We have all watched Star Trek as the captain and crew are beamed down to a planet below from the transporter room. A very similar process is used to bring Billy up into the ship. He says he will receive a telepathic communication leading him to a contact site. He then will be taken up into the ship which is usually 100 meters or so overhead by a process that breaks his body down into atoms and then reassembles it inside the ship. The difficulty is in the fact that he must be of clear mind for this to work right. If he is full of negativity or anger he might not come back together right. For this reason they often beam him up without warning while he is working and clear of mind. It is considered safe to do this.