establishing the basic 1-G background medical data against which the flight data will be compared. Yerkes also set up a minimum primate breeding compound to assure the availability of healthy animals for the experiment.

ADVANCED PROPULSION SYSTEMS

The Chemical Propulsion Research and Technology Program supports goals arising from probable future NASA propulsion requirements. Its objectives include the advancement of capabilities in engineering disciplines, the design and testing of key components, improvements in space propulsion system performance, advances in component reliability, and better understanding of the factors affecting selection of any propulsion system to meet the requirements of a specific mission.

Solid Propulsion Systems

The first experimental high energy hybrid system proposed for upper stage applications and planetary missions was fired successfully, producing an equivalent specific impulse of 385 seconds. A hybrid system is one in which the propellants are part liquid and part solid. The motors, which weighed about 3,000 pounds, developed over 10,000 pounds of thrust.

The liquid propellant was a mixture of fluorine and oxygen, the

solid a mixture of lithium, lithium hydride, and rubber. The first motor was fired once for about 15 seconds, stopped for inspection, then refired for about 50 seconds more. Performance was satisfactory. The second motor was fired for a single pulse lasting about 35 seconds, with similar results. (Fig. 4-24.) Small scale motors containing a 400-second impulse fuel combination were also success

fully test fired and will be tested on a 3,000-pound version in 1970. (Fig. 4-25.) The liquid component in this system is also fluorine and oxygen, but the solid is much higher in lithium content.

Another spacecraft propulsion system which made satisfactory progress in its test program, is a solid motor with a very low thrust and a long burning time. It would be used with spacecraft payloads which have extended booms and are therefore sensitive to acceleration. Current test motors use existing hardware and the new low-burn-rate propellant. A motor weighing 800 pounds and several 60-pound motors have been fired. By casting the motors essentially full of propellant, without a central bore, and burning only on the end, it was possible to attain burning durations two to three times as long as those originally produced in this hardware. This motor concept has the potential for exceptional propellantweight efficiency-up to 93 percent. It is a candidate for use on a Jupiter orbiter mission and other missions requiring a reliable orbit insertion motor after lengthy exposure to space conditions during planetary transfer. (Fig. 4-26.)

Under a third spacecraft propulsion program, the manufacture of a 3,000-pound high energy restartable solid motor was completed. Plans were made for test firing this motor in early 1970. It is expected to develop the highest specific impulse of any solid propellant space motor-about 325 seconds. In the first test, a system for stopping the motor on command will be demonstrated. In

addition, preparations were underway for follow-on tests to show stop, restart, and a final stop, ultimately under simulated altitude conditions. (Fig. 4-27.)

The technology program for large solid motor components continued as contracts were let to study low-cost materials of motor cases, nozzles, insulation, and propellants. Other areas being studied included propellants with improved processing characteristics, methods of inspecting large motors, and ways of handling and transporting motors. Work on materials, components, and subsystems resulted in improvements in nozzles for hotter propellants and restartable systems.

Propellant research emphasized binder development, processing and handling of more energetic systems, and fit of propellants to specific missions. Significant progress was made in development of lower burning rate propellants that do not suffer a performance loss (and are thus suitable for planetary spacecraft applications). Progress was also made in a number of other areas: a new propellant binder (principally a saturated aliphatic hydrocarbon) was developed; it is potentially compatible with reactive oxidizers and is stable with ammonium perchlorate under heat-sterilization conditions and in the space environment. A theory of viscoelastic behavior was evolved and substantiated; it makes it possible to

predict more accurately the response of solid propellants to generalized stress-time-temperature fields. This ability is important because of the catastrophic nature of solid propellant grain failure. The scanning electron microscope was used to study solid propellant combustion. Its use gave researchers new knowledge and experimental methods which offer a basis for more realistic qualitative modeling of propellant combustion and potential means to control combustion characteristics. Improved analytical techniques were established for determining rocket plume characteristics in space and in planetary atmospheres. This work is important because there are indications that rocket plumes have caused interference with scientific instruments or have exerted unexpected forces on spacecraft.

Also, techniques for ignition of pyrotechnics by laser were investigated. Such methods of ignition offer advantages—immunity from radio frequency interference, elimination of bridgewires, and the potential ability to ignite less sensitive mixtures thereby enhancing safety.

Lastly, significant progress was made in establishing accept-reject criteria for defects in fiber glass rocket motors with the development of ways of repairing defects that would otherwise cause rejection of the motor, and the refining of analytical techniques for consideration of damaged motor cases.