct research, and help build the International Space Station. The space shuttle program created the world’s first reusable spacecraft and led to the creation of advanced technologies that both support space exploration and Americans’ everyday lives.

Scientists successfully used Hubble to find suitable targets for NASA’s New Horizons mission after it zoomed past Pluto in July 2015 and continued across our solar system’s Kuiper Belt, a vast rim of ice bodies left over from the birth of our solar system more than 4.5 billion years ago.

Hubble identified two Kuiper Belt objects moving against a background field of stars in the constellation Sagittarius. The exceedingly challenging observations amounted to finding charcoal-black objects no bigger than Manhattan Island 4 billion miles away.

Hubble took deep exposures on 20 areas of the sky and found suitable targets about 1 billion miles beyond Pluto. Following NASA approval for a mission extension in 2016, the team selected 2014 MU69, later nicknamed Arrokoth, as the target for its January 2019 flyby.

New Horizons’ observations revealed a very red, 22-mile long, double-lobed object. The object's strange shape—unlike any ever seen—was the biggest surprise. In the years since, Hubble has measured Arrokoth’s color and refined its orbit with additional observations.

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NASA announced that it approved formulation of the Wide Field Infrared Survey Telescope (WFIRST), an astrophysics mission designed to perform a broad set of scientific investigations: studying dark energy, measuring the history of cosmic acceleration, completing the exoplanet census, and demonstrating technology for direct imaging and characterization of exoplanets. WFIRST will also have guest observer and archival guest investigator programs that will use surveys to address science across all areas of astrophysics.

WFIRST will survey large regions of the sky in near-infrared light. It will carry a Wide Field Instrument for surveys and a Coronagraph Instrument designed to block the glare of individual stars and reveal the faint light of planets orbiting around them. The Space Telescope Science Institute, which will conduct its science operations after its launch, leads the work on the mission’s observation scheduling system, Wide Field Instrument data processing system for the direct-imaging mode, and its entire data archive.

WFIRST is now known as the Nancy Grace Roman Space Telescope.

NASA’s Spitzer Space Telescope revealed the first known system of seven Earth-sized planets around a single star. The system is named TRAPPIST-1, for the Transiting Planets and Planetesimals Small Telescope (TRAPPIST) in Chile, and is located about 40 light-years (235 trillion miles) from Earth.

TRAPPIST-1 contains the greatest number of habitable-zone planets discovered around a single star outside our solar system to date: three. Future spectroscopic study of the planets’ atmospheres will determine if any or all of them have liquid water, the key to life as we know it. Finding so many Earth-like exoplanets in the habitable zone was an exciting milestone toward one of NASA’s top science priorities: investigating the question, Are we alone?

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In an unprecedented collaboration, scientists worldwide combined the newly proven gravitational wave observatories LIGO and Virgo with telescope observations to view the source of a gravitational wave for the first time. Two seconds after LIGO detected a gravitational wave, the Fermi Gamma-ray Space Telescope detected a short, bright gamma ray burst.

The Swift, Chandra, and Hubble missions all followed up with observations in their respective light wavelengths. Across the globe, telescopes turned toward the source in hopes of seeing the quickly fading light signature. Together they confirmed the source as the collision of two neutron stars.

It was the first time telescopes and gravitational wave detectors had been used together to study one astronomical event. Astronomers anticipate that this is the first of many such detections, a new multi-method approach to observing the cosmos and decoding the messages it has for us.

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NASA’s Transiting Exoplanet Survey Satellite (TESS) will survey the entire sky over the course of two years to make observations of 200,000 of the brightest stars near the Sun to find exoplanets using the transit method—measuring the detection of a planet when it passes in front of a star. Scientists expect the mission will catalog thousands of planet candidates and vastly increase the current number of known exoplanets.

The stars TESS will study are 30 to 100 times brighter than those NASA’s Kepler/K2 mission studied, which will enable easier follow-up observations with both ground- and space-based telescopes. TESS will also cover a sky area 400 times larger than that monitored by Kepler.

This rich set of targets will provide researchers opportunities for more comprehensive follow-up studies. All of TESS’s data is stored in the Space Telescope Science Institute’s Barbara A. Mikulski Archive for Space Telescopes (MAST).

Astronomers used Hubble to confirm evidence that an intense X-ray glow in a distant galaxy could be traced back to a mid-sized black hole. Weighing in at about 50,000 times the mass of our sun, the black hole is smaller than the supermassive black holes (at millions or billions of solar masses), but larger than stellar-mass black holes formed by the collapse of a massive star.

Intermediate-mass black holes are a long-sought “missing link” in black hole evolution. Though there have been a few other candidates, researchers consider these new observations the strongest evidence yet for mid-sized black holes in the universe.

It took the combined power of NASA’s Chandra X-ray Observatory, ESA’s XMM-Newton mission, and Hubble to nail down the cosmic beast. Hubble was pointed at the previously identified X-ray source to resolve its precise location. Deep, high-resolution imaging provided strong evidence that the X-rays emanated not from an isolated source in our galaxy, but instead in a distant, dense star cluster on the outskirts of another galaxy. The X-rays are generated as a shredded star’s superheated gas flows into the black hole, but before that material dips below the event horizon—the point beyond which any light emitted is forever hidden from our view.

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NASA announced that its next large space-based mission, the Wide Field Infrared Survey Telescope (WFIRST), will be named the Nancy Grace Roman Space Telescope in honor of the agency’s first chief astronomer. Dr. Roman was instrumental in establishing space-based astronomy, including her role as project scientist for the first large space-based observatory, the Hubble Space Telescope.

As the chief of NASA’s astronomy and relativity programs, Dr. Roman was involved with planning a program of satellites and rockets with input from a wide sample of the nation’s astronomical community.

Of her career path and impact, Dr. Roman said, “I knew that taking on this responsibility would mean that I could no longer do research, but the challenge of formulating a program from scratch that I believed would influence astronomy for decades to come was too great to resist.”

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NASA’s James Webb Space Telescope successfully underwent a comprehensive systems test, the first full systems evaluation that has ever been run on the assembled observatory. Similar performance evaluations have been completed in Webb’s history, using simulations and surrogates to infer data about pieces of the spacecraft that had not yet been assembled. Now that Webb is fully built, simulations and simulators are no longer needed, and engineers confidently assessed both its software and electronic performance.

The importance of testing cannot be overstated in software development. To complete the test, personnel was staffed 24 hours a day for 15 consecutive days, and approximately 1,070 scripts or sequences of instructions were executed and nearly 1,370 procedural steps were performed.

Webb is comprised of many components that must all communicate and work in unison to achieve mission success. Systems evaluations like these ensure that this happens by verifying and validating that each of them is communicating and performing as designed.

The Roman Space Telescope successfully completed a preliminary design review of the mission’s ground systems, including the science operations center that will be hosted by the Space Telescope Science Institute (STScI) in Baltimore, Maryland. This means the plan for science operations has met all of the design, schedule, and budget requirements.

The mission will now proceed to the next phase: building the newly designed systems that will enable planning and scheduling of Roman observations and managing the resulting data. In its role as science operations center, STScI will plan, schedule, and carry out observations; process and archive mission datasets in the Barbara A. Mikulski Archive for Space Telescopes (MAST); and engage and inform the astronomical community and the public.

STScI collaborates closely with NASA’s Goddard Space Flight Center, which manages the mission; the Jet Propulsion Laboratory (JPL), which is developing the Coronagraphic Instrument; and IPAC/Caltech, which provides science support for the Coronagraphic Instrument and elements of the Wide Field Instrument as the observatory’s Science Support Center.

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Once a decade, the National Academies of Sciences, Engineering, and Medicine seeks input from the U.S. astronomical community, requesting that scientists identify priorities in astronomy and astrophysics, and develop a comprehensive strategy for the upcoming decade. The latest survey, led by a steering committee, recommends a mission and technology maturation program for large missions to consider technology and science needs and tradeoffs. This will lower risks and lead to a better understanding of project cost before mission adoption.

The first large space telescope the committee recommended for this program would be significantly larger than the Hubble Space Telescope, but also designed to observe infrared, visible, and ultraviolet light. A major driver for this observatory is that it should be capable of observing planets 10 billion times fainter than their star, and capture spectra (or data) about the planets’ compositions. This telescope’s target launch date is the early 2040s.

The report also calls for two more large space-based projects of equal priority—a telescope that captures far-infrared light and a mission designed to capture high-resolution X-rays—ensuring astronomers have access to light all along the electromagnetic spectrum.  

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