European Space Agency

Objectives

One of the main objectives of the designers of electric propulsion system for space applications is the reduction of power, volume and weight of electric coils and other electric components required to generate magnetic fields or to connect the thrusters with their power conditioning and control systems. High power electric propulsion systems intended to perform orbit raising manoeuvres or North South Station Keeping operations in telecommunication spacecraft will require high current coils that will benefit from a technology capable to reduce the mass of these coils.

The aim of the activity is to theoretically and experimentally study and address the potentiality of superconductor materials to be implemented in space electric propulsion units, helping to overcome limitations or enhance performances of the current conventional devices present on such units. The project aims to understand the potentialities and problems derived of using superconductors in space, specifically for electric propulsion, to identify the critical areas and to provide recommendations for future works. The study will be supported by measurements on breadboards of critical elements.

Potentiality of superconductors to be implemented in space electric propulsion units has been theoretically addressed. Larger potentiality has been detected on magnet sub-systems for HETs.

Magnetic numerical simulations have been run to design a demonstrator that has been subsequently constructed and tested at laboratory scale, but based on full-scale dimensional specifications. Moreover, and taken into account that thermal issues may become the highest constraints for the potential application of the technology, a complete discussion based on thermal simulations has been run to address the applicability of such cryogenic system on high-temperature plasma-driven thrusters.

Finally a technological roadmap has been produced.

Challenges

BSSCuO SC tape has been successfully handled and integrated into self-sustained double pancake coil assemblies including inner / outer Cu terminal elements brazed to both ends. They show an appropriate SC behaviour, maintaining the basic properties of the SC tape after the assembly process.

Moreover, using an specific test rig, the technical feasibility of SC technology to produce a radial B field inside an annular cavity, similar to the one required on a HET thruster unit, has been experimentally evaluated and demonstrated. Predicted values determined by finite elements procedure are in clear agreement with that obtained by experimental measurement.

Benefits

The technical feasibility of generating a radial B field in the discharge chamber, showing similar features to the one obtained using conventional electromagnets, has been demonstrated trough numerical simulations and experimental results of the demonstrator unit.

Detailed thermal simulations on complete 3D models have been conducted to end up with an optimised design of the cryostat and additional elements that allow assuring the cryogenic temperature (50K) on the SC materials while the discharge chamber is working at temperature levels above 600ºC.

SC magnets for HET units have been shown to be an attractive solution for medium to large up-scaling from SOA units. Preliminary calculations show that above 10kW, the weight and size reduction is significant. In case of very large up-scaling, SC solution can be an enabling technology since conventional electromagnets might no longer be applicable.

Features

The experimental breadboard designed, constructed and evaluated is an appropriate technological demonstrator rather than a full scale prototype. To consider a full scale real prototype will surely lead to important technological problems not directly linked to the SC concept. They will be engineering-nature problems, more linked to shape and size limitations, that could certainly be solved but with a considerable cost level (need of large size cryogenic test chambers/cryogenerators and auxiliary systems) and important technical effort that will not contribute to the real objective of the project.

The following conceptual design has been proposed:


click for larger image

Its main features are the following: (1) the full unit is inside a vacuum chamber simulating space conditions. 4 coils manufactured using BSCCO “market available” SC tapes, reproducing the required radial B-field. (2) Coils are supported on cooled structures (cryostats) and electrical contacts are conceived also in cooled regions (coolant pipes).

Main envisaged challenge is related to the electrical connexions and the consequent required design of the coil free ends to assure temperature and to avoid mechanical stress.

Plan

Phase 1: dedicated to the assessment of the applicability of superconductive materials. Review of SoA on superconductive materials and related technology. Identification of potential applications on EP systems.

Phase 2: a technological demonstrator breadboard of the most critical elements of the superconductive system chosen for the application decided during phase 1 will be experimentally tested. It will allow validating the concept by means of experimental testing and numerical simulations. Conceived to be representative enough to realistically validate the proposed technology.

A final development roadmap for implementing SC technology be performed based in the findings of the project.

Current status

Project finished.

Technical activities successfully accomplished.

Suitability of SC solutions to obtain the required radial B field inside the annular cavity of a HET discharge chamber has been theoretically and experimentally demonstrated (proof of concept) at laboratory scale and without the presence of the heat source (plasma discharge). Thermal management feasibility has just been theoretically demonstrated through numerical simulations.

Status date

Friday, March 13, 2009 - 10:49