2012.C.1.3 ESTCube-1: Stepping Stone for Fast Interplanetary Travel

Author(s)

Mart Noorma (1), Umas Kvell (1), Andris Slavinskis (1), Jouni Envall (2) and Pekka Janhunen (2)

University of Tartu / Tartu Observatory
Finnish Meteorological Institute

Session

C.1 – Propulsion Issues for Interplanetary Cubesat Missions

Keywords

cubesat; electric sail; spin-up; tether

Abstract

ESTCube-1 is the first satellite that will measure the electric solar wind effect. It is a single unit CubeSat which will be launch-ready by late-2012.

The electric solar wind sail (E-sail) technology relies on long, thin, conductive, centrifugally deployed tethers for extracting thrust from the solar wind dynamic pressure. A 100 kg E-sail module would have a hundred 20 km long tethers that will be charged to 20…40 kV positive potential. This creates a rather large electric field which in interaction with the solar wind at 1 AU distance from the Sun produces 1 N of thrust.

Designing the E-sail experiment for a single unit CubeSat on low Earth orbit (LEO) has the advantage of a low cost in orbit test, but also faces numerous challenges. For maximum benefit to the full-size E-sail development, the ESTCube-1 experiment will deploy a single 10 m long tether in LEO using centrifugal force – the same manner as the full-size E-sail would be.

Limited by the space of the single unit CubeSat standard, only magnetic torquers will be used for attitude control, including single axis spin-up to 1 rev/s for the centrifugal tether deployment. The successful deployment is verified by measuring the change in the spin period – as the tether is unreeled with a controllable motor, the spin rates slows down. A miniaturized on-board imaging system is used for additional verification – this requires the tether end-mass to have a white matte coating.

The tether that will be used is a 4-fold Heytether structure made from 25…50 μm thick aluminum wires. The tether lifetime in LEO will be shorter than in interplanetary space, as in addition to the micrometeoroids, there are numerous space debris particle populations.

When applying a positive potential to the tether, using a cold-cathode electron gun, the interaction between the charged tether and the ionospheric plasma can be observed. By turning the electron gun on and off in sync with the spin half-periods, the resulting change in the spin rate can be measured and the magnitude of E-sail force assessed.

Accurate measurement can only be done in specific regions of the satellite’s high-inclination orbit as to compromise between minimizing the Lorentz force from the tether’s interaction with the Earth’s magnetic field, having accurate enough ionospheric plasma measurement data available and assuring ground contact during the experiment.