The Zenit rocket has successfully conducted what is likely to be its final flight Friday, successfully delivering Russia’s Elektro-L No.2 weather satellite into orbit following a lengthy flight. Liftoff occurred at 19:45 local time (13:45 UTC) from the Baikonur Cosmodrome in Kazakhstan.
The launch of Elektro-L No.2 was the first outing for a Zenit in eighteen months, following last May’s deployment of Eutelsat 3B via a Sea Launch Zenit-3SL flying from the Odyssey launch platform.
Although two further Zenit launches are currently scheduled, doubts surround both of these and the only other completed Zenit vehicle remains at Baikonur having exceeded its design lifespan.
Primarily a Ukrainian vehicle, tensions between Russia and Ukraine make it unlikely that any further vehicles would be manufactured, so Friday’s mission will probably become the rocket’s final flight.
The Zenit – which is the last surviving member of the same family of rockets and shared significant hardware with the Soviet Union’s ultra-heavy Energia vehicle – evolved from a program which began in the Soviet Union in the 1970s to develop a new fleet of rockets to replace the older designs then in service – including the Soyuz and Proton which remain in service today.
The medium-capacity design, which would later become the Zenit-2, was authorised to begin development in 1976. The Zenit-2 was the initial two-stage version of the Zenit, designed to place satellites into low Earth orbit, while a single-stage version was developed alongside it as a liquid rocket booster for the much larger Energia vehicle.
The Zenit-2 made its maiden flight in April 1985 – three years behind schedule due to delays in the development of the RD-170-series engines that would power it – however the test launch was unsuccessful. An RD-170 engine powered the single-stage Zenit while an RD-171 was used for the standalone multi-stage vehicles.
In June 1985 another Zenit lifted off on what was intended to be another suborbital test launch, however some objects from the launch briefly achieved orbit. This paved the way for the first intentionally orbital launch in October 1985 carrying a mass simulator for the Tselina-2 electronic intelligence satellite, Kosmos 1697.
The first Zenit launch with a live payload occurred in December 1985, however a second stage malfunction resulted in Kosmos 1714 being placed into an unusable orbit which decayed after a few months.
Equipped with four single-stage Zenit boosters, the Energia made its maiden flight in May 1987 carrying the Polyus experimental military satellite.
This launch was unsuccessful, with the spacecraft’s propulsion system – serving as the final part of the launch system after Energia separated from the satellite on a suborbital trajectory – ignited with the spacecraft in the wrong orientation and failed to circularise its orbit.
The loss of Polyus, one of the largest satellites ever launched, was attributed to a programing error in the rocket’s guidance system that caused it to rotate through 360 degrees rather than the 180 degrees that had been planned after spacecraft separation.
A second Energia launch, eighteen months later, successfully carried the Buran spaceplane on the first leg of its only mission.
Early Zenit launches took place from a single launch pad at the Baikonur Cosmodrome, Site 45/1. Construction began on a pad at the Plesetsk Cosmodrome for polar orbit launches, however this was later abandoned.
The uncompleted pad, Site 35/1, was eventually rebuilt for the Angara rocket and saw its first launch last July. A second pad at Baikonur, 45/2, opened in May 1990. During the very next launch, less than five months later, the first stage engine failed five seconds into flight.
The Zenit fell back onto the launch pad and exploded, destroying the newly completed complex. The second pad was never rebuilt, with all further Zenit launches – other than those flown through the Sea Launch program – departing from Site 45/1.
When the Soviet Union was dissolved, the PA Yuzhmash production facility and Yuzhnoye design bureau became part of Ukraine. With the newly-formed Russian Federation unwilling to rely on a now-foreign rocket for access to space, combined with a spell of poor reliability that the rocket had been going through, the Zenit fell out of favour. Around the same time, the Energia program was cancelled due to political and financial factors.
Zenit launches continued through the 1990s, mostly carrying Tselina-2 satellites. The Zenit also became part of Russia’s entry into the commercial launch market, with the type’s first commercial launch occurring in September 1998.
A Zenit-2 rocket lifted off from Baikonur carrying twelve Globalstar communications satellites, however a fault in the rocket’s guidance system shut the second stage engine down ahead of schedule and the vehicle failed to achieve orbit.
Another attempt to commercialise the Zenit was the Sea Launch consortium, formed between Boeing, RKK Energia, Yuzhnoye, Yuzhmash and Kvaerner Maritime of Norway in 1995. Geared towards geosynchronous launches, the Sea Launch venture saw the development of a three-stage Zenit, the Zenit-3SL, which added a modified Blok-DM upper stage to the vehicle as well as making upgrades to the core vehicle.
This first flew in March 1999 with a demonstration payload, before carrying the DirecTV-1R satellite into orbit in October of the same year.
Sea Launch missions were flown from the Odyssey launch platform, a converted oil rig based out of Long Beach, California.
Prior to launch the platform would sail to the equator, allowing the rocket to launch due East into a zero-inclination orbit, reducing the amount of fuel expenditure needed to reach geostationary orbit. Between 1999 and 2014, thirty-six Zenits were launched from Odyssey – with three failures and a partial failure.
Despite success in the early-mid 2000s, Sea Launch never recovered from a January 2007 failure when a Zenit-3SL carrying the NSS-8 communications satellite exploded on the launch platform.
It took almost a year to resume launch operations, with payloads switching to other providers.
Following the 2014 launch of Eutelsat 3B, Sea Launch entered a hiatus due to lack of launch contracts and laid off staff. While the company has not yet called time on its launch operations, it is reported to be selling off assets and looks unlikely to resume Zenit launches, leaving the land-based Zenits the last of their kind.
Between 2000 and 2007 only five Zenits launched from Baikonur – with the last three Tselina-2 spacecraft, the Meteor-3M No.1 weather satellite and an Orlets-2 reconnaissance satellite. The 2007 launch marked the debut of a modernised Zenit-2M vehicle incorporating upgrades from the Sea Launch program.
The following year, Land Launch – a subsidiary of Sea Launch carrying out missions from Baikonur – made its first launch with a new Zenit-3SLB configuration. The first launch resulted in a partial failure, with the Blok-DM upper stage underperforming; however it was followed by five successful launches between 2009 and 2013 that were performed initially by Land Launch and later by Space International Services.
The final Zenit configuration to be introduced was the Zenit-3F, another three-stage vehicle but with a Fregat-SB upper stage in place of the Blok-DM used on the 3SL and 3SLB. This was first used for the launch of Elektro-L No.1 in January 2011, as well as to deploy the Spektr-R radio astronomy satellite later in the year. The only Zenit configuration currently flying, it is the Zenit-3F which will be used for Friday’s launch.
November 2011’s launch of the ill-fated Fobos-Grunt probe to Mars and its moon Phobos made use of a modified Zenit-2M that incorporated the second-to-third-stage adaptor of the Zenit-3F to accommodate its Fregat-derived payload.
Friday’s launch was the eighty-third for the Zenit as a stand-alone rocket, although if the Energia flights are included it is the eighty-fifth Zenit flight and the ninety-first vehicle to fly – each Energia having incorporated four Zenit-derived boosters. The mission was the third for the Zenit-3F configuration.
The Zenit’s first stage is powered by an RD-171M engine, a modernised version of the RD-171 which was introduced with the Zenit-2M and 3SLB configurations in the mid-200s and which is the most powerful liquid-propellant rocket engine ever flown.
Burning refined petroleum fuel (kerosene in the United States or paraffin in the UK and elsewhere) in liquid oxygen, the RD-171M is a four-chamber engine generating 7.4 meganewtons (740 tonnes-force, 1.7 million pounds-force) – almost ten percent more thrust than the F-1 engines which powered the American Saturn V.
This engine is only used by Zenit, so if Friday’s launch was the Zenit’s final flight it will also mark the end of the RD-170/171/M’s service.
Several derivatives of the RD-170 series are still flying; United Launch Alliance’s Atlas V uses a two-chamber version, the RD-180; a single-chamber RD-181 is under development to replace the NK-33 currently flown on Orbital ATK’s Antares.
An RD-190 series has also been spun off of the RD-170 for future Russian vehicles, including the RD-191 for Angara and the RD-193 which may be intended as an NK-33 replacement on the Souyz-2-1v rocket. The Antares rocket’s first stage is also derived from the Zenit.
From liftoff, the first stage fired for approximately 145 seconds before separating to allow the second stage to take over. Igniting its RD-120 engine, this stage burned for six minutes and ten seconds to attain an initial parking orbit.
The third stage, a Russian-built Fregat-SB, performed three burns during a nine-hour ascent that injected Elektro-L No.2 directly into geosynchronous orbit. The first burn began around an hour and a quarter after liftoff, with the second and third burns about three and a half hours and eight and a quarter hours into the mission.
The Fregat uses an S5.92 engine, burning unsymmetrical dimethylhydrazine and dinitrogen tetroxide. In the Fregat-SB configuration, the long-nozzle version of this engine is used to increase the engine’s specific impulse – a measure of its fuel efficiency.
The SB version of the Fregat, which is only launched by Zenit, also features a toroidal drop tank to increase its propellant capacity. This will be jettisoned during the mission, once empty, to reduce weight.
With the launch successful, Elektro-L No.2 separated from the Fregat eight hours and fifty-two minutes after liftoff, into a near-geostationary orbit at 35,400 by 35,800 kilometres (22,000 by 22,200 miles or 19,100 by 19,300 nautical miles) and an inclination of 0.5 degrees. Slightly below geostationary altitude, this orbit will allow the spacecraft to drift into its planned operational position at a longitude of 77.8 degrees East.
Elektro-L No.2 is the second Elektro-L weather satellite to be launched by Russia. From geostationary orbit the satellite will observe the Earth as a disc, from a static position relative to the planet’s surface. Its mission is similar to that of the US Geostationary Operational Environmental Satellite (GOES) spacecraft, Europe’s EUMETSAT series and China’s Fengyun-II.
The satellite was constructed by NPO Lavochkin, and is based on the company’s Navigator satellite bus. It is a 1,740 kilogram (3,840 lb) vehicle which is expected to operate for ten years.
Following Friday’s launch two Zenit missions remain on Russia’s launch manifest.
These are the deployments of Ukraine’s Lybid communications satellite and Russia’s own Spektr-RG astronomy spacecraft.
With the Lybid launch in doubt due to political and military tensions between Russia and Ukraine, and reports that Spektr-RG may switch to a Proton, it is unclear whether the Zenit will fly again. Further Elektro launches, including one scheduled for next year, will be carried by Proton rockets.
The Zenit launch was Russia’s twenty-second of the year, and the first after the failure of a Soyuz-2-1v rocket last Saturday.
Despite reaching its planned orbit, the Soyuz failed to deploy its payload and its upper stage subsequently performed a deorbit burn with the Kanopus-ST satellite still attached, reentering the atmosphere three days after launch. A secondary payload separated from the upper stage successfully.
Worldwide, Friday’s launch was the seventy-eighth of the year, including three which failed to achieve orbit and February’s Vega launch which did not receive a satellite catalogue number or international designation despite briefly achieving orbit during a series of upper stage tests at the end of a successful suborbital primary mission.