Artificial Satellites of the Sun

(also called artificial planets), spacecraft inserted into heliocentric orbit; their motion, like that of all planets within the solar system, is determined mainly by solar gravitational attraction.

Artificial satellites of the sun built before 1971 lack independent scientific value and represent a kind of by-product of space probes to the moon and planets. During such launches a speed somewhat greater than earth escape velocity is imparted to the spacecraft either at the end of the powered phase of the launch vehicle’s trajectory or in orbit (if the spacecraft had previously been inserted into earth orbit). After this, the spacecraft moves along a leg of a hyperbolic orbit relative to the earth and leaves the earth’s field of gravitational influence, entering an orbit around the sun (if it does not impact on the moon as, for example, took place with the Soviet Luna 2 space probe, launched Sept. 12, 1959). From this point on three possibilities exist:

The spacecraft does not approach any planet, in which case its orbit is nearly elliptical and resembles the orbits of astroids; deviations from elliptical orbits are the result of the gravitational attraction of the earth and other major planets. One example of such a satellite is the Soviet Luna 1 space probe, which was inserted into a hyperbolic orbit relative to the earth on Jan. 2, 1959, and flew by the moon on Jan. 4, 1959, at a distance of about 6,000 km and entered an elliptical orbit around the sun with an aphelion and perihelion of 196.9 million and 146.1 million km, respectively, and an orbital period of 450 days.

(1) The spacecraft’s trajectory is calculated so that it flies past a given planet; in this case it moves along a section of a nearly elliptical orbit until planet approach. As the spacecraft approaches a planet, the latter’s attraction draws it into another nearly elliptical orbit around the sun—an orbit along which it will continue to move, if it does not subsequently approach this or some other planet. An example of this type of trajectory is the American Mariner 2 space probe, which was launched Aug. 27, 1962, and made a fly-by of Venus on Dec. 14, 1962, at a distance of about 35,000 km. It was subsequently injected into a planetary orbit with aphelion and perihelion of 182.1 and 104.8 million km, respectively, and an orbital period of 343 days.

(2) The spacecraft’s path is calculated so that the spacecraft reaches the surface or the dense layers of the atmosphere of a planet and is destroyed. An example is the Soviet Venera 3 space probe, which was launched on Nov. 16, 1965, and impacted on the surface of Venus on May 1, 1966.