The Inertial Measurement Instrument for Space (NIMIS) is an Inertial Reference Unit (IRU) specifically designed for space applications, which utilizes three independent quartz hemispherical resonator gyroscopes (Q-HRGs) to provide measurements of the system’s angular velocities with respect to an inertial reference system.

The unit is based on a new European high-precision hemispherical resonator gyro (HRG) led by Northrop Grumman Italia and named Q-HRG. The HRG technology has proven unrivalled success in space, providing the best level of accuracy and reliability available on the market since the 1990s. The SSIRU, developed in the US by Northrop Grumman Corporation, recently achieved 50 million hours of operation in space without a single mission failure. The

core technologies behind the Q-HRG ensure a similarly level of reliability to that demonstrated by the US gyroscope, but in a cost-effective ITAR Free product.

The system consists of: a power supply module, which includes an EMI/EMC filter; a CPU module, which incorporates computing power, long-term memory and communication capabilities; a sensor block, which consists of a set of three hemispherical resonance gyroscope (Q-HRG) sensor assemblies; and an electronics module, called a conversion board.

To provide accurate angular measurements, the Q-HRGs require feedback control to maintain a constant operating regime. The control loop involves analogue and digital components.

The system can provide outputs on three different electrical interfaces. The main bus communicates according to the MIL-1553B standard, which is the basis of the system. The main output can also use an alternative interface according to the Controller Area Network (CAN) communication standard. A separate interface provides additional data for development and maintenance and utilizes the Synchronous Data Link Control (SDLC) communication protocol.

The unit is being developed as part of an Italian governmental satellite communication program (Ital-GovSatCom) and FESR (European Regional Development Fund – LAerospaZIO) that meets demanding requirements in terms of performance, radiation environment and reliability.