featured knowledge

Military/Aerospace/High Reliability COTS/Automotive/COTS Plus

NASA wisdom is based on broad and NASA wisdom says: use these parts very
deep knowledge of these parts that Wisdom carefully, test extensively, and gather as
has enabled reliable use for decades. Broad much knowledge as possible.
Knowledge

Extensively documented experience Access to detailed information gen-

(good and bad) collected and shared
Knowledge erally limited to important customers.
Collected information, NASA has limited experience with
about parts that have evolved steadily.
experience, expertise, and insight large-scale use of these parts.

Data generated over more than Information Market-focused reports

40 years analyzed and reported Organized and analyzed data that can available. NASA must
to provide extensive information. be used for a purpose generate own information.

NASA has ready access to Manufacturers supply

Data extensive data aimed at
mandated data, common
Discrete, objective, but unorganized facts about an event
to all suppliers. their target market.

COTS Components in Spacecraft

Systems: Understanding the Risk
N ASA’s Commercial Crew Program (CCP) is stimulating
efforts within the private sector to develop and
demonstrate safe, reliable, and cost-effective space
basis depending on criticality, are intended to identify
defects and abnormalities that serve as warning signs of
a potential for premature failure, reduced performance,
transportation capabilities to the International Space and safety.
Station. One initiative involved investigating the possible
Parts screening approaches
use of commercial grade electronic parts in launch
vehicle and spacecraft designs. The CCP was interested There is a wide spectrum of approaches to parts
in data that would help frame the technical, cost, and screening. At one end of the spectrum, EEE parts used
schedule risk trades associated with the use of electrical, in critical space systems in general are subjected to
electronic, and electromechanical (EEE) parts of a lower 100% parts-level inspections and testing to provide
grade than traditionally used in most NASA safety-critical high assurance of quality and reliability. At the other
applications. end of the spectrum are commercial catalog parts
that have not been subjected to any testing other than
The fundamental question
those established by the manufacturer. An NESC team
The fundamental question is “Can commercial-off-the- analyzed two COTS parts screening approaches: one
shelf EEE parts with limited screening be used in crewed that employs only card-level testing coupled with box-
flight hardware systems?” The terms “commercial-off- level and system-level testing versus the traditional
the-shelf parts,” or “COTS,” and “screening” are broadly approach of screening at the parts level prior to card,
defined and not applied consistently. Automotive, box and system-level testing. The team concluded that
commercial aviation, medical, and safety conscious there are fundamental concerns with replacing parts-
consumer electronics industries engage in assurance level screening and qualification with card and box-level
processes within their supply chain to establish a or system-level testing only.
basis for the quality and reliability of the EEE parts
Assembling COTS EEE parts on circuit boards for space
used in their products before assembling them into
applications without proper parts-level qualification or
critical applications. These assurance processes, with
additional screening could result in assembling good
inspections and tests possibly performed on a sample
parts along with any weak parts (parts containing
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latent defects and infant mortals and/or parts not
suitable for the application) into flight hardware, with
the questionable assumption that board-, box-, and Important definitions
system-level testing can effectively identify parts that
might fail during the anticipated mission lifetime. Proper COTS: An assembly or part designed for commercial
parts-level qualification is essential to: 1) ensure the applications for which the item manufacturer
or vendor solely establishes and controls the
part technology, design, and construction is capable
specifications for performance, configuration, and
of predictable and required performance in the space
reliability (including design, materials, processes, and
environment and 2) identify parts that function properly in
testing) without additional requirements imposed by
terrestrial applications but may not perform safely in the
users and external organizations. For example, this
more extreme space radiation, vacuum, vibration, and
would include any type of assembly or part from a
thermal environments found in spaceflight applications.
catalog without any additional parts-level testing after
Card-level, box-level, and system-level testing cannot
delivery of the part from the manufacturer.
replicate accelerated failure factors that voltage, current,
and temperature stresses can provide during parts-level COTS Plus: A COTS part supported by test data
screening prior to installation on a circuit board. available to end users establishing random failure
rate assumptions, performance consistent with the
Commercial parts use at NASA manufacturers data sheet and methods to exclude
NASA has successfully used commercial parts in infant mortal parts, parts with latent defects, weak
spacecraft for specific and sometimes mission-critical parts, or counterfeit parts. For example, automotive
applications throughout the Agency’s history. This electronics council-certified or compliant automotive
has been achieved by careful selection, qualification, parts are one type of COTS Plus.
and screening. The level of screening required for Parts Qualification: Sample-based mechanical,
commercial parts to ensure they will work successfully is electrical, and environmental tests at the piece
highly dependent on the mission, intended application, parts level intended to verify that materials, design,
environment, mission duration, and part technology. The performance, and long-term reliability of parts on
level of screening is quite well characterized in existing the same production line are consistent with the
NASA parts documents such as EEE-INST-002. NASA specification and intended application until a major
flies non-MIL (non-military) grade parts when the required process change.
functionality and/or performance is not available in MIL
Parts Screening: A series of tests and inspections
parts. If a MIL part can be used, they are preferred.
at the piece parts level intended to remove
Initial qualitative analysis indicates significant differences nonconforming and/or infant mortal parts (parts
in reliability and safety can result between screened MIL with defects that are likely to result in early and/or
parts and unscreened commercial parts. Parts quality, cluster failures) and thus increase confidence in the
architecture (including the selection of like or diverse reliability of the parts selected for use.
backup systems), and mission duration are inseparable
variables that must be traded in a mission design. One
system architecture could use lower grade parts for
short-duration missions (a few minutes to a few days) or similar NASA documents, requires a firm basis for
and possibly exhibit acceptable analytical system substantiation. Any approach based on architecturally
reliability. That same architecture may not provide the similar redundancy and card-level, box-level, and system-
analytical reliability required for long-duration missions level testing alone is not sufficient to enable widespread
(a few weeks to many months) when using lower grade use of unscreened parts acquired from commercial
parts. Parts quality dominates system reliability in long- catalog distributors in critical applications. To reduce the
duration missions where environmental effects like likelihood that parts failures result in unacceptable mission
space radiation and single event upsets are more likely to risk, standard practice dictates designers to: 1) develop
occur. A system design for long-duration missions is an and implement a systems engineering-oriented mission
example where NASA would typically employ in critical assurance program to address EEE parts derating,
applications high reliability space-qualified military grade qualification, traceability, and counterfeit control, and
parts or use highly screened and qualified COTS parts. demonstrate how it mitigates the risks associated with
Alternative approaches EEE parts applications, and 2) provide data supporting
the effectiveness of the proposed screening approach,
Any alternative approach for the use of COTS EEE ensuring part failure rates are adequately bounded. □
parts in critical applications other than those that have
proven successful, such as described in EEEINST-002 Reference NASA/TM-2014-218261
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