Integrated vehicle health management (IVHM) or integrated system health management (ISHM) is the unified capability of systems to assess the current or future state of the member system health and integrate that picture of system health within a framework of available resources and operational demand.
Aims of IVHM
The aims of IVHM are to enable better management of vehicle and vehicle fleet health. Improve safety through use of diagnostics and prognostics to fix faults before they are an issue. Improve availability through better maintenance scheduling Improve reliability through a more thorough understanding of the current health of the system and prognosis based maintenance Reduce total cost of maintenance through reduction of unnecessary maintenance and avoidance of unscheduled maintenance
This is achieved through correct use of reliable sensing and prognosis systems to monitor part health and also using usage data to assist in understanding the load experienced and likely future vehicle load.
History
Origins
It has been suggested that IVHM as a named concept has been around since the 1970s. However, there does not seem to be much in the way of written evidence of this. IVHM as a concept grew out of popular aviation maintenance methods. It was a natural next step from condition based maintenance. As sensors improved and our understanding of the systems concerned grew, it became possible to not just detect failure but also to predict it. The high unit cost & high maintenance cost of aircraft & spacecraft made any advance in maintenance methods very attractive. NASA was one of the first organisations to use the name IVHM to describe how they wanted to approach maintenance of spacecraft in the future. They created NASA-CR-192656, in 1992 with the assistance of the General Research Corporation and the Orbital Technologies Corporation. This was a goals & objectives document in which they discussed the technology and maintenance concepts that they believed would be necessary to enhance safety while reducing maintenance costs in their next generation vehicles. Many companies since then have become interested in IVHM and body of literature has increased substantially. There are now IVHM solutions for many different types of vehicle from the JSF to commercial haulage vehicles.
First space prognostics
The first published history of predicting spacecraft equipment failures occurred on the 12 Rockwell/U.S. Air Force Global Positioning System Block I (Phase 1) satellites using non-repeatable transient events (NRTE) and GPS Kalman filter data from the GPS Master Control Station, between 1978 and 1984 by the GPS Space and Ground Segment Manager. NRTEs were isolated to the GPS satellites after mission operations support personnel replayed the real-time satellite telemetry ruling out RF and land-line noise caused from poor Eb/No or S/N and data acquisition and display system processing problems. The GPS satellite's subsystem equipment vendors diagnosed the NRTEs as systemic noise that preceded the equipment failures because at the time, it was believed that all equipment failures occurred instantaneously and randomly and so equipment failures could not be predicted (e.g. equipment failures exhibited memoryless behavior). Rockwell International GPS Systems Engineering Manager ordered a stop to predicting GPS satellite equipment failures in 1983 claiming it wasn't possible and the company was not on contract to do so. The prognostic analysis that was completed on the GPS satellite telemetry was published quarterly contractually as a CDRL to the GPS Program Office personnel and a wide variety of Air Force subcontractors working on the GPS program.
Further development
One of the key milestones in the creation of IVHM for aircraft was the series of ARINC standards that enabled different manufacturers to create equipment that would work together and be able to send diagnostic data from the aircraft to the maintenance organisation on the ground. ACARS is frequently used to communicate maintenance and operational data between the flight crew and the ground crew. This has led to concepts which have been adopted in IVHM.