On April 24, 1990, the Space Shuttle Discovery was launched in its STS-31 mission. In its cargo bay, it carried a really special payload, the Hubble Space Telescope. The day after it was deployed in its orbit, just over 550 km (about 342 miles) altitude. On June 25, Hubble sent its first images, which revealed a flaw in its primary mirror that reduced its usefulness. The first of a series of service missions turned what had threatened to turn into a terrible failure into a symbol for science and technology that goes far beyond astronomy.

In 1923, the rocket science pioneer Hermann Oberth wrote an article in which proposed the idea of ​​a telescope in orbit around the Earth. In 1946, the astronomer Lyman Spitzer wrote an article in which discussed the advantages that an observatory in space would have over the ground-based ones. Promoting a project to build a space telescope became an important part of Spitzer’s career.

In the ’60s, the first experiments on space telescopes by NASA started with the OAO (Orbiting Astronomical Observatory) program. Between 1966 and 1972 some space telescopes were launched into orbit with mixed results but still very useful for the development of the LST (Large Space Telescope) project.

Because of budget problems, ESA was contacted for collaboration in the new project and that’s how it became international cooperation. In 1983 it was decided that the LST would be named after the astronomer Edwin Hubble Hubble, who discovered the expansion of the universe.

The Hubble Space Telescope was supposed to be put into orbit in the ’80s but because of the Space Shuttle Challenger tragedy, its launch was postponed to 1990. The discovery of the flaw of Hubble’s primary mirror caused general consternation. Technically it’s called spherical aberration and is caused by the fact that the light reflecting on the edge of the mirror is focused on a different point from the light reflecting off its center.

To try to use the pictures taken by the Hubble Space Telescope, various software correction techniques were used, perfected for this purpose. Some years later, those techniques were adapted to make mammograms more easily to interpret by physicians to detect microcalcifications which constitute one of the early symptoms of breast cancer.

The Hubble Space Telescope’s mission could continue at least in part but it was the butt of many jokes. However, the design was based on the possibility to service the telescope so, once the flaw was identified, they started designing an instrument that would correct it, similarly to spectacles for humans.

The COSTAR (Corrective Optics Space Telescope Axial Replacement) system was built together with the WFPC2 (Wide Field and Planetary Camera 2), a new camera to replace the original WF/PC (Wide Field and Planetary Camera). Both were designed keeping in mind the Hubble’s primary mirror’s flaw.

In 1993, the Space Shuttle Endeavour included in its STS-61 mission the first service mission that installed the new instruments. Finally, at the beginning of 1994, the first images started arriving and they had the quality that was expected from the beginning.

In 1997, the Space Shuttle Discovery included in its STS-82 mission the second service mission to the Hubble Space Telescope. Some repairs were made and they installed the new STIS (Space Telescope Imaging Spectrograph) and NICMOS (Near Infrared Camera and Multi-Object Spectrometer) instruments replacing the original GHRS and FOS.

In 1999, the Space Shuttle Discovery included in its STS-103 mission the first part of the third service mission to the Hubble Space Telescope. There were mainly updates to the computer systems and various repairs, especially the gyroscope system, which was having some problems.

In 2002, the Space Shuttle Columbia included in its STS-109 mission the second part of the third service mission to the Hubble Space Telescope. The ACS (Advanced Camera for Surveys) instrument was installed to replace the FOC, some repairs were made and they replaced the solar panels with more efficient ones.

In 2009, the space shuttle Atlantis included in its STS-125 mission the fourth service mission to the Hubble Space Telescope. Various repairs were made and the new WFC3 (Wide Field Camera 3) and COS (Cosmic Origins Spectrograph) instruments were installed. The Soft Capture and Rendezvous System was also installed to allow future rendezvous with a crewed or an automated mission.

It’s thanks to these missions to service the Hubble Space Telescope not only could keep on working but has become better and better with the installation of new generation instruments. Some technologies developed for the Hubble service missions were later applied to commonly used devices such as digital cameras.

Thanks to the installation of new instruments, sometimes astronomers used the Hubble Space Telescope to observe again targets already studied. This allowed to make further discoveries and occasionally new versions of old iconic photographs were produced.

In 25 years, the Hubble Space Telescope has contributed to many discoveries in the field of astronomy. For example, it allowed observing the most distant and oldest galaxies. It contributed to the calculation of the age of the universe and allowed to discover that its expansion is accelerating. It helped to revolutionize our understanding of the birth and death of stars. It allowed finding the supermassive black holes at the center of galaxies.

Besides very distant and huge objects, the Hubble Space Telescope was used to study other closer or smaller ones. For example, in the solar system, it was used to observe planets, asteroids, and comets. It was also used to study exoplanets and solar systems in their formation stage.

Other space telescopes have been built thanks to Hubble’s success and one of them was named Spitzer after Lyman Spitzer. Some are in a more or less advanced design or building stage, starting with the most ambitious of all, the James Webb. Nevertheless, Hubble is still a key instrument in today’s astronomy and will remain so for a long time as it can keep on operating for several more years.

In theory, when the new spacecraft under development will be in service, it will be possible to set up a new service mission to further extend Hubble’s life and to augment it again. At the moment that seems unlikely to happen but it’s not totally excluded.

This anniversary celebrates the past triumphs of science and technology but also a mission with a great present and surely new discoveries in the future. The websites dedicated to this extraordinary instrument, NASA’s HubbleSite and ESA’s Hubble Space Telescope, are updated all the time as well as the YouTube channel dedicated to Hubble’s videos.

Today anyone in the world can go watch the pictures taken by the Hubble Space Telescope and the videos created thanks to them. That’s appropriate for an instrument that has become iconic and known also outside the scientific field.