It is not so much a journey through time, more a mission to buy more time for a telescope which has provided a glimpse of the distant past. Later today, Shuttle astronauts will blast off from Cape Canaveral in Florida for a mission to the Hubble Space Telescope designed to keep it working for at least another five years.
In the 18 years since Hubble was launched, the space telescope has astounded scientists and the public with its amazing views of the nearest as well as the most distant objects in the visible universe. It has lasted so long precisely because it was designed to be repaired and serviced.
One of the Hubble telescope's greatest achievements has been its ability to see objects that are billions of light years from Earth. Seeing so far away is equivalent to seeing back in time because light from the furthest reaches of the known Universe has taken billions of years to reach the telescope's orbit around Earth.
Now the fifth and final servicing mission should see the telescope continue its groundbreaking observa-tions until 2014, and possibly beyond, providing everything goes as planned when the shuttle Atlantis is scheduled to take off from Kennedy Space Centre at 6pm BST today.
A range of new instruments to replace old, worn-out ones will give the Hubble a new lease of life, enabling it to improve its powers of observation by between 10 and 30 times. One improvement will enable it to see even deeper into space, and so further back in time, to a point when the first galaxies formed a few hundred million years after the Big Bang, 13.7 billion years ago.
"We can already see back about 13 billion years but this is not the most interesting time in the history of the Universe. We hope with the new Hubble instruments to go back to within 300 or 400 million years after the Big Bang and so see the galaxies themselves being born," said Kim Weaver, an astrophysicist at Nasa Goddard Space Flight Centre in Greenbelt, Maryland.
"We hope to get a picture of the earliest possible galaxies soon after or during their formation. We've not been able to do this before, but after the servicing mission this should be possible," Dr Weaver said.
The mission involves five space walks each lasting about six-and-a-half hours. Some repairs involve intricate operations involving the painstaking removal of up to 100 screws. "It's more like brain surgery than construction. Hubble spacewalks are comparable to standing at an operating table, doing very dextrous work," said shuttle flight director Tony Ceccacci.
One of the most important repairs will be replacement of the guidance sensors to hold the telescope steady over long periods of time so it can see into the darkest recesses of space. These sensors point the Hubble telescope with a precision comparable to firing a laser beam from London on to a penny in Liverpool – 200 miles away.
Seeing stars Hubble's greatest achievements
* Hubble recorded the oldest visible objects in space, dating to shortly after the Big Bang some 13.7 billion years ago. Light from one of the objects in the million-second-long exposure started its journey to Earth about 700 million years after the Big Bang.
*In 2002, a dull star known as V838 Mons in an obscure constellation became the brightest star in the Milky Way. The "light echo" of this event, captured by Hubble, is so unique it may represent a transitory stage in a star's evolution, making it a rarely observed phenomenon.