Hubble's heir
Your working life began on 24th April 1990. You have traversed unexplored regions, travelled millions of miles, been battered and abused in the course of your duties to enlighten the human race about the mysteries of the universe, and now they’re considering retiring you in the year 2005. They won’t allow you to drift aimlessly once you complete your service, you may be ruthlessly exterminated so you pose no threat to them although some romantic souls have proposed that you are consigned to a museum.
No, you aren’t some benighted encyclopedia salesman, although there are uncanny parallels. You are Hubble, the remarkable space telescope, responsible for revealing some of the secrets of the universe.
The space shuttle, Discovery, met up with Hubble recently in order to service the first general purpose orbiting observatory. The ten day mission to repair and maintain the telescope was successfully completed. Two more such missions are planned for 1999 and 2002 but the costs prohibit a longer working life for the Hubble. The demand is for a bigger, better, lighter and cheaper version, and the race is on to provide one.
That isn’t all, in the search for new clues to the origins of the universe, scientists need the space telescope to orbit the Earth at a distance of about one million miles, at a point in deep space where the gravities exerted by the Sun and the Earth counteract each other. At this point the temperature is constant. Presently Hubble hovers a mere 400 miles above us, battered by gravitational forces and affected by extreme shifts in temperature.
There are three major runners in the competition to produce what is known as the Next Generation Space Telescope (NGST). NASA’s Goddard Space Flight Centre (GSFC), Lockheed-Martin and TRW Space and Electronics are jostling for first place. The rules are tough. The NGST must not exceed $500 million dollars in building costs, Hubble cost $2.5 billion to build. Running costs must also be considerably less, at only $40 million a year.
One of the primary ways to reduce costs is to reduce the weight of the telescope and the NGST will be constructed such that it will weigh 2,500 kg, about one-fifth of Hubble’s weight. This will mean that the cost of launching the telescope will be relatively modest. Hubble required the space shuttle to put its 11.6 tonnes into orbit. By incorporating a new generation of extremely lightweight mirrors into the designs it is possible to meet the weight requirements. "We may have to build its giant mirror in segments so they can be fitted into a cheap reusable rocket. Once in space these will be unfolded and slotted into place" said GSFC’s John Mather. TRW has a similar proposal for their telescopes’ mirror with a stacked set of hexagonal segments that will swivel into place when in orbit.
Both of these designs only require a small rocket such as the US Atlas II booster, however the Lockheed-Martin proposal would need a bigger launcher. Either the Russian Proton or European Ariane 5 may be suitable to carry the uniquely designed mirror. This system has a thin membrane of fused silica that can be moulded into exactly the right shape once it reaches its destination, away from the distorting influence of Earth’s gravity.
NASA have yet to finalise their course of action. Finance will be a deciding factor in the selection of the heir to Hubble, and to Hubble’s eventual destiny be it oblivion or as a honourable retirement as a museum’s centrepiece.
