ground antenna tracking devices due to their geostationary orbit.)

The next Applications Technology Satellite (ATS-E) was scheduled for a 1969 launch.

GEOS

GEODETIC SATELLITES

The passive gravity gradient attitude stabilization system of GEOS-I continued to position the satellite so that ground sta tions could track it precisely through its 334 laser corner cube retroreflectors. (19th Semiannual Report, p. 67.) No other instruments aboard the spacecraft, launched in 1965, can be used. GEOS-II, orbited January 11, was also operating successfully, although its power supply was reduced. The satellite was expected to support Air Force camera teams in their geodetic observations of South America; help calibrate a selected group of C-band radar systems and determine if useful geodetic data might be supplied; and aid in comparing and calibrating ground tracking equipment at NASA's Carnarvon, Australia, tracking site. GEOS-C is planned for a 1970 launch. This satellite will carry a radar altimeter to measure mean sea level and the dynamic variations of the ocean's surface. In a low inclination orbit of about 20°, it will provide data vital to further describing the gravity field of the earth.

PAGEOS

Geodetic information was still being provided by the large passive balloon satellite, PAGEOS-I, which was launched in 1966.

Aircraft Program

EARTH RESOURCES SURVEY

NASA-cooperating with the Departments of Interior, Agriculture, Commerce, and Navy-continued to investigate possible uses of space-acquired data in surveying the world's natural resources. In support of these studies (detailed in the 19th Semiannual Report), aircraft at low and intermediate altitudes were flying remote sensors over a network of ground test sites to provide scientists with earth resources information.

The low altitude flight missions (from 500 to 20,000 feet) and the intermediate altitude flight missions (20,000 to 40,000 feet) are two of the three major phases of the aircraft program. A

third phase-flights above 40,000 feet-will be carried out beginning next summer through the use of a high altitude aircraft loaned to NASA by the Air Force's Air Weather Service. By flying remote sensors at altitudes above about 90 percent of the earth's atmosphere, the range of sensor performance is extended, and data handling and analysis techniques are verified. Space flight sensing can most nearly be simulated at such heights. The ground test sites over which these missions are flown were developed by scientific investigators from the agencies and universities participating in this aircraft program, as well as by instrument teams. Sites were chosen to provide earth resources data on crops, forests, water, fisheries, and cities. These data were then compared with "ground truth" information collected by the investigating agencies and cooperating scientists to find out if the sensing methods were feasible. Nineteen flight missions were conducted over 75 test sites during 1968 (some repeated above several sites). The Manned Spacecraft Center publishes a monthly accession list of information gathered from these flights.

A data processing and distributing facility at the Center handles the data acquired by the sensors during each mission. This information is collected in the form of film, magnetic tapes, strip charts, and logs and processed quickly for the convenience of scientific investigators.

Spacecraft Studies

Substantial progress toward realizing the basic goals of the Earth Resources Survey Program through this airborne remote sensor testing has led to the beginning of the design of flight hardware for an Earth Resources Technology Satellite (ERTS) Involved are aircraft-based investigations, development of remote sensors, spacecraft data analyses, systems and benefits studies, spacecraft definition, and interagency coordination of ERTS requirements.

Remote sensor data from aircraft, infrared imagery from Nimbus II, and photography from Projects Gemini and Apollo when evaluated by investigators from many Government agencies have permitted users to refine further their various needs for satellite-based sensors. Nine systems and benefit studies by NASA, the Departments of Interior and Agriculture, and the Na tional Council on Marine Resources and Engineering Develop ment were made to estimate benefits and costs of operationa

space-assisted earth resources survey systems and assist in evaluating priorities for ERTS experiments. These studies have indicated that potential benefits may overshadow estimated system costs for geographic areas about as large as the United States or larger.

Plans were being completed to begin the final Earth Resources Technology Satellite definition/design study. Also, advanced sensor studies were started and were extensively reviewed with the user agencies. To ensure interagency coordination, an Earth Resources Survey Program Review Committee was established in July chaired by NASA's Associate Administrator for Space Science and Applications. Members of this committee are assistant secretaries of the Departments of Interior, Agriculture, Commerce, and Navy.

The Office of Advanced Research and Technology continued to carry out the many and various programs which support current activities and anticipate future requirements in aeronautics and space. This was a particularly fruitful period as indicated by the multitude of accomplishments reported in the following pages.

SPACE FOWER TECHNOLOGY

Solar and Chemical Power

Commercial and normal space-type batteries, which may be used in spacecraft intended to land on planets, do not have the ability to withstand sterilization or the hard impacts of planetary landings. To adapt such batteries to this type of use, it was necessary to develop new separator and case materials that could withstand the temperatures and pressures of sterilization without chemical attack and physical weakening. Structura! changes made to convert the parts of a normal cell to those of an impact resistant cell are shown in Fig. 4-1. The improvements include a more elaborate lid and special insert to hold the plates in place, substantial tabs and reinforcement of the plates themselves, and a larger and heavier case.

Batteries composed of 12 of the new cells were built into a prototype Mars lander package and dropped twice from a height of 250 feet. The second time, the package landed on asphalt and was subjected to a shock 2,500 times the force of normal grav

ity. The sterilized batteries operated as required both times. Preliminary results from another test program indicated that conventional cells and batteries can also be improved by the application of these tough new plastics.

The Power Systems Laboratory at the NASA Electronics Research Center demonstrated an operating laboratory model of a watt meter with a near linear response from DC to 1 mega