Exploring the Unknown: Selected Documents in ... - The Black Vault

Exploring the Unknown 181
and in the provision of alternative modes of procedure. Thus, there is both an
automatic control system and an essentially independent manual control system;
there are regular and emergency oxygen supplies, two modes of egress, and
the like. Such redundancy is a standard and effective way of creating over-all
reliability with the use of individually less than perfect components. It is necessary
to keep this consideration in mind when examining reliabilities of individual
components. [5]
2. Subsystem reliabilities
The subsystems are common to both the orbital and ballistic missions,
and hence at this point it is not necessary to make a distinction between the
Redstone and Atlas missions. When the ultimate probabilities of mission success
and astronaut survival are considered, the distinction is, of course, a very
important one.
There is a considerable body of test data on components and subsystems
to which the panel has had access. Also, both NASA and McDonnell perform
continuing reliability analyses of the over-all system on the basis of these data.
For present purposes, it seems undesirable to present such detailed analyses,
even in summary form. What follows, then, represents a distillation into very
general terms of the Panel’s considered reaction to these data. Reliabilities are
aggregated into three categories:
Class
Reliability Range
Class 1 95 – 100%
Class 2 85 – 95%
Class 3 70 – 85%
The following chart indicates the major subsystems and lists our judgment
of the reliability of each. It should be emphasized that the numerical categorization
in the chart is the result not of calculations but rather of the subjective judgment
of the panel. Following the chart is a brief discussion of certain of its entries.
Those to be discussed are marked by and asterisk.
[6]
Subsystem or Component
Reliability Category
Capsule structure and
Class 1
re-entry properties
Separation mechanism and
Class 1
Posigrade Rocket
Tower and Abort Rockets Class 1
Voice Communications Class 1
*Abort sensing instrumentation
Class 1
system