Energia

Energia was a 7.75 metre hydrogen core with four boosters strapped around it, roughly 34,800 kilonewtons at sea level and 100 tonnes to low orbit. No source states that liftoff figure directly; it is the published booster and core numbers added together, and the booster half is corroborated by the RD-170 rating of 740 tonnes-force per engine.

It was a better piece of engineering than the vehicle it was answering. The Shuttle put its main engines on the orbiter, which meant the orbiter had to fly on every mission whether or not the payload needed wings. Energia kept the engines on the rocket and hung the payload on the side, so the same launcher could carry Buran or carry anything else. The Soviets built the general-purpose heavy lifter that NASA had talked itself out of.

The first flight in May 1987 carried Polyus, an orbital weapons testbed that the rocket delivered correctly and that then failed to insert itself because its own attitude control fired the engine the wrong way. The second, in November 1988, put Buran into orbit and brought it back to an automatic landing at Baikonur, uncrewed. Nothing else has done that since.

It was ruinous. The cited figure is 764 million dollars a launch in 1985 money, more per flight than a Shuttle mission, for a vehicle with no payloads waiting for it and no economy able to pay for the ones that were proposed. The programme was cancelled in 1993 with five completed vehicles in storage.

The engines outlived the rocket, and this is the part that matters. The RD-170 is still the most powerful liquid rocket engine ever flown. Its half-sized descendant, the RD-180, went on to power American Atlas V launches for two decades, which means the Soviet Union built a super-heavy lifter it could not afford and accidentally built the United States a first stage engine supply.