(covers information from several alternate timelines)
The Rigellian scoutship was a heavily-armed starship used under the authority of the Rigellian Trade Commission during the mid-22nd century. As scouts, these starships had small crew complements of around seventeen.
In late-2154, a Rigellian scoutship was attacked by what appeared to be the United Earth starship Enterprise NX-01. The scoutship was able to inflict moderate damage on its attacker, and transmit a distress call, before being destroyed.
Following the incident, the Rigellian Trade Commission recognized the attacking vessel, and demanded compensation from Starfleet and the arrest of Jonathan Archer, Enterprise's commander, for the loss of their vessel.
Ships of the class
In scene descriptions from the final draft script of "United", this type of craft was repeatedly referred to as a "Rigellian Corsair".
For more information, and further appearances of this design, see: studio model.