What is it?

Okay,

In Kingdom Come we see this massive structre:

So is it just a GL construct?

And if so,

What power do you think he was at in this arc, to be able to indefinitely maintain such a construct?

In Kingdom Come, GL has his power battery in his armor giving him an infinite supply of energy so i'm guessing he made it permanent

Other than that, Alan didn't really do anything.

It's a construct, some people smuggled some wooden sticks aboard and broke it