You can retrieve the transmission in several places: On the blockstream api, on a site that saves most of the transmissions: http://thehuntison.xyz/ (it is a Satoshi's Treasure hunter;) The first clues were sent by satellite transmissions ! ^^^' That explains the design of the site:) ) or having an antenna that pointed to one of its 5 geostationary satellites at the right time: 
RE: My first important Tweet ! A tweet from SPACE !