The Mobile Tracking Station (DSIF 1) is a movable installation designed for emplacement near the point of injection of a space probe to assist the permanent stations in early acquisition of the spacecraft. This station is necessary because at this point the spacecraft is relatively low in altitude and consequently appears to move very fast across the sky. The Mobile Tracking Station has a fast-tracking antenna for use under these conditions. DSIF 1 was located near the South African station for Mariner II. It has a 10-foot parabolic antenna capable of tracking at a 10-degree-per-second rate. A 25-watt, 890-megacycle transmitter is used for obtaining tracking information. A diplexer permits simultaneous transmission and reception on the same antenna without interference. The equipment is installed in mobile vans so that the station can be operated in remote areas. The antenna is enclosed in a plastic dome and is mounted on a modified radar pedestal. The radome is inflatable with air and protects the antenna from wind and weather conditions. These stations of the DSIF tracked Mariner II in flight and sent commands to the spacecraft for the execution of maneuvers. The telemetry data received from the spacecraft during the 129 days of its mission were recorded and transmitted to JPL, where the information was processed and reduced by the computers of the space flight operations complex. CHAPTER 7 THIRTEEN MILLION WORDS The task of receiving, relaying, processing, and interpreting the data coming in simultaneously on a twenty-four-hour basis for several months from the several scientific and many engineering sources of the Mariner spacecraft was of truly monumental proportions. This activity involved five DSIF tracking stations scattered around the world, a communication network, two computing stations and auxiliary facilities, and some 400 personnel over a four-month period. Although the Mariner scientific information could be stored and subsequently processed at a later (non-real) time, it was necessary to make tracking and position data available almost as soon as it was received (in real time) so that the midcourse maneuver might be computed and transmitted to the spacecraft, and to further perfect the predicted trajectory and arrival time at Venus. The engineering performance of the many spacecraft subsystems was also of vital concern. Inaccurate operation in any of several areas could endanger the success of the entire mission. The performance of the attitude control system, the Earth and Sun sensors, the power system, and communications were all of critical importance. Corrective action was possible in certain subsystems where trouble could be predicted from the data or where limited breakdown had occurred.