Can you redownload a previously purchased audiobook?

I have purchased so audiobooks in the past. To conserve space, I deleted them from my iPad and iPhone once I completed listening to them. Now I would like to redownload them and listen to them. Is this possible, if so how do I do it. Also, I do not have access to a computer and won't have access to one for a very long time so I only have my two devices and wifi to get me through this.