1

The orbital will inevitably destruct very soon

2

The orbital somehow changes those trapped there

3

It's far harder to leave it than enter it

4

The orbital's loot is extravagantly illegal

5

Getting the orbital's best loot will destroy it rapidly

6

The orbital's real purpose is disguised

7

A government inspection team arrives soon after the PCs

8

The orbital is full of a space plague or dangerous miasma