TEPCE Spacecraft

Joined by a 1 km tether to test electrodynamic tether propulsion.

Joined by a 1 km tether to test electrodynamic tether propulsion.

Jonathan McDowell reported that change in decay rate on 2020-11-17 suggests tether was deployed.

The end-masses were separated on November 15, 2019. The exposed tether increased the area for TEPCE, which resulted in a significant increase in the decay rate. The last element set published was on February 2, 2020, which was 78 days after separation of the end-masses. As seen in Fig. 39, the last few element sets exhibited marked increase in decay. The date of the last element set provided by Space-track.org was February 2, 2020, which indicated that was the date TEPCE reentered the atmosphere. The enormous drag produced by the tether shortened the life of TEPCE by some 6 years. It is well known that electrodynamics can further decelerate the orbit of a tethered satellite. Many papers have been published on the deceleration effects of electrodynamics thrusting, [9].

The communications and battery-life issues discussed in previous sections severely limited electrody-namic tether operations once TEPCE‘s tether was deployed. Nonetheless, TEPCE was able to return some interesting physical measurements. Since Stimpy was basically nonoperational after tether deployment, tests in which a bias voltage was to have been applied to its collector tape could not be conducted; in fact, the collector tape was never made part of the electrodynamic circuit.

Presentation in November 2023 shared additional details:

• ACS Showed TEPCE was Tumbling End-Over-End at a Rate of 4.4 Revolutions per. Far Above the Maximum Acceptable Rate. Magnetorquers Engaged to Slow Tumble Below One RPM.
• TEPCE’s Orbit Encountered the South Atlantic Anomaly Causing Frequent System Resets.
• At 0147 EST on November 16, 2019 the Command was Given to Deploy the Tether. Acknowledgement was Not Obtained. Increase in Rotation About the Roll Axis was Consistent with Stacer Unwinding per Prelaunch Tests. A Sixfold Increase to the Drag Term on November 17, 2019, Further Confirmed Separation.
• On November 22, 2019, Commands were Given to Deploy the Impedance Probes (iProbes) and Collector Tapes. Confirmation was Received from Ren. Confirmation was Not Received From Stimpy.
• Imagery on November 21, 2019, Confirmed Separation but Showed Separation of Only About 270 m.
• Further Imagery on November 27, 2019, Showed a Separation of 450 m. Also Showed an Anomalous Reflective Area in the Center of the Tether Suspected to Be a Snag in the Tether or a Rebound.
  • Possible Causes:
    • Braking Hooks Did Not Release
    • Braking Hooks Did Not Slow Release
    • Snag of a Piece of Hardware
    • Memory Effect Within the Tether. 
• TEPCE Suffered From Varying Communication Issues
  • Communication Difficulties Between the TMOC and RGS Computers (Resolved Prior to Launch).
  • Difficulties Closing the Link With the Satellite.
  • Tracking Issues with the Ground Station.
  • Power Management Issues.
• Closing the Downlink With Stimpy Became Very Difficult Post-tether Deployment.
  • Gravity Gradient Caused Stimpy to Remain at a Higher Altitude.
  • It Was Hypothesized That the Tether May Have Modified the Antenna Pattern .
  • Cause Could Not Be Definitively Determined.
  • Operations Team Made 1,230 Communication Links with Ren, But Only 41 to Stimpy.
• Tests Involving Stimpy’s Collection Tape Were Not Viable.
• Tests Utilizing Ren Were Conducted
  • Tether Was Conductive
  • Ren Was Situated on the Negative End of the Tether.
  • Ignition of Electron-Emitting Filament Allowed Flow in the Electrodynamic Circuit Driven by the Naturally Occurring Potential Drop in the Tether
• On December 6, 2019 Ren Was Able to Collect Data for a Significant Portion of Two Orbits.
  • Due to Natural Negative Bias on Ren, the iProbe Was Not Able to Measure Electron Density.
  • Electron Density Estimates Based on International Reference Ionosphere (IRI) Models Were Used and Behavior of Current in the Electrodynamic Circuit Was Consistent With the Estimated Level of Variation.