Maintainability: The Forgotten "Ility", Essential for Long Term Mission Success"
Fragola, Joseph1; Pettit, Donald2; Putney, Blake1
1Valador Inc.; 2NASA Johnson Spaceflight Center
The space age is just over a half-century old. Over the past two score and ten years there have been many advances in systems performance and in systems reliability. However, until the advent of the space shuttle, and because all systems were either disposable or single use, maintainability had been an afterthought. Even in the case of the space shuttle, the focus was on ground replacement and the level of online repair was therefore directed at the Line Replaceable Unit (LRU). The International Space Station envisioned an even higher level of repair, the Orbital Replaceable Unit (ORU) level. The original concept relying on the shuttle to return failed ORUs to the earth for repair using the significant down mass capabilities of the space shuttle. While this repair concept may have been well intentioned it soon showed its weaknesses when shuttle downtime after the Columbia accident, and the associated re-supply limitations of alternative vehicles, left some major systems unavailable due to failure and unavailability of replacement hardware. This eventuality motivated the on-board crew of Expedition 6 to undertake innovative, and completely unplanned, maintenance activities at the component and materials levels. These activities were successful in restoring functionality without the need of massive unit replacement. Similar experience on missions to Antarctica with astronaut participation on the part of an Expedition 6 crewmember have shown the value of scavenging and low level repairability in remote locations. At the same time analytical studies carried out in conjunction with the ongoing Lunar and Mars Architecture Teams (LAT/MAT) efforts have shown that lunar base missions would be severely limited if repair were reduced even to the LRU level of shuttle replacement, and crewed missions to Mars would be untenable. These analytical studies have further indicated the significant benefits of extremely low levels of repair and scavenging from less vital systems to support mission continuance. An experimental repair activity currently taking place on the International Space Station called Component Repair EXP-1, based out of NASA Glenn, is specifically looking at circuit board repair at the component level. In this experiment crew members will simulate the repair of test circuit boards, populated with a variety of discrete electronic components as well as surface mounted integrated circuits, by removing these components and integrated circuits and re-soldering replacements into place while on the International Space Station. The functionality and electrical integrity of the repairs will be subsequently evaluated on the ground. This research effort, although in its infancy, is a step in the right direction for lunar and Mars missions where the duration will guarantee a high probability of failure and the lack of space parts, dictated by limitations on mission mass, will necessitate such repairs. The combination of these practical and analytical efforts have indicated that designing systems to be maintained at low levels, and carrying raw materials rather than spares must be their mainstay, and the development of crew skills, tool sets, multi-use materials complements, and systems commonality is essential to long term mission success. This paper will discuss the experiences that led to these insights and the implications on the design of new mission systems, component, and materials complements.