Concepts for detection of extraterrestrial life/Chapter 12
The Mars Mariners and Voyagers
The first spacecraft destined for Mars will be Mariner C, a NASA planetary flyby scheduled for launching in 1964.
Mars and Earth both orbit the' Sun in the same direction, but not at the same speed or distance. The mean distance of Earth from the Sun is 93 million miles, while the mean distance of Mars from the Sun is 141 million miles. Earth makes one revolution around the Sun each 365¼ days, while Mars revolves around the Sun once every 687 earth days.
The maximum distance between Earth and Mars is about 247 million miles, which occurs at the aphelion conjunction. However, when Mars is at opposition, the two planets (Earth and Mars) can be as close together as 34.5 million miles or as far away from each other as 63 million miles. Oppositions are usually considered in planning missions to Mars. It is emphasized that neither spacecraft launch nor encounter would occur exactly at these opposition distances because the planets are in orbital motion at different velocities, as was already mentioned. From a search-for-life point of view, it is important to launch so that arrival coincides with those times when the wave of darkening on Mars is most pronounced.
Mariner C is not intended to land on Mars, but to fly past it at a distance of about 15,000 km. It will carry instrumentation to obtain data on interplanetary dust and plasma and to take television photographs of Mars. In addition, experiments are to be aboard to obtain data on the magnetic field and cosmic rays. The final dimensions of Mariner C will be similar to Mariner II which flew past Venus on December 14, 1962.
The hexagonal framework of Mariner II housed a liquid-fuel rocket motor for trajectory correction. It had six modules or compartments containing the attitude control system, electronic circuitry for the scientific experiments, power supply, battery and charger, data encoder, and command subsystem for receiving and obeying signals from Earth, digital computer and sequencer, and radio transmitter and receiver.
The solar panels, with 9,800 solar cells, collected energy from the Sun and converted it into electrical power. Two-way communications were supplied by the receiver/transmitter, two transmitting antennas and the command antenna for receiving. Stabilization for yaw, pitch, and roll was provided by 10 cold-gas jets mounted in four locations and fed by two titanium bottles.
A later Mariner will carry additional devices past Mars in 1966–67. If an instrumented package does land on the Martian surface it will be to determine the density profile of the Martian atmosphere. Not until 1969, 1971, or 1973 will actual life-detection devices, using systems evolved from Mariner-level payloads to larger payloads of the Voyager class, be considered for effective surface landing and operation.
One of the flyby experiments may consist of an infrared scanning system capable of measuring reflected visible radiation, emitted surface radiation (thermal), and radiation absorbed by atmospheric water vapor. Figure 19 shows the general optical scheme for the instrument. This type of Mars “mapping” will provide useful information with respect to microenvironments for possible extraterrestrial life.
Figure 19.—Optical schematic diagram for Mars scanner.