D10 Controller described a loss of separation event; one of the aircraft involved executing an unexpected go around leading to the error. The reporter listed constricted airspace as a causal factor.

Narrative

Aircraft X was doing multiple IFR practice instrument approaches. I was working MN which controls the final for FTW. MS controls the departures off FTW. I coordinated with MS for Aircraft X to fly runway heading; maintain 3;000 FT on the missed and call me for vectors to another ILS. Aircraft Y was a King Air following Aircraft X on the approach. Aircraft Y encountered some problem with the GS and informed tower he was executing the missed approach. Tower coordinated with MS for missed approach instructions. I had turned Aircraft X West to 270 degrees. MS issued heading 190 to Aircraft Y. I had gone West with Aircraft X on the previous missed and told MS I was turning to heading 270. MS informed me they had just issued heading 190 to the King Air on the missed approach. I turned Aircraft X back to heading 160. This is a cost of doing business error. There is just not enough airspace to accomplish everything we try to do within all applicable rules. NFW is less than 3 miles West of FTW so we cannot turn Westbound until 3;000 without coordination with NFW tower. The final for NFW is less than 3 miles from the FTW final. AFW final is exactly 3 miles East of FTW. If there is any traffic for AFW you cannot turn East off FTW. The aircraft were always at least 2.5 miles apart; so there was nothing unsafe about any part of this operation; but there is also almost nothing that could be done differently. You cannot anticipate a good weather go-around. There was well more than 3 miles between these aircraft at the threshold; probably 4-plus. It is silly and inefficient to make the practice approach hand off and switch back and forth between MN and MS when coordination can accomplish the same thing. In this one case out of thousands; the turns would have been issued differently by a few seconds. I can't see anything to do differently.