firing and adequate shielding to protect both the propellant and the crew.

The NERVA program provides for a series of reactor and ine tests, which include qualification tests supported by compo: development to demonstrate performance and reliability. testing and the supporting analysis and documentation will vide a propulsion system suitable for vehicle application.

Test Cell "C" will be used to conduct all NERVA reactor tests, and the NERVA engine will be tested in ETS-1. However, the hot hydrogen exhaust system, propellant plumbing, and altitude simulation system of ETS-1 will have to be modified to permit fullpower testing of the engine.

ADVANCED NUCLEAR ROCKET CONCEPTS

In this area, experimental and theoretical work was continued on two advanced ideas: the light bulb concept and the coaxial flow concept (19th Semiannual Report, p. 106).

The NASA tracking and data acquisition networks again supported a large number of space missions, including earlier launched spacecraft and fourteen launched during this period. Among the major missions were Pioneer IX, Orbiting Astronomical Observatory (OAO) II, Radio Astronomy Explorer (Explorer XXXVIII), Apollo 7, and Apollo 8.

The December launches alone illustrate the wide variety of space flight projects supported by the networks: An international cooperative project (HEOS-I); a satellite for the Environmental Science Services Administration (TOS-F); a commercial communications satellite for ComSat (INTELSAT III); a NASA scientific satellite (OAO-II); and the Apollo 8 mission.

MANNED SPACE FLIGHT NETWORK

The Manned Space Flight Network played a vital role in supporting the first manned Apollo mission, Apollo 7. (Fig. 6–1) Launched October 11, this earth-orbital eleven-day flight placed many first-time support requirements on the network. One such requirement was the real-time reception and relay of television transmissions from the astronauts.

After a highly satisfactory performance, extensive network checkouts and simulations were begun in preparation for the first manned lunar mission, Apollo 8. Such realistic simulations, designed to assure constant operational readiness of facilities, equipment, and personnel, are conducted before each Apollo flight and contribute significantly to the reliability of the network.

The success of the Apollo 8 mission, launched December 21, stressed the importance of the network in support of manned space flight projects. The mission clearly demonstrated the net

work's ability to track and communicate with spacecraft at lunar distances, a prerequisite for a successful manned lunar landing. Voice communications with the astronauts excellent throughout the mission, and the telemetry received by the network provided data essential to mission control in its assessment of launch vehicle, spacecraft, and astronaut functioning.

The Unified S-Band System-a sophisticated electronic tracking, command, and telemetry system installed in the network specifically for Apollo lunar mission navigation and control-operated in an outstanding manner. (Fig. 6-2) Actually, it exceeded the flight project's requirements for tracking accuracy and communications quality. This accuracy contributed significantly to the Apollo 8 spacecraft's precise navigation to and from the moon. The network's performance during this mission conclusively demonstrated that the navigational accuracies required for the lunar landing mission can be achieved.

The quality of in-flight television from the Apollo 8 spacecraft was noticeably better than that from Apollo 7. This was a result of the network improvement program in which the capability of the network is continuously updated to incorporate important new advances.

Besides improving the network's tracking, communications, and television capabilities, NASA began work aimed at reducing the time required for the network to switch its mode of support from one flight mission to the next. Such time reduction is very important to future requirements for the network to support both Apollo Applications multi-spacecraft rendezvous missions and experiment packages left on the lunar surface by Apollo astronauts. The improvement is necessary also to allow for the network's cross-support of future unmanned planetary missions. The turnaround time must be much less than the network's present capability permits.

SATELLITE NETWORK

The Satellite Network also continued to carry a substantial workload. (Fig. 6-3) This is the network which supports all of NASA's scientific and application satellites. In addition, these facilities furnish support to a wide variety of space projects conducted by other government agencies, by private industry, and through cooperative international programs. The network participated in the Apollo mission by providing priority support to the orbiting ATS-III and IMP-IV spacecraft so that their vital proton monitoring information could be sent to the Mission Con