History: How Hubble Came About

300 million solar-mass black hole in galaxy NGC 7052.
Hubble blueprint

The Earth's atmosphere is the bane of astronomers. The idea of sending a telescope into space to avoid it was first proposed long before the first satellites were launched, long before anyone even dreamt of sending astronauts to space, German rocket scientist Herman Oberth was a pioneering thinker of his time and suggested a space bound telescope as early as 1923 in his book "Die Rakete zu den Planeträumen". A space telescope avoids frustrating problems such as cloudy and misty observing nights, the twinkling of stars even on clear nights and absorption of the ultraviolet and infrared parts of the spectrum.

It took many years before technology caught up with Oberth's idea. The American Lyman Spitzer proposed a more realistic plan for a space telescope in 1946 and lobbied for his idea for almost 30 years. In the 1970s NASA and the European Space Agency took up the idea and proposed a 3 metre space telescope. Funding began to flow in 1977 and it was decided to name the telescope after Edwin Powell Hubble who had discovered the expansion of the Universe in the 1920s. Although the Hubble Space Telescope was down-sized to 2.4 metres the project started to attract significant attention from astronomers.

The precision-ground mirror was finished in 1981 and the assembly of the entire spacecraft was completed in 1985. The plan called for a launch on NASA's Space Shuttle in 1986, but just months before, the scheduled launch the Challenger disaster caused a year long delay of the entire Shuttle programme. Hubble was finally launched in 1990 and the tension built up as astronomers examined the first images through Hubble's eyes.

As in all good adventures, success does not come easily: it did not take long to realise that Hubble's mirror had a serious flaw. A focusing defect prevented Hubble from taking sharp images — the mirror edge was too flat by a mere fiftieth of the width of a human hair. Over the next months scientists and engineers from NASA and ESA worked together and came up with a superb corrective optics package that would restore Hubble's eyesight completely.

A crew of astronauts carried out the repairs necessary to restore the telescope to its intended level of performance during the first Hubble Servicing Mission (SM1) in December 1993.

Although the four subsequent servicing missions were at least as demanding in terms of complexity and work load, SM1 captured the attention of both astronomers and the public at large to a degree that no other Shuttle mission since has achieved. Meticulously planned and brilliantly executed, the mission succeeded on all counts. It will go down in history as one of the highlights of human spaceflight. Hubble was back in business.

Since SM1 four other Servicing Missions have been carried out. During SM2 in 1997 two new instruments were installed. Servicing Mission 3 was split into two, leading to a slightly confusing numbering system: in SM3A, 1999, many of Hubble's crucial technical systems were exchanged, and in 2002 came SM3B when Hubble again got new science instruments.

Servicing Mission 4 (the fifth trip to Hubble by astronauts since launch) took place in spring 2009. During SM4, astronauts upgraded Hubble’s scientific capabilities again, installing a new main camera and an instrument designed to help answer profound questions about the large-scale structure and origins of the cosmos. They also carried out a number of other maintenance tasks, including repairing the Advanced Camera for Surveys and the Space Telescope Imaging Spectrograph, both of which had broken down since the previous mission.

With the retirement of the US Space Shuttle in 2011, no further servicing missions will be possible. However with the telescope fully repaired and upgraded, it is expected to function well for around 7-8 years, possibly longer.

Hubblecast episode 41 tells Hubble’s history through the personal stories of some of the scientists involved.