Artificial Mars Satellites

Artificial Mars Satellites 

spacecraft inserted into orbit around Mars; their motion is determined mainly by the gravitational attraction of Mars. In 1971 two Soviet space probes, Mars 2 (launched May 19) and Mars 3 (May 28), and an American space probe, Mariner 9 (May 31), were launched from earth toward Mars during its favorable opposition. After traveling about 470 million km, the probes became the first artificial satellites of Mars (November 27, December 2, and December 14, respectively).

For the transition from the interplanetary trajectory to Mars orbit, the probes were equipped with a self-contained astronavigation system, which determines with great accuracy the probe’s position relative to Mars and maintains its proper orientation; an on-board computer, which, on the basis of instrument measurements, calculates the magnitude, direction, and time of the necessary corrective thrust; and a braking engine, which performs the final corrections near the planet. The performance of such a correction using only ground-based trajectory measurements would not provide the required accuracy for injecting the satellite into Mars’ orbit.

The goal of the first artificial satellite of Mars was the study of space in the vicinity of the planet, as well as the planet’s atmosphere and surface. Since Mars 2, Mars 3, and Mariner 9 were inserted into considerably different elliptical orbits (orbital periods of 18 hrs, 11.5 days, and 12 hrs; minimum ordinates of 1,380 km, 1,500 km, and 1,380 km, respectively), their scientific investigations augment one another. The Soviet Mars 2 and Mars 3 satellites were used to study the nature of the flow of the solar wind past the planet and its interaction with the Martian ionosphere, the charged particle spectra, the magnetic field variations, the ionosphere and atmosphere, the temperature distribution on the planet’s surface, the planet’s terrain, the amount of water vapor in the atmosphere, the reflectivity, radiance temperature, and dielectric constant of the surface, the temperature of the subsurface layer to a depth of 30–50 cm, the density of the upper atmosphere, and the content of atomic oxygen, hydrogen, and argon in the atmosphere. Mars was photographed by television cameras. The Stereo joint Soviet-French experiment, which studied solar radio emission, was conducted on Mars 3. Most of the Mariner 9 program was devoted to television filming of 70 percent of the Martian surface for purposes of mapmaking.