I am not 100% sure but I think we are looking at the aperture cover. In the picture below I've pointed out what looks like hinges (top) and a latch (bottom).
There's a cutaway of the scope here which does not show such a large obstruction.
As another example: the Gaia mission illustrates that modern CCD production techniques allow to have form follow function: it uses an creatively laid-out array of CCDs to be able to integrate multiple functions in a single instrument:
[T]he three functions are built into a single instrument by using common telescopes and a shared focal plane:
Silicon wafers are sliced from a giant single crystal of silicon called a boule, which is grown from a seed crystal dipped in and then slowly pulled from molten silicon.
Circuits such as CCDs (and everything else) are patterend on silicon wafers aligned to the crystal axes of the wafers indicated by the wafer flat or notch (1, 2 see alignment flat on bottom,...
There were a lot of square format cameras.
The Voyager cameras had 800*800 pixels.
The LORRI cameras of New Horizons had 1024*1024 pixels.
The Galileo cameras had 800*800 pixels.
The Cassini WAC and NAC cameras had 1024*1024 pixels.
The narrow and wide angel OSIRIS cameras of Rosetta had 2048*2048 pixels.
The FC camera of Dawn had 1024*1024 pixels.
The Kepler space telescope uses a bank of 21 rectangular CCD modules - each with two 2200x1024 pixel CCDs). Each module covers 5 square degrees on the sky.
Giving a field of vision of:
For Hubble, the wide field camera CCD sensor is again rectangular/square
The idea behind DAMPE is that, if there is something we currently think of as dark matter (and AFAIK that's a big "if", but that's only an opinion...), every now and then a so-called WIMP or Weakly Interacting Massive Particle must hit a "normal matter" particle, producing one or a few high-energy photons. In order to maximize the chances of catching a WIMP, ...