Space Technology Experiments, or STEX, also known as NRO Launch 8 or NROL-8, was an experimental National Reconnaissance Office (NRO) satellite built by Lockheed Martin. It was launched on 3 October 1998.[1] One of the experiments was ATEx (Advanced Tether Experiment), which was deployed on 22 January 1999, and subsequently jettisoned.[2]

Science Technology Experiments
STEX during ground-testing
USA 140
Mission typeTechnology demonstration
COSPAR ID1998-055A Edit this at Wikidata
SATCAT no.25489
Spacecraft properties
ManufacturerLockheed Martin
Launch mass539.4 kg (1,189 lb)
Start of mission
Launch date10:04:49, October 3, 1998 (UTC) (1998-10-03T10:04:49Z)
RocketTaurus (rocket)
Launch siteVandenberg AFB


Advanced Tether Experiment (ATEx) with partially deployed upper end-body

The Advanced Tether Experiment (ATEx), was a follow on to the TiPS experiment, designed and built by the Naval Center for Space Technology, flown as one of the experiments on STEX. ATEx had two end masses connected by a polyethylene tether that was intended to deploy to a length of 6 km, and was intended to test a new space tether deployment scheme, new tether material, active control, and survivability. ATEx was deployed on 16 January 1999 and ended 18 minutes later after deploying only 22 m of tether. The jettison was triggered by an automatic protection system designed to save STEX if the tether began to stray from its expected departure angle,[3] which was ultimately caused by excessive slack tether.[4] As a result of the deployment failure, none of the desired ATEx goals were achieved.[5] ATEx is now tracked as a separate object as USA 141 or COSPAR ID 1998-055C.[6]


  1. ^ "STEX". NSSDC Master Catalog Search. 8 October 2010.
  2. ^ "ATEx". NSSDC Master Catalog Search. 8 October 2010.
  3. ^ "Advanced Tether Experiment (ATEx)". U. S. Naval Research Laboratory. Archived from the original on 6 September 2015.
  4. ^ Gates, Stephen S.; Koss, Stephen M.; Zedd, Michael F. (January–February 2001). "Advanced Tether Experiment Deployment Failure". Journal of Spacecraft and Rockets. pp. 60–68. doi:10.2514/2.3655.
  5. ^ Kramer, Herbert J. "STEX (Space Technology Experiment) / ATEx". eoPortal. European Space Agency. Retrieved 18 January 2022.
  6. ^ "NSSDCA – STEX – Details". NASA. Retrieved 23 June 2016.

External linksEdit

  • STEX at Gunter's Space Page