'cept that it works for spacecraft ones for me, too...
In fact, I used it to add spacecraft to one of the systems I have done, and it worked pretty well (aside from not taking into account that planet-around-system period is calculated in Standard Earth Years, while moon/spacecraft-around-planet is calculated in Earth Standard Days or Lunar Months or some other thing (that I can't recall off the top of my head...)
You also can't use it to create a new SSC file from scratch.
I also wouldn't mind seeing a Traveller version, that uses "orbit numbers" (and fractions thereof) instead of AU, and automatically calculates the Orbital Period (at least for planets) based on Solar Mass, though calculating the orbital period for Moons would be much more valuable, particularly when the moon is a sizeable fraction of the planet's size.
Even better would be a barycenter for the World/Moon combination...
But, I digress.