Each row of aliens has 11 of them. This populates the graphics used to render a row. It builds the data structure at _ALIEN_ROWS_DATA.

It enters with IX pointing to the alien row data. It populates 22 bytes of UDG data which is 2 bytes side-by-side on one screen scan, for 11 aliens. All 11 aliens are set up the same, so that's one scan for one row. It then moves down one scan of the source alien graphic data and repeats. Alien data is at _RED_ALIEN_LOOK_LEFT, which shows that each alien is make up of 2 sprites, one looking left, one looking right. That's 16 scans for the graphic, twice. The whole lot is copied, so 32 times in total. 22*32 is 704 bytes.

Used by the routine at init_alien_row_data.