Phobos Supertether

The Phobos Supertether is a human megastructure built in the 2180s from high-strength, low-weight materials like titanium and poly(p-phenylene-2,6-benzobisoxazole), better known under the trademarked name of Zylon. Using Phobos as its anchor, the Phobos Supertether extends downwards into the Martian mesosphere and out the other side of Phobos, coming in at a total length of over 5.8 thousand kilometers. 
Due to its anchor being one of Mars' moons, it shares its orbital period, making a full trip across Mars' equator once every 11.1 hours at a speed of over 1900 km/h. 
The counterweight and base station at the far end was used to launch vessels and cargo throughout the Sol system without the use of expensive warp fuels in the earlier days of human interplanetary travel. 
It was capable of reaching the outer solar system as well as the inner solar system far more easily than any Earthbound effort would have been, especially since an Earth space elevator was not technologically feasible at the time. This was also the best alternative available to Mars at the time due to the fact that Phobos's subsynchronous orbit would have interfered with efforts to create a Martian space elevator. 
The destruction of Deimos led to the weakening of the upper cable, as pieces of the moon that had fallen into a lower orbit collided with the tether and its base station. This ultimately made it easier for the Earth military to sever the upper tether and cripple the Martian war effort early in the Interplanetary Civil War. The base station and its cable were launched into a higher orbit, where it remained for decades before it was salvaged for parts to be used in building its replacement. 
While no longer as relevant with the advent of much cheaper FTL technologies, it is still the hub for sublight travel in the Sol system, and is vital for in-system commerce and vessels arriving and departing the Sol system. It is now used as the spaceport for the Deimos Transit Gate, which was placed in Deimos' former orbit and remains the most prominent entrance into the system as a whole.
Category:Human Technology