For those of you who haven't heard of Explorators, they're basically Adeptus Mechanicus "Explorers". They search the Unknown for planets/resources/Space Hulks/lost technological treasures...
Pretty much along the same lines as Rogue Traders, only they're headed up by rather independently minded Techpriests. INQ (Inquisitor) had rules for creating Explorator Warbands and running non-Inquisitorial campaigns revolving around these most interesting of Techpriests. There's already character templates for Techpriests in DH, so what is keeping one from a WH40kRP Campaign revolving around Explorators? Just the Ship rules in RT.
Keep these in mind for Allies, Rivals, One-off Scenario encounters etc. Even if you don't run Explorators as PC's (a techpriest working for an RT isn't really an Explorator) they make interesting non-associated NPC's.
Some scenario ideas off the top of my head:
The Players find a planet rich in resources, unpopulated and ripe for exploitation...unfortunately there's an Explorator survey ship orbiting the other side of the planet and have already laid claim to it....
While surveying an unpromising planet, the "away teams" are about to return when auspexes discover a pattern of archeological digs. After investigating a few of them, the Players discover some fairly fresh, but dead Techpriests, Skitarri, Adepts and Servitors...along with several valuable pieces of Archeotech which appear to have been discarded. Looks like the Techpriests found something they considered valuable enough to kill each other over...
Perhaps the Players want something, but lack the firepower to get it. Cut a deal with a nearby Explorator ship?
Anyway, you get the idea. I hope the RT designers at least mention them. I personally don't think a RT campaign is entirely complete without them.