program, a very exciting program, and is the one which makes the best use of this Nation's capability with the resources available.

For each of these programs, I will first review our goals for that programwhat we want to accomplish, the rationale for these goals-why they are important and why this Nation should have such a program at this time; and our strategy-our approach for accomplishing these goals. Then I will comment on the most significant accomplishments during Calendar Year 1968 and will give you a status report of our programs, including any major problems we encountered in the past year. Lastly, I will review in some detail the new projects we are proposing to start in Fiscal Year 1970.

PHYSICS AND ASTRONOMY

The Physics and Astronomy Program goals and objectives are related to: (Chart SG69-204)

The study of the space environment;

The influence of the Sun on the Earth's environment;

Observations of radiations from the Sun and stars in those wavelengths not visible to Earth-bound telescopes; and

Space as a laboratory for scientific investigations.

Sounding rockets, automated Earth satellites, deep space probes, and manned space vehicles (Chart SG69-253) are used as appropriate in the conduct of investigations to achieve these goals. These major flight activities are supplemented by balloon and aircraft flights where they are adequate for the task at hand. In addition, research is performed in Earth-based laboratories to complement and support the flight projects.

In 1968 there were eight spacecraft launched in this Program (Chart SG69-255) all successfully accomplishing their misison objectives. These missions included the Orbiting Astronomical Observatory (OAO-II), the most complex automated spacecraft launched to date; the fifth Orbiting Geophysical Observatory (OGOV); the first Radio Astronomy Explorer (RAE-A) (Explorer XXXVIII); and five smaller Scout-launched Explorers.

In addition, there were 127 sounding rockets and 70 balloons launched, and about 200 hours of observations from jet aircraft.

In January 1969 there were two launches in this Program: an Orbiting Solar Observatory, OSO-V; and a US/Canadian cooperative satellite, the International Satellite for Ionospheric Studies, ISIS-I.

Physics

In the past decade of space exploration we have learned to make physical measurements in the space environment and have chartered the phenomena to be found there. We are entering a new phase of the program in which we will consolidate our knowledge of the phenomena involved and will attempt to understand the mechanisms responsible for them. An excellent summary of the progress, the state of our knowledge today, and the important unresolved questions are given in a report entitled, "Physics of the Earth in Space-A Program of Research 1968-75," prepared in August 1968 by the Space Science Board of the National Academy of Sciences.

The dramatic change in our concept of the Earth's environment over the past 10 years is illustrated in Chart SG69-263. In 1958 the model of the Earth's environment generally envisioned had an atmosphere and an ionosphere limited to low altitudes with a dipole-like magnetic field in which the field lines presumably extended without limit into distant space. A very high vacuum was assumed to exist beyond the ionosphere with little or no matter or phenomena of interest in this space.

In contrast, the discoveries of the past decade, primarily through our Explorer and OGO satellites, have shown that between 800 and 25,000 miles above the Earth there is a region containing highly energetic particles that are controlled by the Earth's magnetic field. Interplanetary space is constantly filled with an ionized gas called the solar wind, which blows at a velocity of about 1 million miles an hour. This solar wind reacts with the magnetic field of the Earth. Because of this reaction, the magnetic field of the Earth does not extend into space in all directions, but is bounded in the direction toward the Sun at about 40,000 miles above the surface of the Earth and extends in the direction away from the Sun, a distance as yet unknown but probably more than a million miles.

In addition to the effect of the solar wind on the Earth's environment, there is a major effect due to the Sun's electromagnetic radiation. In particular the ultraviolet and X-ray portions of this radiation are absorbed by the atmosphere. During the past decade the Orbiting Solar Observatories have made extensive observations of the Sun in these wavelengths. The complexity of this radiation is illustrated by the ultra-violet spectrum from OSO-III (Chart SG68-403). Now that this more accurate model of the structure of the Earth's environment is available we are asking primarily, "What processes control the Earth's environment?" rather than the question we posed during the last 10 years, "What is the Earth's environment?"

The space physics flight program (Chart SG69-433) is only beginning to reflect the requirements of the new phase of the program, that is, understanding the mechanisms responsible for the phenomena. The missions to be flown in the next 2 to 3 years were initiated in previous years and are designed to continue the exploration phase. These missions are predominantly small Explorer-class satellites. The last of the OGO spacecraft to explore the upper atmosphere is scheduled for launch in early 1969. The Explorer missions include: the Scout-launched interplanetary probe Explorers, the Delta-launched IMP series to investigate the near Earth interplanetary environment and the far reaches of the Earth's magnetosphere, and Scout-launched Explorers called Small Scientific Satellites (SSS) for studies within the magnetosphere.

Also included in the physics flight program are a number of international cooperative projects: the ISIS project for ionospheric studies with the Canadians; the San Marco project to explore the lower equatorial atmosphere with the Italians; a radiation belt satellite, and a probe payload to study magnetic and electric fields with the West Germans.

In addition to these international cooperative projects, the Air Force Cambridge Research Laboratories personnel are developing a satellite for magnetospheric studies. Preliminary technical discussions about additional cooperative satellite projects shown on the chart for the early 1970's have been held with representatives of the United Kingdom, West Germany, Sweden, and ESRO.

We are considering an extension of the cooperative effort with the Navy for an additional Solar Explorer. Finally, some new effort is also proposed toward the next phase of the Program with small Scout-launched Explorer missions and a new Delta-launched Atmosphere Explorer.

Geophysical Observatories

The five OGO spacecraft, all of which are still operating except OGO-II, have accumulated over 1 million hours of experiment operation. The data from these experiments have contributed in a major way to the picture we now have of the environment of the Earth in space and the influence of the Sun on this environment. Fiscal Year 1970 funds provide for operational support for data acquisition, and data analysis for OGO-IV, V, and F.

Physics explorers

With the phasing out of OGO, Explorer-class satellites represent the mainstay of the Physics Program.

The physics Explorers launched in 1968 demonstrated their versatility and the continuing importance of this class of satellites. The Air Density Explorer XXXIX (Chart SG69-362) is a 12-foot inflatable sphere designed, developed, and constructed by the Langley Research Center (LaRC) for atmospheric density investigations. The Injun-V Explorer XL spacecraft has been designed, developed and constructed by the University of Iowa under LaRC management for corollary energetic particle and field measurements particularly in the polar regions. The next chart (SG69-363) shows the three cooperative Explorers launched by Scout vehicles in 1968. The Naval Research Laboratory (NRL) Solar Radiation Explorer XXXVII is monitoring solar X-ray activity during this portion of maximum solar activity. Two satellites developed by the European Space Research Organization (ESRO) were launched. The first of these, called IRIS-I (International Radiation Investigation Satellite-I), carries instrumentation for investigations of cosmic rays, solar X-rays and trapped radiation. The second, named Aurora, carries experiments to study the high latitude ionosphere.