... The spacecraft clock is the onboard time-keeping mechanism that triggers most spacecraft events, such as shuttering of a camera. ... Most of the complexity of dealing with SCLK time values arises from the fact that the rate at which any spacecraft clock runs varies over time. ... Leapseconds kernels are described in the TIME required reading document. ... Each spacecraft clock type has its own set of parameters that the CSPICE SCLK functions require in order to convert SCLK values of that type. ...