UPSC Prelims 2022 Q34: Fractional Orbital Bombardment System — Explained

Which one of the following statements best reflects the idea behind the "Fractional Orbital Bombardment System" often talked about in media?

  1. A hypersonic missile is launched into space to counter the asteroid approaching the Earth and explode it in space.
  2. A spacecraft lands on another planet after making several orbital motions.
  3. A missile is put into a stable orbit around the Earth and deorbits over a target on the Earth.
  4. A spacecraft moves along a comet with the same speed and places a probe on its surface.

Answer: (c) A missile is put into a stable orbit around the Earth and deorbits over a target on the Earth.

Statement-wise explanation

  • a: incorrect — This describes planetary defence, which means deflecting or destroying an asteroid heading for Earth. NASA's DART mission tested this in 2022 by striking the asteroid Dimorphos. FOBS points a weapon at a target on Earth, not at an object in space. The word "hypersonic" is a distractor: China's 2021 test combined FOBS with a hypersonic glide vehicle, but the bombardment system still strikes the ground.
  • b: incorrect — This describes an interplanetary probe. Such probes often enter orbit around a planet before landing, as orbiters and landers on Mars do. FOBS is not used for exploration and does not go to another planet. It uses low Earth orbit only as a route to a target on Earth.
  • c: correct — In a Fractional Orbital Bombardment System, a missile places its warhead in low Earth orbit. A retro-rocket then slows it so it deorbits onto its target, usually before one full orbit is complete. That partial orbit is what "fractional" means. The Soviet Union deployed this as the R-36O (8K69) from 1968–69 and phased it out in January 1983 under the SALT II terms. The warhead can approach from any direction, including over the South Pole, and its target stays hidden until late in the flight.
  • d: incorrect — This describes a comet rendezvous and landing. The European Space Agency's Rosetta did this, matching the speed of Comet 67P/Churyumov–Gerasimenko and sending the Philae lander to its surface in 2014. That is a science mission. It has nothing to do with bombarding a target on Earth.

How to eliminate

The name gives most of it away. "Bombardment" means a weapon striking a target. "Orbital" means the weapon travels through orbit. "Fractional" means it uses only part of an orbit. A planet landing and a comet rendezvous are peaceful science missions, so they fail on "bombardment". The asteroid-interception option involves a weapon, but its target is in space, not on the ground, and it does not use an orbit. Only the remaining option has both an orbit and a strike on Earth. That option says "stable orbit", while a real FOBS warhead usually comes down before finishing one orbit. The question asks which option "best reflects" the idea, so small inaccuracies like this are acceptable. The fact to remember: FOBS = orbit partway around the Earth, then deorbit onto a ground target.

Know more

Fractional Orbital Bombardment System (FOBS) is a way of delivering a warhead in which the warhead goes into low Earth orbit and is deorbited onto its target before it completes a full orbit.

Why build it? An ordinary intercontinental ballistic missile (ICBM) flies a predictable arc that early-warning radars watch for. A FOBS warhead can take the long way round, for example over the South Pole, where radar cover was weaker. It has no range limit, and the target is hard to predict until the deorbit burn.

History

  • The Soviet Union developed it in the 1960s. Yangel's R-36O (8K69) was deployed in 1968–69.
  • The Outer Space Treaty of 1967 bans placing nuclear weapons in orbit around the Earth. The Soviet Union argued that a weapon making less than one full orbit did not break this rule.
  • SALT II (1979) banned FOBS. The US never ratified SALT II, but the Soviet Union retired the system in January 1983.
  • In 2021, China tested a FOBS-type launch that carried a hypersonic glide vehicle. US officials confirmed the test in October 2021.
Delivery mode Path Predictability Range
ICBM Ballistic arc through space High (fixed trajectory) Limited (about 5,500 km and above)
Hypersonic glide vehicle Boost, then glides in the upper atmosphere and manoeuvres Low Long
FOBS Partial orbit, then deorbit burn Very low (can come from any direction) Unlimited
FOBS + HGV Partial orbit, then the glider re-enters and manoeuvres Lowest Unlimited

Exam angle: UPSC likes to ask about weapon terms that are in the news, such as hypersonic, scramjet, FOBS and anti-satellite (ASAT) weapons. It also likes the treaties around them: the Outer Space Treaty, SALT and the Prevention of an Arms Race in Outer Space (PAROS) talks.

In the news

In October 2021, reports said China had tested a nuclear-capable hypersonic glide vehicle that circled the globe on a fractional-orbit trajectory, and US military leaders confirmed the test. This brought FOBS back into the news months before the 2022 Prelims.

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