The SLS Pioneer was an Avatar-class WarShip in service with the Star League Defense Force during the era of the Star League. At some point during her history the Pioneer underwent an extensive refit and modification process that filled almost half of her sixty thousand tonnes of cargo space with specialised astronomic sensors, labs and crew quarters to turn the ship into a highly specialised space exploration vessel. The Pioneer was then assigned to the Star League Expeditionary Brigade until the research and exploration programme conducted by the SLEB was shut down after the death of First Lord Simon Cameron.
While suffering heavy damage, the Pioneer would survive the collapse of the Star League in the wake of the Amaris Civil War but would not join the Exodus Fleet, with survivors of the SLEB taking control of the ship to escape the maelstrom of the First Succession War. By 2819 the Pioneer had reached the Paran system when its KF drive failed, its crew eventually joining with the Paranese and forming the Paran Free System in 2835. Even as it began to deteriorate due to lack of parts and the technical decline of the Succession Wars era, the Pioneer would be the backbone of the PFS defensive forces, the mere sight of the WarShip generally scaring off any attempt at large-scale invasion or raiding against Paran. 
But by 2860, the Pioneer was on its last legs, its weapons were either empty or nonfunctional and its transit drive was failing. By 2875 the PFS set the virtually dead Pioneer adrift in the outer system, ostensibly claiming it was to be called upon only when needed. By the era of the Word of Blake Jihad and the arrival Clan Diamond Shark in Paran, nobody alive knew the location of the Pioneer and the Sharks survey efforts in the system had no luck in locating the wreck either.
The first printing of Interstellar Players 3: Interstellar Expeditions incorrectly referred to the Pioneer as being a Vigilant-class corvette; this was confirmed to be an error via the Ask The Writers forum of the official website, where the author confirmed that the correct class for the Pioneer was the Avatar-class heavy cruiser as previously recorded in Era Report: 2750.
|‚Äú||Avatar. Don't know where I got Vigilant from...||‚ÄĚ|
|— GhostBear, Assistant Line Developer, 06 Dec 2012|
- Era Report: 2750, p. 55, "Star League Expeditionary Brigade (The Seekers)"
- Interstellar Players 3: Interstellar Expeditions, p. 39 "Coreward Legacies - States of Survival: Chainlane Isles - Paran"
- Ask The Writers question dated 06 Dec 2012 - "SLS Pioneer class"