The chart above indicates the number of components removed and replaced on the Space Shuttle orbiters per flow.
Flights above are STS-42 through STS-62 ; data through Feb. 28, 1994.
This data does not include Space Shuttle Main Engine (SSME) and Thermal Protection Systems (TPS) such as tile or blankets. The numbers shown here would be much higher if these were included. Engine work is done offline in the engine shop and TPS is accounted for separately.
This data does not include planned removal and replacements. For example, all three engines are R+R'ed every flight. Since this is not done in the problem reporting (PR) system, but rather in the maintenance system, they would not show up in the above count.
A breakdown to resources is not available. How many people are associated with the repair and replacement of parts on the main propulsion system? How many dollars were drawn by the hydraulics system? This is valuable information that is key to making decisions for now and for future launch vehicle improvement. Various efforts are being worked in this area.
Also, some of the above R+R's are worked routinely but not transferred into planned work for purposes of flexibility for the system engineers working the various areas.
The PR system from which this data was obtained is a constraint system. It's intent is to trace and document work and constraints to work that feed into preparing the shuttle. It is not a system for tracking resource (dollars and headcounts by system) information.
STS-49, 50 and 53 are not included in the chart.
STS 49 was first flight of OV-105/Endeavour.
STS-50 was OMDP for OV-102/Columbia.
STS-53 was OMDP for OV-103/Discovery.
The relevance to certification is in the difference between practices that certify for one flight rather than many flights.
The Space Shuttle "certification" has certain key characteristics. First, the certification is "one time only". It is not intended in the Shuttle use of the term certification to apply to the launch-worthiness of a fleet of vehicles or to a system of similar design. The certificate applies only to the case at hand and expires immediately upon landing of that vehicle. The whole process is repeated for this vehicle and the others in the fleet every flight. Also, under close scrutiny, neither is the process one of "maintaining airworthiness" given the degree to which much of the vehicle is replaced from launch to launch. This last point applies not only to new and major expendable elements such as the shuttle ET and practically new elements such as the SRB's but also to the large number of new components on each of the orbiters. This last number may be 100 to 150 LRU's from flow to flow not counting some major components in the main engines and tile work on the TPS.
To one day be able to certify for many flights a fully reusable launch vehicle takes one large step simply by not having expendable launch elements. However, it is just as necessary to eliminate the steady consumption of spares to fully realize the goal of aircraft-like operations and systems certified once for many, perhaps hundreds, of flights.
This data is one piece of the larger puzzle of certification for future launch systems. Various projects are working this subject. One such project will be posted on this homepage sometime around August 1995.
Return to KSC Next Gen Site
Edgar Zapata, NASA Kennedy Space Center
Shuttle Process Engineering Directorate, Fluid Systems Division