Hey guys, I have a quick question:
Can Astropath use some of the Dark Heresy minor powers and the Disciplines?

The rules never clearly say that an Astropath can ONLY use the Disciples listed in the RT core, but they mention several times on how to clearly convert powers across DH and RT. It also mentions the "other" powers and abilities in the universe and notes that the ones mentioned in the book are only potential abilities.

They also limit an Astropaths to three possible Disciplines. Why limit them to three Disciplines if there are only three listed in the book? I see this as a way to keep psykers and astropaths from spreading their abilities too far apart, essentially making them more effective in their given Disciplines.

Mostly, I am referring the page 158 the section titled "Psychic Disciplines", the last three paragraphs.

Like I said, it never clearly states on way or another, but the vibe I get after reading through the chapter a few times allow leeway. The only Disciples I see that is mandatory for an Astropath is Telepathy, since obviously that is their primary duty....and the fact you start with it

Thanks for your time and let me know what you think.

I'd say no. Astropaths aren't as varying as Sanctioned Psykers, they are skilled in only a subset of psychic skills, namely mental abilities (Telepath, Telekinisis, and Divination). They simply do not have the ability to learn powers outside of those disciplines.

I'd also argue that as well as disciplines outside of those specified three, they wouldn't have access to minor powers either.

If you want a full psyker, go for a full psyker. Astropaths, in their soulbound and power-limited states, are designed for a specific function, long-distance communications.