Anti-hierarchy should not be a moral obligation. Meaning this: if space exploration is only possible through hierarchical organization, that is not an argument against it. If people are willing to submit to a hierarchy in order to travel through space, and this involves no economic exploitation, then who gives a shit?
The only question is: will people want to use the time and material goods of society in order to implement it? If designing a space program is something that would have to be forced on people, then obviously it won't happen. Namely because that would be impossible.
So, when there comes a time for you and your friends to propose the development of a space program (or keep the current ones running), figure out how much of the resources at our disposal it will require and give everybody else the details and I'm sure we'll all be happy to talk about it for a while and decide something. Why should it be any different from any other idea? Meaning: large-scale decision-making will most likely take place in a regular, pre-determined way, and the particular decisions will always fall under whatever general process that may be. Space geek stuff included. Get it?
Also, for now, this isn't something that you should really concern yourself with... even if anyone could tell you that space travel will not happen in a post-revolutionary society (How could they? They simply don't know), that is no refutation of the criticism of capitalism, which is the entire reason why we're revolutionaries. It has nothing to do with space travel or anything else like that. Therefore my advice is to not worry about it too much. That is, UNLESS you would rather have a capitalism WITH space travel than a communism WITHOUT space travel. In which case, your criticism of capitalism is not very good and you should just focus on your space stuff and be done with all this pointless anti-capitalism that is keeping you here on this "rock" for the remainder of your existence.
As we do not yet have the technology atm, i am hoping that by the time we do (and the bloody cynics need to know a scientific breakthrough can happen anytime! ) we will be in a position to maximise this opportunity for the good of all. 
I state right away that I'm a space geek. I have space.com bookmarked and check frequently for updates. I know this stuff like terraforming and Sagittarius A* refer to. The idea of space colonization almost causes me to orgasm. Now, I'm wondering how this sort of thing would be organized in an anarchist society. I am very displeased with the idea that it simply won't happen, that we'll simply stay tied to this rock for the remainder of our existence. So, how would it work? I figure that people would have to make an agreement of sorts that they know what will happen if they do not pull their weight. I'm certain that it can be done without a whole lot of hierarchy, but some may be necessary for manned travel, as it would count as a very special case, at least in the early years.