The final version of the 11K77 was approved by a government decree released on 16 March 1976, which set the maiden launch for the second quarter of 1979.
Zenit on the pad at Baykonur. Crew access tower is still in place (source: Russian Space Agency).
However, the project soon ran into substantial delays, mainly due to development problems with the RD-170/171 engines, highlighted by the explosion of a Zenit first stage at the test stand of NHkhimmash in June 1982. The switch to the single-chamber MD-185 engines considered for Energiya was also weighed for Zenit. Eventually, Zenit made its maiden flight on 13 April 1985, almost six years later than originally planned (see Chapter 6).
Original specifications for the 11K77 were to launch payloads into orbits with inclinations between 46° and 98° from both Baykonur and Plesetsk. The Zenit used highly automated launch facilities developed by the Design Bureau of Transport Machine Building (KBTM). These enabled several rockets to be placed on standby and be launched in quick succession. The idea was that the Zenit could swiftly replenish constellations of military satellites in case of an impending conflict or if some of them were knocked out by the enemy. Two launch pads were built at Baykonur. Construction of a Zenit pad at Plesetsk got underway in 1986, but the work was suspended in 1994 and the pad is being rebuilt for the Angara rocket family.
The vast majority of Zenit launches have carried KB Yuzhnoye’s Tselina-2 electronic intelligence satellites, placed into 850 km circular orbits inclined 71° to the equator. Actually, the Tselina-2 satellites are far underweight for Zenit, having been originally developed for launch by the lighter Tsiklon-3 rocket and then reoriented to Zenit because of slight increases in dimensions and mass. This was also the case for the Resurs-O1 and Meteor-3M satellites, originally built for launch by the Soyuz and Tsiklon-3 rockets. Most of the payloads really tailored for Zenit never flew as a result of the break-up of the Soviet Union in 1991, which not only led to a major economic crisis but also turned Zenit into a Ukrainian booster. Exceptions were two heavy photoreconnaissance satellites launched in 1994 and 2000 and the Okean-O ocean-monitoring satellite orbited in 1999.
From the outset Zenit was also developed as a man-rated launch vehicle with the necessary built-in redundancy and safety features. In the late 1980s NPO Energiya designed a Zenit-launched vehicle called Zarya (“Dawn”), which outwardly resembled an enlarged Soyuz descent capsule. A relic of those plans is a crew access tower still in place at the Baykonur Zenit pad. Zenit was also supposed to launch a variety of cargo ships and modules to Mir-2 and later to the International Space Station, but those plans were abandoned in 1996.
Compounding the problems for Zenit were three back-to-back launch failures that the rocket suffered in the 1990-1992 timeframe. The first of these resulted in the rocket crashing back seconds after lift-off, completely devastating one of the two Baykonur Zenit pads, which still lies in ruins today. But, while the end of the Cold War spelled bad news for Zenit as a domestic launch vehicle, it opened up new frontiers for its use in international programs. The first such opportunity arose in 1989, when Glavkosmos signed a deal to launch Zenits with Blok-DM upper stages from Cape York in Australia. Located on the east coast of Australia’s northernmost peninsula just 12 degrees south of the equator, Cape York was ideal for due east launches over the Pacific Ocean to place communications satellites into geostationary orbits.
Zenit-3SL lifts off from its ocean launch pad (source: Sea Launch).
A three-stage version of the 11K77 had already been envisaged for Soviet domestic missions by the original March 1976 government decree on Zenit. Although the Blok-DM had been considered from the outset, KB Yuzhnoye had preferred an upper stage with storable propellants (nitric acid and dimethyl hydrazine) plus an additional solid-fuel apogee kick motor, together capable of placing 1.3-ton payloads into geostationary orbit from Baykonur (compared with 1 ton for the Blok-DM). However, the use of the toxic storable propellants was considered unacceptable for launches from Australian territory, leaving Yuzhnoye no choice but to revert to NPO Energiya’s Blok-DM. Eventually, the Cape York plan fell through because of a lack of investor support.
The big break for the Zenit came in May 1995 with the official establishment of Sea Launch, a joint venture between KB Yuzhnoye, RKK Energiya, Boeing, and Kvaerner to launch three-stage Zenit rockets (Zenit-3SL) with Blok-DM upper stages on commercial satellite deployment missions from a converted Norwegian oil rig near the equator. Initial studies of sea-launched versions of Energiya, Energiya-M, and Zenit had been conducted at NPO Energiya in November 1991-December 1992 because of uncertainty over the future use of the Baykonur cosmodrome and rocket stage impact zones in independent Kazakhstan. Realizing that such a venture would require foreign investors, NPO Energiya officials pitched the idea of a sea-launched Zenit or Energiya-M to Boeing during a visit to the company’s Seattle headquarters in March 1993, with the final choice falling on Zenit in July 1993. Unknown to most of the parties involved (even Energiya), KB Yuzhnoye itself had studied sea-launched versions of Zenit together with KBTM in 1976-1980 under a research program known as Plavuchest (“Buoyancy’’). This would have seen the use of two catamaran-type vehicles, one acting as a launch pad and the other as a command center and storage facility for as many as five Zenit rockets with hypergolic upper stages. Many of the ideas worked out under Plavuchest were later incorporated into Sea Launch.
Sea Launch saw its inaugural mission on 27 March 1999 and has since averaged three launches per year, securing a solid place in the international commercial launch market. The company did suffer a significant setback on 31 January 2007, when one of its rockets exploded during lift-off. Although the launch platform escaped relatively unscathed, the commercial implications of this accident are as of yet unclear.
Significant differences between the heritage Zenit and the Sea Launch version were a new navigation system, a next-generation flight computer, and increased performance by mass reductions. The propulsion system remained essentially unchanged. Originally, the hope was to use an improved first-stage engine called RD-173 on which Energomash had begun work in the second half of the 1980s. This engine delivered 5 percent more thrust than the RD-171, had an improved turbopump assembly, and a modernized guidance and control system. Experimental versions of the engine underwent static test firings between 1990 and 1996, but further testing was suspended for financial reasons.
With the production line for the standard RD-171 closed due to a lack of state orders, Energomash had no other option but to modify existing RD-170 Energiya engines for use in the Sea Launch program. In 1996-1997 a total of fourteen RD-170 engines were “cannibalized” from mothballed Energiya strap-on boosters and shipped back to Energomash for modification. This batch was enough to ensure several years of Sea Launch operations, but eventually Energomash returned to its RD-173 plans. The modified engine, now redesignated RD-171M, has the same thrust as the RD-171, but is 200 kg lighter and has an improved guidance and control system. Testing started in 2004 and the engine made its debut in February 2006. In May 2004 Sea Launch also introduced a slightly improved RD-120 engine for the second stage (93 tons of thrust vs. 85 tons for the earlier version). Further performance improvements may be achieved by adding suspended propellant tanks to the first stage.
In late 2003 the Sea Launch Board of Directors resolved to go forward with plans to offer launch services from Baykonur in Kazakhstan, in addition to its sea-based launches at the equator. An earlier attempt by Yuzhnoye to commercialize the two-stage Zenit from Baykonur had ended with an embarrassing launch failure in 1998 in which 12 Globalstar satellites came tumbling back to Earth minutes after liftoff. The new offering, Land Launch, is based on the collaboration of the Sea Launch Company and Space International Services (SIS) of Russia to meet the launch needs of commercial customers with medium-weight satellites. The Land Launch Zenits will have the same modifications as the Sea Launch version and can fly in a two-stage configuration for launches to low and elliptical orbits and with three stages to geostationary orbits .