NASA Scientific and Technical Aerospace Reports

20040111432 NASA Glenn Research Center, Cleveland, OH, USA
Power Management and Distribution Trades Studies for a Deep-Space Mission Scientific Spacecraft
Kimnach, Greg L.; Soltis, James V.; January 1, 2004; 9 pp.; In English; STAIF 2004, 8-12 Feb. 2004, Albuquerque, NM, USA
Contract(s)/Grant(s): 22-982-10-03
Report No.(s): Paper-70; No Copyright; Avail: CASI; A02, Hardcopy
As part of NASA’s Project Prometheus, the Nuclear Systems Program, NASA GRC performed trade studies on the
various Power Management and Distribution (PMAD) options for a deep-space scientific spacecraft which would have a
nominal electrical power requirement of 100 kWe. These options included AC (1000Hz and 1500Hz and DC primary
distribution at various voltages. The distribution system efficiency, reliability, mass, thermal, corona, space radiation levels and
technology readiness of devices and components were considered. The final proposed system consisted of two independent
power distribution channels, sourced by two 3-phase, 110 kVA alternators nominally operating at half-rated power. Each
alternator nominally supplies 50kWe to one half of the ion thrusters and science modules but is capable of supplying the total
power re3quirements in the event of loss of one alternator. This paper is an introduction to the methodology for the trades done
to arrive at the proposed PMAD architecture. Any opinions expressed are those of the author(s) and do not necessarily reflect
the views of Project Prometheus.
Author
Ion Engines; Power Effıciency; Spacecraft Power Supplies; Technology Assessment; Deep Space; Power Conditioning
20040111982 NASA Glenn Research Center, Cleveland, OH, USA
System Mass Variation and Entropy Generation in 100-kWe Closed-Brayton-Cycle Space Power Systems
Barrett, Michael J.; Reid, Bryan M.; [2004]; 21 pp.; In English; 21st Symposium on Space Nuclear Power and Propulsion,
8-12 Feb. 2004, Albuquerque, NM, USA
Contract(s)/Grant(s): WBS 22-973-80-10; Copyright; Avail: CASI; A03, Hardcopy
State-of-the-art closed-Brayton-cycle (CBC) space power systems were modeled to study performance trends in a trade
space characteristic of interplanetary orbiters. For working-fluid molar masses of 48.6, 39.9, and 11.9 kg/kmol, peak system
pressures of 1.38 and 3.0 MPa and compressor pressure ratios ranging from 1.6 to 2.4, total system masses were estimated.
System mass increased as peak operating pressure increased for all compressor pressure ratios and molar mass values
examined. Minimum mass point comparison between 72 percent He at 1.38 MPa peak and 94 percent He at 3.0 MPa peak
showed an increase in system mass of 14 percent. Converter flow loop entropy generation rates were calculated for 1.38 and
3.0 MPa peak pressure cases. Physical system behavior was approximated using a pedigreed NASA Glenn modeling code,
Closed Cycle Engine Program (CCEP), which included realistic performance prediction for heat exchangers, radiators and
turbomachinery.
Author
Closed Cycles; Brayton Cycle; Spacecraft Power Supplies
20040112040 NASA Glenn Research Center, Cleveland, OH, USA
Performance Expectations of Closed-Brayton-Cycle Heat Exchangers in 100-kWe Nuclear Space Power Systems
Barrett, Michael J.; [2003]; 21 pp.; In English; 1st International Energy Conversion Engineering Conference (IECEC), 17-21
Aug. 2003, Portsmouth, VA, USA
Contract(s)/Grant(s): WBS 973-80-10
Report No.(s): AIAA Paper 2003-5956; No Copyright; Avail: CASI; A03, Hardcopy
Performance expectations of closed-Brayton-cycle heat exchangers to be used in 100-k We nuclear space power systems
were forecast. Proposed cycle state points for a system supporting a mission to three of Jupiter’s moons required effectiveness
values for the heat-source exchanger, recuperator and rejection exchanger (gas cooler) of 0.98, 0.95, and 0.97, respectively.
Performance parameters such as number of thermal units (Ntu), equivalent thermal conductance (UA), and entropy generation
numbers (Ns) varied from 11 to 19, 23 to 39 kW/K, and 0.019 to 0.023 for some standard heat exchanger configurations.
Pressure-loss contributions to entropy generation were significant; the largest frictional contribution was 114% of the heat
transfer irreversibility. Using conventional recuperator designs, the 0.95 effectiveness proved difficult to achieve without
exceeding other performance targets; a metallic, plate-fin counterflow solution called for 15% more mass and 33% higher
pressure-loss than the target values. Two types of gas-coolers showed promise. Single-pass counterflow and multipass
cross-counterflow arrangements both met the 0.97 effectiveness requirement. Potential reliability-related advantages of the
cross-counterflow design were noted. Cycle modifications, enhanced heat transfer techniques and incorporation of advanced
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