The Orbital Defence Initiative (abbreviated ODIN) is an orbital satellite weapon; a potent relic of the Sixty Minute War and a major feature of the third and fourth books in the series, Infernal Devices and A Darkling Plain.
History
Construction
ODIN was built as part of the arms race between the American Empire and Greater China and may have been fired during the Sixty Minute War. It and MEDUSA are the only superweapons known to have survived the war in a functional state - although there are several references to other orbital superweapons (Diamond Bat, Jinju 14, and The Nine Sisters for example) they are hinted to have broken up over time and fallen from the sky. ODIN is most likely an American Empire satellite as the code for controlling the satellite was acquired from an American submarine.
Manchester being destroyed by ODIN
Reactivation
The Tin Book of Anchorage, copied from a military document recovered by the refugees of the original Anchorage from a submarine, is a codebook for controlling ODIN. It is stolen by the Lost Boys and, later, Brighton. It then falls into the hands of the Stalker Fang, who memorises its contents and then leaves it to be destroyed on Cloud 9 when she is attacked by Shrike. The Tin Book is then destroyed in a fire. When Fang is rebuilt by Fishcake, her Stalker alter-ego travels towards Batmunkh Gompa to acquire technology with which to build a transmitter to contact the orbital weapon.
Firing for the last time
When ODIN is reactivated and fired on the Stalker Fang's orders a number of cities both mobile and static are destroyed; confusion ensues on the part of the Green Storm and Tractionists. Both sides try to find the transmitter, leading to the Green Storm assault on London, but it is Tom, Hester, Shrike and Pennyroyal who find Fang. As the Stalker Fang prepares to target all the volcanoes on the earth and so destroy humanity, a final confrontation brings Anna to the fore once more and she orders ODIN to turn its weapon upon itself, destroying it.
Technical overview
Weaponry
ODIN is armed with a directed-energy weapon which apparently converts the energy of a small nuclear weapon into a coherent beam of incinerating energy which is visible from long distances. This has the power to destroy cities (both traction and static) and can also provoke volcanic eruptions. Being mounted on an orbital platform the weapon has a longer reach than the ground-based MEDUSA.
Firing the weapon seems to interfere with the mechanical minds of Stalkers; Even Shrike and the Stalker Fang with their advanced Old-Tech brains went into a fit-like state, while lesser Stalkers just lose power or explode.
Artifical intelligence
As well as its immensely powerful weaponry, ODIN appears to show signs of autonomous cognitive capability. When it is reactivated, it queries its new position and briefly searches for its old masters, noting the vast difference in geography since its last awakening. This seems to suggests that by the time of the Sixty Minute War the American Empire had developed self-aware artificial intelligences.
miscellaneous information
ODIN's sensors can zoom in with sufficient resolution to view an individual's face on the Earth, an impressive feat even though the picture is low in quality. It can change its orbit when directed to target all over the globe.
Trivia
The first-person shooter game Call of Duty: Ghosts also features an orbital weapon, with the same name and abbreivation, which also destroys multiple cities as a central plot point. It's unknown if this is just a coincidence or if the game's development team were influenced by the books.