AIAA 95-3620 System Testability - A Russian Solution for Space Power Systems

D. Mulder P h iI lips Laboratory Albuquerque, NM

V. Sinkevich Central Design Bureau for Machine Building St. Petersburg, Russia

T. D. McCarson New Mexico Engineering Research Institute Albuquerque, NM

G. L. Schmidt New Mexico Engineering Research Institute Albuquerque, NM

AIAA 1995 Space Programs and Technologies Conference

September 26-28, 1995/Huntsville, AL For permission to copy or republish, contact the American Institute of Aeronautics and Astronautics 370 L'Enfant Promenade, S.W., Washington, D.C. 20024

SYSTEM TESTABILITY-A RUSSIAN SOLUTION FOR SPACE POWER SYSTEMS*

Dan Mulderl Phillips Laboratory

Albuquerque, NM 87106

Valeri Sinkevich2 Central Design Bureau for Machine Building

St. Petersburg, Russia

T. D. McCarson3 New Mexico Engineering Research Institute

Albuquerque, NM 87106

Glen Schmidt4 New Mexico Engineering Research Institute

Albuquerque, NM 87106

Abstract

This paper presents an overview of Russian space nuclear power system development, from concept through qualification, and how testability require- ments were included in the engineering process.

In the early 1950s, designs of space reactor power systems began secretly in Russia and in America. During the last 40 years, space reactor designs evolved from systems providing hundreds of electrical watts to those producing hundreds of kilowatts or more. As power levels, operating temperatures, design complexity and system sizes increased, so did costs for equipment and facilities for system testing, development and qualification. Higher efficiencies, more reliability, longer life, and safer power systems required non-nuclear and nuclear ground tests to prove advancements in technology.

* This work was performed at the Air Force Phillips Lab in support of the Ballistic Missile Defense Organization and Defense Nuclear Agency. The views expressed in this paper are those of the authors and do not reflect official policies or positions of the U S . Department of Defense or the U S . Government.

Evaluation Test. On assignment from Sandia National Laboratories through the Intergovernmental Personnel Act.

Topaz II Specialist, Central Design Bureau for Machine Building, St. Petersburg, Russia.

Senior Research Engineer, New Mexico Engineering Research Institute, University of New Mexico.

Senior Research Engineer, New Mexico Engineering Research Institute, University of New Mexico.

This paper is declared a work of the U S . Government and i s not subject to copyright

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Project Technical Director, Thermionic Systems

4 protection In the United States.

The users wanted specific proof that performance requirements were met or could be achieved prior to deployment.

In Russia. as in America, users became participants in design reviews and tests to demonstrate space reactor power systems. They demanded to know how systems would be qualified and tested to determine acceptable performance.

As space reactor power system technology matured, system testability issues became important factors to be evaluated during concept and preliminary design reviews.

Introduction

The Russian approach to space power technology development is very different from the American approach. Their approach is to design, build, test, fix problems, retest, test, and accept. Identification of system design weakness by extensive testing, accessibility to permit repair of systems following failures, and capability to test and retest modified systems until proven acceptable are part of the Russian system engineering and manufacturing process.

To accommodate this process, Russian system designers include unique features and flexibility in their space power systems. For example: the Topaz I1 space power system permits non-nuclear thermal vacuum tests at design conditions using removable electrical heaters. The tests permit orbital startup, system optimization, steady-state, shutdown, restart, stability tests, and off-design operation. Following

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such tests, the heaters can be removed, mass mockups of nuclear fuel installed, and vibration, shock, and acoustic tests performed at simulated launch loads. If desired, non-nuclear thermal vacuum tests can be repeated as many times as necessary to verify performance following mechanical testing.

After completion of previous tests, several options for use of the same system remain: 1) the system can be installed in a nuclear test facility, loaded with nuclear fuel, and sub-critical (zero power) tests performed to confirm fuel loading calculations; and/or 2) the system can be installed in a nuclear thermal vacuum test facility, loaded with nuclear fuel and operated to demonstrate startup, steady- state, life, shutdown, and restart operations, as previously performed during non-nuclear tests; or 3) the system can be transported, without nuclear fuel, to the launch site, inspected and checked, loaded with fuel, integrated with spacecraft, encapsulated, and prepared for launch.

The Russian approach to space power technology development emphasizes the need to consider system testability, from concept through qual- ification, in the system engineering process. The advantages, benefits, and options of this approach provide opportunities to reduce development costs, shorten schedules, simplify transportation and storage requirements, improve safety, and lower security risks for future development of American space nuclear power systems.

The Russian Topaz I1 space reactor development program began in 1969. Twenty-six systems were manufactured and nineteen systems were tested during the period from 1970 to 1989 to assure that flight systems would provide 5 to 6 kilowatts of electrical power for space missions lasting between one and three years. The basic design remained the same, although a number of design changes were made during the development period.

The Russian test program included thirteen non- nuclear and six ground nuclear system tests. The Russians performed four types of system tests; thermal management, mechanical, electrically heated thermal vacuum, and ground nuclear tests. This program confirmed that Topaz I1 flight systems were robust, durable, and ready for launching and orbital operation with Russian spacecraft.

The U.S. Thermionic Systems Evaluation Test (TSET) Program includes four Topaz I1 operating systems and two engineering mockups purchased from Russia. The TSET Program is to transfer Russian thermionic technology to the U.S. through

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non-nuclear testing and evaluation of components and systems previously manufactured and tested to Russian standards.

Guidance during U.S. test planning, testing, and testability assessments of the purchased Topaz I1 systems and components was provided by MIL-STD- 1540C, DoD-HDBK-343, and QA Program Implementation Guide, DOE 5700.6C.

ToDaz 11 Svstem Description

The Topaz 11, illustrated by Figure 1, is a 5 to 6 kWe thermionic space nuclear system. Major subsystems include: 1) the nuclear reactor which contains the thermionic converters, 2) the radiation shield, 3) the NaK coolant system, 4) the cesium supply system, 5) the support smcture, 6) a thermal cover, and 7) an automatic control system.

The nuclear reactor contains thirty-seven single-cell thermionic fuel elements (TFEs), which are fueled by uranium dioxide WO2) fuel pellets that are 96% enriched. Three TFEs provide electrical power to an electromagnetic (EM) coolant pump and thirty-four provide power to operate the reactor and spacecraft payloads. The TFEs are located within channels of the ZrH moderator blocks that are canned in stainless steel.

Radial and axial beryllium (Be) reflectors surround the reactor core. The radial reflector contains three safety and nine control drums for control of reactor power during the system's operating life.

During nuclear operation, the fuel heats the TFE emitters to temperatures between 1527°C and 1827°C (1800 K to 2100 K). Waste heat is removed from the outer surface of the TFE collectors by the NaK coolant which maintains collector temperatures within a range of 470°C to 600°C (743 K to 873 K).

A lithium hydride (LiH) radiation shield is attached to the lower end of the reactor. The stainless steel container for the LiH serves as a gamma shield and structural member between the reactor and main system smcture located within the radiator.

Eutectic NaK coolant is circulated through the stainless steel heat rejection system by a single electromagnetic (EM) pump located between the radiation shield and the bottom of the reactor. The coolant flows through the reactor core, exits the upper plenum through two outlet pipes, and enters the upper radiator manifold and radiator.

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Reactor

EM Pump Location

Shield

Control Dnve U"lt

Radiator

FIGURE 1. Topaz II Space Nuclear Power System

Cold NaK flows from the lower radiator manifold through the radiation shield to the pump and returns to the lower inlet plenum of the reactor core.

Cesium vapor is supplied to the interelectrode gap of the TFEs by a cesium system. The system includes a cesium reservoir, a capillary wick, throttle valve, a vapor supply line, heat exchanger, .vapor plenum, and two vent lines to space. Approximately 0.5 giday of cesium vapor is vented through orifices to space, along with other gases following system startup.

A tripod structure, located within the conical radiator, is atiached to the bottom of the radiation shield, suppom the reactor system and provides the mechanical interface to the spacecraft.

Following fuel loading prior to launch, a segmented ejectable thermal cover is placed around the system to keep the NaK coolant from freezing during orbital injection and reactor startup. A startup battery is installed below the radiation shield and provides electrical power to the EM pump whenever NaK coolant temperature in the lower manifold is less than 5°C (278K). After reactor startup in orbit, the thermal cover is ejected when a preselected NaK coolant temperature is reached. When the thermionic converter reaches the selected power level, the startup battery is disconnected and h e electrolyte is vented to space.

Russian Svstem Develoument, Acceutance. and Oualification

Russian space power system, subsystem, and component designs include unique features that are simple, improve testability, reduce costs, and shorten the manufacturing and development effort. Examples of these unique features are:

* The single cell TFE design, as illustrated by Figure 2. This design permits: 1) reactor fuel to be installed and removed easily during subcritical and zero power nuclear testing; 2) electrical heaters, as illustrated by Figure 3, to be inserted in the nuclear fuel cavities of TFEs to enable performance testing of each TFE at operating temperatures and power levels prior to final assembly in the reactor core: 3) full system testing in a non-nuclear test facility, using the same electrical heaters, to calibrate and optimize performance at design power levels, temperatures, cesium vapor pressures, and thermionic convener loads; and 4) full non-nuclear system testing, prior to fuel loading and nuclear operation, in the nuclear test facility. This permits checkout of the test article, facility interface connections and functional performance of the balance of plant without the inconveniences related to nuclear fuel.

The cesium source and regulator design, as illustrated by Figure 4. The cesium sonrce and regulator (cesium block) uses waste heat from the NaK coolant system to vaporize the cesium and maintain temperature control during operation. This unique design permits:

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1) cesium supply: flow, temperature, and pressure control; and gas venting to be contained in a single

2) cesium block assembly, cesium charging, operation at design temperatures, calibration, hermetic sealing, and easy installation into the space power system (and removal, if required): 3) autonomous operation during orbital startup of the space power system, stabilization, and steady-state lifetime operation: 4) adjustment and optimization of the cesium vapor pressure to maximize system power output during thermal vacuum qualification and acceptance testing prior to delivery to launch facilities; 5 ) off-design operation of the TFEs and thermionic converter to explore startup transients, off-normal loads, accelerated degradation modes, and reduced standbylstation keeping power levels; and 6) increasing the reservoir volume and cesium supply to extend system life with minimum modification of the cesium block.

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* The reactor control system, as illustrated by Figure 5. The Topaz I1 reactor control system design includes radial and axial reflectors that surround the reactor core. Upper and lower stainless steel tension bands secure the radial reflectors to the reactor. Tension is maintained by fusible links and can be released to provide instant reflector ejection at any time during power system operation.

The radial reflector contains three safety drums, driven by three separate actuators located above the reactor, and nine control drums, driven by a single actuator located below the radiation shield. Each of the nine control dnuns is connected by a flexible coupling to a large ring mechanism secured to the base of the reactor. The single actuator rotates the main control drum and ring mechanism which rotates the remaining eight control drums. The Topaz I1 control system design permits:

1) radial reflector component or assembly removal and replacement: 2) safety drum actuator removal prior to non-nuclear high temperature thermal vacuum testing and to enable attachment of remote ground test actuators for nuclear fuel loading, zero power criticality tests and nuclear power tests; 3) disconnection of control drums from single actnator to enable attachment of remote ground test actuators for nuclear fuel loading, zero power criticality tests and nuclear power tests: 4) direct measurement of designed backlash and staticldynamic torques of each control drum drive link and bearing set: 5 ) direct measurement and adjustment of single actuator position indicators and limit switches, and

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6) removal and replacement of the single actuator for the nine control drums.

* Direct access to the system's gas and coolant cavities, as illustrated by Figure 6. Subsystem interface connections are conveniently provided to permit high temperature-high vacuum outgassing and leak checking of the helium, oxidizer, cesium, and NaK cmlant piping and plena prior to charging, pressure sensor recalibration, hermetic sealing, and thermal vacuum acceptance testing. In addition, special membrane puncture valves are provided for reconnection of cesium vapor vent piping to the test stand to enable repeated the& vacuum system performance tests following mechanical acceptance and proto-qualification testing.

Ground support equipment and handling fixtures, as illustrated by Figure 7. With the exception of the site specific nuclear system tests, all other system inspections, calibrations, pretest activities, test operations, transportation, and short and long term storage are performed in non-nuclear facilities with the nuclear fuel removed from the reactor and safely stored elsewhere in secure enclosures.

The above system engineering design features, which simplify the Topaz I1 system's factory through launch sequence, were incorporated in the Russian concept system designs and maintained throughout component and system development and qualification.

Russian development, acceptance, and qualification testing requirements of space nuclear power systems were similar to those recommended by MIL-STD- 154oC. Tests were performed on components and systems that subjected them to the environmental conditions and stress levels experienced during the factory through launch and orbital operation sequence. Russians used significant margins in system designs that were verified during development. However, during Russian acceptance and qualification testing, these margins were not usually verified.

As indicated by Table 1, many systems were tested to demonstrate the enhanced capabilities of improved system designs and production runs. Russian systems designated for flight testing were subjected to environmental tests at reduced stress levels similar to the strategies and levels recommended by ML-STD-154oC. This test and retest strategy assures consistent workmanship and quality and avoids over stressing of flight comp- onents and systems prior to launch.

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Monocrystal Poiycryslal Pol ycryalal Monocrystal

A I 0 3 lnS"lat0r

AI203 Plasma insuiator

Ah03 l"s"la1or

A'*O, l"5"lalOl

Seal Seal

2 Core

uo2 Monocryslai MO Fuel Eminer

Region

FIGURE 2. TOPAZ I1 Single Cell Thermionic Fuel Element

Thermal Ins"lalors/Spacen Ceramic outer compensator strip9 Typical Pi" Electrode

Eleclncal Power Terminals (A, B)

FIGURE 3. TOPAZ I1 Tungsten Heater For Thermionic Fuel Elements

Reactor Coolant

Coolant Outlet

Cerium Release

ium Supply Tube

CSS Thmftle/ ' '1 1 Ground Puncture R e l e a ~ e Valve, V3 Valve, v2

\ Copper Bridge

NaK Coolant Inlet

ti FIGURE 4. TOPAZ I1 Single Cesium Source and Regulator

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Elentic Leads

FIGURE 5. Reactor Control System and Top View of Reactor Core He Gas Evacuation Connedions

' TtSA Heated Nuclear Fuel Cavity

Radiation Shield He 6 AI CO""ecli0"

. cs vapor Thronte Valve Coonenion

* Nes~esary tor Gmund Peitomance Tests

FIGURE 6. System Interface Test Connections.

NaK System Gas Bleed Connection

'Em Pump Electtical Power Connedion

Cs Plenum Outgarzing Connedion

Volume Compensator Ar6 He Connenion (Back Side)

. c s vapor Vent Connection

He Gas lor He Plenum COnnectio" (Inshie)

Moderator Mixed Gas He a COP Connection (Inside)

NaK Syatem EYaCUatio" B Fiilmlai" connenion

FIGURE 7. Ground Support and Handling Attributes

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TABLE 1. Russian Topaz I1 System Tests.

System Group Type TFEs Life Period Hours Ident. System No. Years Year Test

v-11 1 Proto 3 1 71/72 3200 v-12 1 Proto 31 1 72/73 850 V-13 1 Proto 31 1 72/73 Y-20 1 Proto 31 1 72/74 2500 Ya-21 1 Proto 31 1 Ya-22 1 Proto 31 1 V-15 2 Ser #1 31 1-1.5 80/80 V-16 2 Ser #2 31 1-1.5 75/79 2300 Ya-23 2 Ser #3 31 1-1.5 75/76 5000 E-31 2 Ser #4 31 1-1.5 76/78 4600 Ya-24 2 Ser #5 31 1-1.5 78/81 14000

Ya-25 2 Ser #7 31 1-1.5 --------

Ya-26 2 Ser #9 31 1-1.5 --------

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E-32 2 Ser#6 31 1-1.5

E-35 2 Ser#8 31 1-1.5 .......-._____..

V-71 3 Ser#10 37 1.5 81/87 1300 V-71* 3 Ser#10 37 1.5 91/92 -1500 Ya-81 3 Ser #11 37 1.5 80/83 12500 .~~ ~~ ~ ~ ~ ~~ .- .~ Ya-82 3 Ser#12 37 1.5 83/84 8300 E-37 3 Ser #13 37 1.5 84/86 E-38 3 Ser#14 37 1.5 86/86 4700 E-39 3 Ser #15 37 1.5 E-40 3 Ser #16 37 1.5 88/88

*\ j E41 3 Ser #17 37 1.5 88/88 E 4 2 3 Ser #18 37 1.5 88/88 ------- Ya-21U 4 Ser#19 37 3.0 87/89 2500 Ya-21U* 4 Ser#19 37 3.0 92/95 -3500 E43 4 Ser #20 37 3.0 88/88 ------

Description of Tests

Development of test methods and operation. Development of prelaunch technology & operations. Transportation, shock, dynamic, & cold testing. Neutron characteristic, radiation fields, & zero power. Neutron characteristic, radiation fields, & prelaunch. Not assembled. Cold tests - Used 2nd generation TFEs Transportation, shock, vibration & electrical tests. Fuel loading, radiation & nuclear safety - steady state. Nuclear ground test, ACS startup & steady state. Steady state system testing with 2nd generation TFEs. Used as mockup for transport & handling procedures. Used as mockup with spacecraft. Used for experiments in Baikal test stand. Damaged during fabrication & not tested. Mechanical, cold test, zero power crits, electric tests. Baikal stand checkout/acceptance & operator training Nuclear ground tests & steady state operation. Nuclear ground test, ACS startup & LOCA. Zero power crits, static & torsion tests. Nuclear, prelaunch, ACS startup, & steady state tests. Changed reactor-changed system identification to E-41. Cold testing with thermal cover. Mechanical & leak tests, & changed radiation shield. Welding error in fabrication - system not to be used. Used improved TFEs & performed electric tests. Pathfinder system testing & technology assessments Flight unit-has not been tested. Flight unit-has not been tested. Flight unit-assembly not completed. Static test mockups for special testing.

* Topaz I1 system tests performed at US . TSET Facility with technical support from Russian Specialists

Technologv Transfer and Testabilitv Assessment ORpo rtunities Two engineering mockups and two flight systems

were also made available for future testing and evaluation. The TSET Program included the following non-nuclear system tests :

me V-71 s v s m was tested extensively in Russia before shipment to the TSET Facility, as indicated by Table 1. The system was installed in the Baikal vacuum chamber and used to check out the Baikal test stand, train *e American operators, and

Americans. The v-71 system operated successfully at heater power levels up to 115 kWt and NaK outlet temperatures up to 520 "C (793 K).

The original goal of the TSET Pro, oram was to qualify the Topaz I1 reactor as closely as possible to the guidelines provided by MIL-STt-1540C. This has been partially achieved by acquiring and using valid and verifiable test results obtained from the Russian Topaz I1 program to supplement that obtained during the TSET component and system testing program. Specific non-nuclear system tests,

performed to enable comparison of TSET results with that obtained previously in Russia.

using tungsten electric heaters, were and are being compare Russian test results with &at obtained by

Considerable technology was transferred to American scientists during non-nuclear testing of the Topaz I1 V-71 and Ya-21U thermionic space power systems. 'id'

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The Ya-21lJ s y s m was also tested extensively in Russia before shipment to the TSET Facility, as indicated by Table 1. Ya-21U is a prototype of the flight systems, was designated the "Pathfinder System", and used to demonstrate the protoqual test strategy of MIL-STD-1540C.

A modal survey was performed to verify the dynamic characteristics of Russian systems. The system was installed in the Baikal vacuum chamber and operated at heater power levels up to 105 kWt and outlet temperatures to 570 "C for a period of >1500 hours to demonstrate the system integrity and obtain baseline performance information. After the thermal vacuum tests, vibration and shock tests were performed at acceptance levels.

After mechanical tests, &e system was reinstalled in the vacuum chamber and tests repeated at outlet temperatures up to 570°C for more than 2000 hours to demonstrate robustness, durability, integrity, and stable performance of the system during simulated orbital startup and steady-state operation.

The EH -40 svswq is a thermal-hydraulic engineering mockup of a flight system, has a functional heat rejection NaK system and can be used for "cold-test" demonstration of prelaunch heating, launch, and orbital injection sequence.

TheEH -41 svsteq is a structural engineering mockup of a flight system and can be used for demonstration of suuctural integrity of flight systems and minor modifications required to adapt them to future launch vehicles.

The EH-43 and EH-44 svstems are flight systems that can be used for potential flight demonstration or extended ground testing to demonstrate the long-life durability and performance of the Russian single-cell thermionic converter technology. One of the flight systems will be selected for acceptance level testing and technology evaluation. Gas cavities and coolant system will be outgassed and charged and a 1000 hour thermal vacuum steady-state system integrity test will be performed. After completion of thermal vacuum tests and evaluations, the selected system may undergo mechanical vibration and shock tests and may be followed by a short duration thermal vacuum system performance test to verify previous results and identify variances, if any.

Protoqual test levels will be used for guidance during performance of the flight system tests. Results of the flight system tests will be compared with Russian test results from other system tests and with results obtained during the Ya-21U Pathfinder test program.

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Six Nuclear Svstem were manufactured and tested by Russians from 1975 to 1988. Testresults and data were determined to be valid and applicable to fulfill most of the Russian nuclear qualification test requirements. Additional testing was subsequently performed by Russians to demonstrate the inherent safety of the Topaz I1 reactor design and control. A brief summary of the six ground nuclear tests is provided in Table 2.

Conclusions

The Thermionic Systems Evaluation Test (TSET) Program has provided excellent opportunities to do the following:

to evaluate Russian thermionic space reactor power system technology, testing strategies, and unique design features to improve system testability;

* to develop the infrasuucture, capability, and resources to undertake and accomplish mission essential technology transfer, research, and demonstrations of thermionic conversion system technology; and

experiences, skills, resources, and future technologies.

to identify follow-on opportunities for sharing of

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. TABLE 2. Russian Topaz I1 Ground Nuclear System Tests

'ci System Group Type' TFEs Life Period Hours Description of Nuclear Tests Ident. System No. Years Year Test

Ya-23 2 Ser #3 31 1-1.5 75/76 5000 Fuel loading, radiation k nuclear safety - steady state. System operated 2500 hours at 6 kWe power output. TFEs degraded due to fuel swelling.

TFEs were the same as those in Ya-23 system. 4600 hours was the planned duration of test.

Ya-24 2 Ser #5 31 1 -1.5 78/81 14000 Steady state system testing with 2nd generation TFEs. TFEs were the same as those in Ya-23 & E-31 System startup with ACS. Test provided life testing of many system components.

E-31 2 Ser #4 31 1-1.5 76/78 4600 Nuclear ground test, ACS startup & steady state.

Ya-81 3 Ser #11 37 1.5 80/83 12500 Nuclear ground tests & steady state operation. TFEs were new design. NaK leaked within 150 hours. Leak fixed & test continued for 12500 hours at 4.5-5.5 kWe power level. Material certification for NaK system was changed.

Ya-82 3 Ser #12 37 1.5 83/84 8300 Nuclear ground test, ACS startup, System produced 4.5 - 5.5 kWe for 8300 hours. Loss of NaK coolant due to leak in EM pump throat. System continued to operate until loss of hydrogen from moderator caused reactor to shut down.

3 Ser #14 37 1.5 86/86 4700 Nuclear, prelaunch, ACS startup, & steady state tests. System produced 4.5 - 5.5 kWe for 4700 hours. NaK leak in upper collector of radiator required system shutdown.

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Acknowledgment$

Funding for this project was provided by the Ballistic Missile Defense Organization, Thermionic Systems Evaluation Test Program. The work is being conducted at the New Mexico Engineering Research Institute (NMERI) Facility by the US. Air Force Phillips Laboratory with technical assistance and support provided by Sandia National Laboratory, Los Alamos National Laboratory, University of New Mexico, and INERTEK (a Russian joint venture organization).

References

Nikitin, V.P., Ogloblin, B.G., Sinkevich, V.G., (1992) "Special Features and Results of the Topaz I1 Nuclear Power System Tests with Electric Heating" in Proc. Ninlh Symposium on Space Nuclear Power Sysrem, COW-920104, M.S. El- Genk and M.D. Hoover, eds., American Institute of Physics, New York.

Polansky, G. F., G. L. Schmidt, E. L. Reynolds, E. D. Schaefer, B. Ogloblin and A. Bocharov (1993), "A Plan to Flight Qualify a Russian Space Nuclear Reactor for Launch by the United States," 29th Joint Propulsion Conference and Exhibil, American Institute of Aeronautics and Astronautics, AIAA- 93-1788.

Voss, S . S . and E. A. Rodriquez (1994h), "Russian Topaz I1 System Test Program (1970-1989), "Proc., 11th Symposium on Space Nuclear Power and Propulsion, COW-940101, M. S. El-genk and M. D. Hoover, eds., American Institute of Physics, AIP Conference Proc. No. 301, pp. 803-812

Nikitin, V.P., Ogloblin, B.G., Ponomarev-Stepnoi, N.N., (1993) "Program on the Topaz-2 System Preparation for Flight Tests" in Proc. Tenth Symposium on Space Nuclear Power and Propulsion,"ISBN # 1-56396-137-7, M.S. El-Genk and M.D. Hoover. eds., American Institute of Physics, New York.

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