This preview shows page 1. Sign up to view the full content.
Unformatted text preview: in a substantial improvement in that
The risk management method requires an
estimate of the probability distribution for the final TPM
value. (See sidebar on tracking spacecraft mass.) Early
in the TPM tracking program, when the demonstrated
value is based on indirect means of estimation, this
distribution typically has a larger statistical variance than
later, when it is based on measured data, such as a test
result. When a TPM stays along its planned profile (or
equivalently, when its margin remains above the
corresponding margin requirement), the narrowing of the
statistical distribution should allow the TPM to remain in
the green alert zone (in Figure 22(c)) despite its growth.
The three methods represent different ways to assess
TPMs and communicate that information to
management, but whichever is chosen, the pattern of
success or failure should be the same for all three.
Relationship of TPM Tracking Program to the SEMP .
The SEMP is the usual document for describing the
project's TPM tracking program. This description should
include a master list of those TPMs to be tracked, and
the measurement and assessment methods to be
employed. If analytical methods and models are used to
measure certain high-level TPMs, then these need to be
identified. The reporting frequency and timing of
assessments should be specified as well. In determining
these, the system engineer must balance the project's
needs for accurate, timely, and effective TPM tracking
against the cost of the TPM NASA Systems Engineering Handbook
Management Issues in Systems Engineering
tracking program. The TPM tracking program plan,
which elaborates on the SEMP, should specify each
TPM's allocation, time-phased planned profile or margin
requirement, and alert zones, as appropriate to the
selected assessment method.
4.9.3 Systems Engineering Process Metrics Status reporting and assessment of systems
engineering process metrics provides additional visibility
into the performance of the "system that produces the
system." As such, these metrics supplement the cost
and schedule control measures d...
View Full Document