Electric Sailing under Observed Solar Wind Conditions P. K. Toivanen and P. Janhunen Finnish Meteorological Institute, Finland
Received: 04 Dec 2008 – Accepted: 04 May 2009 – Published: 26 Oct 2009
Abstract. In this paper, sailing and navigation in the solar wind with a
spacecraft powered by an electric sail is addressed. The electric sail
is a novel propellantless spacecraft propulsion concept based on
positively charged tethers that are centrifugally uncoiled and
stabilised to extract the solar wind momentum by repelling the solar
wind protons. Steering of such a sail ship is realised either by
changing the tether voltage or the sail spin plane. To model the solar
wind, we use spacecraft observations for the density and wind speed at
1 AU and assume that the speed is constant and density decreases in
square of the distance from the Sun. Using the electric sail thrust
formula, we describe the sail response to the solar wind variations,
especially, the self-reefing effect leading to a smooth spacecraft
acceleration even during periods of large densities or fast winds. As
a result, the variations of the acceleration are statistically small
relative to the density and wind speed variations. Considering the
navigation, we adopt an optimal transfer orbit to Mars originally
obtained for constant solar wind speed and density. The orbit and
associated sail operations including a coasting phase are then used as
the navigation plan to Mars. We show that passive navigation based
only on the statistical results is far too inaccurate for planetary
missions and active navigation is required. We assume a simple active
navigation system that monitors only the actual orbital speed with an
onboard accelerometer and matches it with the optimal orbital speed by
altering the tether voltage independently from the future solar wind
conditions. We launch 100 test spacecraft with a random launch date
and show that with the active navigation 85% (100%) of the
spacecraft reach a distance relative to Mars less than about 10 (70)
Mars radii with a residual speed less than 20 m/s (80 m/s). As a
conclusion, the electric sail is highly navigable and it suits for
targeting planets and asteroids, in addition to broad
targets such as the heliopause.
Citation: Toivanen, P. K. and Janhunen, P.: Electric Sailing under Observed Solar Wind Conditions, Astrophys. Space Sci. Trans., 5, 61-69, doi:10.5194/astra-5-61-2009, 2009.