Stellar Inertial Navigation System, familiarly known as SINS, was a standard navigation system used aboard United Federation of Planets starships during the 23rd century. (Star Fleet Technical Manual) After a transfer to USS Avenger in 2292, Hayden Pope improved the efficiency of Avenger's warp engines — resulting in the ship being displaced enough to have to realign its SINS. (Star Trek: Avenger: "Belonging")