Tethers Unlimited, Inc. (TUI) is an American private aerospace company headquartered near Seattle, Washington, which performs research and development of new products and technologies for space, sea, and air.

TUI has since broadened its suite of technologies to include power, propulsion, actuation, and communications systems for small satellites, robotic technologies for on-orbit fabrication and assembly, optical fiber winding and deployment, software defined radio communications, and 3D printed radiation shielding.

[5][6][7] In 2016 it was reported by SpaceNews and Yahoo that the company's subdivision Firmamentum signed a deal with SSL to fly its in-space manufacturing technologies on SSL's Dragonfly program which is funded by NASA's Tipping point initiative.

[8][9] In December 2018 it was reported that Tethers Unlimited delivered a Refabricator to the ISS that accepts plastic material and converts it into high-quality 3D printer filament,[10] for the mission duration of October 2018 to April 2019.

[11] According to TUI's website, Firmamentum is currently working on building the 'Spiderfab' technology to "enable on-orbit fabrication of large spacecraft components such as antennas, solar panels, trusses, and other multifunctional structures.