FOUR years after astronauts flew into orbit to correct the Hubble Space
Telescope鈥檚 blurry vision, another space maintenance crew is preparing to
install new instruments that should be able to view the farthest reaches of the
Universe with the most stunning clarity yet.
From the beginning, the Hubble telescope was designed to be serviced in orbit
by NASA鈥檚 space shuttle, so that astronomers could replace ageing instruments
with newer versions. This is common practice with ground-based telescopes, where
the same basic optics are used for several decades with a succession of
different instruments.
The latest servicing mission aboard the shuttle Discovery is scheduled to
blast off on 11 February, and will install two new instruments. 鈥淲e鈥檙e replacing
1970s technology in our instruments with 1990s technology,鈥� says Edward Weiler,
NASA鈥檚 chief scientist for the telescope.
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The first new instrument, the Space Telescope Imaging Spectrograph, will
gather observations at more infrared wavelengths than the two spectrographs it
will replace. It will record the spectra of stars in several locations within a
galaxy simultaneously, rather than having to observe them one by one. This will
allow it to work at 30 times the speed of its predecessors.
The other major instrument is the Near Infrared Camera and Multi-Object
Spectrometer (NICMOS). This will allow Hubble to see objects that are farther
away鈥攁nd therefore older鈥攖han anything previously observed by the
telescope. NICMOS will study emissions from celestial bodies at wavelengths
between 0.8 and 2.5 micrometres. Emissions from incredibly distant objects are
red-shifted to these wavelengths due to a Doppler effect caused by the expansion
of the Universe.
With NICMOS, astronomers should be able to see objects as they were when the
Universe was only about 10 per cent of its current age, says Rodger Thompson of
the University of Arizona, head of the instrument鈥檚 scientific team. Until now
the space telescope has only been able to detect emissions that started their
journey across space when the Universe was one-third of its present age.
Unlike radiation at other wavelengths, infrared radiation passes through
clouds of dust relatively easily, so NICMOS should also be able see embryonic
galaxies, stars and even planets, which tend to form in dust clouds. 鈥淚t can
peer into the womb of dust,鈥� says Thompson.
The last Hubble servicing mission went off without a hitch. But NASA stresses
that the task facing Discovery鈥檚 seven-strong crew is far from easy. After it
catches up with Hubble, the shuttle must deploy its robotic arm to grab the
telescope. Pairs of astronauts will then work in shifts, taking spacewalks into
the shuttle鈥檚 payload bay to install the new instruments and to replace other
components鈥攕uch as a guidance sensor and tape recorder鈥攖hat are in
danger of failing. 鈥淚t鈥檚 going to be three years before we get back to Hubble
again, and we don鈥檛 want those minor problems to turn into major problems,鈥� says
NASA official John Campbell.
Discovery has only enough fuel for one attempt at reaching the telescope, and
unexpected problems could prevent the astronauts from completing all their
repair tasks. The astronauts will have to take special care to avoid damaging
the telescope鈥檚 solar panels, which were supplied by the European Space Agency.
The panels, which were installed during the last servicing mission, are held by
fragile metal arms that could easily break if jolted. As Weiler says: 鈥淚t鈥檚 not
just like a trip to Grandma鈥檚 house to fix her VCR.鈥�