The systems engineering process for thermal nuclear propulsion requirements and configuration definition is described in outline and graphic form. Functional analysis and mission attributes for a Mars exploration mission are also addressed

Robbins, Red

English

NASA Technical Reports Server

NTP: 
REQUIREMENTS 
MANAGEMENT 
AND LONTROL 
N 9 3 - 2 6 9 1 8  
a.L . . 
ANALYTICAL @' Presented by: Red Robbins 
ENGINEERINOV' 
DISCUSSION 
Nuclear Thermal Propulsion Systems Engineering 
Systems Requirements Status 
Functions That Need To Be Performed 
Attributes Associated With The Functions 
I 
ANALYTICAL p 2 : '  
ENOINEERINGI~ 
NP-TIM-92 tern Concepts 48 
ANALYTICAL 
https://ntrs.nasa.gov/search.jsp?R=19930017727 2020-03-17T05:26:56+00:00Z
SYSTEMS ENGINEERING PROCESS FOR 
REQUIREMENTSlCONFlGURATlON DEFINITION 
SYSTEMS CONTRACTOR I NASA I + - - - - - - - - - - - + - - -  NASA - - - _ - _ - - _ - _  
I FMClbnal 
Anatyrb (NA) Yhsbn 
RequQements - Program 
~e qukement s 
Process 
Ve hkWSpacecmft - Tmde ----C Ve hklelSpacecmft 
+ St ud k Defhitbn Re quire me nt s 8- 
Pmce ss 
StagelEnghe 
D e f M b n  Trade 
Pmpulsbn System - 
1 S t u d i e  s +' Facllty Deflnnbn 
Fkq u h  me nt s 
StagelEnghe 
Trade 
Re quhme nt s tudies 
The systems engineering process for requirements and configuration definition, 
shown in the figure above, includes roles and responsibilities of NASA and the 
Systems Contractor. The overall program requirements are derived from the mission 
to  be performed. The program requirements, in turn, are utilized as the basis for the 
definition of all lower level documents that contain incneasing detail concerning design 
requirements assoclated with performance, safety, operat Ions and environment. The 
lower level documents are dynamic in nature. Many studies are conducted involving 
trades between lower level requirements and engineering system definition. The 
propulsion system requirements am highlighted because they are the focus of this 
discussion. Stage/Engine requirements have been generated, baselined by NASA and 
are under formal change control and propulsion system definition is underway. The 
Functional Analysis activity shown is simply the process of systematically identifying 
the generic functions to  be performed at all levels and leads ultimately t o  the definition 
of the System Architecture. Since Program and Vehicle Requirements are not 
currently available, the propulsion system requirements were generated on the basis 
of representative manned lunar and Mars missions. 
NP-TIM-92 49 NTP: System Concepts 
MARS MISSION FUNCTIONAL ANALYSIS \ 
LEVEL f -
PROVIDE MANNED MARS USSK) I TRANSPORTATION 1 I 1 
I n 
I, 
I 
I iv  
I 
C R W E  SPEClRC PRovlDEp(Kyuuuow 
C0NII)oL 
PROVIDE THRUST 
IMPULSE 
\ / MARS MISSION FUNCTIONAL ANALYSIS (continued) 
I I .  V I 
I I PROVlDEPROPEUANT ACCELERAllON 
1 I I I 
I I r 1 
MARS MISSON FUNCTIONAL ANALYSIS (continued) 
LEVEL 
N IMPULSE 
V 
TRANSFER H U T  TO 
THERNAL ENERQV 
M 
/ MARS MISSION FUNCTIONAL ANALYSIS (continued) 
LEVEL 
WNTROL N 
PROVIDE FLIGHT 
0PERAM)NS 
I  
I PROVIDE HEALTH YONTOIING 
The Mars Mission functional 
analysis shown defines the 
mission functions to be 
performed in successive levels of 
detail. The highlighted functions 
at each level are those that are 
directly related to the propulsion 
system. Those functions that are 
not highlighted are the principal 
interfaces with the propulsion 
system. The three functions of 
the propulsion module are to 
provide thrust, provide specific 
impulse and control of the engine 
operations. The three charts 
which follow are simply 
functional breakdowns of the 
main engine functions to 
successively lower levels of 
detail. On the basis of this 
analysis, the system architecture 
or system definition can be 
completed. It should be noted 
that these functions are generic 
and are required for any nuclear 
rocket. No deslgn solutions have 
been assumed. It is the role of 
the systems d efinition 
contractors to perform the 
system trades which result in the 
definition of the propulsion 
system. 
NTP: System Concepts 50 NP-TN-92 
/ MARS MISSION ATTRIBUTES 
I PROVIDE PROPULSION I MODULE 
MARS MISSION ATTRIBUTES (continued) \ T 
PROVIDE n THRUST 
(-) PROVIDE PROPELLANT PROVIDE PROPELLANT 
ACCELERAllON U 
. wmnc ENERGY CONVERSION . STARTUP NPSP REOUIREMENT 
. OPERAllNC ENVELOPE - PRESSURE EFFICIENCY 
VOLUME REQUIRED (LENGTH 
AND DIAMETER) 
GROUND TEST QUAUFICAllW, 
AND FLOW 
. NUMBER OF HAZARDS ASSOCIATED 
WlTH LOSS OF FLOW 
Y 
MARS MISSION ATTRIBUTES (continued) T 
PROVIDE 
SPECIFIC n IMPULSE 
PROVIDE NUCLEAR 
THERMAL ENERGY 
TRANSFER HEAT TO 
PROPELLANT 
OPERATING TEMPERATURE MARGIN . MATERIAUPROPELUNT AT 
PROPELLANTTEMPERATURE UNFORWTY 
FISSION PRODUCT RELEASE 
. POWERDENSITY 
. STARTUP WWER MARGIN 
* DEVELOPMENT TEST REOUlREMENTS 
. TEMPERATURUUFE CHARACTErUSllCS 
. FAILURE TOLERANCE 
* COOLDOWN PROPELWT REWIREYNTS 
* PROPELLANT PRESSURE DROP 
F MARS MISSION ATTRIBUTES (continued) 
PROVIDE 
PROPULSION 
UlNYZE EXTERNAL CLOSED LOOP CONTROL INTERFACES 
. FAILURE PROPAGATION ACROSS EXTERNAL INTERFACES 
RECOCNZE AND RESPOND TO ALL ABNORMAUTIES . PROVIDE REPEATABLE STEADY STATE AND TAANSIENT OPERAllON 
. PROVIDE RELIABLE AND RESPONSIVE INSTRUMENTATION 
. MIMYZE REOUIREMENT FOR MANUAL OVERRIDE 
PROVIDE YIYlMUY REDUNDANCY AT YNMUM COST 
The completion of the functional 
analysis previously described 
permits the definition propulsion 
system attributes that can be 
utilized to assess the relative 
merits of competing systems and 
to establish criteria for 
technology thrusts to enhance 
performance, safety and 
reliability. The attributes 
associated with the functions are 
outlined in the four charts that 
follow. These attributes, in 
addition to the system 
requirements, can be utilized for 
the evaluation of any nuclear 
rocket system and can provide 
the system contractors guidance 
about system characteristics that 
are considered to be important. 
NP-TIM-92 51 N?P: System Concepts 
SUMMARY REMARKS 
A Consistent Set Of Propulsion System Requirements Has Been 
Developed By NASA 
Traceable To Mission Needs 
Under Formal Change Control 
Propulsion System Functions Traceable To System Requirements 
Also Been Generated 
Preliminary Propulsion System Attributes Traceable To Functions 
Been Derived To: 
Assess The Relative Merits Of Competing Systems/Elements 
Establish Criteria For The Definition Of Technology Thrusts 
4ave 
iave 
We Request Feedback From The Program Participants - Particularlv The 
System Definition Contractors 
Future Work Will Be Directed To The Development Of An Integrated 
Propulsion Systems Model Coupled With Propulsion Systems 
Requirements Traceable From The Lowest Level To Mission Needs 41 
ANALYTICAL 
I NTP: System Concepts 52 NP-’IIM-92 


Requirements management and control

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