The Hubble Space Telescope: Our Window on the Universe

NASA

One of the most powerful and productive scientific tools ever developed, Hubble continues to capture scenes of profound beauty and intellectual challenge. Learn about the innovative design and storied history that have helped make Hubble a cultural icon.

Our Window on the Universe
Hubble is the first major optical telescope to be placed in space, the ultimate mountaintop. Orbiting 340 miles up — above the distortion of the atmosphere, clouds, and light pollution — Hubble has an unobstructed view of the universe. This unique perspective allows Hubble to study cosmic objects both in our solar system and far across the universe, some more than 13 billion light-years away.

Hubble is big. Excluding its aperture door and solar arrays, the spacecraft is 43.5 feet (13.3 meters) long and 14 feet (4.3 meters) across at its widest point. Altogether, Hubble would weigh about 27,000 pounds (12,200 kilograms) on the ground, although it is weightless in orbit.

Hubble is a reflecting telescope. It uses mirrors to collect light from the universe and reflect that light to its cameras and other scientific instruments.

The primary mirror is 1,825 pounds and almost 8 feet (2.4 meters) across. It collects light from an astronomical target and reflects it to a secondary mirror that is 12 inches (0.3 meter) wide.

This secondary mirror then reflects the light through a hole in the primary mirror and then on to its scientific instruments.

Unlike most other spacecraft, Hubble was designed to be serviced periodically by astronauts. So it was built with modular components that are made for astronauts to handle and replace.

At the back end of the spacecraft are the scientific instruments. Four are rectangular, each the size of a large refrigerator. Just above them are four additional instruments (three of which are used to track guide stars) that are shaped like pie wedges.

Four 100-pound wheels (two illustrated in the center of this diagram), each two feet wide, are used to turn Hubble using Sir Isaac Newton's third law of motion: for every action there is an equal and opposite reaction. When one wheel spins clockwise, the spacecraft spins counterclockwise.

Hubble is powered by two gallium-arsenide solar arrays that produce more than 5,000 watts or power.

Hubble's observations are converted to radio waves and then beamed through one of the spacecraft’s high-gain antennas to a NASA communications satellite, which relays the data to the ground. Here one of the high-gain antennas appears in its stowed position.

Hubble’s aperture door is usually kept open, but it can close, if necessary, to prevent light from the Sun from entering and potentially damaging the telescope or its instruments.

Yellow handrails are attached all over Hubble to help astronauts traverse the spacecraft during servicing missions.

A Story of Adversity and Success
Theoretical physicist and astronomer Lyman Spitzer first proposed a large space telescope in 1946 — more than a decade before the Soviet Union launched its first satellite and 12 years before the United States formed NASA. The project was approved by Congress in 1977.

Serious technological and managerial challenges arose during the turbulent years of Hubble’s development, causing delays for the project. In January of 1986, the nation suffered the loss of the Space Shuttle Challenger, further delaying Hubble's launch.

Hubble eventually launched on April 24, 1990, aboard Space Shuttle Discovery and was deployed into space the next day using the shuttle's robotic arm.

When Hubble began taking images, they were blurred. The problem was spherical aberration — the edges of Hubble’s primary mirror were ground too flat by just a fraction of the width of a human hair. Although engineers had designed Hubble with replaceable components, the mirror was not one of them.

Scientists and engineers devised a set of nickel- and quarter-sized mirrors to remedy the blurring effects of the primary mirror. Called the Corrective Optics Space Telescope Axial Replacement (COSTAR), this device deployed the small mirrors into the light paths going to the scientific instruments.

In December 1993, astronauts aboard Space Shuttle Endeavour flew on a mission to install the corrective mirrors, add a new camera that had corrective mirrors already built into it, and perform other repairs to the spacecraft.

The camera was the Wide Field and Planetary Camera 2 (WFPC2), designed and built at NASA's Jet Propulsion Laboratory.

WFPC2, which actually contains four cameras, would go on to produce many of Hubble's breathtaking images, helping transform our view of the cosmos.

As seen in these before-and-after images of galaxy M100, the corrective mirrors successfully fixed Hubble's blurred vision.

During four more servicing missions over the next 16 years, astronauts repaired and replaced problematic hardware and installed new instruments on Hubble.

Hubble has been operating for over a quarter century, yet it is still at the peak of its scientific capability. The mission is managed and operated from this control center at NASA's Goddard Space Flight Center, with science operations conducted at the Space Telescope Science Institute.

Hubble by the Numbers: Spacecraft
Hubble is about the size of a school bus: 43.5 feet (13.3 meters) long and 14 feet (4.2 meters) wide. It would weigh ~27,000 pounds (~12,200 kg) on Earth and turns at about the speed of a minute hand on a clock, taking 15 minutes to turn 90 degrees. Hubble's pointing system is so accurate that it could shine a laser beam on Franklin D. Roosevelt's head on a dime roughly 200 miles (320 km) away. 
Hubble by the Numbers: Spaceflight
Hubble has traveled more than 4 billion miles along a circular, low Earth orbit currently about 340 miles (547 km) in altitude. It travels at approximately 17,000 miles per hour (27,300 kph) and orbits Earth every 95 minutes. Hubble is in Earth's shadow about one-third of the time.
Hubble by the Numbers: Optics
Hubble's primary mirror is 7 feet, 10.5 inches (2.4 meters) across and weighed 1,825 pounds (828 kg) on Earth. It was so finely polished that if it were scaled up to the diameter of Earth, the biggest bump on its surface would be only six inches tall. The fine optics, together with Hubble's detectors, would allow the telescope to see a pair of fireflies less than 10 feet apart in Tokyo, Japan, from Washington, DC, if there was no air to interfere with the light. Similarly, Hubble could spot a night light on the surface of the Moon from Earth.
Hubble by the Numbers: Science Data
As of 2019, Hubble has taken over 1.4 million observations that have resulted in more than 16,000 published scientific papers. Those papers have been referenced (cited) in other papers about 800,000 times. The Hubble archive contains more than 150 terabytes of data with about 10 terabytes or more of new archive data added per year. Hubble's first observation was taken on May 20, 1990, of star cluster NGC 3532. The farthest object Hubble has imaged is a galaxy about 13.4 billion light-years away, seen when the universe was less than 4 percent of its current age.

During Hubble’s time in orbit, the telescope's discoveries have changed our fundamental understanding of the universe, and its memorable photos have reinvigorated the public’s interest in astronomy. Not since the days of Galileo has a telescope revolutionized our understanding of the cosmos and so broadly piqued the curiosity of the human race.

Credits: Story

Credit: NASA Goddard Space Flight Center

NASA's Hubble Space Telescope

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