Distant galaxies, dark matter, dark energy and the origin and evolution of
the universe itself are some of the many scientific goals of China's newly
announced space telescope. If all goes according to plan, the China Space
Station Telescope (CSST) will blast off atop a Long March 5B rocket sometime
in late 2023. Once in a safe orbit, CSST should begin observations in 2024.
Judging by these research topics, it looks like the Chinese Academy of
Sciences is throwing down an impressive scientific gauntlet for itself and
its astronomers.
What it means to have a space telescope
Owning and operating a space telescope really opens the doors to a treasury
of information about the universe. Certainly, that's what motivated the
creation of the Hubble Space Telescope (HST). The dream of cosmic
exploration motivated Hermann Oberth in the 1920s to write
semi-science-fictional treatises about orbiting telescopes on asteroids. In
his view, astronomers would live and work in space while using the telescope
for extended periods of time. Their view would be unobstructed by Earth and
its atmosphere. That vision inspired a number of later scientists to start
planning a space telescope for real. Their work culminated in HST, the first
of the so-called "great observatories" lofted to orbit. The others are
Chandra X-Ray Observatory, Compton Gamma Ray Observatory, and Spitzer Space
Telescope.
Scientifically, orbiting space telescopes offer huge payoffs across a wide
range of the electromagnetic spectrum. For example, before HST, no one
really had a good idea of the extent of galaxies in the universe. The famous
Hubble Deep Field views let astronomers observe stars and galaxies as they
were shortly after the Big Bang, in both visible and infrared light. HST
revealed glimpses of the large-scale structure in the cosmos and objects as
small as exoplanets, comets, and asteroids. All the great observatories set
the stage for new generations of orbiting instruments, such as the James
Webb Space Telescope, the European Space Agency's GAIA, NASA's WISE
telescope, and now, the CSST.
China enters the space telescope fray
Given the potential scientific rewards, it's not surprising that China is
joining the "big space telescope club." It's also a source of national
pride, especially if they can "out-Hubble Hubble." For example, once CSST is
operational, Chinese scientists hope to survey the sky and observe more than
1 billion galaxies. Their instruments should let them get highly precise
measurements of galaxy shapes, positions and brightnesses. They'll use the
telescope to go after exoplanets, star birth regions, and other distant
objects, gathering incredible amounts of high-resolution data.
China's astronomers hope their telescope will provide, as HST has done and
JWST will do, more insight into the extent and distribution of dark matter.
It might even give them better clues about the dark energy that affects the
expansion of the universe. And, as HST and other telescopes have been, CSST
will be a point of inspiration. It will, its designers hope, show new
generations of Chinese scientists how to explore the cosmos.
Explore CSST: A next-generation space telescope
So what do we know about CSST? Picture in your mind a giant orbiting
observatory. It's about the length of a three-story building and the width
of a school bus. It has a 2-meter aperture and a three-mirror array set in
an off-axis configuration. This observatory has a state-of-the-art survey
camera, multi-channel imager, integral field spectrograph, cool-planet
imaging coronagraph, and a terahertz receiver. The telescope can scan the
sky using 30 81-megapixel detectors, and it is sensitive to near-infrared,
visible, and near-ultraviolet light.
That's just a small taste of what CSST promises to do and be, according to
scientists at the academy. Not surprisingly, they often compare it to Hubble
and its 32 years of breathtaking observations. If the telescope goes up as
planned, it will definitely surpass HST in many ways.
Li Ran, project scientist for CSST's Scientific Data Reduction System,
pointed out that HST's field of view is small compared to the CSST's, which
is 300 times larger. Where Hubble sees a small part of the sky at one time,
CSST will see a much bigger picture. Li used the analogy of photographing a
flock of sheep to explain its capabilities by comparison. "Hubble may see a
sheep, but the CSST sees thousands, all at the same resolution," he said in
a press release statement.
An observatory with its own service bay
One of the most unique aspects of CSST is where it will go in space.
Originally, the telescope was going to be attached to the Tiangong space
station, but that changed. For one thing, there's too much chance of
cross-contamination from spacecraft coming and going. For another, CSST is
so sensitive that it can't be attached to the station. Vibration, stray
light, and possible obstructed views would interfere with the telescope
operations. Current plans are to put it in the same orbit as the station (at
about 265 miles altitude), but a safe distance away.
When the observatory needs any kind of servicing, it can maneuver over to
Tiangong for refueling and other maintenance activities. That plan reflects
a lesson learned from HST's 70's-era design. NASA paid for five on-orbit
visits by astronauts to refurbish the observatory. So making the CSST
serviceable by the station astronauts turns out to be a money-saver for the
Chinese.
CSST (also known as Xuntian and Chinese Survey Space Telescope) is currently
under final construction. It has been in planning and development since
2010.
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Space & Astrophysics