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Abstract

TianQin is a planned space-based gravitational wave (GW) observatory
consisting of three earth orbiting satellites with an orbital radius of about
$10^5~{\rm km}$. The satellites will form a equilateral triangle constellation
the plane of which is nearly perpendicular to the ecliptic plane. TianQin aims
to detect GWs between $10^{-4}~{\rm Hz}$ and $1~{\rm Hz}$ that can be generated
by a wide variety of important astrophysical and cosmological sources,
including the inspiral of Galactic ultra-compact binaries, the inspiral of
stellar-mass black hole binaries, extreme mass ratio inspirals, the merger of
massive black hole binaries, and possibly the energetic processes in the very
early universe or exotic sources such as cosmic strings. In order to start
science operations around 2035, a roadmap called the 0123 plan is being used to
bring the key technologies of TianQin to maturity, supported by the
construction of a series of research facilities on the ground. Two major
projects of the 0123 plan are being carried out. In this process, the team has
created a new generation $17~{\rm cm}$ single-body hollow corner-cube
retro-reflector which has been launched with the QueQiao satellite on 21 May
2018; a new laser ranging station equipped with a $1.2~{\rm m}$ telescope has
been constructed and the station has successfully ranged to all the five
retro-reflectors on the Moon; and the TianQin-1 experimental satellite has been
launched on 20 December 2019 and the first round result shows that the
satellite has exceeded all of its mission requirements.