spheric temperature. (This instrument is similar to the one flown on Nimbus II.) The HRIR supplied daytime and nighttime global cloud cover photographs (fig. 3-5.). Nighttime data were transmitted to the APT (Automatic Picture Transmission System) stations. Daylight HRIR pictures showed details of the terrain as well as the cloud cover. High quality pictures furnished by the Image Dissector Camera System during the daylight portion of the satellite's orbit were transmitted via the APT system to ground stations around the world. The Interrogation, Recording, and Location System (fig. 3-6) interrogated platforms at Point Barrow, Alaska; Melbourne, Fla.; Boulder, Colo.; and Goddard Space Flight Center. An IRLS Nimbus D platform was also interrogated at Melbourne, Fla. to demonstrate the compatibility of this system with Nimbus III and D. The Monitor of Ultraviolet Solar Energy experiment continued to measure the solar flux in the area controlling the photochemistry of the ozone region, although two or its five photodiode sensors could no longer provide useful data. The SNAP-19 radioisotope thermoelectric generator developed by the Atomic Energy Commission performed as designed, producing between 24.4 and 25.5 watts. (20th Semiannual Report, p. 80.) Nimbus D.-Nine experiments for Nimbus D were being developed and tested. They include the Image Dissector Camera System as carried aboard Nimbus III, and refined versions of the other five Nimbus III experiments. The three additional experiments, which will use new techniques for making meteorological measurements, are: SPACE APPLICATIONS • A Backscatter Ultraviolet experiment developed by the National Center for Atmospheric Research and NASA to determine the vertical atmospheric distribution of ozone above 15 miles. • A Filter Wedge Spectrometer developed at Goddard Space Flight Center to measure water vapor content and its vertical distribution in the atmosphere along a continuous strip about 150 miles wide under the orbital path of the satellite. • A Selective Chopper Radiometer being developed by the United Kingdom to measure the atmospheric temperature structure between the ground (or highest cloud top) and an altitude of 30 miles. Nimbus D will have a new control system, but will not use a SNAP-19 power system. It is scheduled to be launched in the spring of 1970. Nimbus E and F.-Plans call for Nimbus E and F spacecraft to be launched in the first half of 1972 and of 1973, respectively. Proposals were received for the Nimbus E experiments, and the flight payload was being selected. The payload for Nimbus F was also being determined. Its experiments will include extension of remote sensing of the earth's atmosphere and surface to use the "windows" and absorption bands in the microwave portion of the elctromagnetic spectrum. Meteorological Sounding Rockets To explore the atmosphere 20 to 60 miles above the earth, NASA launched 39 research sounding rockets of the Nike-Cajun class. Fifteen coordinated grenade firings and two ozone soundings were made from Wallops Station, Va.; Pt. Barrow, Alaska; Ft. Churchill, Canada; and Kiruna, Sweden during minor warmings of the stratosphere in January and February. They were also coordinated with experiments measuring electron density, nitric oxide, and ion composition. Four grenade type rockets were launched from El Arenosillo, Spain and four from Wallops Station at approximately the same local time in a coordinated series of soundings to compare atmospheric structure and winds, and to study the mesosphere and stratosphere at the two sites, which are at about the same latitude but separated by 70° of longitude. Preliminary analysis of data obtained indicated a maximum temperature difference of 15° C at an altitude of 45 miles. Operational Rocket System.-Progress was made toward developing an inexpensive operational meteorological sounding rocket |