Proceedings of the Workshop on Voltage Breakdown in Electronic Equipment at Low Air Pressures

Problems of voltage breakdown in spacecraft electronic equipment operating in a region of low air pressure, where the dielectric strength drops from the sea level value of 75 kv to a few hundred volts per inch, became more and more of concern as the numbers and complexities of U. S. spacecraft increased. The approximate limits of this critical pressure region (arbitrarily defined as that region in which the dielectric strength is less than 20% of the sea level value in terms of Earth altitude) are 60,000 to 310,000 ft. Originally, the problem of operating spacecraft electronic equipment in the critical region was not considered significant by many designers because spacecraft systems employing high voltages usually are not required to be functional until the hard vacuum of space is reached, which has a very high dielectric strength. In other words, the problem could be neatly circumvented by including a timer or similar device that would energize the high-voltage circuits after the critical region was passed. However, hard experience has shown that inadvertent turnon of
the high voltage while the spacecraft was passing through this critical region, the pressure lag in inadequately vented high-voltage enclosures after hard vacuum was reached, or failures of vacuum equipment or personnel during tests with full power on-all contributed to catastrophic failures in spacecraft electronic equipment. The problem is now given further emphasis for Mars soft landers, as it is estimated that the pressure of the atmosphere of Mars is probably equivalent to 110,000-ft Earth altitude, right in the critical region. Assuming a similar gaseous mixture as air on Earth, high-voltage electronic equipment in the soft lander would thus be required to operate in a gaseous environment of minimum dielectric strength.