NASA was developing the next generation of operational weather satellites for the Environmental Science Services Administration, planning to continue providing launch services for the Communications Satellite Corporation, and demonstrating that the Applications Technology Satellites could provide meteorological coverage of the mid-Atlantic and Pacific Oceans and the middle part of the U.S.; pinpoint vehicle locations on land, sea, and in the air; and communicate with ships at sea. In addition, a NASA geodetic satellite transmitted data to hundreds of tracking stations around the world.

ESSA and TIROS

Meteorological Satellites

On May 27 the one-millionth cloud cover picture from the combined TIROS and ESSA (TOS) satellites was received from the ESSA VI spacecraft. (Fig. 3-1.) These photographs include all taken by the ten TIROS research and development satellites and the six ESSA satellites which NASA turned over to the Environmental Science Services Administration. The other ESSA satellites, II, III, and V, also continued to provide global meteorological satellite data on an operational basis. Spacecraft yet to be launched in the ESSA series— TOS-E, -F, -G, and -H-were ready to be orbited as needed to maintain the national operational meteorological system.

The next generation of operational weather satellites (the TIROS-M class) were being developed by NASA for ESSA. The mechanical and thermal test models, and the antenna test model of this new TIROS were tested successfully. (Fig. 3-2.) Also, assembly of the electrical test model began, and some components of the flight spacecraft were delivered.

Meteorological Experiments on ATS

The spin scan camera aboard the first Applications Technology Satellite (ATS-I), launched in December 1966, was providing excellent meteorological coverage of the Pacific. (Fig. 3-3.) Evaluation of its Weather Data Relay (WEFAX) experiment indicated that such a system is extremely useful. The ATS-III spin scan color camera. (p. 67), image dissector camera, and Omega Position Location Experiment, OPLE, were supplying similar meteorological coverage of the mid-Atlantic and the middle section of the United States.

Nimbus

The Nimbus II spacecraft successfully completed two years in orbit on May 15. Although its Automatic Picture Transmission system and yaw rate gyro ceased operating after 23 months, sun sensors on the solar paddles and a yaw rate gyro back-up system provided yaw data

and prevented the loss of the spacecraft. The Advanced Vidicon Camera System was operating over North America in real time only due to the position of Nimbus II in relation to the command and data acquisition stations. (18th Semiannual Report, p. 65.)

The third Nimbus (Nimbus B) was launched on May 18 on a long tank, thrust-augmented Thor-Agena. Fourteen earlier launches by this vehicle were successful, but in this case, about 13 seconds after lift-off an unstable oscillation began to appear in the yaw channel of the Thor control system. The instability increased during the flight, and after about 2 minutes the range safety officer destroyed the vehicle. Preliminary analyses of flight telemetry data indicated that the most likely cause of the failure was a mechanical misalignment of the Thor yaw rate gyro.

Since there were enough Nimbus B experiments (fig. 3-4) and subsystem back-up hardware, a replacement for Nimbus B could be assembled quickly and tested. The repeat mission (Nimbus B2) was scheduled to be launched in April 1969.

Nimbus D was on schedule for a 1970 launch, its harness mock-up about 80 percent completed. The satellite's Cloud Altitude Radiometer experiment (fig. 3-5) was deleted from the payload.

Thirty-three proposals were received from industry for the Nimbus E mission, and a definition contract was signed in June. Reviews by

appropriate committees were made, and a payload will be selected in a few weeks.

Meteorological Sounding Rockets

Sounding rockets obtained meteorological data and explored the atmosphere between 20 and 60 miles above the earth. Nike Apache rockets used acoustic grenades, pitot-static tubes, and light-reflecting or luminous-vapor experiments to determine wind, density, temperature, and pressure vertical profiles. In addition, special sensors for measuring ozone, water vapor, and ultraviolet radiation were flown in studies of energy sources in the upper atmosphere.

NASA and the U.S. Army continued to work together to develop an inexpensive meteorological sounding rocket system for obtaining data from the atmosphere at altitudes of 20 and 60 miles. Feasibility demonstrations of a self-consuming rocket case and fragmentable rocket nozzle were conducted. After performing reliably in ground tests during rocket motor burning, the rocket case broke up into particles which could not be a falling mass hazard in a free fall to earth. Descent devices to replace the conventional parachute were also under development. Such items would be able to function in air less than one hundredth of one percent the density of air at sea level.