LoL, saying the moon doesn't exist is like saying that the ISS (International Space Station) does not exist either. Obviously the fumes from the "space shuttles" are fake, and seeing that shuttle bust through our atmosphere is fake as well. /end sarcasm.
Basically, wtf is there to say that if we can send dozens of satellites into our atmosphere, that we could not go the extra mile and send to Mars/Moon. In space, no energy is required to speed up, via Newtons third law. So yes, although Jagex has not made space shuttles/ a moon in runescape, it is possible to get to the moon.