Ok
/etc/mothership/mothership.conf:
  file.managed:
    - source: mothership/files/mothership.conf
    - require:
      - file: /etc/mothership

Better
mothership_config_file:
  file.managed:
    - name: /etc/mothership/mothership.conf
    - source: mothership/files/mothership.conf
    - require:
      - file: mothership_config_dir

Even better
mothership_config_file:
  file.managed:
    - name: {{ mothership.config.dir }}/{{ mothership.config.file }}
    - source: mothership/files/{{ mothership.config.dir }}/{{ mothership.config.file }}
    - require:
      - file: mothership_config_dir