Soviet Union, just before collapse, possessed impressive military power - ICBM missiles, warships, bombers, tanks. Generally in terms of size Soviet Army exceed NATO forces multiple times. American cure for this fact was increasing quality of weapon to rectify superiority in the matter of size. Crowning achievement was to become the program of Strategic Defense Initiative - SDI.
After official announcement in 1983 SDI quickly became a problem for Soviet government. This weapon was shock for both allies and enemies of USA. It was denying basic paradigms of Cold War. Firstly, mutual assured destruction was not working in case possessing by USA fully operational SDI system (it was planned for year 2000). Second, it was confirming USA supremacy in military industry, and pushed USSR to second place. Since seventies, armaments race was rather balanced. USSR military power was in assumption always based on size not quality. It was changing from late seventies. New strategic bomber comparative with American B1B Lancer - Tu160 was designed in late seventies and started being manufactured in 1984. New Typhoon class submarines designed for silent reaching coasts of USA were developed. But in the half of eighties it seemed that USSR is delayed with modern technologies. B2 bomber developed in the eighties had not any competitor in Soviet Air Forces. American antisatellite weapon was put into mass production - ASM-135 missile was operational since 1984 was able to destroy Soviet satellites being launched from conventional F15 Eagle fighter. Modern tanks like M1 Abrams were developed and upgraded with new types of amour preventing from being destroyed by any modern Soviet tank. It became clear that SDI program will strength position of the USA and will make Soviet nuclear arsenal installed on ICBM quite useless. Of course, large amount on warheads were installed on missiles launched from submarines or bombs and maneuvering rockets dropped from bombers. But submarines and bombers could be stopped before before they would reach a distance of guaranteeing the effective destruction of targets. Another problem was fact that USSR was mainly relying on ICBM as a main carrier of nuclear weapon. It became crucial for USSR to prevent SDI operating in every possible way.
Strategic Defense Initiative was planned to base on observation satellites detecting possible launch of ICBM, satellites equipped with rocket launchers, lasers and launchers of kinetic missiles to destroy ICBM over enemy's territory, ground launchers and lasers for destroying missiles which passed through space part of the system and ground control systems. For Soviet strategists, destroying ground systems was less possible (actually it was only possible with utilization of sabotage). Destroying space part of SDI was easier to perform - but still Soviet Union was not in possession such weapon. Buran space shuttle was still under development and it was clear that it will not be sufficient solution. Space shuttles or space planes (like MiG-105) were considered as space interceptors but they were not able to stay on orbit for a long time. Utilizing antisatellite missile launched from jet fighter would be sufficient, but in spite of Vympel antisatellite missile, which was still under development (in 1986 two MiG-31 jet fighters were modified for further tests of the Vympel), there was no such system available. Soviet way of developing antisatellite weapon was previously rather focused on manned battle space stations like Almaz or offensive satellites like IS (Istrebitel Sputnik) system. Other attempts, like building ground laser to blind satellites was developed but still they were in early phase. In spite of fact that IS satellites started to be operational in 1974, their possibilities were limited. IS satellite had to reach for about 1 km to other satellite to explode and destroy target. Satellite could be used only once, so destroying couple enemy spacecrafts by one IS satellite was not possible. Finally IS program was halted by Yuri Andropov in 1983, just before starting tests of ASM-135 in the USA. After starting SDI program, leadership of Soviet Union decided about starting developing new antisatellite system. NPO Energia Design Bureau was chosen due its engagement in developing counter ICBM weapon since half of seventies. Basing of previous experiences, NPO Energia prepared, in the beginning of the eighties, proposition of antisatellite weapon to fill the gap after cancelling Almaz program and IS program. New weapon was designed to be used before attacking enemy with ICBM, with main objective of destroying SDI satellites. New spacecraft was called Polyus and it was designed as large satellite with weight at 80000 kg, length at around 37 m and diameter at 4.1 m. It consist two modules; first smaller module was called service block. It was very similar to Salyut space station. To reduce time and costs it was built with wide usage of parts from various spacecrafts (Cosmos-929, Cosmos-1267, Cosmos-1443, and Cosmos-1668) and from modules of MIR space station. Module consisted antennas, telemetric control, onboard computers, transponders and heating system. Also two deployable solar panels were attached to service module. Second module was larger and was equipped with defense cannon and nuclear mine dispenser (with special anti-recoil system), laser reflector for blinding satellites, and one 1-megawatt carbon-dioxide laser for destroying enemy spacecrafts. Whole Polyus (called also Skif-DM) was designed to be lift on Energia rocket (same as used for Buran shuttle). Here is another interesting fact. Polyus was designed to be lifted upside-down. After separation, maneuvering engines would rotate spacecraft for 180 degrees and inject into correct orbit. Whole spacecraft was painted with special black paint absorbing radio waves which was considered as an element of stealth technology (or to make spacecraft harder to detect with optic sensors). Propulsion of the Polyus was four main engines, twenty stabilizing engines and sixteen precision engines.
First flight of Polyus was planned on 15th May 1987. To keep it in secret, it was called officially "research satellite for scientific experiments in upper atmosphere". Due the problems with fuel valve, lift off was postponed from 03:00 PM to 08:30 PM. After successful ignition and releasing suspending arm, Energia started to lift off. Rocket started to lean left, but onboard computers were able to stabilize rocket before anything wrong happened. After planned 460 seconds of flight Energia reached 110 km altitude and separated from Polyus. Unfortunately only one of 16 engines of Polyus ignites correctly, and on T+512 s rotating spacecraft for 180 degrees started. Unfortunately engines responsible for rotating Polyus did not stop and rocket started to fly into the Earth. It crashed close to place where second stage of Energia fall - in the Pacific Ocean.
Polyus was amazing project in some aspects closer to science-fiction than to reality. Using laser for destroying satellites was reasonable, but idea to use space nuclear mines was rather crazy then reasonable. It is not hard to imagine what kind of results would give accidently explosion of nuclear space mine or not intentional reentry spacecraft filled with nuclear bombs onboard. Dimensions of spacecraft were enormous - it was rather impossible to avoid detecting Polyus during moving to target, even with utilizing stealth technology (still spacecraft with working thrusters is easy to detect). Engaging resources and money for concept from sixties was not rather reasonable - probably more economical and effective would be designing antisatellite missile launched from jet fighters, or continuing development of ground lasers blinding enemy satellites like weapons tested in Terra-3 facility in Kazakhstan. It seems that Polyus was rather temporary solution built with available technologies for cost cutting. Still it remains last antisatellite weapon developed in USSR.