Its a universe with vast differences in government, law, religious, and technological beliefs. An alignment system will only do 1 of 2 things:
First, It will force your players into a set scale of morality as you determine, which may run counter to their own personal beliefs and most certainly the beliefs of societies they may encounter. I.e. they land on a primitive planet whom sacrifices vegans to a volcano, but otherwise are peaceful people. Do your players attempt to force their morality upon them, upholding their own beliefs? Or do they ignore the situation, allowing it to continue and therefore disregarding their own beliefs? It's an untenable position to maintain any sort of morality, as intervening could lead them to having to murder an otherwise peaceful people, or intervening in itself may be seen as immoral. To make it more complicated, perhaps the volcano is actually a large creature that expects fed regularly, and your intervention now leads to the slaughter of the entire people. Still the right decision?
Or second, you simply apply a universal morality to your entire universe. While that's certainly an option, you curtail a large amount of creative options and how the travellers interact with those options.
Of the two, option 1 has the best potential for conflict which can help drive the adventure, but allowing them to make those choices fluidly as they arise can allow a morality to naturally come out for that character without having to confine them into a box, and without making them feel as if they have to choose an action based on a pre-determined morality. "Alignment" is more of a background based on character creation. Many career choices and event rolls help build a person's "alignment" but they are free to become better or worse than the sum of their experiences. Ask yourself, do you want an alignment system for their benefit to guide their decisions, or for you so you can call them on it when they violate that alignment?