Tethers Unlimited, Inc. (AMERGINT)

Tethers Unlimited, Inc. (TUI) is an American aerospace technology company founded in 1994 by Robert Hoyt and science-fiction author Robert Forward, headquartered in Bothell, Washington. Growing out of early research into space tether systems, TUI built a broad portfolio of small-satellite hardware: the SWIFT family of software-defined radios for telemetry, tracking and command; the HYDROS water-electrolysis thruster, which splits stored water into hydrogen and oxygen propellant for green in-space propulsion; the Terminator Tape passive deorbit module for CubeSats; the COBRA gimbal and MANTIS robotic-arm mechanisms; and deployable booms and solar-array structures used on numerous NASA, DoD and commercial small-satellite missions.

TUI's Firmamentum division pioneered in-space additive manufacturing and assembly technology, including the SpiderFab / Trusselator concept for on-orbit fabrication of large structures such as antenna reflectors and solar arrays, funded through NASA and DARPA research contracts. TUI hardware has flown on missions including NASA's PUNCH heliophysics constellation and numerous CubeSat and smallsat programs across government and commercial customers.

In May 2020, TUI was acquired by AMERGINT Technology Holdings, becoming a wholly owned subsidiary alongside AMERGINT's satellite ground-system and signal-processing business. AMERGINT subsequently rebranded as ARKA Group, which brought together TUI, AMERGINT, Danbury Mission Technologies, The Stratagem Group and Lumacron under a single space-and-defense enterprise. In 2026, ARKA Group was acquired by CACI International, folding TUI's flight-hardware and radio product lines into CACI's broader national-security space portfolio. TUI's original tethers.com web presence has since been retired as its product lines and support now operate under the ARKA/CACI corporate site.