After the American triumph of Mariner-4 in 1965, the 1969 Mars launch window again saw the United States and the Soviet Union in competition with each other.
After the aborted attempt at developing a new Mars spacecraft, begun by Babakin in March of 1966 and terminated only one month later, the Soviet team started working on an heavy Mars probe called M-69 or 2M just a few weeks after the launch of Venera-4 during the summer of 1967. In its first version the probe was based on the architecture of the E-8 heavy lunar probe, launched in several versions between 1969 and 1976. The Proton-launched mission would have two main objectives: entering orbit around Mars for the first time, at least two years before the first planned US attempt and releasing a probe into the atmosphere to collect some basic data. In fact, the Martian ephemerides produced by the Soviet scientists still included a quite
large uncertainty, so much so that the atmospheric entry angle of the capsule was estimated between 10 and 20 degrees and, as a consequence the descent time could vary between 30 and 900 seconds. For the same reason, the planned apoastron of the orbiter could vary between 13,000 and 120,000 km. The periastron was instead fixed in both cases at 2,000 km.

A drawing of the E-8 based M-69 design, abandoned in early 1968. (NASA Image)

After seven months studying a configuration based on the E-8 it was discovered that it presented several shortcomings, including a large center of mass shift as propellants were used. Despite the launch window being a little more than an year away, Babakin decided to abandon the E-8 based probe and start developing a completely new probe. The new design was entirely built around a large spherical tank that, thanks to an internal membrane, housed both the fuel and the oxydizer for the orbit insertion engine. On top of the tank was mounted a cylindrical compartment for on board systems, on which was mounted a 2.8 meters diameter high gain antenna. On the tank were also mounted the thermal control system radiators and two wings of solar panels having a total surface of 7 sq. meters The scientific payload was enclosed inside two pressurized cylindrical containers and the conical atmospheric capsule was mounted on top of the system module. No less than thirteen instruments for a total mass of 99.5 kg were to be carried by the orbiter: a magnetometer; a meteoroid sensor; a low frequency radioastronomy receiver; a charged particle detector; a radiometer; a gamma-ray spectrometer; a mass spectrometer; X-ray, ultraviolet and infrared photometers and finally three cameras with three different focal lengths (35, 50 and 250 mm). As usual on Soviet spacecraft, the cameras were to take a total of 160 pictures on a special photographic film that would be developed on board, scanned and then relayed to Earth with a resolution of 1.024 x 1.024 pixels. The maximum ground resolution would be between 200 and 500 meters per pixel and every image would cover an area between 100 x 100 or 1.500 x 1.500 km depending on the camera objective. On the atmospheric capsule was an instrument suite similar to the one of the Venus probes: an atmospheric composition analyzer and pressure, density and temperature sensors. The capsule was not expected to survive the landing and therefore no surface science instruments were carried.
According to the Soviet engineers themselves, the probes were a very good example of how not to design a spacecraft: not only were the electronic components obsolete even for the Soviet standards, but the internal arrangement of the pressurized compartment did not allow for a simple access to the equipments in case they needed to be replaced.
Moreover, it soon became evident that the spacecraft had grown too heavy for their Proton launcher and it was thus decided to discard the atmospheric capsule and attempt a "simple" three months orbiting mission.
The two 4,850 kg M-69 probes were transported to the Tyuratam range in January of 1969. It was a particularly cold winter and to further exacerbate this the explosion of the first huge N1 lunar rocket, on 20 January, shattered the windows of all of the buildings within a range of many kilometers. The development of the probes was all but complete, so much so that it had to be completed directly at the cosmodrome. Moreover the programme suffered from the fact that it did not have a sufficiently high priority with respect to the human lunar exploration programme and to the lunar automatic exploration programme. One of the Lavochkin lunar probes was prepared for launch inside the same building were the M-69 spacecraft were being readied.
Eventually, consensus was reached among the engineers that the probes had very little chance of successfully completing their missions.
The M-69 mission eventually envisaged first of all the Earth parking orbit insertion of the probes and then the inertion into a very eccentric Earth orbit thanks to the Proton fourth stage, called stage D. A firing of the on-board engine would then send the probes to Mars. During the six months interplanetary cruise the probes would be stabilized spinning around an axis perpendicular to the solar panels and directed toward the Sun. A first course correction would be carried out forty days after launch, reducing the uncertainty of the Mars encounter distance to 10,000 km. The second correction, ten to fifteen days before the encounter, would reduce the uncertainty to some 1,000 km. For course corrections, as well as for the orbital mission proper, the spacecraft would be three-axis stabilized. After reaching the red planet the spacecraft would enter very similar orbits, with 40 degrees inclination, twenty-four hours period, periastron at 1,700 km and apoastron at 34,000 km. After a preliminary phase the orbit would be lowered to 500 km from the Martian surface for the imaging mission. The other objectives of the mission were the study of the atmosphere with both the scientific instruments and a series of radiooccultation experiences.
The first M-69 was launched on 27 March, the same day as Mariner-7, with insertion into the Mars orbit expected on September 11. The third stage fuel pump however, seized and caught fire. 436 seconds after launch the engine stopped and the debris of the probe reentered over the Altai mountains. The second M-69 was launched on April 2 (with orbit insertion expected on 15 September) for an even shorter flight: after just two hundreds of second one of the six first stage engines exploded and forty-one seconds later the whole rocket crashed some three kilometers from the pad, causing a small environmental catastrophe with its toxic and corrosive propellants.
According to the Soviet engineers themselves, destiny had saved the probes from the unavoidable failure of their missions.

Bibliography
Lantranov, K., Hendrickx, B.: Mars-69: the Forgotten Mission to the Red Planet; Quest, vol. 7, No. 2, pp. 26-31
Perminov, V. G.: The Difficult Road to Mars; Washington, NASA
Siddiqi, A. A.: Deep Space Chronicle; Washington, NASA
1969 Mars Proton booster launch explosions. VideoCosmos Website

For questions, suggestions and comments you can email me

Back