just as it would be if the Earth did not exist at all. The boundary layer itself is a turbulent region, caused by the impact of the solar wind against the Earth's magnetic field. An important goal that still lies ahead of us is the experimental measurement of the shape and detailed character of the magnetospheric boundary region and the theoretical understanding of the reasons for its being the way it is. Figure 111 shows the orbits of all the spacecraft that have contributed to our knowledge of the boundary's shape and characteristics. Only one of these was not launched by the United States. Trajectories of probes are shown as single arcs. The areas swept out by Earth satellites as the Earth moves around the Sun are indicated by shading. One major step forward made in the last year was the detailed coverage of nearly the entire region of the equatorial magnetospheric boundary by EXPLORER XIV during its 10-month lifetime. The gigantic sweep of the satellite EXPLORER XVIII shows clearly how powerful eccentric orbit satellites can be in studying the interplanetary environment. On the sunward side, the results from EXPLORER XIV verified the earlier observations of EXPLORER XII, that the solar wind compresses the Earth's magnetic field inward to a distance of about 10 earth radii, with a turbulent transition layer about 3 or 4 earth radii thick. On its passage through the antisolar direction, EXPLORER XIV found, as EXPLORER X had previously, that the Earth's magnetic field is stretched out into a long tail. The end of the tail could not be penetrated by EXPLORER XIV because its apogee was not high enough (about 17 earth radii). Whether the recently launched EXPLORER XVIII (apogee 32 earth radii) will reach the boundary in the rear is not yet known. EXPLORER XIV found out several interesting things about the magnetosphere and the region of trapped radiation. One surprising result was that the trapping region is bounded closer to the Earth on the night side than on the day side. Another was the discovery on the dawn and evening sides of energetic electrons attached to magnetic field lines that appear to trail off to infinity. These results are shown in figure 112, which is a view of the magnetosphere and the boundary perpendicular to that plane containing the Earth-Sun line. In the chart will be seen the trapping region, the boundary, its transition region, and the shock front. In addition, the view shows the lines of magnetic force. These results present a new and somewhat unexpected idea that a portion of the Earth's magnetic field that emanates from the polar regions always remains behind the Earth, on the dark side, blown there by the solar wind, while the inner section containing the Van Allen radiation belts rotates with the Earth, and undulates in size as it rotates. This idea is little more than a speculation right now. It will be verified in detail, modified, or rejected on the basis of more information that we expect to obtain from the interplanetary monitoring platform (IMP) series of EXPLORERS (including EXPLORER XVIII) and future PIONEERS. Preparation for future investigations of space environments.—Considerable progress was also made in the preparation for further investigations of the space environment. STRUCTURE OF MAGNETOSPHERE PERPENDICULAR TO ORBIT PLANE Under the Supporting Research and Technology (S.R. & T.) portion of our program significant advances were made in the development of particle detectors with greatly increased capability for the detection of low-energy particles which are an important constituent of the magnetosphere and interplanetary space. These detectors are now available for use on spacecraft and will be flight tested on sounding rockets in the near future. A greatly improved calibration technique for instrumentation designed to measure cosmic dust and micrometeoroids was developed utilizing an electrostatic particle accelerator. In addition to these important developments, there were significant improvements in the instrumentation and techniques for study of the atmospheric composition and structure. The progress in the preparation of the flight program for the coming year is indicated in the following discussion of the status of various projects which are designed to contribute to our understanding of the space environment during the next 2 years. The flight programs for this period, which is one of minimum solar activity, have been planned to take full advantage of the opportunity to conduct experiments in space during the International Years of the Quiet Sun (IQSY) (fig. 113). This is being done as part of a continuing program in the investigation of the space environment and thus reflects additional emphasis in some areas of the program rather than the development of a special program for the IQSY. The following table indicates the approximate status of the spacecraft and the portion of the space environment that will be studied by each spacecraft: INTERNATIONAL QUIET SOLAR YEAR EXPLOYER XVII..... Measured atmospheric pressure, density, temperature, and composition EXPLORER XVIII... EXPLORER XIX. Type of spacecraft 160 to 650 miles altitude. Measured radiation environment and magnetic field in cislunar and inter planetary space out to 30 earth radii. Measuring atmospheric density in the polar regions. Prepared for launch Objectives EXPLORER, Ionosphere/Geodetic Beacon. To determine the total electron count of a vertical EXPLORER, Topside To examine the ionosphere from above by meas- EXPLORER, United Continues investigations begun by EXPLORER VIII. ALOUETTE I. ARIEL I. Type of spacecraft EXPLORER, Air Density/ Nearing preparation for launch Objectives Air density EXPLORER: To determine density EXPLORER, Energetic To study the injection, trapping, and loss mecha- EXPLORER, Interplanetary. EXPLORER, Italian San nism of the trapped radiation belts, the energy To study the radiation in cislunar space over a First satellite to make as many as 20 coordinated Continues investigations begun by EXPLORER IX and EXPLORER XIV. EXPLORER XII, EXPLORER XVIII Complements EX- Explorer status.-A typical EXPLORER is shown in figure 114 whereas figure 115 depicts the 1964 EXPLORER status. The first launch of the Interplanetary EXPLORER series, EXPLORER XVIII, was successfully made on November 26, 1963. Construction of the second interplanetary EXPLORER spacecraft has been completed. It is about to undergo environmental tests in preparation for launch. The second launch is planned for the second half of calendar year 1964; the third launch will take place during calendar year 1965. |