What it was: A large nuclear-powered space station, in the 220-250 tonne range, that would be the main part of a “cloud station”—a set of orbital installations that would define the USSR’s presence in space during the late 1970s and into the 80s.
Details: Sergei Korolev was surprisingly uninterested in landing on the Moon (an attitude he shared with his counterpart Wernher von Braun). Doing so was just a small step in a chain that ran orbit-space station-lunar flyby/landing-Mars landing. He got the laurels on the first link, and of course no-one got the last link, so that leaves the station in low Earth orbit.
Korolev sketched out his first space station in the late 1950s. By 1961 this had grown into the TKS (the acronym for “Heavy Space Station” in Russian) and was to have been lifted by the N1 as that rocket was conceived at that early stage. This station was built around 50-ton modules, a core feature that would last through various redesigns and upgrades for more than a decade to follow.
As an attempt to get the Soviet military on his side, the first redesign came in spring of 1962, when TKS became the OP (Orbitalnky Poyas, or “Orbital Belt”), a name which hints at where Korolev’s thinking was going. Yes, it would be a military station, supporting spaceplane strikes on an enemy during wartime, but it would also be part of a belt of space stations—rather than being an independent piece, the Chief Designer was coming around to the idea that a large space station could be the headquarters of Russian orbital operations. From this point on Korolev’s stations became more and more embedded in a group of hardware and procedures that would make an integrated whole.
While OP was too ambitious, Khrushchev became interested in the general idea and approved the nuclear-armed, Soyuz-serviced, single-module OS-1 in September 1962. It had reached the mock-up stage by 1965 when the 1964-65 shakeup of the Soviet space program resulted in the USSR’s commitment to a lunar landing. The N1 was repurposed to that end and work on a large Soviet station stopped. Vladimir Chelomei got his (much smaller) Almaz instead.
OKB-1 never did give up, though, and after Vasili Mishin took over following Korolev’s death in early 1966 they kept pushing forward proposals. By then the OS-1 had evolved even further into what is sometimes called the TOS, once again based around a single 50-ton module. It’s unclear how far the station itself got—it seems not to have got off paper this time, though there are some hints that the final two N1 test flights had an aerodynamic mockup of the station’s main module on it (a borderline conspiracy theory has it that they were working modules). Whatever they were, they were both blown to pieces when their boosters failed.
Somewhat more interestingly from a long-term perspective, the TOS was part of an ambitious plan called MOK—the “Manned Orbital Complex”. Its intention was to amalgamate all the lines of Soviet space development, rationalizing them and defining their purposes closely so that as much as possible could be squeezed out of the hardware they’d already developed while keeping costs down by avoiding new hardware as much as possible. The station was the keystone of this arch, but there were other commitments. Among these were Soyuz derivatives for ferrying crews and supplies, semi-autonomous manned stations for scientific research (including one called Aelita for infrared astronomy and one called Gamma for gamma-ray astronomy), and eventually a single-stage-to-orbit spaceplane perched on an N1 lower stage called the N1-MOK. Work began on all of these in 1969 under Vitaliy Bezverby and really got underway in 1972.
While the complex evolved, the space station was swapped out one more time and replaced with a more ambitious one called MKBS (“Multi-Module Orbital Base”). Weighing in at about 250 tonnes (which is to say, twice the size of Mir, and about 60% of the size of the ISS), the station would have consisted of two main modules lifted by an N1 apiece, and several smaller components launched aboard smaller Proton rockets. It would have eight docking ports for Soyuz crew and supply craft and to act as berths for spacecraft headed elsewhere on semi-autonomous missions; essentially the MKBS was intended to be the first orbiting spaceport. Anywhere from six to ten cosmonauts would live aboard, with three at a time swapping in and out in overlapping schedules.
The MKBS had a number of unusual details that top even the ISS. First, it would have had a section equipped with artificial gravity: two Salyut-like modules attached to the end of long booms that would rotate around the central axis of the station. Second, it would have been nuclear powered, with a small (200 kW) reactor located at the end of three long pylons trailing aft of the main body of the station. This is quite a lot of power, especially considering that the MKBS would have also had two solar panels providing about 14kW of additional electricity; the ISS gets by on about 30kW in total. While some of this would have been used to power an electric ion engine that would have helped with station keeping, it’s worth pointing out that the most powerful ion engines are only just reaching 200kW in the early 21st century. This excess capacity of the reactor led some sources to suggest that the station would have a third remarkable detail: it would be armed with a particle beam weapon for defense, though it’s difficult to see how one would aim something large enough to be useful without rotating the entire station.
Its orbit was never quite settled. One option was to put it at about 51 degrees inclination, somewhat like the ISS, so that it could be accessed easily from Baikonur. The other was to put it in a polar orbit so that it would pass over every part of the earth, thus making it particular useful for reconnaissance. That orbit’s height and exact inclination could also be selected so that the station would precess around the Earth once per year (and so be able to keep its solar panels in the sun 24/7 every day of the year).
What happened to make it fail: Like so many Russian plans of the late 60s and early 1970s, it depended on the success of the N1. When OKB-1 was taken away from Vasili Mishin and given to Valentin Glushko in 1974, the N1 was cancelled and so it became impossible to lift the MKBS’ two main modules. Soviet space station efforts would be focused on the DOS-based Salyut and Almaz, which would eventually lead to the small-module method used to build Mir.
What was necessary for it to succeed: First it needed the N1. But even if the N1 had successfully flown, the MKBS would have had to make it through the other major watershed in Soviet spaceflight during the 70s: the start of the Tenth Five-Year Plan in 1976. That time was used as an opportunity to shake up and refocus the USSR’s space program on military uses. The MKBS would have avoided being folded into Chelomei’s already-flying Almaz station only if the initial stages of the MKBS had made it into orbit by then—and to make it by that year there would have had to be no delays. As it was, even that alternative work got put on the backburner: Mir was authorized in 1976 but ended up underfunded and shunted into the background until Energia and Buran were well underway. It took until 1986 for the smaller Mir, based on technology that was already underway by 1970, to make it into the skies. If MKBS had been selected over Mir, it would have taken years more than that to build and eventually run up against the economic collapse of the Soviet Union.
So MKBS had a tough row to hoe even with a working heavy launcher. Any delay at all would have had Chelomei’s approach validated and a pathway to Mir and then Mir-2 beckoning to the Soviet leadership. Its only chance for existence would have come down to flying through the tiny hole bounded by a successful N1 starting in, say, 1975 and the spring of 1976.
That’s not to say that the MOK as a whole failed, however. The Gamma station was eventually flown as an unmanned satellite in concert with the French in 1990. Soyuz ferry craft were designed and flown according to plan, and so were Almaz-derived Progress supply ships—they just flew to Mir and ISS. Only the N1-MOK never made it anywhere near completion, and even today Energiya still tries to get Kliper, a spaceplane not a little like it, up and running despite a severe shortage of funds. In a sense, MKBS was just arrived at by a different route, following Chelomei’s space station path after it was chopped off and grafted to the stationless MOK plan. That in turn was then grafted on to the ISS’ development, and goes a long way to explaining why what is largely an American station has its crews arrive in Russian spacecraft.