The NASA tracking and data acquisition networks continued to support a substantial number of space missions during the period. Support was provided to 69 flight missions, 10 of which were launched during the period. The major NASA missions successfully launched included Surveyor VII, Orbiting Geophysical Observatory (OGO) V, and Apollo 5 and 6.

The Apollo instrumentation ships and aircraft reached operational status during the period, thus completing the Manned Space Flight Network facilities required to support the Apollo lunar landing mission. The network facilities and operating personnel were engaged in mission simulations and preflight checkout for the AS-205 mission, scheduled for the last quarter of 1968.

Deep Space Network

During the report period, the Deep Space Network supported the final flight in a series of highly successful Surveyor spacecraft. From liftoff (January 7, 1968), the network facilities maintained continuous contact with Surveyor VII, transmitting the data received to the Space Flight Operations Facility (SFOF), the control center for the Deep Space Network. (Fig. 6-1.) At the SFOF, located at JPL, Pasadena, California, the data were processed and displayed in real time, enabling project personnel to make the necessary decisions for mission control. Based on these data, commands were sent via the network stations to the spacecraft, directing the midcourse maneuvers, the soft lunar landing, and the on-board visual imaging cameras.

Guided by commands from the SFOF, Surveyor VII successfully soft-landed on the moon near the crater Tycho on a mission of scientific exploration. The last contact with the spacecraft occurred on February 20, 1968, at which time over 21,000 television pictures had been received by the network stations, including several pictures viewing the earth. The stations also received many hours of data from the Alpha scattering experiment, designed to determine lunar material properties. Despite completion of the unmanned lunar programs (Lunar Orbiter and Surveyor), the network continued to have a substantial workload, supporting the Pioneer VI, VII, and VIII missions. Originally planned with a useful lifetime of six months, these reliable spacecraft have exceeded all expectations and their lifetimes are now estimated at five years. The increased lifetimes now allow near simultaneous sampling of important phenomena and solar particles in our solar system at widely distributed points. While yielding a true bonus of scientific data, the extended lifetimes saturated the capability of the single 210-foot antenna at Goldstone (the only facility capable of receiving data from the Pioneers at the maximum distances from earth as they proceed in their trajectories around the sun). (Fig. 6-2.) To vide total support to the Pioneers, the 85-foot antennas were im

proved to increase their capability for receiving data from greater ranges. These improvements have allowed a significant increase in the support provided the Pioneer missions during the report period.

In addition to supporting NASA spacecraft during the report period, two of the Deep Space Network tracking stations at Goldstone, California, were used to successfully track the Asteroid Icarus as it passed within 4 million miles of the earth on June 14. An 85-foot diameter antenna, with a powerful 450-kilowatt transmitter, was used to transmit radio waves to the asteroid and the 210-foot diameter antenna received the radio wave echoes some 42 seconds later. The first signal was detected at 11 p.m. PDT on June 13, and the last signal was received at 4 a.m. PDT on June 16. The asteroid's orbital path made it possible to maintain continuous coverage of Icarus from the Goldstone location. Except for an eight-hour interruption while the 210foot antenna was supporting the Pioneer spacecraft, the Deep Space Network obtained over 40 hours of data from the asteroid.

The Satellite Network continued to carry a very substantial workload, providing tracking and data acquisition support to some 63 satellites. (Seven of these were launched during this period.)

One of the highlights of the report period was the support of the second Geodetic Earth Orbiting Satellite (GEOS-II). Launched January 11, 1968, GEOS-II was receiving support from STADAN and the SAO optical network. Also participating in the tracking effort were camera stations of the Coast and Geodetic Survey, the U.S. Air Force, and the U.S. Army Map Service. Additional radio ranging and tracking support was being provided by the Navy Doppler Tracking Network (TRANET). The information obtained by these additional tracking facilities will provide the experimenters and participating Federal agencies with very precise geodetic data.

The launch of the highly successful OGO-V on March 4, 1968, marked the last of the missions requiring support by the mobile tracking and telemetry facility in the Darwin, Australia, locality. Subsequently, the van-mounted 14-foot parabolic antenna and related equipment were being refurbished at Goddard. This mobile facility is

to be installed aboard a Department of Defense ship for support of the next, and final, OGO mission.

On May 23, 1968, the Satellite Network's support of the world's first passive communications satellite, Echo I, ended when the satellite reentered the atmosphere. The Satellite Network supported Echo I throughout its lifetime, providing the news media with daily predictions indicating where the satellite would pass and when. Easily visible to the unaided eye, Echo I had been viewed by millions of people around the world for nearly eight years.

Manned Space Flight Network

The Manned Space Flight Network continued to play an active role in supporting NASA's flight missions, despite the delay in manned Apollo missions. Selected network stations provided launch support during the report period to many unmanned missions, including Surveyor and the Orbiting Geophysical Observatory. In addition, the network continued its support of the Titan III-C vehicle development lights and other Department of Defense programs.

As noted in the 18th Semiannual Report, all the land stations required to support the Apollo lunar landing were operational, and the

construction and modification of the Apollo ships and aircraft were completed. During this report period, the ships and aircraft became operational, enabling the Manned Space Flight Network to provide full support for the lunar landing. NASA now has no further need for the two Department of Defense tracking ships, the Rose Knot Victor and the Coastal Sentry Quebec. The NASA tracking equipment was being removed from them and will be used at the network ground stations.

The first flight (Apollo 5) of the Lunar Module (LM) was successfully launched January 22. During this mission, the importance of a reliable ground-based network, staffed by skilled operating personnel, was again illustrated. As has been the case in certain past missions, both manned and unmanned, the capability to transmit precise commands to the spacecraft became the determining factor in assuring mission success. The Apollo 5 mission was headed for failure-premature shutdown of the descent engine-until corrective commands were sent up from the ground stations. Working with data received by the network, flight controllers at the Mission Control Center, Houston, Texas, quickly determined the cause of the shutdown and issued commands to correct the problem. The competence demonstrated by the network in its support of Apollo 5 added to NASA's confidence in its ability to support the lunar landing.

The network performed equally well during its support of Apollo 6, launched April 4. In addition to the land stations, seven of the eight Apollo/Range Instrumentation Aircraft were deployed for mission support: two in the Pacific, two in the Atlantic, one in the Gulf of Mexico, and two available for backup in the Gulf and at Bermuda. The aircraft in the Pacific acquired the spacecraft during terminal reentry and followed it to splashdown.

The network's successful support of the Apollo 5 and 6 missions resulted in large measure from the experience gained from the numerous mission simulations conducted between flight missions. A Test and Training Satellite (TETR, formerly TTS) provided the means of conducting realistic simulation of network and control center operations for Apollo orbital missions.

The first such satellite, TETR-1, which was launched during the previous reporting period (see 18th Semiannual Report), reentered the earth's atmosphere on April 26. During the satellite's lifetime over 600 orbital passes were supported by the network, including the Apollo ships, in training and checkout exercises. In addition, the spacecraft was used in network mission simulations involving real-time orbit computation and prediction, dispersal of acquisition messages, and checkout of the Unified S-band system. A second Test and Training Satellite is scheduled for launch in the last half of 1968.