In the area of advanced reactor technology, several avenues of activity are being pursued in a joint program by the AEC and NASA. The objective and scope of this work is illustrated by figure 196. Work on higher power graphite reactors is continuing at Los Alamos under the PHOEBUS program. The most significant forward step in this program has been the recent beginning of criticality experiments in large diameter reactor cores having higher power levels than present designs. A basic program of research on a watermoderated tungsten reactor concept is continuing at the Lewis Research Center, and work on a fast tungsten reactor concept is underway at the Argonne National Laboratory. In other AEC-NASA programs, preliminary work is underway on gaseous and liquid fuel reactors.

In addition to reactor research and development, work on the nonnuclear components of nuclear rocket systems is continuing. Such components include the hydrogen tank, turbopump, valves and other propellant feed system controls, exhaust nozzle and instrumentation. Examples of recent progress in these areas include the development of a nozzle fabrication technique which simplifies construction and reduces cost, and the demonstration that turbopump bearings can be operated at full load and speed in the combined environments of nuclear radiation and liquid hydrogen. The further development of nonnuclear components will be closely tied to systems analyses to assure adequate attention to the dynamic interactions of these components in an engine system and to the restraints which must be observed in the design and operation of these components. An essential element of this part of the program is work on experimental

ADVANCED RESEARCH AND TECHNOLOGY

NUCLEAR ROCKET PROGRAM

OBJECTIVES

• SUPPORT CURRENT PROGRAM

• IMPROVE TECHNOLOGY FOR FUTURE ENGINES

• EVALUATE ADVANCED AND ALTERNATE CONCEPTS

• DEFINE POSSIBLE APPLICATIONS AND REQUIREMENTS

SCOPE

• ADVANCED GRAPHITE REACTOR TECHNOLOGY (PHOEBUS)

• ALTERNATE CONCEPTS (METAL SYSTEMS)

• ADVANCED CONCEPTS (GASEOUS, LIQUID FUELED)

• ENGINE SYSTEM TECHNOLOGY

FIGURE 196

NASA RN64-346

ground test engine systems to demonstrate a full understanding of these interactions. In supporting work at the Lewis Plum Brook Station, tests of a simulated nuclear rocket engine are in progress using a KIWI turbopump and nozzle and a KIWI-B1 cold flow reactor. The facility in which this work is conducted is illustrated by figure 197. On completion of this work, NERVA components will be installed to obtain comparative data on start transients of the system.

In the engine development program, components for NERVA engine system testing will be designed, fabricated, and tested with the objective of running experimental engine system tests in 1967. Figure 198 shows engine test stand No. 1, ETS-1, which is one of the several facilities at the nuclear rocket development station devoted to the development of NERVA and nuclear rocket technology. Significant features of this engine test stand are its large run-tank located on the superstructure above the test position, the vault below the test position for the exhaust duct, and large liquid hydrogen storage dewars. The facility permits operation of a nuclear rocket engine with proper physical arrangement of the components of the engine and the liquid hydrogen tank. Altitude conditions can be simulated at power levels greater than 40 percent of rated power. Run times on the order of 5 minutes at rated power will be possible for tests of NERVA engines.

During the past year, the RIFT project was constrained from major hardware and facility commitments pending demonstration of further progress in the reactor and engine program. As a conse

quence, the project emphasized those areas of nuclear vehicle technology related to fabrication and structural development, cryogenic insulation, and radiation effects. For example, a welding device for large diameter tanks was developed, as shown in figure 199, where the welding tool rather than the tank was rotated. The technique of using a movable welding machine will permit tank fabrication at lower costs with improved tolerances. A byproduct of this welding program has been a determination of causes of faulty welds in aluminum vehicle tanks. The RIFT project also made contributions to the development of internal insulation for liquid hydrogen tanks.

As a result of a decision made in December 1963, the RIFT program will be terminated shortly. This action was a part of a general policy decision to reduce the pace of the nuclear rocket program and to carry the present NERVA engine only through ground testing and not through flight testing as was previously planned in the RIFT program.

Nuclear-electric propulsion

The concept of nuclear-electric propulsion has, for some time, been regarded as a promising approach to the propulsion requirements for certain very deep space missions. In this mode of propulsion, the nuclear energy is converted first to electrical energy. The electrical energy is then employed by various means to accelerate a working fluid to very high velocities. In some cases, the electrical energy heats the working fluid thermally by an electric arc. In other cases,

the fluid is accelerated by forces which are induced by electromagnetic or electrostatic fields. Although all of these schemes are receiving some attention, the greater portion of the effort has been concentrated on the electrostatic or ion thrustor.

A nuclear-electric primary propulsion system using an ion engine is illustrated schematically in figure 200. It is comprised of two major parts: the electric power generation equipment consisting of a reactor, turboelectric system, and power regulator; and the thrustor equipment consisting of a thrustor with its associated propellant storage, feed and control equipment. For attitude control and station-keeping applications where the power requirements are low, the reactor can be replaced with a solar energy system utilizing the turboelectric conversion subsystem shown on the figure or other energy conversion devices such as photovoltaic cells.

The power generation system, which will be described later, represents by far the predominant weight of the system and is the primary reason for the very low thrust-to-weight values--one ten-thousandths to one one-millionth-characteristic of electric propulsion concepts. Figure 201 portrays approximate thrust levels required for the four applications listed. These vary from a thousandth of a pound of thrust for attitude control systems of small satellites to a hundred pounds of thrust for propulsion of large manned spacecraft. Such propulsion systems are of great interest for the long trip times needed for missions to the outer planets because their propellant consumption is very low-on the order of a tenth to a twentieth of that of a chemical propulsion system.

A flight project known as SERT I is being planned in support of the thrustor program. The objective is to obtain information on ion thrustor characteristics in the true space environment. The high voltage arcing problems which were encountered in the SERT I power conditioning equipment are a good example of the need to conduct extensive ground tests of flight configurations in a simulated space environment. During thrustor startup in a vacuum tank at the Lewis Research Center, high voltage arcs developed resulting in severe transient overloads which, in turn, caused a power failure. If uncorrected, these arcs would have resulted in an early flight failure. A solution has been found and verified by ground tests of the flight configuration. The first launch of SERT I is planned before mid1965, with succeeding launches dependent upon the information obtained from the previous flights.

Research the past 5 years has established the basic technology for the small electric thrustors useful for attitude and orbit control in thrust levels up to about one-tenth of a pound. Remaining to be solved are the problems of obtaining the required thrustor endurance, up to several years, and optimum thrustor and attitude control system performance characteristics. Future programs will be directed toward obtaining solutions to these problems utilizing vacuum tank facilities at the Lewis Research Center and a special attitude control system simulator now being assembled at the Goddard Space Flight Center. This latter facility, while quite small and relatively inexpensive, will permit the realistic evaluation of the many subsystem performance modes and characteristics needed to define an optimum overall system.