Engine test firings

While the facilities of Nllkhimmash near Zagorsk allowed full-scale test firings of entire Blok-A modular sections to be carried out, there was no infrastructure at the site to do the same with the core stage. NASA’s method of testing the Space Shuttle Main Engines in a realistic structural environment was by mounting an Orbiter aft fuselage and a truss simulating the mid fuselage on an External Tank at the National Space Technology Laboratory (now the Stennis Space Center) in Mississippi and, ultimately, by firing the engines with the entire stack on the pad during the Flight Readiness Firings.

The Soviet approach to integrated testing of the RD-0120 was to fire all four engines with the core stage and strap-on boosters bolted to the UKSS test stand/ launch pad at Baykonur. For this purpose, two core stages were built, designated 5S and 6S. These were to undergo 17 test firings lasting a total of 3,700 seconds. All the engines involved in these tests had already been test-fired at the NIIMash test stands in Nizhnyaya Salda before being mounted on the rockets.

The 5S core stage, flanked by inert strap-on boosters, was rolled out to the UKSS on 23 January 1986. As the core stage was being prepared for the first test firing, other events were shaping the future of world space programs. America was in mourning following the loss of Challenger and its seven-person crew on 28 January 1986 and the Soviet Union successfully launched its Mir space station on 20 February. Two days after that landmark event, the 5S core stage was ready for an initial 17.8-second test firing of its four RD-0120 engines. However, just 2.58 seconds after ignition, as the engines were building up thrust, on-board automatic devices shut down all four engines due to high temperature readings in one of the gas generators.

Barely had ground controllers realized what had happened, when they found themselves faced with a problem of catastrophic potential. As the engines shut down, a leak occurred in the pneumatic lines that supplied helium to operate the rocket’s fill and drain valves, making it impossible to drain the core stage. Loaded with 600 tons of liquid oxygen and 100 tons of liquid hydrogen and with pressure in the cryogenic tanks gradually building, Energiya 5S was slowly turning into a bomb with an explosive potential of 450 tons of TNT. Ground controllers had no choice but to send a crew of volunteers out to the pad to hook up a back-up helium supply system to the rocket. Working in hazardous conditions under the launch table, they suc-

ceeded in finishing the job in just an hour’s time, allowing detanking operations to begin.

Subsequent analysis traced the cause of the helium leak to a damaged pipe measuring just 20 mm in diameter. As a result of the incident, back-up helium lines were introduced for future vehicles as well as additional means of controlling the valves electrically. The engine shutdown itself was blamed on a faulty low-pressure hydrogen pump in engine nr. 1, which had apparently been inadvertently damaged during repair work in the Energiya assembly building needed after the test firings in Nizhnyaya Salda. In the following weeks the pump was successfully swapped with

another one, an operation that had never been done on the pad before. On 25 April Energiya 5S was ready for another test firing, scheduled to last 390 seconds. This time all four engines operated flawlessly, throttling up and down as scheduled and going through a full gimbaling program. With Energiya virtually ready to fly, the focus shifted to pad tests of the entire Energiya-Buran system (see Chapter 7) [9].