**Review Type:** ENG. Technical Review

**Title:** ISO/WD 14620-3 Space systems -- Safety requirements -- Part
3: Flight safety systems

**Originator:** Walt Thomas **Code** 302 **ext.** 8896 **Organization:**
NASA/GSFC

**6.1.3** FTS reliability shall be set at 0.999 at the 95% confidence
level, or shall be compliant with the quantitative flight safety
objectives if the later are more stringent. The reliability should be
established by analysis of all components and supporting test data.

\* Redundancy needs to be specified to specific level of reliability (&
confidence; or be specific in saying that redundancy shall be
implemented to assure reliability) specified 6.1.3

**6.1.14** The launch vehicle operator shall verify the FTS has
sufficient service life for the specified mission prior to launch.

\* How to verify analysis, testing?

**6.1.16** For externally controlled FTS, all equipment shall be
adequate to assure a radio-frequency propagation path from the command
transmitter/antenna system to the launch vehicle antenna.

\* The word adequate is too "loose" a term here.

**6.1.17** For externally controlled FTS, the response time of each
function shall be between 4 and 25 milliseconds.

\* "each function", is unclear

**6.1.18** For externally controlled FTS, the FTS antenna system shall
have adequate radio coverage over 95% of the radiation sphere.

\* "Adequate", is too loose a term, needs to be more precise

**6.2.2** For launch vehicles where propulsive ignition occurs after
first motion, the FTS S&A devices shall contain an ignition interlock
which shall be designed such that ignition cannot occur unless at least
one of the FTS arming devices is in the armed position.

\* "One of the FTS arming devices", probably needs at least two
(redundant) to meet 6.1.11.

**6.3.3** Ordnance items and others that are conductive and interface
with ordnance shall be kept at the same voltage potential through
grounding.

\* "Ordnance items and others", what others?

**7.2.10** Design RTS reliability shall be 0.995 at the 95% confidence
level for transponder systems and 0.999 at the 95% confidence level for
space based systems such as GPS, or shall be compliant with the
quantitative flight safety objectives if the later are more stringent.

The reliability should be established by analysis of all components and
supporting test data.

\* RTS shall be designed to a reliability of 0.995, at a 95% confidence
level, for transponder system and 0.999, at a 95% confidence level, for
space based systems such as GPS; or shall be compliant with quantitative
flight safety objectives, if the later are more stringent. Then
reliabilities shall be established etc.

**8.2.12** Design TDTS reliability shall be 0.995 at the 95% confidence
level, or shall be compliant with the quantitative flight safety
objectives if the later are more stringent. The reliability should be
established by analysis of all components and supporting test data.

-   TDTS shall be designed to a 0.995, at a 95% confidence level; or
    shall be compliant with quantitative flight safety objects, if the
    later are more stringent. This reliability shall be established by
    analysis etc.

Worse Case

FTS RTS TDTS

.999 (95%) .995 (95%) .995 (95%) = 0.989 (95%)

Level of Risk, assuming all three "subsystems" are serial (i.e., all
three must operate successfully for FSS to operated successfully) is a
reliability of 0.989 (95% confidence); that is, a probability of failure
of 1.1%, or, nominally, 1 in 100. If this FSS "risk" is deemed to high,
then "subsystem" reliabilities will need to be increase.

Note: For subsystems (FTS, RTS, TDTS) reliabilities established by
component analysis, e.g. by a typical MIL-HDBK-217F analysis, this type
of analysis (-217) Does Not provide a confidence level for the assembly
of components. Thus, either extensive testing or analyses based on field
data of component parts would be required.