IKAROS Solar Wind Sail

Imagine silent, clean power that brings us to distant planets and leaves almost no carbon footprint or other pollution in space. No longer science fiction, the solar sail has been designed, built and is now undergoing a first flight. IKAROS (Interplanetary Kite-craft Accelerated by Radiation Of the Sun) is the first of two missions from the Japanese Space Agency (JAXA) that will evaluate solar sails as propulsion systems for interplanetary spacecraft. The sail membrane of IKAROS utilizes photons from the solar wind to generate power. This sounds simple, but it is not. This innovative solar sail is a sophisticated, new design.

Solar Wind

The solar winds streams outward from the upper atmosphere of the Sun, and consists mostly of electrons and protons between 10ev and 100ev, but the particle stream varies in temperature and velocity. Particles escape the Sun’s gravity because of the high temperature of the Sun’s corona (>1 million degrees Celsius) and their very high kinetic energy. Think of the solar wind as the continual expansion of the Sun’s corona. This activity has very high amplitude, extreme variation and no apparent repeatable pattern. Coronal Mass Ejections (CMEs) resupply and reinvigorate the solar wind which supplies the ‘fuel’ (photons) for the solar sail of IKAROS.

IKAROS launched from the Tanegashima Space Center using the H-IIA rocket on May 20, 2010 and will reach Venus in December, 2010. After separation from the H-IIA, and spinning up to 20 rpm, sail deployment began on June 3, 2010.

The centrifugal force created by the spinning of the main body of IKAROS will be used to deploy the solar sail membrane, first quasi-statically by an onboard deployment mechanism on the side of IKAROS, then to a dynamic second stage. Because no rigid struts or supporting frame are required, the membrane can be quite large. This approach also significantly reduced spacecraft weight. Yet another new engineering challenge was met with a successful approach to targeted solar navigation. IKAROS is not at the mercy of hourly changes in solar radiation flux.

IKAROS has a companion for that portion of its journey that is within the inner solar system – the Venus probe ATAKSUKI (Planet-C). At Venus, ATAKSUKI will deploy into the upper atmosphere. It’s mission is to gather data so that a dynamic 3-D model of that Venusian atmosphere can be constructed.

IKAROS achieves targeted navigation by changing solar sail reflectivity. Sail reflectivity can be changed like that on frosted glass by frosting part of the plastic film which then reduces the reflectivity of that area of aluminum coating. Reduced area reflectivity reduces the amount of solar power produced by that area of sail polyimide. Change the reflectivity on the right and left sides of the sail and sail attitude can be controlled and modified. Targeted solar navigation has been activated and is now operational.

Control of Solar Sail Reflectivity
Control of Solar Sail ReflectivityPhoto: JAXA

IKAROS – Solar Sail Unfurled
IKAROS Solar SailPhoto: JAXA

The large solar sail has several parts and is a creative invention of beauty and utility. Sunlight is gathered by a large ‘membrane’. Photons of light reflecting off the sail transfer their forward momentum to the sail and thereby ‘push’ the spacecraft forward. Thin film photovoltaic solar cells on the membrane generate electricity. Solar radiation also supplies acceleration and drives an ion propulsion engine with high specific impulses. Photon acceleration working with the ion propulsion engine results in a hybrid engine that is the ultimate in clean power ad flexibility. IKAROS is also testing first generation solar-sail navigation by adjusting the direction of the reflected sunlight. IKAROS moves along a targeted orbit, it does not travel randomly as a passive spacecraft dependent upon the Sun’s location minute by minute.

Advantages of Solar wind power.

  • The scientists say that whereas the entire energy generated from solar wind will not be able to reach the planet for consumption as a lot of energy generated by the satellite has to be pumped back to copper wire to create the electron-harvesting magnetic field, yet the amount that reaches earth is more than sufficient to fulfill the needs of entire human, irrespective of the environment condition.
  • Moreover, the team of scientists at Washington State University hopes that it can generate 1 billion billion gigawatts of power by using a massive 8,400-kilometer-wide solar sail to harvest the power in solar wind.
  • According to the team at Washington State University, 1000 homes can be lit by generating enough power for them with the help of 300 meters (984 feet) of copper wire, which is attached to a two-meter-wide (6.6-foot-wide) receiver and a 10-meter (32.8-foot) sail.
  • One billion gigawatts of power could also be generated by a satellite having 1,000-meter (3,280-foot) cable with a sail 8,400 kilometers (5,220 miles) across, which are placed at roughly the same orbit.
  • The scientists feel that if some of the practical issued are solved, Solar wind power will generate the amount of power that no one including the scientists working to find new means of generating power ever expected.

How does the Solar wind power technology work?
The satellite launched to tap solar wind power, instead of working like a wind mill, where a blade attached to the turbine is physically rotated to generate electricity, would use charged copper wire for capturing electrons zooming away from the sun at several hundred kilometers per second.

Disadvantages of Solar wind power
But despite the fact that Solar wind power will solve almost all the problems that we were to face in future due to power generating resources getting exhausted, it has some disadvantages as well. These may include:

  • Brooks Harrop, the co-author of the journal paper says that while scientists are keen to tap solar wind to generate power, they also need to keep provisions for engineering difficulties and these engineering difficulties will have to be solved before satellites to tap solar wind power are deployed.
  • The distance between the satellite and earth will be so huge that as the laser beam travels millions of miles, it makes even the tightest laser beam spread out and lose most of the energy. To solve this problem, a more focused laser is needed.
  • But even if these laser beams reach our satellites, it is very doubtful that our satellites in their present form will be able to tap them. As Greg Howes, a scientist at the University of Iowa puts it, “The energy is there but to tap that energy from solar wind, we require big satellites. There may be practical constraints in this.”

Source: www.jspec.jaxa.jp
Source: www.EnvironmentalGraffiti.com
Source: www.Alternative-Energy-news.info
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