The space nuclear thermal propulsion program was initiated by LTG James Abrahamson, Director of the Strategic Defense Initiative Organization, in November 1987. The program was classified as Special Access Required, and given the program name Timberwind (TW).(1) The goals of the Timberwind program focused on the development of a PBR engine with the following characteristics:
Power Density 40 MWt / liter
Thrust/Weight Ratio 30 : 1
Exhaust Temperature 2750o K
Specific Impulse 869 seconds
Thrust 178 kN
Run Time 100 seconds
Restart Capability No
Throttlable No
Management of the program includes a number of government agencies and contractors (Figure IV-5, IV-6).(2) A number of participants in the program have been added since its initiation.(3)
Air Force Phillips Laboratory at Kirtland Air Force Base, New Mexico, has primary responsibility for the Space Nuclear Thermal Propulsion program, which was initially managed by LTC Roger Lenard, and CAPT Jay Moody.
Dames & Moore provides other special services.
Fluor-Daniel, Inc. (FDI), of Irvine, California, is conducting Effluent Treatment System (ETS) engineering analyses.
Raytheon Services Nevada (RSN), of Las Vegas, Nevada, provides facility and Coolant Supply System (CSS) engineering, and facility construction management.
Reynolds Electrical and Engineering Company, Inc. (REECo), of Los Vegas, Nevada, also supports facility construction activities.
Xerad of Santa Monica, California, provides program support and independent review services for the Air Force.
Air Force Western Space and Missile Center at Vandenberg Air Force Base provides flight test planning support.
Air Force Arnold Engineering Development Center at Tullahoma, Tennessee may provide hydrogen flow engine test support.
Grumman Corporation's Space & Electronics Division, of Bethpage, New York has the prime contract for the SNTP effort (Contract F29601-89-C-0086), which was awarded in November 1987 on a sole-source basis. The company serves as the system integrating contractor, and provides vehicle design and fabrication and overall program management services. Grumman's Calverton Facility on Long Island may be used for hydrogen testing. Other companies working with Grumman include:
Airesearch Los Angeles Division of Allied Signal Corporation, of Torrance, California, is responsible for turbine wheel testing.
Garrett Fluid Systems Division of Allied Signal Corporation, of Tempe and San Tan, Arizona, is responsible design and fabrication of fluid management and energy conversion components, including engine turbopump and propellant flow control development, as well as attitude control systems.
General Dynamics, of San Diego, California, has conducted launch vehicle and other vehicle integration studies.
Hercules, of Magna, Utah, is conducting work in advanced composite structures for engine lower structure, rocket nozzles and propellant tanks.
L-Systems is responsible for system engineering services.
United Nuclear Corporation (UNC) a Norwich and Uncasville, Connecticut division of United Technologies, is responsible for nuclear element canister development, manufacturing and test support. This company, which has supported US Navy nuclear systems in the past, is phasing out this line of work, which is being consolidated at Babcock & Wilcox.
Babcock & Wilcox Nuclear Power Division of Lynchburg, Virginia (a subsidiary of McDermott International), is responsible for detailed design of reactor subsystems and fabrication and assembly of reactor technology, including fuel particles. Companies assisting Babcock & Wilcox include:
Aerojet Division of Gencorp, of Sacramento, California, is a subcontractor providing engine technology support, as well as element component design and fabrication, alternate fuel element materials development, and test facility design support.
The Energy Department's participation is managed through the Defense Programs Office, with support from the Nuclear Energy Office. Laboratories actively involved in the SNTP effort include:
Brookhaven National Laboratory in Upton, New York, is responsible for reactor materials and component testing, thermal-hydraulic and neutronic analyses, reactor design studies, and fuel development activities.
Idaho National Engineering Laboratory, Idaho Falls, Idaho, is involved in test facility and mission application conceptual design activities.
Nevada Test Site, Las Vegas, Nevada, is involved in test facility conceptual design activities.
Sandia National Laboratory in Albuquerque, New Mexico, is involved in nuclear safety, nuclear instrumentation and operation, reactor control systems, nuclear testing, and test facility development and conceptual design activities.
The National Aeronautics and Space Administration (NASA) has taken an interest in PBR rocket systems, with field centers concerned including:
Lewis Research Center, of Cleveland, Ohio, also involved in Space Exploration Initiative mission applications analyses.
Marshall Space Flight Center, of Huntsville, Alabama, involved in Space Exploration Initiative mission applications analyses.
A Defense Science Board review of the Timberwind program concluded in March 1990 that:
The program was technically sound, with a high probability that projected goals could be met.
Progress to date had been good, with future activities based on an event-driven rather than schedule-driven milestones.
Cost and schedule estimates are reasonable to demonstrate critical technologies.
There was no obvious reason why safety and environmental criteria could not be met.
The program would provide an enabling technology for a wide range of space and military missions, and deserves broader support.
The existing management structure has been particularly effective to date.
The classification of the program may be counterproductive.
The DSB review concluded recommendation that:
Remove the Space Access Required classification from the program at the appropriate time.
Ensure that all steps are taken to meet applicable safety and environmental requirements for both ground and space testing.
DOD and NASA should apply the technology to missions of interest.
The program be managed and funded through a Joint Program Office, including participation and support from DOD, DOE and NASA.
The existing management structure should continue in place through subsequent changes in sponsorship.
Funding be provided at a level of about $125 million annually for six to eight years, through the conclusion of ground test activities.
Total costs from 1987 through 1991 were approximately $130 million. The 1992 budget request was $40 million, though the Congress finally appropriated about $45 million for Research and Development, with an additional $7 million for Military Construction. A total of approximately 1,500 personnel are involved in the program.(4) Total estimated costs through the ground test phase were estimated to total $800 million. However, despite the DSB recommendations, total DOD funding for the SNTP effort is presently estimated at only $40 million annually.
Major tests conducted during the Timberwind phase of this project include:
Critical Experiments (CX) are conducted at the Sandia Pulsed Reactor (SPR) facility, beginning in October 1989, to support physics experiments with a zero-power PBR reactor core, which included establishing benchmarks for neutronics simulations codes.(5)
Pulsed Irradiation of PBR Fuel Element (PIPE) early fuel particle tests, which were conducted at 5% of the scale of an operational system in the Sandia National Laboratory Annular Core Research Reactor (ACRR), identified several fuel particle design issues.(6) These tests indicated that the PBR fuel element is a highly complex thermo-mechanical system, which is vulnerable to disruption at low power densities and low hydrogen flow rates. The tests also demonstrated an increase in propellant flow resistance during power operations, and a need for further understanding of local flow anomalies.
PIPE-1, conducted in October 1988, consisted of five cycles at increasing power levels, with a 1600 K average and 1900 K peak outlet temperatures. Power density levels reached 1.5 to 2.0 MW/liter. No off-normal results were observed.
PIPE-2, conducted in July 1989, experienced anomalies not exhibited in PIPE-1, causing the experiment to be terminated after only 24 seconds of operation.(7) Experiment induced flow blockages in the cold frit which may have been caused by foreign material in the motor, resulting in significant undercooling of the PIPE-2 fuel element, which led to extensive fuel particle fractures, leading to frit clogging by particle fragments and release of fission product inventories (Figure IV-7). Resolution of these issues resulted in the development of more robust fuel element configurations, which were designed to accommodate more severe thermal cycling than was available in the PIPE test environment.
Major program accomplishments in 1991 included:
Completion of Level II sub-scale test site designs;
Completion of coolant supply system designs;
Completion of first prototype fuel element;
Completion of Critical Experiment (CX) test series;
Completion of Nuclear Element Test Zero (NET-0) hardware fabrication;
Completion of Advanced Upper Stage studies;
Baselined high-temperature fuel particle;
Issued Program Safety Policy document;
Environmental Impact Statement (EIS) approved;
Preliminary Safety Analysis Review completed and in review cycle;
Effluent Treatment System (ETS) for subscale PIPET test site started.
4 - Space Thermal Nuclear Propulsion
The Air Force officially established the Space Nuclear Thermal Propulsion program on 1 October 1991, when program responsibility transitioned from the Strategic Defense Initiative Organization to the Air Force Phillips Laboratory. In January 1992 the Timberwind program classification was terminated, and much of the activity associated with this project was declassified.(8) LTC Gary Bleeker of Phillips Laboratory was designated SNTP Program Manager in February 1992. Some ongoing technical activity remained classified, with some activity remaining at the Special Access Required level, although under a new name, given the extent to which the Timberwind designation had been compromised.
The FY1992 funding request for SNTP included $44 million for Research and Development, as well as $10 million in Military Construction funding for preliminary design work. Military Construction funding is slated to rise to $84 million by FY1994.
It is claimed that the SNTP budget will be substantially less than that of NERVA:(9)
"... because a different management approach is being used. The NERVA program used the prevalent management style of the time. It involved testing technologies within complete engines, rather than the in-depth component, subassembly development and testing approach in the SNTP program. This change in management philosophy will identify technology roadblocks that would stop the program earlier than the previous management style. Additionally, scientists today have vastly improved analytical tools, computational capability, and more durable high -temperature materials, as well as lessons that were learned from the NERVA program."
However, the estimated $800 million of the third phase of the SNTP program, through concept validation, would not result in a flight-qualified engine. Full scale development of an engine for upper stage applications would require an additional $1 to $2 billion, while development of an engine for piloted applications would require an additional $4 billion for further testing and evaluation.
The priorities of the SNTP program have been characterized as:
1 - Safety;
2 - Reliability;
3 - Operability;
4 - Performance.
The goal of the SNTP effort is the demonstration of the technology needed for a nuclear
rocket engine using liquid hydrogen propellant. (Figure IV-8) Target engine characteristics include:(10)
Thrust Baseline kN 333 - 370
Options kN 90 - 380
Throttle 5 : 1 ratio
Run Time 100% Thrust seconds 500
20% Thrust seconds 700
Specific impulse seconds 930 - 1000
Thrust-to-weight ratio 25:1 - 30:1
Number of Fuel Elements 19, 37 or 61
Power MWt 2000
Power Density MW / liter 40
Exhaust Temperature K 3000
Depending on the application, from 37 to 61 or more fuel elements may be incorporated into a reactor engine. Total Uranium fuel inventory is anticipated to be less than 50 kg, with a total engine weight of about 1,650 kg. The engine is intended to have the potential or being ramped to full power in less than ten seconds.
Development activities are slated to continue for the remainder of this decade (Figures IV-9, IV-10). Major milestones anticipated for 1992 include:
Completion of Nuclear Element Test NET-0 and NET-1 tests;
Completion of initial Hot Hydrogen Test Facility experiments;
Completion of Thermal Hydraulics experiment;
Completion of Environmental Impact Statement Title-I design;
Definition of Advanced Fuel Particle design;
Initiation of Advanced Fuel Particle testing;
Initiation of Carbon-Carbon Turbopump cold spin tests;
Initiation of Sub-Scale Facility construction;
Review of engine design;
Review of PIPET design;
Approval of Preliminary Safety Analysis Review.
The Draft Environmental Impact Statement for the PIPET effort at the NTS Saddle Mountain Site was available for public comment from 20 May through 3 July 1992, with publication of the Final EIS planned for the end of July 1992. This will serve as an input to the final Record of Decision on the project, which is planned for 1 September 1992.
1. While no special meaning is attached to either the Timberwind or TW designations, it is interesting to note that one of the claimed advantages of this technology is the high Thrust to Weight (T/W) ratio it may provide for propulsion applications.
2. Although these figures are for the Space Nuclear Thermal Propulsion program, they are generally representative of the organizational relationships under the Timberwind program.
3. Department of the Air Force, Space Nuclear Thermal Propulsion (SNTP) Program -Final Environmental Impact Statement, 19 September 1991, partially declassified 11 March 1992, pages 2.1-4 - 2.1-6.
4. Broad, William, "Rocket Run by Nuclear Power Being Developed for Star Wars," The New York Times, 3 April 1991, pages A1, B6.
5. Department of the Air Force, Space Nuclear Thermal Propulsion (SNTP) Program -Final Environmental Impact Statement, 19 September 1991, partially declassified 11 March 1992, page 2.3-7.
6. Davis, Bob, "Nuclear-Powered Rocket is Studied By Project in Pentagon's SDI Office," The Wall Street Journal, 3 April 1991, page A22.
7. Asker, Jim, "Particle Bed Reactor Central to SDI Nuclear Rocket Idea," Aviation Week & Space Technology, 8 April 1991, pages 18-19.
8. Some references to this activity use the nomenclature "Space Thermal Nuclear Propulsion."
9. United States Air Force Systems Command Phillips Laboratory, "Phillips Laboratory Announces Program in Space Propulsion," Office of Public Affairs release 92-02, 13 January 1992.
10. United States Air Force Systems Command Phillips Laboratory, "Phillips Laboratory Announces Program in Space Propulsion," Office of Public Affairs release 92-02, 13 January 1992.
Henderson, Breck, "New Thermal Propulsion Gains to Speed Rocket Production," Aviation Week & Space Technology, 20 January 1992, pages 20-21.