Terminator Tape and Terminator Tether Satellite Deorbit Systems:
Low-Cost, Low-Mass End-of-Mission Disposal for Space Debris Mitigation
Tethers Unlimited Inc. is currently developing two low-cost satellite deorbit modules that will provide cost-effective, lightweight, and reliable means of removing objects from low-Earth-orbit (LEO) to mitigate the growth of orbital debris. For microsatellite-class systems (<500 kg) operating at altitudes less than 1000 km, our Terminator Tape™ deorbit module will use passive drag enhancement to enable compliance with 25-year orbital lifetime restrictions with very low mass, cost, footprint, and technical risk. For larger satellites, or satellites operating at higher altitudes, our Terminator Tether™ module will use electrodynamic drag techniques to deorbit satellites within a period of several months. In addition, we have developed an innovative deployable net system called "GRASP" that can be used to capture space debris.
The Terminator Tape deorbit module is intended for microsatellites operating at altitudes of less than 1000 km. The Terminator Tape is a 'pizza-box' shaped module that mounts to any face of a microsatellite. When the host spacecraft has completed its mission, the spacecraft will activate the module by sending it a pyro signal. The module will then deploy a 250 meter long conductive tape. Gravity gradient forces will then orient the tape along the local vertical direction. This tape will significantly increase the aerodynamic cross-section of the satellite, enhancing the drag it experiences due to neutral particles. In addition, the motion of this tape across the Earth's magnetic field will induce a voltage along the tape. This voltage will drive a current to flow up the tape, with electrons collected from the conducting ionospheric plasma at the top of the tape and ions collected at the bottom. This current will induce a 'passive electrodynamic' drag force on the tape. The enhanced aerodynamic drag and the passive electrodynamic drag force will lower the microsatellite's orbit, deorbiting it within 25 years. The Terminator Tape is a highly scalable technology. To date, TUI has developed two Terminator Tape modules. The CubeSat Terminator Tape (CSTT) is sized for CubeSats, shown in Figure 2, the NanoSat Terminator Tape is sized for large nanosats to small microsats (<100 kg), and the MicroSat Terminator Tape (MSTT) is sized for ESPA-class microsats (<200 kg), illustrated in Figure 3.
Fig. 1. Concept of operations of the Terminator Tape™.
Fig. 2. CubeSat Terminator Tape mounted on a 3U CubeSat structure. Shown with mass simulator solar cell models.
Fig. 3. The MicroSat Terminator Tape module is sized to fit within the Mark 2 Lightband used on the ESPA ring.
For heavier spacecraft, or spacecraft operating at higher altitudes, larger amounts of drag are required to deorbit the spacecraft within the 25-year requirement. To enable cost-effective compliance with debris mitigation requirements for these spacecraft, Tethers Unlimited is developing the Terminator Tether™ module. This module uses active electron emission technologies to greatly increase the electrodynamic forces, enabling it to deorbit most LEO spacecraft with in a period of several months. The Terminator Tether modules will typically mass less than 2% of the host spacecraft's dry mass.
Fig. 4. Concept of operations of the Terminator Tether™.
Fig. 5. Prototype Terminator Tether™ Deployer sized for a 3 ton spacecraft.
Before the spacecraft is launched, the Terminator Tether™ is bolted onto the satelite. When the Terminator Tether™ receives a command to deorbit the spacecraft, it deploys a 5 kilometer long tether below the spacecraft. This tether interacts with the ionospheric plasma and the geomagnetic field to produce currents running along the tether, and these currents in turn cause forces on the tether that lower the orbit of the tethered spacecraft. Over a period of several weeks or months, the Terminator Tether™ will reduce the orbital altitude of the spacecraft until it vaporizes in the upper atmosphere.
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