In the same way that the Chinese are rather heedless of tense, the Chinese are also very willy-nilly with pronouns. In most sentences, pronouns are optional in a way that make Western language speakers extremely uncomfortable. In fact, the less pronouns you use, the more Chinese you typically sound - I find that, in spoken Chinese, they tend to establish who is being discussed ("I went to the store..."), and then they never say "I" again until the person being discussed changes. In other words, they don't say "I went to the store and then I bought two apples and when I went home, I ate those apples." They say, "I went to the store, bought some apples, and when went home, ate apples." 

This isn't a formal grammar point, it's just an observation, though. Try dropping your pronouns in all but the most crucial cases - you'll sound much more native.

They also don't always use "you" the way we do, and they really don't often use it when addressing anonymous groups of readers. Instead, no pronoun is used at all. That sentence would be more accurately translated as "If it was desired to experience weightlessness...". But of course that sounds stupid in English.