Aerospace Control Systems

Spacecraft GNC Systems Engineering

RADICAL RIMU Attitude Determination/Calibration Filter PDF Print E-mail
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RADICAL RIMU Attitude Determination/Calibration Filter
Software Components
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Precise attitude determination requires that attitude sensor and gyro parameters be calibrated accurately. It is often the case that attitude sensor and gyro calibration are not carefully considered in the design and operation of a system, or the calibration algorithm and its software implementation are limited in their capability or performance. A well designed calibration algorithm and software tools are necessary to conduct early trade studies and to predict performance, to quickly design and implement a system, and to achieve optimum system performance during operation.

A large number of spacecraft carry a Redundant IMU (RIMU). A RIMU is an Inertial Measurement Unit (IMU) that comprises more than three sense axes. In this context we are talking about active redundancy rather than passive functional redundancy, so we assume that all gyros are active in the RIMU. Examples of a RIMU are the Northrop Grumman SIRU, four or more interferometric fiber-optic gyros (IFOG), a set of two or more two-axis gyros such as dry-tuned rotor gyros (DTG), and two 3-axis IMUs. Calibration filters in common use treat the RIMU as a 3-axis IMU and estimate only a minimal set of calibration parameters and do not fully exploit the capability of a RIMU.

The Redundant IMU (RIMU) Attitude Determination/Calibration (RADICAL TM) Filter takes full advantage of the redundancy in a RIMU to optimally estimate spacecraft attitude and a full set of calibration parameters for n ≥ 3 gyro sense axes and relative misalignments (interlocks) for m attitude sensors. The RADICAL filter is ideal for

  • desktop analysis and design,
  • automated or semi-automated ground-based processing of telemetry,
  • real-time on-orbit processing of attitude sensor data.

RADICAL has been used to support several missions and has processed thousands of hours of telemetry. Its performance has been verified through extensive testing via simulation and processing of in-flight telemetry, and demonstrated by accurate geolocation results based on attitude estimates produced by the RADICAL filter.

The RADICAL solution makes sense in a world of tighter requirements, shorter procurement schedules, smaller design teams, and limited research and development funds. RADICAL is a cost-effective alternative to in-house development. The RADICAL software incorporates not only the best algorithms, but also relevant experience.

The RADICAL software can support your project through either a support contract or by licensing the software. Contact ACS to discuss how we can best address your technical and programmatic requirements.