Main Image Credit DF-17 Dongfeng medium-range ballistic missiles equipped with a DF-ZF hypersonic glide vehicle involved in a military parade to mark the 70th anniversary of the People's Republic of China in 2019. Courtesy of Zoya Rusinova / Alamy Stock Photo
What is a Fractional Orbit Bombardment System and what does it mean for China?
In August 2021, China launched a Long March rocket carrying a hypersonic glide vehicle (HGV) into low earth orbit. The HGV then re-entered the earth’s atmosphere, landing ‘about two-dozen miles’ from its intended target. Details of the report are consistent with prior evidence regarding the accuracy of such systems and implies that they have a primarily countervalue (city targeting) role. This is, in many ways, positive as it suggests these capabilities exist to reinforce China’s second-strike capability rather than enable first strikes. This reflects the fact that the old Chinese nuclear doctrine of living with uncertain second-strike capabilities is giving way to an approach emphasising assured retaliation.
Current reports suggest that China has tested a fractional orbit bombardment system (FOBS). The concept of a FOBS was pursued by the Soviet Union during the 1960s and led to the fielding of the R-36-0 Orbital Bombardment Missile in 1969. The Soviet design was estimated to be capable of flying via the South Pole, which would minimise the time available for the US Ballistic Missile Early Warning System to detect the incoming threat. The lower accuracy and yield of the FOBS compared with an ICBM would make it better suited to pre-emptive strikes against ‘time-urgent, soft targets, such as SAC [Strategic Air Command] bases…and key governmental and control centres’.
The underlying technology of an FOBS is simple, but mastering the design presents complicated material challenges. A primary rocket and second-stage booster is used to accelerate the warhead into orbit, at which point the warhead coasts and reorients itself to the target. The final stage involves the use of a retrograde rocket to reduce the warhead’s speed and de-orbit it for its final approach to the target. Typically, the final stage is carried out before the warhead has completed its first orbit of the Earth, hence ‘fractional orbit’.
The old Chinese nuclear doctrine of living with uncertain second-strike capabilities is giving way to an approach emphasising assured retaliation
The first stage necessarily involves rockets with extreme levels of thrust. The Soviet R-36-0 and a competitor design designated UR-200A both supplied 241 and 228 tons of thrust in a vacuum. The second stage engines provided 96 and 62 tons of thrust. The third stage, known as de-orbiting, presents multiple challenges as the retro-grade rocket must reliably activate to de-orbit the warhead at the right time and on an accurate course heading.
Beijing’s tests reportedly employed an HGV, which adds further complexity to the design challenges. As the vehicle re-enters the Earth’s atmosphere it will begin to heat up, approaching 3,000 degrees Celsius. A China Aerospace Studies Institute paper published in 2020 notes that China has historically struggled to develop ceramics capable of withstanding this heat and has turned to international cooperation with universities to resolve this issue. This problem will be exacerbated by the apparent emphasis on HGVs capable of skip glide manoeuvres designed to confound missile defences. Skip glide manoeuvres are a particular form of hypersonic flight that involve a vehicle skipping along the earth’s atmosphere multiple times, like a stone skipping over water, before beginning its final descent. This increases the range, speed at impact and unpredictability of an HGV but at the cost of lower accuracy. The HGV must also be capable of withstanding extreme heat and forces imposed by the warhead manoeuvring at speed to ensure that it is on target.
These technical restraints result in a design spiral whereby every consideration affects the next, leading to a weapon that is limited in some respects when compared with a conventional ICBM. Its yield is likely lower, as is the accuracy, as a result of the way in which the warhead is orbited and targeted before launch. Its benefits are the inability of an opponent to predict the target until the very last moment, as well as the unusual and unpredictable flight paths that can be used to deploy the warhead.
The FOBS test is part of a wider effort to rectify China’s nuclear weaknesses. Currently, China’s nuclear second-strike capability is based on shaky foundations. For example, the geography of the first island chain forces Chinese submarines to traverse a few well-known choke points, which combined with the noisiness of the Type 094 submarine and the limited range of the JL-2 SLBM, limit the effectiveness of the subsurface leg of China’s nuclear triad. The submarines would likely not survive US antisubmarine efforts in the event of a conflict. The same can be said of China’s silo-based DF-5A/B which, by virtue of being at fixed sites, are assessed as being vulnerable to increasingly accurate precision-guided munitions capable of penetrating hardened targets. Road-mobile missiles such as the DF-31A and the new DF-41 are more survivable, though this depends on whether they have been put on alert and dispersed to forward sites.
What appears to be of greatest concern to Chinese planners is that adversarial improvements in both conventional prompt strike and nuclear strike capabilities, coupled with a substantial improvement in US missile defences, could undercut China’s deterrent. According to modelling, if caught by a surprise attack under current circumstances the Chinese system has a 10% chance of effective retaliation against at least 3 US cities. This could decrease in the long run if the effectiveness of the US homeland missile defence system’s tracking and discrimination capabilities improves with the eventual fielding of a space-based sensor layer.
The weapon's benefits are the inability of an opponent to predict the target until the very last moment, as well as its unusual and unpredictable flight paths
It is within this context that we might situate a raft of Chinese initiatives in the nuclear domain, all of which appear geared to restoring retaliatory credibility. This includes the incorporation of multiple independent re-entry vehicles and penetration aids on the DF-41. To this we might add the construction of additional ICBM silos which may be intended either to hold additional missiles or to complicate adversary targeting and compel an opponent to waste munitions on empty silos. The FOBS fits neatly within this framework. It is likely too inaccurate for a first-strike weapon, but can readily serve the role of reinforcing the likelihood of Chinese retaliation against US cities. What is notable, however, is that unlike previous periods where Chinese leaders deemed a reasonable probability of effective retaliation sufficient for deterrence – even if that probability was less than 100% – the diversified arsenal they are now building appears to aim for assured retaliation. This is more an evolutionary than a revolutionary change but is an important distinction nonetheless.
Notably, Hu Xijin, the editor in chief of China’s Global Times, tweeted that China would improve its nuclear arsenal ‘to ensure that the US abandons the idea of nuclear blackmail…or using nuclear forces to fill the gap as US forces cannot crush China’. This echoes a sentiment observed by M Taylor Fravel in his book Active Defense, which quotes Marshal Nie Rongzhen as saying, ‘when the Chinese people have this weapon [in reference to China’s own nuclear programme], nuclear blackmail toward the people of the world will be completely destroyed’.
In many ways, this represents a logical step for China. Should China achieve its desired aim of shifting the conventional balance in the Pacific in its favour, the US could attempt to offset this through the threat of early use of a superior nuclear arsenal, as it did against the Soviet Union during the Eisenhower administration. Against a Chinese nuclear arsenal that is currently highly limited, this would be particularly effective. Recent developments within China thus reflect a desire to anticipate and forestall such a possibility.
The views expressed in this Commentary are the authors’, and do not represent those of RUSI or any other institution.
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Dr Sidharth Kaushal
Research Fellow, Sea Power