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The STEX (Space Technology Experiments) satellite carried 29 new technologies intended to result in lower cost and higher performance spacecraft for future missions. Among the technologies were Russian-derived Xenon Hall-effect electric thrusters capable of delivering 40 mN of thrust, a 51 Gbit solid-state data recorder, and high-density NiH batteries designed to last longer and provide more energy with less weight. ATEx (Advanced Tether Experiment), a 6 km tether with TiPS heritage, was to be deployed as a separate sub-satellite. Frangibolts were used on the mission for shockless deployment of the spacecraft and tether. Experimental solar panels with high-efficiency solar cells were also carried. The planned lifetime of STEX was two years.

The spacecraft was comprised of a body shell and two tracking solar panels. A blowdown liquid propulsion system was carried. The spacecraft was three-axis stablized. A lightweight precision star tracker was used to determine satellite pointing.

On January 16, 1999, ATEx was deployed, but failed. It was deployed but its two masses separated only by 22 m. It is now tracked as a separate object (USA 141, 1998-055C).

Alternate Names

  • Space Technology Experiments
  • 25489
  • USA 140

Facts in Brief

Launch Date: 1998-10-03
Launch Vehicle: Taurus
Launch Site: Vandenberg AFB, United States
Mass: 539.4 kg

Funding Agency

  • National Reconnaissance Office (United States)


  • Surveillance and Other Military
  • Engineering

Additional Information

Questions and comments about this spacecraft can be directed to: Coordinated Request and User Support Office

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