316 AKNTUAL REPORT SMITHSONIAN INSTITUTION, 1961 



might be adopted for satellite computations. Their views about 

 values for the earth constants were widely divergent, and the par- 

 ticipants felt that it would be premature and outside their province 

 to recommend the adoption of one system to be used by all scientists 

 who would be concerned with computing satellite orbits. They did 

 decide, however, that since the U.S. standard atmosphere was based 

 on the most recent observations available and differed greatly from 

 earlier atmospheres, it should serve as the basis in computing satellite 

 drag. 



As a second step the Observatory made arrangements with In- 

 ternational Business Machines Corporation to use the 704-computer 

 installation at the Massachusetts Institute of Technology. IBM con- 

 tributed the machine time and agreed to supply one or two program- 

 mers for part-time technical assistance, and Dr. John Kossoni was 

 engaged full time on the satellite program. 



The computer was to be used to convert satellite observations into 

 what are called the orbital elements, which in turn would serve as a 

 basis for predicting future transits of the satellite and for analyzing 

 atmospheric density and gravitation properties. The orbital ele- 

 ments refer to the size and shape of the elliptical orbit of a satellite 

 in motion around the earth, the orientation of that orbit in space, and 

 the position of the satellite in its orbit at any particular time. 



In accordance with the laws of Kepler, an astronomical body orbit- 

 ing a larger one moves in an ellipse ; the apogee is the point in that 

 ellipse farthest from the center of the larger body, the perigee, the 

 point nearest. The first orbital element is thG semimajor axis (a) 

 of the ellipse, that is, half the length of the long axis. The second 

 element is the eccentricity (e), which is the degree of "flattening" of 

 the ellipse; it can vary from for a circle to 1 for a parabola. 



The orientation of the plane of the orbit is given by the next two 

 elements, the right ascension of the ascending node (Q,) and the 

 inclination (i). The former is the angle between the vernal equinox 

 and the point at which the orbit crosses the Equator in a northerly 

 direction ; and the inclination is the angle that the plane of the orbit 

 makes with the plane of the Equator. 



The orientation of the orbit in its plane is specified by the fifth ele- 

 ment {<j}), called the argument of perigee, which is the angle from 

 the ascending node to the perigee point. 



The sixth orbital element is the time of perigee passage (T) , that is, 

 the moment at which the satellite is at perigee. 



If a satellite were orbiting a perfectly spherical body without at- 

 mosphere, and if there were no forces such as radiation from the sun 

 or lunar gravity, the orbit would be stationary and conform to 

 Kepler's laws. From three accurate observations of the satellite, it 



