From Halopedia, the Halo wiki
The Mombasa Tether, also known as the Mombasa Space Tether or the New Mombasa Orbital Elevator, was a space elevator located at the heart of the East African Protectorate city of New Mombasa on Earth. It was used for lifting heavy ordnance from the surrounding port facilities into a station in geosynchronous orbit at the top of the elevator structure, a transport method much cheaper and more efficient than booster rockets filled with expensive fuel. The company in charge of the management of the space elevator was called New Mombasa Uplift.
In 2302, Mombasa was chosen to be the Earth's first tether city. As a cheap gateway to space, the elevator is the key to New Mombasa's economic and strategic importance. The presence of the elevator radically changed the structure of the city. The elevator's base resides on an artificial island with service roads and a Maglev train line radiate out from it.
Battle of Earth
During the Battle of Mombasa, the Mombasa Tether was shut down. When the Prophet of Regret retreated, his flagship, Solemn Penance, initiated slipspace transition over the city, right beside the orbital elevator. The resulting shockwave swept through the structure, weakening it considerably.
Under an hour later on the same day, the damage from the Slipspace rupture was too much for the support structure to handle. It exploded at multiple points, and the tether snapped at some two kilometers above the surface. The upper portion of the tether was instantly pulled upward by its orbital counterweight, now severed from the groundside anchor point. The lower section collapsed, leaving only a small portion of the lower support structure intact, even though heavily damaged. Several pieces of debris crashed around the city and the surrounding area, while more fallout presumably caused considerable damage to buildings near the tether.
A large portion of the tower's debris was left scattered around Earth's surface, while most of the tether was pulled into space. Debris such as support rings and cables rained down to the surface far as the town of Voi and its surrounding regions, leaving large areas littered with debris and damaging infrastructure, such as the Tsavo Highway.
After the end of the Human-Covenant War, in March, 2553, some debris from the elevator still remained in the area near Voi. Eventually, the East African Protectorate would decide to rebuild the tether along with much of Mombasa as part of Project Rebirth, a plan to restore areas damaged in the war. Circa 2560, the tether's base had been rebuilt to a height far surpassing any nearby skyscrapers, with a large scaffolding erected to one side seemingly for reinforcement during the building process.
In Halo 2, the space elevator is visible throughout all the Earth levels, first as a thin line on the horizon in Outskirts, then later as a ringed tower in the skyline of Metropolis. Only at the end of that level is the player offered an unobstructed view of the structure from across the artificial canal.
At the end of the campaign level Metropolis, the flagship of the Prophet of Regret flees into slipspace with the In Amber Clad in hot pursuit. This in-atmosphere jump unleashes a wave of energy that scours the area. Originally this was thought to collapse the tower, but as seen in Halo 3: ODST, this wasn't the case.
The elevator was not seen again until the Halo 3 Announcement Trailer, in which several of its stabilizer rings lay shattered in the background hills. Concept art from the Halo 3 Zune confirmed that the wreckage of the space elevator would play an important part in the design of the Earth levels.
The elevator did make an appearance in the final game, with the player fighting through its ruins throughout the level Tsavo Highway and even hearing some dialogue concerning its fate from Marine allies.
Halo 3: ODST
In Halo 3: ODST, the Mombasa Tether plays its most prominent role. The structure has been reimagined from its Halo 2 incarnation; its base is located on an artificial island west of the city center, with MagLev Train lines leading to it, instead of the center of the Mombasa island in Halo 2. Its general appearance has also been changed, with a different, near-symmetrical base structure, and an additional support structure surrounding the lower part of the tether.
While it was originally thought that the elevator collapsed instantly when the slipspace rupture shook it apart, it was first revealed in the "Keep it Clean" teaser that the elevator did not in fact collapse instantly. In the game, the player is able to witness the actual failure and collapse of the elevator during the level Uplift Reserve, played from the perspective of Corporal Taylor "Dutch" Miles. The wreckage of the elevator can be seen throughout the levels of the game, with its debris scattered around the city and the ocean.
Halo 2: Anniversary
In Halo 2: Anniversary, the Mombasa Tether returns to its Halo 2 form albeit in higher definition. In the Blur cutscenes, the buildings along the tether's are seemingly office towers with glass facades.
Halo: Spartan Strike
In Halo: Spartan Strike, the Mombasa Tether is seen in cutscenes, retaining a number of design elements from its Halo 2 incarnation including the taller buildings around the base of the tether.
In Halo Infinite, the partially-rebuilt Mombasa Tether can be seen on the multiplayer maps Bazaar and Streets. While it is difficult to tell due to the structure's incompleteness, the rebuilt tether seems to be of a similar design to that in Halo 3: ODST.
List of appearances