How Do Space Telescopes Work: The Complete Guide (2023)

Have you ever wondered how do space telescopes work?

How does it allow us to see farther and clearer than telescopes on Earth?

This article will explain the key differences between ground and space telescopes, and why space telescopes like Hubble and James Webb offer a unique view of our universe.

How Telescopes Work on Earth vs. In Space

how space telescopes transfer data

On Earth, telescopes have to peer through the atmosphere, which distorts and blocks light from space. But in space, telescopes orbit above the atmosphere, providing a much clearer view. This allows space telescopes to observe infrared and ultraviolet light that doesn’t penetrate Earth’s atmosphere. Space also provides a stable environment without weather and light pollution. With these advantages, space telescopes can see farther back in time and space than ever before.

The Parts of a Space Telescope

spacecraft bus
Photo By NASA

Space telescopes have several key components that allow them to capture crisp images from space. The optical telescope contains the mirrors and lenses that gather and focus light. For example, the James Webb telescope has a massive 21-foot gold mirror made up of 18 hexagonal segments.

There’s also the spacecraft bus which houses support equipment like solar panels, antennas, and propulsion systems. And of course, there are scientific instruments like cameras and spectrometers that analyze the collected light. Advanced space telescopes use new technologies like adaptive optics to compensate for image distortions.

Using Curved Mirrors to Collect Light

Using Curved Mirrors to Collect Light
Photo By Texas Gateway

Curved mirrors play an integral role in collecting and focusing light in space telescopes. The mirrors are precisely shaped and aligned to gather light from distant objects and bring it into focus. Large primary mirrors are parabolic in shape to reduce image aberrations. Segmented mirrors like those on the James Webb telescope can be folded up to fit inside a rocket but unfold to form a large light-collecting surface in space.

Additional secondary and tertiary mirrors are used to direct and further focus the light. Precise actuators bend the mirror segments to achieve perfect alignment down to nanometers. This all enables space telescopes to collect more light from faint, distant objects than any ground-based telescope.

Types of Space Telescopes

Cassegrain space telescopes
Photo By NASA

There are different types of space telescopes optimized for specific purposes. One common type is the Cassegrain reflector, which uses a parabolic primary mirror to collect and focus light onto a secondary convex mirror that reflects the light back through a hole in the primary mirror. The light is then focused at a point behind the primary mirror where the scientific instruments are located. This folded optical path results in a shorter telescope tube length for a given focal length.

Examples of Cassegrain space telescopes include the Hubble Space Telescope and the James Webb Space Telescope. Other types like catadioptric telescopes combine both lenses and mirrors. And radio telescopes use dish antennas to collect radio waves from celestial objects. The design of each space telescope depends on the wavelength of light it is intended to detect and the scientific goals it is tasked to achieve.

Correcting for Atmospheric Distortion

James Webb space telescope
Photo By NASA

One of the main advantages of space telescopes is that they can avoid the blurring effects of Earth’s atmosphere. Atmospheric turbulence and gases distort and absorb incoming light from space, severely limiting the resolution and wavelength coverage that ground-based telescopes can achieve. Space telescopes orbit above the atmosphere, enabling them to collect astronomical data unaffected by these atmospheric distortions. This allows space telescopes to take much sharper images and detect faint objects that would be obscured when viewed through the atmosphere.

Some advanced ground-based telescopes use adaptive optics to partially compensate for atmospheric blurring in real-time. But space telescopes remain the best option for observations requiring high precision, sensitive wavelengths blocked by the atmosphere, or extremely high-resolution imaging across a broad field of view. The freedom to design large telescope optics that don’t have to fold up inside a rocket fairing is another major benefit of space-based platforms for astronomy.

Pointing Telescopes With Gyroscopes

Pointing Telescopes With Gyroscopes
Photo By NASA

One of the key engineering challenges for space telescopes is precise pointing and tracking. With no solid ground to rest on, space telescopes rely on gyroscopes and reaction wheels to maintain their orientation. Gyroscopes provide inertial reference measurements to determine the telescope’s attitude in space. Small thrusters can then make fine adjustments to counteract drift and hold the telescope steadily on target. Reaction wheels provide torque by spinning mass inside the spacecraft, imparting angular momentum to rotate the telescope without expending propellant.

The Hubble Space Telescope uses a combination of gyroscopes and reaction wheels to achieve extremely stable pointing, with a precision of 0.007 arcseconds. This allows Hubble to stay locked onto targets without disruption for many hours or even days. Future space telescopes will push the limits of precision pointing even further, enabling long-duration observations and surveys not possible from the ground.

Transmitting Images and Data Back to Earth

how space telescopes transfer data

After a space telescope captures images and data, transmitting that information back to Earth is another major engineering challenge. Because of the vast distances involved, space telescopes cannot simply use cables to transfer data. Instead, they rely on radio transmitters and large dish antennas to beam data back to Earth via microwave and radio frequencies. The data rate that can be achieved is limited by the power of the transmitter and the size of the antenna.

For example, the Hubble Space Telescope can transmit at about 1 Mbps. Future space telescopes like the James Webb Space Telescope will use advanced transmission techniques to achieve rates up to 28 Mbps. Once the data reaches Earth, it travels to ground stations that are part of NASA’s Deep Space Network. These stations have giant dish antennas to receive faint signals. The data is then processed, analyzed by scientists, and made available for the public to enjoy breathtaking astronomical images and discoveries.

The History and Future of Space Telescopes

the first photo by the hubble telescope
Photo By Hubble Telescope / NASA

Space telescopes have come a long way since the launch of Hubble in 1990. Hubble showed the power of space-based observations, delivering iconic images and major discoveries over multiple decades. The upcoming James Webb Space Telescope will be able to see deeper into the infrared universe than ever before thanks to its giant mirror and advanced instruments. In the more distant future, NASA hopes to launch the Wide Field Infrared Survey Telescope (WFIRST) and the Large UV Optical Infrared Surveyor (LUVOIR) to study dark energy, exoplanets, and the earliest galaxies.

On the more extreme end, concepts like the Habitable Exoplanet Observatory (HabEx) and the Large Interferometer For Exoplanets (LIFE) have been proposed to directly image exoplanets and search for signs of life. As technology improves, space telescopes are becoming more ambitious and capable. The images and discoveries from past, present, and future space telescopes will continue to transform our understanding of the cosmos.

Famous Space Telescopes

the hubble telescope launched to space
Photo By NASA

The Hubble Space Telescope has undoubtedly been the most revolutionary and impactful space telescope to date. Launched in 1990, Hubble delivered the deepest views of the universe humanity had ever seen. Its breathtaking images captivated the public, revealing a dynamic cosmos full of stars, galaxies, and nebulae. Hubble helped measure the expansion rate of the universe, observed galaxies forming shortly after the Big Bang, and enabled numerous other discoveries. After over 30 years of service, Hubble continues to provide valuable data today.

The James Webb Space Telescope launched in 2021 as Hubble’s long-awaited successor. With a massive 6.5-meter mirror, James Webb sees farther into the infrared universe than any telescope before it. It is expected to study the atmospheres of exoplanets, look back in time to the first galaxies that formed after the Big Bang, and advance many areas of astrophysics. The scientific community eagerly awaits the first images and data from James Webb, which has the potential to revolutionize our understanding of the universe just as Hubble did.

The Discoveries Enabled by Space Telescopes

view taken by the hubble telescope
Photo By NASA

Space telescopes have enabled groundbreaking discoveries that fundamentally changed our understanding of the universe. For example, the Hubble Space Telescope provided definitive evidence that the universe is expanding at an accelerating rate, a finding that led to the concepts of dark energy and dark matter. Hubble also peered back in time to capture the Hubble Deep Field images, giving us unprecedented views of early galaxy formation.

The Kepler Space Telescope discovered thousands of exoplanets around distant stars, proving that planetary systems are common throughout the galaxy. Kepler found planets of all types – gas giants, rocky worlds, and even some in the habitable zones of their stars. Its survey indicates that billions of exoplanets likely exist in our galaxy alone.

In the future, the James Webb Space Telescope will probe even farther back in time to the first galaxies that formed after the Big Bang. It will also analyze the atmospheres of exoplanets, searching for potential biomarkers that could indicate the presence of life beyond Earth. Space telescopes continue to transform our understanding of the cosmos and our place within it.


What Do Space Telescopes Actually See?

Space telescopes see electromagnetic radiation like visible light, infrared light, ultraviolet light, X-rays, and more from astronomical objects like stars, galaxies, nebulae, etc. They can see farther and with more detail than ground-based telescopes.

How Do Space Telescopes See So Far?

Space telescopes can see incredibly far because they are above Earth’s atmosphere which distorts and blocks light. In space, telescopes have a clear view without atmospheric interference allowing them to see farther back in time and space.

How Does the James Webb Telescope Stay in Space?

The James Webb telescope stays in space through careful orbital mechanics. It orbits the Sun at the second Lagrange point which balances the gravitational forces from the Sun and Earth to keep it in a stable orbit.

How Does a Telescope See the Universe?

Telescopes see the universe by collecting electromagnetic radiation like visible light from astronomical objects. They use mirrors to gather and focus the light into instruments that can analyze the light to see details about stars, galaxies, black holes, and more in the universe.


Space telescopes allow us to peer deeper into the universe than ever before. By launching advanced telescopes like the James Webb above Earth’s atmosphere, we gain an unobstructed view of the cosmos. Telescopes collect light from distant celestial objects using large mirrors and focus the light on sensitive instruments. This allows us to study how stars and galaxies formed early in the universe’s history and analyze the chemical makeup of planets orbiting other stars. Powerful space telescopes continue to provide new insights into how the universe works.

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