Medium Large Transport
Air Traffic Control Fully Certified
Distraction
Conflict Ground Conflict; Critical; Deviation / Discrepancy - Procedural Clearance; Ground Incursion Runway
Air Traffic Control Issued New Clearance; Flight Crew Executed Go Around / Missed Approach
Human Factors
Aircraft X was on a 6 mile final when I cleared Aircraft Z for takeoff. Aircraft Y was next for departure; and I planned on clearing him after the arrival. I turned my attention to other operational duties (such as VUO departure and practice scramble). When I turned my attention back to Runway 10L; I put Aircraft Y in position for spacing behind the previous departure; somehow forgetting about Aircraft X; and not scanning properly. Aircraft X was trying to call me when I cleared Aircraft Y for takeoff; so we stepped on each others' transmissions; compounding the situation. When ASSC (Airport Surface Surveillance Capability) alerted; I realized my mistake and issued go-around instructions. He turned and climbed before the threshold; so technically it was legal; but that doesn't make me feel much better. I was working combined local positions plus VUO advisory. There were three Military aircraft (one was a practice scramble and on my frequency) taxiing out to Runway 10R for departure; but they stopped in the EOR so I was frequently looking over to see when they would continue taxi so I could figure out a departure sequence. Also had a VUO departure call for flight following. Up until that point the operation wasn't particularly busy; but after the call for a practice scramble; it might have been a good time to split the position. One of the Tower supports at LC1 partially blocks the view of the final approach for 10L; and the controls for the arresting cables are on the other side of the Tower cab. Can't really fix those things; but it's good to be aware [of] their affect on the operation. After having had some time to ponder; I think the biggest factor was fatigue due to a lack of adequate sleep over several consecutive nights. My child has been sick; and I had gotten to bed late or was woken up in the middle of the night several times. I thought I was fine at the time; but in hindsight I was a bit sluggish and my reaction time was a split second slow. In spite of the issues listed above; I should normally have been able to handle all of it. I've worked busier traffic; and I'm appalled that my scan broke down this badly. I hate admitting that I was fatigued because it feels like I'm making excuses and showing weakness. However; I need to be realistic; and be better about recognizing when I'm fatigued to the point that it adversely impacts my ability to function; and ask for help and/or ask for sick leave. On a side note; I spoke with one of the pilots on the phone afterward. He was very polite and more forgiving about the situation than I deserved. The point he wanted to get across is that they have a lot of new pilots right out of school with very little experience. He wants us to keep that in mind anytime we decide to run airplanes a bit tight; especially in a high workload situation such as a go-around. In this case; I didn't intentionally run them tight; but I told him I would relay his concerns.
Portland Tower Controller reported running an arrival and a departure too close causing the arrival to go-around.