The Hubble Space Telescope
Named after famous astronomer Edwin Hubble, the Hubble Space Telescope (or HST) was launched into a low-earth orbit in 1990. It is the world's first space-based optical telescope, and it is gargantuan by optical telescope standards.
It weighs 11 tons and is 15.9 meters long. It is a feat of engineering, with its two large mirrors being carved so precisely that they don't deviate from a perfect curve by more than 31.75 Nanometres (1/800,000th of an inch). Its construction was spearheaded by NASA and contributed to by the European Space Agency (ESA). The project cost $1.5 billion at launch.
Hubble has captured some of the deepest and most detailed images of space in history. It can do this because its orbit is outside of Earth's atmosphere, so unlike mankind's arsenal of ground-based telescopes, HST's images are free of atmospheric distortion. This means that it can take very high-resolution images without background light, creating amazingly clear images.
Though many have seen Hubble's iconic images awash in brilliant colours, the telescope can actually only make observations in black and white. Unbeknownst to most, these colourful images are obtained by combining at least two black-and-white exposures under a coloured filter. And though it's famous for these images, the telescope is also a data mine - Hubble sends back over 120 gigabytes of data each week, contributing to numerous astronomical discoveries.
Perhaps the breakthrough the HST is most famous for contributing to is the narrowing of the universe's age to somewhere between 13 and 14 billion years; before, scientists debated between a range of 10 to 20 billion years. Hubble has also contributed to the discovery and understanding of dark energy, provided images of galaxies in all stages of evolution, and discovered that gamma-ray bursts occur in far-away galaxies when massive stars collapse. When all is said and done, HST data has contributed to over 10,000 scientific articles - a monumental feat.
Hubble's main instruments can make observations in the near ultraviolet, visible, and near-infrared spectra. Its various computers and instruments - which include cameras, spectrographs, and fine guidance sensors - are entirely powered by solar panels. The panels soak in sunlight constantly but also serve to charge six nickel-hydrogen batteries, which power the telescope as it passes through Earth's shadow for about 25 minutes in each orbit. The telescope completes one orbit every 96 minutes, travelling around the Earth at a surprisingly brisk speed of 28,000 kilometres per hour.
Although it has borne witness to the furthest reaches of the universe that mankind has ever seen, there are some surprising targets that the HST can't see. For example, looking at the Sun would damage the telescope's sensors, and since Mercury is so close to the Sun, the HST has to keep its glance away from our first planet. When Hubble is damaged, its repair is a difficult and unique process; the HST is the only telescope designed to be serviced by astronauts in outer space.
What many don't know is that, despite its years of service and its contributions to groundbreaking discoveries, the Hubble's days are numbered. Its vital systems are worn and are expected to fail soon. Although scientists projected that it would stay in operation until around 2020, it is now set to be replaced by the James Webb Space Telescope, which was launched into space on 25 December 2021.