Astrophysics and Space Sciences Transactions www.astrophys-space-sci-trans.net 1810-6528 1810-6536 5 1 2009 10.5194/astra-5-61-2009 http://www.astrophys-space-sci-trans.net/5/61/2009/ http://www.astrophys-space-sci-trans.net/5/61/2009/astra-5-61-2009.html http://www.astrophys-space-sci-trans.net/5/61/2009/astra-5-61-2009.pdf 61 69 2009-10-26 Electric Sailing under Observed Solar Wind Conditions P. K. Toivanen P. Janhunen Finnish Meteorological Institute, Finland 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. Allen,~J E.: Probe theory - the orbital motion approach, Physica Scripta, 45, 497–503, 1992. Hoyt,~R. and Forward,~R L.: Alternate interconnection Hoytether failure resistant multiline tether, US Pat. 6286788 B1, 2001. Janhunen,~P. and Sandroos,~A.: Simulation study of solar wind push on a charged wire: basis of solar wind electric sail propulsion, Ann. Geophys., 25, 755–767, 2007. Janhunen,~P.: Electric sail for spacecraft propulsion, J. Propul. Power, 20(4), 763–764, 2004. King,~J H. and Papitashvili,~N E.: Solar wind spatial scales in and comparisons of hourly Wind and ACE plasma and magnetic field data, J. Geophys. Res., 110, A02209, doi:10.1029/2004JA010804, 2004. Mengali,~G., Quarta,~A A., and Janhunen,~A.: Electric sail performance analysis, J. Spacecraft Rockets, 45, 122–129, 2008. Milligan,~D., Camino,~O., and Gestal,~D.: SMART-1 electric propulsion: An operational perspective, 9th Intern. Conf. on Space Operations, Rome, AIAA paper 2006–5756, 19–23, 2006. Mott-Smith,~H M. and Langmuir,~I.: The theory of collectors in gaseous discharges, Phys. Rev., 28, 727–736, 1926. Newbury,~J A., Russell,~C T., Phillips,~J L., and Gary,~S P.: Electron temperature in the ambient solar wind: Typical properties and a lower bound at 1 AU, J. Geophys. Res., 103, 9553–2566, 1998. Sittler,~E C. and Scutter,~J D.: An empirical polytrope law for solar wind thermal electrons between 0.45 and 4.76 AU: Voyager 2 and Mariner 10, J. Geophys. Res., 85, 5131–5137, 1980. Zubrin,~R M. and Andrews,~D G.: Magnetic sails and interplanetary travel, J. Spacecraft Rockets, 28, 197–203, 1991.