Besides my work as the Head of the English Speaking Branch of the HRM and my work on The War for Christendom book series, I have also written a few works of science fiction (sci-fi), specifically the (as-of-yet) unfinished St. Damian's Chronicles: Tales of Catholicism Amongst the Stars. The St. Damian's Chronicles are a sort of Asimov's Foundation about Catholics on different colony planets struggling to survive and spread the Faith.
That's right, the Holy Empire is back- and it's got a Star Fleet. The Officers of the K.u.K.W.F. (Kaiserlich und Königlich Weltraum Flotte/Imperial and Royal Space Fleet) take pride in their smart blue uniforms and golden insignia, while their motto and rallying cry, Sub Umbra Aquilæ, strikes fear into the heart of any pirate, smuggler, or rebel who dares to threaten Justice and Peace.
When atheist vocal minority groups set up militant Secular Republics on some of Colony Worlds, throwing them into chaos, the K.U.K. Fleet Cruisers are dispatched from the Sol System, and while every officer from the High Admiral to the lowest ranking cadet fights bravely, treachery is a very real danger.
One question about the rules. Why no alien clergy?
My reason is (and of course this could be theologically disputed) that a man (i.e. a human male) is the only valid matter for ordination.
Theologians are going to be overjoyed if aliens are ever discovered.
I'm actually going to go deeper down the rabbit hole. Would a Near-Human count as Men? 🙂 For example, if we found the Star Wars Galaxy, could a Chiss or Zeltron be ordained? Not that you would ever want a Zeltron as a priest though.
If one slightly changes the question, and asks are chimpanzees (near humans of a sort) valid matter, the answer is obviously no; however, this is because chimpanzee does not have a rational Human nature. To get more theological, the priest stands in the Person of Christ Who took on a rational Human Nature. The defining question is do these Near-Humans have a Human Nature or a Nature which is rational but distinct from Humanity.
The question then becomes do these "Human" variant species share Human Nature. If they do, then you have valid matter for ordination.
Planning on having any aliens in the St. Damian's Chronicles?
On the subject of Chiss and Zeltrons (and other Near-Humans for that matter), I would say, albeit theoretically, that being descended from Humans, they would posses human nature.