Please make a donation to support Gunter's Space Page.
Thank you very much for visiting Gunter's Space Page. I hope that this site is useful and informative for you.
If you appreciate the information provided on this site, please consider supporting my work by making a simple and secure donation via PayPal. Please help to run the website and keep everything free of charge. Thank you very much.



The ATEx (Advanced Tether Experiment), designed and built by the Naval Center for Space Technology (NCST), was a mission to extend the knowledge of control and survivability of tethered space systems.

The objectives of ATEx were to:

  • demonstrate tether system stability and control;
  • demonstrate end-body attitude determination and control; and,
  • fly a tether designed for survivability.

ATEx consisted of two parts: ATEx-LEB (Advanced Tether Experiment - Lower End Body) and ATEx-UEB (Advanced Tether Experiment - Upper End Body). Experiments in active control were to study deployment dynamics via a constant-speed motor and utilization of both in-plane and cross-plane thrusters to excite and arrest librations. Additionally, ATEx was to investigate the survivability of long-life tether materials.

The tether's lower end-body was placed on top of an active spacecraft (STEX), permiting the opportunity to perform libration control experiments. Such control was deemed necessary prior to developing more sophisticated tethered space systems.

The upper end-body (UEB) was 0.62 × 0.52 × 0.07 m in dimension and 11.8 kg. The lower end-body (LEB) was 0.53 × 0.43 × 0.60 m and 27.6 kg. The tether was 13.4 kg. When fully deployed, the two masses were to be over 6 km apart.

ATEx was released from the STEX spacecraft on 16 January 1999 after deploying only 22 m. The jettison was triggered by an automatic protection system designed to save STEX if the tether strayed from its expected departure angle. As a result, none of the desired goals were achieved.

Nation: USA
Type / Application: Experimental
Operator: NRL
Propulsion: None
Power: Batteries
Mass: 53 kg (total); 11.8 kg (UEB); 27.6 kg (LEB); 13.4 kg (Tether)
Orbit: 750 km × 766 km, 85.0
Satellite COSPAR Date LS Launch Vehicle Remarks
ATEx-LEB 1998-055C 03.10.1998 Va 576E Taurus-1110 with STEX, ATEx-UEB
ATEx-UEB 1998-055C 03.10.1998 Va 576E Taurus-1110 with STEX, ATEx-LEB