Making Energiya reusable

The ultimate dream of the Energiya designers was to develop a rocket that would be fully reusable (Energiya-2 or GK-175). The plan was to achieve full reusability in various steps, first of all by having the strap-on rockets parachute back to Earth for recovery. In the next step the core stage was to be turned into a reusable winged stage with three RD-0120 engines and a payload compartment in the upper section. Despite the lower amount of propellant, the overall dimensions of the core stage remained the same, freeing up some 610m3 of volume in the payload section, which compared favorably with the 350m3 offered by Buran’s cargo bay.

The massive nose fairing would not separate during ascent, but open in space, somewhat like the forward cargo door of a Lockheed C-5 transport aircraft, allowing it to be reused on subsequent flights. After deployment of the payload (30 to 40 tons), the fairing would slide down over the LOX tank so that the core stage would shrink in size from 60 to 44 m to prevent stability problems during re-entry. In order to cut costs, the core stage would inherit as many systems as possible from Buran (wings, vertical stabilizer, landing gear, avionics, and hydraulic systems). It was not con­sidered expedient though to cover the stage with Buran’s heat-resistant tiles and efforts focused instead on using innovative non-ablative and active cooling thermal protection systems.

The next phase was to replace the standard strap-ons by the same type of flyback boosters being envisaged for Energiya-M. The parachute recovery system imposed a

heavy weight penalty on the rocket, the impact zones limited the number of launch azimuths, and recovery from those distant impact zones would have been a laborious and costly undertaking. The flyback strap-ons would be equipped with long foldout wings, a V-shaped tail, and a small jet engine enabling them to fly back to the launch site after separation from the core stage. Although the idea was tempting, the landing of four strap-ons in quick succession on the single Baykonur runway would probably have caused tremendous logistical problems.

In the final step the four flyback strap-ons would be replaced by a first stage equal in size to the second stage and with similar landing systems, but without thermal protection, and equipped with four RD-170 engines. This vehicle would have a payload capacity of between 30 and 50 tons. By using two such first stages it would be possible to increase payload capacity to 200 tons, about the same as the Vulkan with its eight strap-ons. There was even an idea to use four of the large first stages and lengthen the second stage to reach a phenomenal payload capacity of 500 tons. Despite the impressive prospects, any of those three variants would probably have required major modifications to the existing Energiya launch facilities.

Not surprisingly, all these bold proposals faced an uphill battle as the budgets for the space program became ever tighter towards the end of the 1980s. The only spin-off from the Energiya-2 studies is Baykal, a reusable flyback booster now being proposed as a first stage for the Angara rocket family. This incorporates many ideas that had originally been conceived for Energiya-2’s flyback strap-ons [67].