UR-700M Credit - © Mark Wade

In 1969 the Soviet Union began project Aelita, studying the best method to beat the Americans in landing a man on Mars. Chelomei's team reached the conclusion that a Mars expedition would best be launched by an immense vehicle would allow their MK-700 Mars spacecraft to be orbited in two launches. The proposed UR-700M launch vehicle had a gross lift-off mass of 16,000 metric tons and could deliver 750 metric tons to orbit. By 1972 the Nixon administration had cancelled NASA's plans for manned Mars missions. Perhaps not coincidentally, a Soviet expert commission the same year concluded that the Mars project - and the UR-700M booster - were beyond the technical and economical capabilities of the Soviet Union and should be shelved indefinitely.

In 1962 Vladimir Chelomei proposed a family of modular launch vehicles. The UR-700 was designed for direct manned flight to the surface of the moon. While approval to proceed with development of the UR-500 came in April 1962, no such go-ahead was received for the UR-700. Studies continued however, and report index number 4855CC by TsNIIMASH in 1966 showed that any development of improved versions of the N1 would be practically equivalent to design and qualification of a new rocket, while the UR-700 modular approach allowed a range of payloads without requalification. UR-700 derivatives could better support the DLB lunar base, Venus/Mars manned flybys and Mars landing expeditions. Development of the UR-700 was approved on 17 September 1967. However no go-ahead to proceed past the design phase was forthcoming in 1968.

By January 1969, Chelomei was proposing the UR-900 for the Mars expedition. Chertok asked Chelomei what would happen if, God forbid, such a booster exploded on the launch pad. Wouldn't the entire launch complex be rendered a dead zone for 18 to 20 years? Chelomei's reply was that it wouldn't explode, since Glushko's engines were reliable and didn't fail. Aside from that, these propellants had been used in hundreds of military rockets, deployed in silos, aboard ships and submarines, with no problem. Fear of these propellants was irrational. Related propellants were used by the Americans on the Apollo manned spacecraft.

Less than three months later, on 2 April 1969, the unimaginable happened. A Proton rocket, one tenth the size of the planned UR-900, was launched in an attempt to send an unmanned probe to Mars. The leadership of the Soviet Rocket Forces and most of the Chief Designers were present for the event. The Proton rocket lifted off, but one engine failed. The vehicle flew at an altitude of 50 m horizontally, finally exploding only a few dozen meters from the launch pad, spraying the whole complex with poisonous propellants that were quickly spread by the wind. Everyone took off in their autos to escape, but which direction to go? Finally it was decided that the launch point was the safest, but this proved to be even more dangerous - the second stage was still intact and liable to explode. The contamination was so bad that there was no way to clean up - the only possibility was just had to wait for rain to wash it away. This didn't happen until the Mars 1969 launch window was closed, so the first such probe was not put into space until 1971.

This accident seems to have made a powerful impression on the military, and plans for a new generation of space launchers drawn up in the early 1970's specified use of non-toxic liquid oxygen and kerosene propellants. This also forced Chelomei to specify these propellants in the redesignated UR-700M for the Mars expedition.

By the middle of 1969, in the post-Apollo moon landing euphoria, NASA was pressing for funding for a manned expedition to Mars. Ministry of Defense decree 232 of 30 June 1969 authorized preparation of Soviet draft projects for a manned Mars expedition. Code named Aelita, the TTZ specification for the expedition was prepared by TsNIIMASH and NIITI. The TTZ called for a launch vehicle with a low earth orbit payload of 200 to 250 metric tons to be available by 1976. This vehicle would be used to support a Soviet lunar base, heavy military and civilian space stations, and a Mars expedition spacecraft of 1,500 metric tons mass.

Analysis of the requirement by Chelomei indicated a larger launch vehicle than that required by the TTZ would be optimum. Opportunities for launches to Mars had limited launch windows at two year intervals. The combined probability of successfully launching, docking, and assembling a half dozen payloads in low earth orbit was relatively low. The optimum chance for mission success was to use no more than one or two dockings in earth orbit (NASA came to a similar conclusion in the early 1960's, leading to the Nova launch vehicle studies). Chelomei used a modular approach to the launch vehicle design in order to achieve payloads of 300 to 800 metric tons. By the advanced project stage the MK-700 Mars spacecraft assembly sequence had been reduced to two variants:

• Variant 1, with 750 to 800 metric tons payload (2 launches, 1 docking to assemble Mars spacecraft)
• Variant 2, or PA, with 480 to 520 metric tons payload (3 launches, 2 dockings to assemble spacecraft)

Unit p/ya A-1233 of TsKBM determined that it would be possible to reduce the mass of the Mars spacecraft to 900 to 1,000 metric tons. This would allow the Variant 2 booster to be used with only one docking.

The design evolved considerably over the next three years. The preliminary draft project utilized the following design principles for the UR-700M:

• Expedition to Mars using a single docking in low earth orbit
• Packet scheme for launch vehicle, with first and second stages firing in parallel at launch, as in the UR-700
• Since engines of the thrust and reliability required were not available, engines would be clustered in each block with one reserve engine in the likely event of an engine failure. A total of 8 to 12 engines would be used per rocket block
• The rocket blocks would be modular and their sub-units would be completed at the factory. They would be transported by air (An-22) or water (Soviet national canal system) to a launch site on the Arkhangelsk Peninsula. This would limit the necessary transport investment to 150 million rubles and allow the transport systems to be used for other purposes when not transporting the rocket units.
• Extensive ground stand tests of all systems before flight

• Variant 1: Used a nuclear engine for trans-Mars injection. Payload in low earth orbit 1400 metric tons, requiring two launches.
• Variant 2: Used chemical propulsion for trans-Mars injection. Payload in low earth orbit 2500 metric tons, requiring four launches.

The UR-700M/LK-700 advanced project was reviewed by the expert commission in 1972. Their conclusions were:

• The problem of crew survival of the 650 day long trip to Mars had not been solved. 12 to 15 years of research aboard space stations in low earth orbit on the adaptation of the human organism to the weightlessness and radiation environment of space would be needed.
• The nuclear engines of 3.6 tf and 40 tf in the Mars-injection stage of the first variant were only in the draft project stage at that time. 15 to 20 years of development would be needed before they would be ready for use in manned spacecraft
• The radiation safety problem of nuclear propulsion had only been solved theoretically. Negotiations would be needed with the United States before international permission could be obtained to place large nuclear reactors in orbit.
• Without the use of nuclear energy, the spacecraft mass of 2500 to 3000 metric tons was too large to be practical.
• 30 to 40 billion rubles would be needed at 1973 prices to accomplish this project. No such sum was considered to be available.