E.T.PACK’s overall goal is to develop a Deorbit Kit and related software based on LWT technology with TRL 4.
It will provide the first proof of concept for LWTs and may be followed by a project that can end with a demonstration flight. The Deorbit Kit (DK) will be designed with a set of requirements that are compatible with the needs of the industry and the space agencies to address the space debris problem. The preliminary list of requirements includes an efficient deorbiting from 850 km of altitude, scalability up to 1 ton of spacecraft mass, deorbit time below 25 years, no power consumption from the spacecraft, etc. The DK will include an onboard computer, hardware elements for telemetry and telecommand, and Attitude and Orbital Control System (AOCS) and involves breakthroughs in the following essential hardware and software elements:
- The LWT should gather a set of key characteristics such as: (i) the combination of thermionic and photoelectric electron emissions should give about 10-2A/m2 under solar illumination conditions in LEO, (ii) high conductivity-to-density ratio, (iii) correct solar absorption and emissivity to reach the expected working temperature, (iv) flexible to be packaged in a reel, (v) be compatible with space environment (ATOX, UV), etc. This can be achieved by coating a metallic substrate (Al or Cu) with a low W material. The most promising coating material is the C12A7:e- electride ([Ca24Al28O64]4+(4e-)) because it exhibits high electronic conductivity, its work function is extremely low, and it is not toxic.
- A Deployment mechanism (DM) specifically designed for a LWT with tape geometry will be designed and tested. It will host a tape of a few kilometres with the goal of being as light as possible. The deployer will be designed to be insensitive to reasonable variations of the tether friction characteristics.
- A software tool to compute self-consistently, i.e. via Vlasov-Poisson simulations, the current collected and emitted by a LWT with tape geometry will be developed. Its results will be used to refine actual LWT-plasma interaction models, construct a software for optimal design of LWTs under different scenarios and make analysis of the performance of the system in generation and thruster modes.
Additionally, three non-essential elements related with the C12A7:e- will be developed. Besides giving flexibility to the workplan and enhancing the impact, they can ease a future demonstration flight:
- A hollow cathode emitter based on C12A7:e- to make the DK work as a standard bare tether with an active electron emitter (backup mode for a demonstration flight).
- A hollow cathode thruster based on C12A7:e- with force in the mN range and specific impulse larger than 1000s.
- A Photon Enhanced Thermionic Emission Device to harness Sun’s light and heat to generate electricity. We propose a solid state device based on hetero-junction structure with C12A7:e- as a semiconductor.