The idea of a space based telescope is not new. Lyman Spitzer first suggested the idea of a telescope in space in 1946. This was 11 years before the first satellite, Sputnik 1, was launched by the Soviet Union. His idea suggested that a telescope in space would not be impacted by the atmosphere of the Earth. Spitzer campaigned for the launch of a space telescope and in the 1970s NASA and the European space began exploring the possibility of launching one. This eventually became the Hubble Space Telescope (HST) which launched in 1990. Today there are many types of space telescopes with many different functions.
The main reason to put a telescope in space is to get above the atmosphere of the Earth. The Earth’s atmosphere protects us from certain types of light such as x-rays and infrared and UV light. This is good for us but bad for astronomy. Ground based telescopes also need to contend with moving air currents, dust in the atmosphere the weather. The way to get around this is a space telescope. In theory all telescopes should be space telescopes. However things are not that simple.
The first drawback of a space telescope is cost. It is very expensive to build, launch and maintain a space telescope. Another is size. The weight of a space telescope is limited to the maximum launch weight of the biggest rocket available. There are many ways to limit and reduce the weight of a telescope, including the use of light material and thin mirrors. Even if the weight of the telescope is reduced significantly, it still needs to fit in the rocket fairing. This is the housing at the top of the rocket that holds the payload. Techniques such as folding mirrors can be used to minimize size but this adds to the cost and complexity. Last but not least is the maintenance of the telescope. What happens when something goes wrong? The Hubble Space Telescope launched with a badly grinded mirror and could have been useless only that it was possible for the space shuttle to go back and fix it. The Space Shuttle is now retired so there is no vehicle capable of maintaining a satellite anymore. The HST was also unique in that it was closer to the Earth than some satellites.
Just like ground based telescopes, space telescopes come in many shapes and sizes. The HST was the first and is fairly similar in structure to other telescopes in that there is two mirrors with a camera at the back. The Hubble Space Telescope has probably had one of the biggest impacts of any scientific instrument. One of the most famous images is called the Hubble eXtreme Deep Field Image. It shows approximately 5,500 of the most distant galaxies ever seen. Some of which are so distant that the light left them 13.2 billion years ago.
Another famous space telescope was the Spitzer Space Telescope, named after Lyman Spitzer. It was launched in 2003, operated in the infrared range and was retired in 2020. They were both part of what were known as the four great observatories that also included the Compton Gama Ray Observatory and Chandra X-Ray Observatory.
Since then there have many more observatories launched into space. One of the most eagerly awaited space telescopes in years is the James Webb Space Telescope (JWST). It is currently very far over budget and very far behind scheduled but it due to launch in October 2021. This telescope will allow us to look further back in time than ever before and search for signs of life around distant exoplanets.