UK Looks Forward to Next Generation Space Telescope
As the Hubble Space Telescope (HST) continues to return a succession of staggering new images and data, astronomers on both sides of the Atlantic are preparing the next giant leap for orbital observatories. Three groups in the UK are playing a leading role in studies to decide which scientific instruments Europe will provide for HST's successor, the Next Generation Space Telescope (NGST).
The three studies involving UK groups are:
Hubble and NGST
Despite Hubble's success, a larger, more capable instrument is required to answer some of the questions raised by its discoveries. The NGST will be equipped with a much larger mirror than the HST - probably 8 metres across compared to 2.4 metres. It will also operate for much of the time at infrared wavelengths (0.6-10+ microns). This will enable it to study the most remote galaxies whose light largely reaches us at infrared wavelengths.
The NGST has been chosen by NASA as an essential element of its Origins programme. NASA is currently undertaking definition and feasibility studies before deciding how best to proceed. The European Space Agency (ESA) and the UK Particle Physics and Astronomy Research Council (PPARC) are also keen to be involved. However, the telescope's final design and scientific payload have yet to be decided.
Although the HST was largely built and paid for by NASA, the European Space Agency has provided one science instrument (the Faint Object Camera) and various other pieces of hardware, such as solar panels, for the observatory. In return, European scientists have gained access to 15% of the available observing time on HST. ESA member states hope to continue this highly successful collaboration into the NGST programme.
Why do we need NGST?
Astronomers believe they have a good understanding of how the Universe has evolved in the last few billion years and what it was like when it was quite young (less than about 1 million years old). However, almost nothing is known about the events which took place between 1 million and a few billion years after the Big Bang. It is during this 'Dark Age' that the first stars and galaxies began to form.
'At the moment we can only see the tip of the iceberg. NGST will allow us to see the dwarf galaxies which we believe are the building blocks for the big ones, and the way they interact and grow into the giant galaxies we see today,' said Professor Martin Ward of Leicester University.
NGST is being designed with a number of fundamental questions about the age and nature of the Universe in mind:
1. What is the shape of the Universe? 2. How do galaxies evolve? 3. How do stars and planetary systems form and interact? 4. What are the life cycles of matter in the Universe? 5. What is dark matter?
Answers to most of these questions involve objects which formed extremely early in the history of the Universe. However, since such objects are moving away from us at tremendous speeds, the radiation we receive from them is stretched or redshifted. The best way to look at them is in the infrared portion of the spectrum.
Not only will the NGST be able to detect this infrared radiation, but it will also be able to see objects 400 times fainter than those currently studied with large ground-based infrared telescopes. At the same time, its spatial resolution (image sharpness) will be comparable to that of HST.
The UK and NGST
NGST is expected to operate along similar lines to Hubble, with NASA as the prime contributor and ESA as a major partner. ESA has accordingly assigned a number of technical assessments to groups throughout Europe in an effort to narrow down the options for its hardware contributions to NGST.
Roger Davies and his colleagues at Durham University are working with teams in France and Germany on a design study for a MULTI-OBJECT INFRARED SPECTROGRAPH. Since light from most distant galaxies is shifted towards the red end of the spectrum, this instrument is seen as an essential part of NGST's scientific payload.
The intention is to simultaneously study starlight from large numbers of distant galaxies. The spectrograph would be able to split and analyse light from numerous objects, much as a prism splits sunlight into different colours. This would enable astronomers to learn much more about the composition, distance, and speed of retreat of distant galaxies and quasars. Astronomers would then be able to 'map' the thousands of faint galaxies which lie in the depths of the Universe.
'At present we use spectrographs to analyse light from only a tiny area of sky ' said Dr. Davies. 'Telescopes have to be pointed very accurately to make sure the right object is in view, which is not so easy in space.'
'The new design developed at Durham allows the light from a much larger area of sky to analysed with the spectrograph. This means that we can study more objects at once and we don't have to point the telescope so accurately,' he explained.
Meanwhile, scientists at the University of Leicester heard in December 1998 that they had been chosen to study the implications of installing an OPTICAL CAMERA / SPECTROGRAPH on NGST. Other institutions taking part in the study come from France, Italy, Germany and Spain.
Although this new instrument would be similar to the Wide Field and Planetary Cameras which have been so successful on HST, the added spectrograph would give it the extra capability of dissecting and analysing starlight at optical wavelengths over a large area of sky.
Since NGST will use a mirror 10 times bigger in area than HST's (equivalent to the size of a large living room), the camera would provide even more detailed pictures than Hubble. In particular, it would reveal galaxies as they were when the Universe was young, and perhaps give us clues on how solar systems and planets are formed.
'NGST will be able to see galaxies which are only about 10% the age of the Universe - they were born around 1 billion years after the Big Bang,' said Martin Ward, Scientific Principal Investigator for the ESA Visible Camera study.
'We will also be able to see dusty disks around other stars, and, perhaps, the gaps in these disks which astronomers predict are signatures of the formation of planetary systems,' he added.
In a third ESA study, the UK Astronomy Technology Centre (ATC) in Edinburgh leads a British team which is helping to define the most suitable telescope and instrument payload for NGST. Other participants include industry and astronomical institutes from Germany, France, Spain and the Netherlands.
'We are taking a broad perspective on the overall science case for the NGST and what Europe would like to see on NGST,' said the co-chair of the study science team, Gillian Wright. 'The study is concentrating on the telescope design, how to include all of the instruments astronomers would like, and the design of instruments not covered by the other studies. At the ATC we are particularly responsible for leading the study of an imaging spectrograph operating at mid-infrared wavelengths (5-30 microns).'
The results of these three studies are expected to be published June - September 1999.
The Hubble Space Telescope was launched from the Space Shuttle on 25 April 1990. A number of new instruments were added during the 1993 and 1997 Space Shuttle servicing missions.
Although the HST has been in orbit for almost nine years, the science community hopes that it will continue to operate until 2010. This means that it will be able to operate in parallel with the NGST, which is planned for launch in 2007.
One unusual aspect of the NGST mission will be its stable orbital location about 1.5 million km from Earth in the opposite direction from the Sun. Far from any heat radiated by the Earth and Moon, and protected by a sunshade, NGST will be able to remain very cool. This means that the faint infrared (heat) signatures of remote galaxies will not be swamped by the glow from the telescope itself.
The total cost for the mission including launch and ten years of operation is expected to be approximately $1.2 billion. ESA funding has yet to decided, but is likely to be approximately 15% of the total.
Further Information and Photos of the proposed NGST designs are available on the Web at:
ESA's NGST page is:
Illustrations are available from: http://ngst.gsfc.nasa.gov/Hardware/designs.html