What does IRS stand for?

Indian Remote-sensing Satellite

Information Retrieval Service

Interferon-responsive Sequence

Internal Reflection Spectroscopy

Internal Revenue Service (u.s. Department of The Treasury)

Inertial Reference System(s)  

An inertial reference unit (IRU) is a type of inertial sensor which uses gyroscopes and accelerometers to determine a moving aircraft’s or spacecraft’s change in rotational attitude (angular orientation relative to some reference frame) and translational position over a period of time.