A multiplicity of missions

Abstract

In May 1971 the Soviet Union launched the Mars 2 and Mars 3 missions, each of which was to drop a probe into the planet’s atmosphere. As the landers were to be released several hours before the main spacecraft entered orbit, there was no way to revise either the time of landing or the target site. By sheer bad luck, one of the most extensive dust storms ever observed was raging when they attempted to land on 27 November and 2 December. After entry, the probe was to discard its conical heatshield, employ a parachute to make a’ semi-hard’ landing, and then open four petals to expose its instruments. Nothing was received from the first probe, but the other touched down at 25 metres per second and its mothership relayed 14 seconds of contrast-free television comprising only a few scan lines. It was later found that the autonomous trajectory correction by Mars 2 six days prior to its arrival set the approach hyperbola too low, which caused its probe to penetrate the atmosphere at a very steep angle and hit the surface before its timer could release the parachute. In view of the stable configuration of the deployed lander, it is highly unlikely that Mars 3 was blown over. One suggestion is that the relay system on the mothership failed. Another is that electrical interference from the dust storm either disrupted the radio transmission or caused a discharge that zapped a critical system. The first mothership entered the planned orbit ranging between 1,280 and 25,000 kilometres but its radio link was so weak that little useful data was received. As a result of a propellant leak, Mars 3 limped into an orbit with its apoapsis 10 times higher than intended, severely limiting its opportunities for observing the planet, which was, in any case, obscured by dust, and by the time the storm abated the pre-programmed sequencer had completed its activities.