A fractional orbital bombardment system (FOBS) is a warhead delivery system that uses a low Earth orbit towards its target destination. Just before reaching the target, it deorbits through a retrograde engine burn.
The Soviet Union first developed FOBS as a nuclear-weapons delivery system in the 1960s. It was one of the first Soviet efforts to use space to deliver nuclear weapons. In August 2021, the People's Republic of China tested a weapon that combined a FOBS with a hypersonic glide vehicle.
Like a kinetic bombardment system but with nuclear weapons, FOBS has several attractive qualities: it has no range limit, its flight path would not reveal the target location, and warheads could be directed to North America over the South Pole, evading detection by NORAD's north-facing early warning systems.
The maximum altitude would be around 150 km. Energetically, this would require a launch vehicle powerful enough to be capable of putting the weapon into orbit.
Development history and deployment Lead-up to FOBS development Some Soviet officials began expressing a desire for a FOBS-type weapon around the time of Sputnik's launch. By the early 1960s, the Soviet Union felt that pursuing a system like the FOBS would be a natural next step given its belief that the US was already planning to use space to mount nuclear attacks. The success of the Soviet Vostok program which saw a rocket send a human into orbit and then land at a predesignated location made this kind of weapon seem more feasible.
Competing FOBS designs Soviet rocket engineer Sergei Korolev seems to have been responsible for the first FOBS-type missile design. His offering was the GR-1; it was also known as 'Global Missile 1' within Korolev's design bureau, as SS-X-10 Scrag by NATO authorities, and as 11A513 (or 8K73) by Soviet GRAU index. Korolev's research began as early as 1960 and the GR-1 project was sanctioned by Soviet officials on September 24, 1962.
Korolev brought up the idea of the GR-1 to Soviet Premier Nikita Khrushchev in early 1962. Soon after, Khrushchev announced that the Soviet Union was capable of utilizing "global missiles" that could fly over both the North and South Poles on their way to a target, continuing on to say that this type of weapon would render early warning radar systems practically obsolete and leave the enemy with no time to retaliate before the weapon's impact. Korolev's engineers first estimated that NATO radar systems would detect the GR-1's warhead only two minutes before arrival.
The GR-1 was to use the NK-9 and NK-9V as main engines in its first and second stages respectively. Though the NK-9 and NK-9V weren't created by Korolev's team, the GR-1's 8D726 retrorocket engine was. This engine would prove to be instrumental to the progress of Russian rocketry, specifically for its importance in the development of the Blok-D upper stage of rockets like the N1, Proton, and Zenit.
The GR-1 had three stages and a total vehicle mass of 117 tons. It was 35.31 meters long with a 2.68 meter diameter and could carry a single 2.2 megaton yield nuclear warhead. It was cryogenic liquid propelled, utilizing a mix of RG-1 kerosene with liquid oxygen (LOX).
Two other FOBS-type missile projects emerged around the time of the GR-1's early development. It seems that each of these projects were competing with one another for usage selection.
The first of the two other projects was that of Soviet missile engineer Vladimir Chelomey who proposed two designs: one called the UR-200A (GRAU index 8K83) that was derivative of his UR-200 ICBM and another designated as GR-2 which built off of his colossal UR-500 prototype ICBM and had a much larger explosive yield of 30 megatons. The UR-200A design was eventually selected for further development over the GR-2. It was to use the RD-0202 and RD-0205 engines for its first and second stages respectively and be equipped with an AB-200 aeroballistic warhead. Unlike the GR-1, the UR-200 and its derivatives used storable (or hypergolic) liquid propellants; specifically nitrogen tetroxide and UDMH. Chelomey and his engineers received development authorization for the UR-200 ICBM on March 16, 1961, beginning work on the UR-200A variant at some point after.
The second of the two other projects came from the Soviet missile designer Mikhail Yangel. His proposal was the R-36O (8K69 by GRAU index and SS-9 Mod 3 Scarp by NATO report) which was approved for development by Soviet officials on April 16, 1962. Yangel used an ICBM design of his own, the R-36 (NATO designation SS-9 Scarp), as a base for the R-36O. The missile had three stages, using the RD-251 engine in its first stage and the RD-252 engine in its second stage. The weapon's third stage was related to the deorbiting process as well as warhead guidance and delivery; the Soviets referred to this system as OGCh.
An aiming system inside the OGCh would check and rectify trajectory issues in relation to the desired target location through the use of various instruments (for instance, a radio altimeter used in conjunction with an inertial navigation system). The aiming system would make its checks directly after the missile came into orbit and immediately before third stage ignition. Deorbiting would be induced by the missile's retrorocket, the RD-854 engine, causing the warhead to take on a ballistic path towards its target.
The warhead, retrorocket, and guidance system were each contained inside the OGCh module. A series of nozzles on the RD-854 enabled aerial maneuvering of the OGCh. Other nozzles facilitated the separation of the warhead from the rest of the OGCh, allowing it to fall alone on a ballistic path to the target. The R-36O's 8F021 warhead had an explosive yield between 5-20 megatons according to Soviet sources. Western intelligence suggests that the yield was smaller, being somewhere between 1–3.5 megatons. The missile was 32.60 meters long with a 3.00 meter diameter and a total launch mass of 180 tons. The R-36O used the same hypergolic propellants as the UR-200.
Yangel design selection In 1965, Soviet military officials worked to select one of the three FOBS projects. The R-36O of Yangel's design bureau was chosen for further development over the others. The reasoning behind the Soviet FOBS design selection process remains somewhat unclear. A particularly confounding factor to consider is that none of the three proposed missiles had undergone a single test flight prior to the R-36O's selection. Even so, there are some explanations as to why Yangel's design was chosen in the end. These revolve around the occurrence of negative events in the competing GR-1 and UR-200A projects that effectively knocked them out of contention.
One strike against Korolev's GR-1 was that it used a cryogenic propellant, thereby rendering the missile a poor candidate for operational storage in a missile silo as the Soviet military desired. Other negative factors include that the GR-1's 8D726 retrorocket was demonstrating a proclivity for failure in its initial tests and, as a cause for yet more worry, the troublesome R-9A, the subject of a different ongoing Korolev ICBM project, was quite similar to the GR-1 in construction. Thus, military leadership was encouraged to look elsewhere for more immediate progress.
The GR-1's ability to deal with US ABM systems and its lengthy fueling process were questioned by Soviet analysts. There were also significant delays associated with the production of the GR-1's NK-9 engine, for which the Kuznetsov bureau was responsible. Under the weight of these issues, the GR-1 project fell apart in January 1965.
Chelomey's UR-200A project lost a great deal of support after Khrushchev, his most important political ally, was ousted in 1964. Military authorities under the Brezhnev administration were far less friendly to Chelomey and quick to deem the R-36O a better choice for further FOBS development. Having lost the ability to tap into the Soviet Premier's influence, Chelomey ultimately failed to secure the survival of the UR-200A, its development coming to an end in 1965.
Flight testing and deployment At its missile range near Baikonur, Kazakhstan, the Soviet Union tested and deployed the R-36O. A testing station and a horizontal assembly facility were constructed for the missile's development initially. Over most of 1965, two R-36 test pads were modified to work with the R-36O for its early test flights. In addition, 18 silos capable of launching the R-36O were built over the mid-1960s to 1971; three rounds of construction occurred with six silos being built each time. Those built in the same area were placed 10-15 kilometers away from one another to prevent the possibility of a single nuclear strike destroying multiple silos.
The Soviet Union originally planned nineteen R-36O launches, but 24 were carried out by 1971. The initial four were to begin from a ground-based testing pad and then fly to the Kamchatka Peninsula. The other tests called for the R-36O to be launched from a silo into orbit where it would then execute its third stage deorbit process over the Pacific Ocean; the missile's payload would be retrofired into Soviet territory. Over 2000 Soviet service people participated in the tests. Six of the tests were outright failures while the others achieved either complete or partial success. Prior to the first launches, the Soviet Union stated that a "space vehicle landing system" was being tested over the Pacific.
The first test flight occurred on December 16, 1965. It missed the landing area by a wide margin owing to a stabilization instrument malfunction. The second test was on February 5, 1966, and was also a failure due to a retrorocket issue. The third test took place on March 16, 1966. Nitrogen tetroxide spilled over the surface pad during fueling due to a miscommunication and the missile was quickly destroyed by fire. Some success was had with the fourth test on May 20, 1966, but the payload didn't break away from the missile's guidance system as intended.
The following tests were conducted from silos. The first two tests of the silo phase ended in the intentional destruction (via self-destruct functionality) of the R-36O as a result of the second stage engine accidentally being activated for too long, sending the payload into an unplanned orbit. NATO radar systems picked up on the large mass of resulting debris. In one failed test case, small pieces of the missile rained down on the midwestern United States.
In 1967, the Soviet Union conducted ten more R-36O tests, nine of them seeing some level of success. In that year and beyond, the Soviet Union used public statements about satellite launch tests as cover for any R-36O test that was intended to put its payload into orbit for some period of time.
On November 19, 1968, about a month after the 20th test, the Soviet Union designated the R-36O as operational and began its deployment in three groups of six. By 1971, all 18 of the Soviet Union's R-36O silos were in service in Kazakhstan. NATO intelligence suggests that a primary target was the US Grand Forks Air Force Base where an ABM system was set to be established in the late 1960s to early 1970s. The R-36O wasn't equipped with a nuclear payload until 1972.
Reasons for development
The Soviet Union identified a number of strategic advantages of the FOBS. The following points prompted its development:
The system granted unlimited striking range with a nuclear weapon. The system allowed a strike to be carried out from any direction. For instance, the Soviet Union could launch an attack against the United States using a South Pole or North Pole flight path; technically, it could even execute both of these attack plans simultaneously.