Sen—Last week, Russia's commercial space workhorse, the Proton rocket, marked half a century in operation. The first UR-500 8K82 vehicle, as it was known inside the Soviet space program, lifted off from the test range in Tyuratam (now Baikonur) in Kazakhstan on July 16, 1965. The rocket carried the N-4/Proton-1 scientific laboratory for studying space rays.
Preparations for the first launch of the Proton rocket. Image credit: GKNPTs Khurnichev
The UR-500 was initially proposed for the dual purpose of carrying nuclear weapons and launching payloads into space. However, even in the midst of the Cold War, the Soviet military was apparently not interested in such an oversized ballistic missile. Instead, the Proton was pressed into service in the Moon Race. By 1967, it was hastily adapted for a proposed mission to carry two cosmonauts around the Moon onboard the cramped L1 spacecraft, which was based on the Soyuz, minus its habitation module.
The unmanned flight tests of the L1 capsule required much more time than expected and the risky project became politically redundant after Apollo-8 had circled the Moon at the end of 1968.
A Proton rocket lifts off with an unmanned version of the L1 spacecraft. Image credit: RKK Energia
In the meantime, the Proton rocket was also chosen to carry rovers that would be prepositioned on the lunar surface to provide transport to a single cosmonaut landing on the Moon in a separate lander. Two test rovers, known as Lunokhods, made successful trips across the lunar terrain remotely controlled by drivers at a secret base near Simpheropol in Crimea.
Because of their late start in the Moon Race, Soviet engineers had to play catchup with NASA, while simultaneously fixing numerous "growing pains" of the Proton, of which there were many. However, much bigger problems besieged the giant N1 Moon rocket, which was supposed to bring a pair of cosmonauts into lunar orbit and enable one brave pilot to actually land.
When the possibility of beating Americans to the Moon had finally been ruled out, it was the Proton again that was sent to steal at least some of the limelight from the Apollo program by delivering robotic "scoopers" designed to return lunar soil back to Earth. Three such missions did succeed, but only after the Apollo astronauts had brought home their own pieces of the Moon.
With the Moon Race over, the Proton became a foundation for the new chapter in the Soviet space program, during which Russian engineers did manage to upstage their American rivals. From 1971, a three-stage version of the rocket was employed to carry progressively more sophisticated Salyut and Almaz space stations reaching 20 tons in mass each, as well as similarly sized TKS transport ships. The program culminated with the launch of the Mir space station in 1986, which during its 15 years in orbit was expanded with five add-on modules, all launched by the Proton.
The Proton also became a rocket of choice for the Soviet deep-space exploration program, taking over the job of launching numerous probes to Mars and Venus from smaller Molniya boosters.
Last but not least, the Proton was given an exclusive task in the Soviet space program to deliver civilian and military communications satellites to the hard-to-reach geostationary orbit 36,000 kilometers above the Equator, where they would appear static in the sky to an observer on Earth.
Despite all these high-profile jobs, the rocket remained behind a thick veil of secrecy for almost two decades. Only its existence was initially disclosed without many details. It was publicly identified as 'Proton' after its first payload, because its real designation was supposed to remain classified, like the names of all other Soviet space and military hardware. The overall appearance of the rocket was not fully revealed until December 1984, when the liftoff of the Vega spacecraft bound to Venus and Halley's Comet was shown on Soviet television to the delight of space fans around the world.
With the fall of the USSR, the Proton quickly turned into the main breadwinner for the struggling Russian space industry. Foreign communications satellites heading to the hard-to-reach geostationary orbit have become Proton's most frequent passengers.
A Proton lifts off with a Sirius radio-broadcasting satellite. Image credit: ILS
During the 1990s, Russia won a lion share of the hyper-competitive commercial launch market largely thanks to the Proton. The rocket also continued carrying civilian and military satellites for Russia's own space program. In 1998 and 2000, the Proton launcher delivered two early components of the International Space Station (ISS), including the heart of the outpost—the Zvezda Service Module.
Unfortunately, not everything went as expected. Although the rocket was undergoing constant upgrades aimed to increase its payload and other capabilities, the failure rate started creeping up in the past few years.
The success and failure rate for the Proton rocket. Image credit: Anatoly Zak/RussianSpaceWeb
Since 2001, the Proton has lifted off 121 times, 12 of which have had anomalies. More troublesome is the fact that eight out of those 12 accidents are crammed into the last five years, while only four unsuccessful missions occurred during the first decade of the 2000s. From 2001 to 2005, the Proton suffered just one failure. Paradoxically, the increase in accidents coincided with growth in the Russian space budget!
The problems plaguing Proton struck again on May 16, sending the MexSat-1 communications satellite to its fiery demise in the rocket's third mission this year. As a result, the legendary rocket met its 50th anniversary grounded and out of service. On May 29, the Russian space agency (Roscosmos) announced that the two latest Proton failures were caused by the same defect in the engine of the third stage. Moreover, another launch in January 1988 was also doomed by the same issue and several other Proton flights were a hairline from failure!
Officials from International Launch Services (ILS), a Virginia-based company which markets Protons to commercial customers around the world, are currently conducting a final review of the investigation efforts and corrective measures, with the goal of bringing the rocket back to the launch pad at the end of August or beginning of September. The return-to-flight mission is expected to deliver the Inmarsat-5 F3 satellite for the name-sake operator based in London. Proton should log several successful launches before a critical launch of the European-led ExoMars-2016 mission, featuring a sophisticated orbiter and a small experimental lander bound for the Red Planet at the beginning of next year. The ExoMars project has been in development for almost two decades and its launch window is limited to a one-in-two-years opportunity during a conjunction between the Earth and Mars.
It will be the first assignment for a Proton to carry a planetary spacecraft since the failure of the rocket's upper stage led to the loss of the Russian Mars-96 spacecraft in 1996. For the upcoming mission, the vehicle will be equipped with a newer Briz-M upper stage. However Briz-M has had its own share of problems, releasing its payloads in wrong orbits in six missions since 2001. In two of these cases, it was possible to salvage the satellite at the expense of their onboard propellant, thus likely shortening their operational life.
According to Russian space officials, the Proton will remain in production until 2025, by which time it will be phased out and replaced by the new-generation Angara-5 rocket based in Vostochny and Plesetsk. As a result, the veteran rocket is expected to remain in service for at least six decades.