Great Observatories program

NASA started a special group of space telescopes called the Great Observatories. These four big telescopes were sent into space between 1990 and 2003. Each one was built to look at different kinds of light from the stars and other objects in space, like gamma rays, X-rays, visible light, ultraviolet light, and infrared light.

One of these telescopes is the Hubble Space Telescope. It mainly looks at visible light and a bit of ultraviolet light. Hubble was launched in 1990, but there was a problem with its mirror at first. Astronauts fixed it in 1993, and since then it has been helping us see space very clearly. It is still working today.

Another telescope is the Compton Gamma Ray Observatory, which looked at gamma rays. It was launched in 1991 but had to be brought back to Earth in 2000 after one of its parts stopped working.

The Chandra X-ray Observatory looks at X-rays from hot and energetic places in space. It was launched in 1999 and is still working today.

The last one is the Spitzer Space Telescope, which looked at infrared light. It was launched in 2003. It stopped working fully in 2009 when its cooling liquid ran out, and it was turned off for good in 2020.

Origins of the Great Observatory program

The idea for the Great Observatory program started in 1979 with a report from the NRC. This report helped plan the program and was led by Peter Meyer and later Harlan J. Smith. In the 1980s, leaders at NASA headquarters helped move the plan forward.

NASA created four special satellites for the Great Observatories. Each satellite was built to study a different kind of light that we can't see from Earth. This made the X-ray and infrared satellites part of the same big plan as the Hubble telescope, instead of replacing it. NASA made documents to explain why these telescopes were needed and what questions they could answer, which helped get support for the project.

Great Observatories

Hubble Space Telescope

Main article: Hubble Space Telescope

The Hubble Space Telescope was first imagined in 1946 by astronomer Lyman Spitzer. The telescope was launched in 1990. It has helped us see stars and galaxies very clearly.

Compton Gamma Ray Observatory

Main article: Compton Gamma Ray Observatory

Gamma rays are energy from space. NASA launched the Compton Gamma Ray Observatory in 1991. It worked for almost ten years before it stopped and fell back to Earth in the Pacific Ocean.

Chandra X-ray Observatory

Main article: Chandra X-ray Observatory

X-rays are energy from space. The Chandra X-ray Observatory was launched in 1999. It orbits high above Earth to stay safe from radiation. It shows us hot and energetic places in space.

Spitzer Space Telescope

Main article: Spitzer Space Telescope

Astronomers wanted a telescope that could see heat energy, called infrared light. The Spitzer Space Telescope was launched in 2003. It looked at cooler objects in space, like dust and gas, until it stopped working in 2020.

Timeline

The Great Observatories program was a special set of four big space telescopes made by NASA. These telescopes were sent into space between 1990 and 2003. Each telescope was designed to look at different kinds of light, such as gamma rays, X-rays, visible light, ultraviolet light, and infrared light. One of these telescopes, called the Hubble Space Telescope, mainly looks at visible light and some nearby ultraviolet light.

Strengths

Because the Earth's air blocks some types of light, like X-rays and gamma-rays, space missions were needed for the Compton, Chandra, and Spitzer observatories. The Hubble telescope also benefits from being above the air, which makes images of very faint objects clearer. Brighter objects can sometimes be seen from the ground using special tools.

Each observatory was built to explore new areas of light and improve technology. Compton was much larger than earlier gamma-ray instruments and could see energy levels from 20 keV to 30 GeV. Gamma rays come from energetic places like black holes, fast-spinning stars called pulsars, and exploding stars called supernovae.

Chandra was the first of its kind for X-rays and could see very faint X-ray sources. Spitzer observed infrared light, which is important for studying very distant objects, cool objects, and areas hidden by dust.

Synergies

The Great Observatories program lets different space telescopes work together to learn more about space. Each telescope looks at light in a different way. Using more than one telescope on the same object helps scientists understand it better.

For example, telescopes that look at X-rays and gamma rays can work with the Hubble Space Telescope to get better details about where objects are and how big they are. Hubble can also add more detail to pictures taken by other telescopes. In 2016, Hubble and another telescope discovered a very distant galaxy called GN-z11. This showed how the universe looked 13.4 billion years ago.

Hubble is great for looking at stars and galaxies, but it cannot study every interesting object. Other telescopes often find new objects that Hubble can then study in more detail. By combining observations from different telescopes, scientists have created a detailed picture of how galaxies formed and changed in the early universe.

Impact

The launch of powerful space telescopes like Compton, Chandra, and Spitzer opened new ways to study the universe. These telescopes helped scientists discover thousands of new objects by looking at different kinds of light. The Hubble Space Telescope became very famous because it could take clear pictures of stars and galaxies at any time. Hubble’s special ability to take good pictures helped scientists compare many objects in the sky. For example, Hubble’s Deep Field images showed distant galaxies in great detail, making them easier to study.

Successors to Great Observatories

• The James Webb Space Telescope (JWST) launched in December 2021 and works with Hubble. It has a large mirror that helps it see farther and more clearly. JWST looks at infrared light, which helps it see through space dust. It can see much better in near-infrared light than Spitzer.

• The Fermi Gamma-ray Space Telescope (FGRST) was launched on June 11, 2008, as a follow-up to an earlier telescope. It is smaller and studies certain types of light. It has two tools for this work. It works with Swift, which launched in 2004, and before that with HETE-2, launched in 2000.

• The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) studied certain types of light from February 2002 until April 2023. RHESSI always pointed at the Sun but sometimes saw other bright objects nearby.

• Another big telescope for high-energy light is INTEGRAL, launched in 2002. It looks at similar types of light as another telescope but uses different technology for special studies.

Later programs

NASA has planned new science programs that build on the Great Observatories. The Beyond Einstein program aims to explore new scientific areas. Two parts of this program, Constellation-X and the Laser Interferometer Space Antenna (LISA), are sometimes called the Einstein Great Observatories, but they are not part of the original Great Observatories program.

Another effort, the International Solar-Terrestrial Physics Science Initiative (ISTP), follows the Great Observatories spirit. It uses a set of instruments to study the Sun and its effects on space around Earth.

Next Great Observatory

In 2016, NASA began studying four big ideas for new space telescopes. These ideas are called the Habitable Exoplanet Imaging Mission (HabEx), Large UV Optical Infrared Surveyor (LUVOIR), Origins Space Telescope (OST), and Lynx X-ray Observatory. By 2019, the teams shared their final plans with the National Academy of Sciences. This group helps NASA choose which new telescope project should be the most important.

In 2023, NASA introduced the Habitable Worlds Observatory (HWO). This new idea builds on the plans from the Large UV Optical Infrared Surveyor (LUVOIR) and Habitable Exoplanet Imaging Mission (HabEx). NASA also started a special program called the Great Observatory Maturation Program to help develop the Habitable Worlds Observatory.