Zenit (Ukrainian: Зеніт, Russian: Зени́т; meaning Zenith) was a family of space launch vehicles designed by the Yuzhnoye Design Bureau in Dnipro, Ukraine, which was then part of the Soviet Union. Zenit was originally built in the 1980s for two purposes: as a liquid rocket booster for the Energia rocket and, equipped with a second stage, as a stand-alone middle-weight launcher with a payload greater than the 7 tonnes of the Soyuz but smaller than the 20 tonnes payload of the Proton. The last rocket family developed in the USSR, the Zenit was intended as an eventual replacement for the dated Soyuz and Proton families, and it would employ propellants which were safer and less toxic than the Proton's nitrogen tetroxide/UDMH mix. Zenit was planned to take over crewed spaceship launches from Soyuz, but these plans were abandoned after the dissolution of the Soviet Union in 1991.

Many of components of the Zenit rockets were produced in Russia. The Ukrainian space industry was highly integrated with that of Russia due to its Soviet heritage, but that cooperation was interrupted by the Russo-Ukrainian War beginning in 2014, which has effectively led to a hiatus in the Zenit program.^[2] The subsequent Russian invasion of Ukraine in 2022 saw damage to its manufacturing facilities due to Russian missile strikes, and what survived those strikes pivoted to producing military weapons.^[3]

Zenit-3SL was launched by the Sea Launch consortium's floating launch platform in the Pacific Ocean and Zenit-2 was launched from Baikonur Cosmodrome in Kazakhstan. RD-171M engines of the Zenit's first and second stages as well as the upper stage of the Zenit-3SL rocket were supplied by Russia. An improved Zenit-3SLB rocket was used for commercial launches from Baikonur Cosmodrome beginning in April 2008, marketed as Land Launch.^[4]

Zenit-3SL was launched 36 times with 32 successes, one partial success, and three failures. The first failure, the launch of a Hughes-built communications satellite owned by ICO Global Communications, occurred during the second commercial launch on March 12, 2000, and was blamed on a software error that failed to close a valve in the second stage of the rocket. The second failure occurred on January 30, 2007, when the rocket exploded on the Odyssey launch platform, seconds after engine ignition. The NSS-8 communication satellite on board was destroyed.^[5]

On September 24, 2011 Zenit-3SL launched successfully from the Odyssey launch platform under a renewed Sea Launch project with RSC Energia as the majority stakeholder. The rocket delivered the European communication satellite Atlantic Bird 7 to its planned orbit. On February 1, 2013, another Zenit-3SL failed while launching the Intelsat 27 satellite.^[6]

The Zenit-2 was the first Zenit to be designed for use as an orbital carrier rocket. It consists of two stages. The first uses an RD-171 engine, and an RD-120 engine powers the second stage. It first flew on 13 April 1985, two years before the Energia, due to delays relating to the Energia's development.^{[citation needed]} Zenit-2 would be certified for crewed launches and placed in specially built launch pad at Baykonur spaceport, carrying the new crewed partially reusable Zarya spacecraft that developed in end of the 1980s but was canceled. Also in the 1980s Vladimir Chelomey's firm proposed never realised 15-ton Uragan spaceplane launched by Zenit-2.

Two launch facilities were constructed for the Zenit at Baikonour, however the second was only ever used twice. On October 4, 1990, an attempted launch of a Tselina-2 naval reconnaissance satellite ended in disaster as the booster suffered a first stage engine failure seconds into launch and fell back onto the pad, which was severely damaged in the ensuing explosion. The failure was traced to a leak in a LOX line that caused a fire in the thrust section of the booster. Estimated repair costs were about 45 million rubles, but the collapse of the Soviet Union meant that there were no funds available, so the pad was abandoned.

Following two failures in 1991–92 both caused by the second stage, the Zenit was on the verge of being cancelled entirely, but a successful flight in November 1992 saved the program.

The rate of Zenit launches slowed to a trickle during the 1990s due to the severely cash-strapped Russian Federation, and also because of Russia's reluctance to fly military payloads on a booster manufactured in now-independent Ukraine. On May 20, 1997, a launch of a Tselina-2 satellite failed when the first stage shut down 48 seconds into launch. The booster crashed downrange.

During the 2000s, Zenit would find a new lease on life as the basis of the international Sea Launch project whereby commercial flights would be undertaken from an offshore launch platform. The basic Zenit booster received several upgrades to the propulsion and avionics systems for Sea Launch as well as a third stage, and the first test with a dummy payload was carried out on March 27, 1999. In October, a Direct TV 1-R satellite was orbited successfully. An ICO F-1 comsat was lost in March 2000 due to a second stage guidance malfunction. There followed eight consecutive successful launches until Apstar 5 in 2004 suffered a premature third stage shutdown that left it in an incorrect orbit, but the satellite's onboard engines corrected it.

After nine successful launches, the Zenit produced a repeat performance of the 1990 disaster when on January 30, 2007, the first stage lost thrust and exploded. The flame deflector on the Sea Launch platform broke off and sank into the water. Loose debris had been sucked into a turbopump, resulting in engine failure.

By the late 2000s, the Zenit program at Baikonour was reviving and would see considerable success.

On February 1, 2013, an Intelsat satellite launched from the Sea Launch Odyssey platform in the equatorial Pacific. The nighttime launch performed nominally for about 20 seconds when the first stage abruptly lost thrust. Approximately 40 seconds after liftoff, all telemetry data ceased. Subsequent investigation showed that the Zenit had begun deviating from its flight path when the pitch and roll maneuver started. The onboard computer sensed an abnormal situation and sent an automatic shutdown command to the first stage at T+23 seconds, and impact with the ocean occurred about one minute after liftoff. Ultimately, the failure was traced to a defective hydraulic pump that controlled gimbaling of the first stage engines. This resulted in the booster starting an uncontrolled rolling motion which caused the computer system to terminate all thrust. Although anomalous conditions began around T+11 seconds, the Zenit's flight computer was "locked" to prevent engine shutdown until at least 20 seconds after liftoff so the booster would not come down on or near the launch complex. Impact occurred about two miles downrange, but attempts to recover booster debris were unsuccessful.

In February 2015, following a year of strained relations as a result of a Russian military intervention into Ukraine, Russia announced that it would discontinue its "joint program with Ukraine to launch Dnepr rockets and [was] no longer interested in buying Ukrainian Zenit boosters, deepening problems for [Ukraine's] space program and its struggling Yuzhmash factory."^[7]

Strained relations between Ukraine and Russia after 2014 have led to Russian Federal Space Agency intending to purchase no more of the Zenit first-stage boosters made by Yuzhmash (powered by Russian engines). However 2 Zenit rockets that have been delivered to Russia for Russian Federal Space Agency missions will still be used; another Zenit rocket for launching a Ukrainian satellite has been completed but without engines due to lack of funding for payments.^[8] The world market for Zenit launch vehicles has shriveled since Sea Launch suspended operations, and the future of Zenit is uncertain.^[9]

Despite the ongoing conflict between the two governments, a Zenit rocket was launched in December 2017, after a two-year hiatus, to deliver AngoSat 1.^[10]

The first and the second stages of the Zenit were designed by Yuzhnoye and are manufactured by Yuzhmash.^[11]

• Comparison of orbital launcher families
• Tsyklon-4
• State Space Agency of Ukraine