The document discusses the 20-year history and impact of the Hubble Space Telescope. Key points include: (1) Hubble was launched in 1990 and has been serviced multiple times to increase its lifespan, with a final servicing in 2009; (2) It has greatly improved imaging quality over its lifetime and increased our understanding of galaxies, stars and planetary formation; (3) Hubble has made groundbreaking discoveries like observing comet Shoemaker-Levy's impact on Jupiter and helped capture humanity's imagination about space.

1. “Twenty Years Of The Hubble Space Telescope”
On his ninth visit to Barrow-in-Furness on 29th September 2010, Dr. Robin Catchpole, Research
Astronomer at the Institute of Astronomy in Cambridge, told an audience of around 400 in Forum 28,
Barrow-in-Furness, that the idea of a telescope in space was first suggested in 1946. However, it
was not until the mid 1980s before the money had been allocated and the Hubble Space Telescope
(HST) was actually built. The aftermath of the Challenger Space Shuttle disaster delayed the actual
launch till April 1990. The original idea was to bring it back to Earth every 5 years for maintenance
but when they realised how much stress this would place on the telescope, servicing in space was
preferred.
Hubble was a Cassegrain reflecting telescope with a 2.4m diameter mirror. The mirror was ground
to a very high accuracy but, unfortunately, to the wrong curvature. The optics were corrected in
1993, which did, in fact, improve the resolution from what it would have been originally. HST has 6
gyroscopes to stabilise it and can be moved by flywheels, which are rotated by electric motors and
cause a reaction on the telescope to point it in the desired direction. Two small telescopes, with 5o
fields of view, recognise star patterns (from information in their databases) and control the directional
accuracy to 1/60th of a degree (1 minute of arc). Fine adjustment is by moving the instruments at the
eyepiece to an accuracy of 1/1000th of a second of arc.
HST has been serviced regularly and improvements in instrumentation have increased imaging
clarity 100-fold over its 20-year life. The final maintenance was in May 2009 and should give it 10-15
more years of useful life. HST gradually loses orbital height and, at the end of its life, it will be
deliberately crashed into the sea. The replacement will be the James Webb infrared telescope, due
for launch in 2014 / 15. It will have an 8m segmented mirror and will be located at one of the
Lagrangian points 1 million miles from Earth, where the Earth’s and Sun’s gravitational attractions
balance each other.
Any Astronomer could make a proposal to be allocated time on HST. It had to be a viable piece of
research, not available from archive records, would have to define when and where the telescope
must be pointed and for how long. As HST was moving in its orbit, the fine directional adjustment
had to be used constantly to keep it pointing at the same angle. As this adjustment was limited,
exposure times were restricted to about 10 minutes. Thus, for faint objects multiple exposures were
needed with the images being superimposed to create the incredibly-detailed, coloured images for
which HST was famous; hundreds of separate exposures were needed to create some images.
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2. A panel of peer-group astronomers would sift the proposals – usually for about six times the
observing time available – and select the most promising, scheduling them to make best use of the
directions in which the telescope was already pointing and so minimise unnecessary movement,
which wasted time. This was quite a management task and often became controversial.
Successful proposers had a year of exclusivity to analyse their pictures and produce research
papers before the data was put onto the free-access database for anyone to use. Though the Space
Telescope Science Institute and NASA retained the Copyright, HST data was free to anyone.
In addition to the time reserved for specific researchers on proposed projects, the Director of the
Space Telescope Science Institute had 10% of the available time to allocate at his discretion. This
allowed time to be made available for anything which occurred unexpectedly to be viewed at the
most opportune time, for example a supernova or comet fragments crashing into Jupiter, etc.
Frequently, HST was used in conjunction with other telescopes using non-visible light wavelengths,
such as UV, IR or X-rays, and if these users suddenly found something interesting, they might want
to compare their images with those in visible light. This 10% gave the necessary flexibility.
HST had made some remarkable discoveries. One was the break up of comet Shoemaker Levy,
when it passed too close to Jupiter, and the subsequent impact of the pieces into the planet. These
impacts had caused disturbances greater than the area of the Earth and led to the setting up of
organisations to monitor asteroids and comets, which could hit the Earth. HST had added whole
new dimensions to almost every branch of astronomy, with pictures in both visible and IR light. One
of its most important spins off was that its images had led to an upsurge in interest in space, related
sciences and engineering and this was one reason why the UK Government supported space
research and which had led the country’s pre-eminent place in space engineering.
Robin showed images of the search for planets orbiting distant stars, of galaxies colliding and the
remains of supernovae. In areas of star formation, discs of dust had been seen around new stars
indicating the formation of orbiting planets, as had happened in our own Solar System 4.6By ago.
Stars were giant gas balls, where the convective heat of nuclear fusion balanced its gravity and he
showed graphs of brightness against size indicating the different types of star from massive
blue-white, through normal stars, like the Sun, and red giants to white dwarfs. At the ends of their
lives, stars exploded as supernovae, blowing their substance out into space. One such occurred on
22/2/87 and, an image taken 9 years later, showed a glowing ring of gas 1½ light years in diameter.
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3. In 1969, the Nuclear Test Ban Treaty lead to a series of satellites monitoring the planet for signs of
illegal tests, i.e. gamma ray bursts. No evidence had been on the planet but massive gamma bursts
were regularly seen out in space. When HST looked at these, they came from very old, possible
colliding, galaxies at massive distances from the Earth. The energy releases were so large that, if
one happened near Earth, it would strip the atmosphere from the planet and extinguish life
immediately. Fortunately, there was nothing likely to do this in our galaxy.
Robin explained the basics of black holes and the concepts of dark matter and vacuum energy.
HST had taken some a visible light image of very early galaxies so far away that it was at a time
when the universe was only about 20% of its present age and an IR image of when it was even
younger. These showed small separate galaxies, which had not yet collided with one another to
form the big elliptical galaxies that we see today. What of the future? As the universe evolved, more
galaxies would collide and more stars would be born. The universe might continue to expand at the
same rate as now or at an increasing rate or stop expanding and collapse in on itself, leading to a
big crunch.
HST had greatly increased our perspective on the visible universe and we could now see around
one hundred thousand million (1011) separate galaxies and each of these galaxies contained, on
average, a hundred thousand million individual stars. This was a number beyond most people’s
comprehension but it was also the approximate number of cells in the human brain!
Hubble’s legacy to astronomy was incalculable, both in what it had revealed on its own but also
when used in conjunction with other telescopes. However, perhaps even more important was the
inspiration it had given to so many young people to turn towards careers in science and engineering.
Ian Palmer
Secretary, Chartered Management Institute (Cumbria Branch)
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