IKAROS: Sailing the Solar Wind to the Sun

Photo: JAXA
IKAROS / Solar Sail Unfurled

IKAROS - Sailing With the Solar Wind to Venus

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.

For readers who want "to get technical", place mouse cursor over photos and images to reveal 'hidden text.

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.

Origins of the Solar Wind - Extreme Flare Activity on the Sun's Surface
Photo: NASA / TRACE
Patterns of Plasma Flow are set by the Sun's magnetic fields

Origins of the Solar Wind 2 - Extreme Flare Activity on the Sun's Surface
Photo: NASA / TRACE
An extreme flare that could produce CME

Origins of the Solar Wind 3 - Extreme Flare Activity on the Sun's Surface
Photo: NASA / TRACE
Temperature / color codes: coolest - red, warm -green; and hottest in blue

IKAROS Mission
Photo: JAXA

IKAROS Mission Overview

(Japanese)

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.

See technical note behind 'Solar Sail Unfurled.

IKAROS / Deployment of Solar Sail as Seen from Spacecraft
Photo: JAXA

IKAROS / Deployment of Solar Sail - Static to Dynamic Configuration
Photo: JAXA

IKAROS / Deployment of Solar Sail Membrane

(Japanese)

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
Photo: JAXA

IKAROS - Solar Sail Unfurled
Photo: 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.

Solar Sail Membrane / Solar Cells
Photo: JAXA

The small gas-powered jet engine can also change the direction of the sail and perform other brief tasks. Additional instruments on board IKAROS measure interplanetary dust, and gamma ray bursts from newly born stars. This spacecraft does leave a carbon footprint but it is very small.

In several years, the second JAXA mission to test the solar power sail design will utilize a medium-sized, 50m solar power sail and integrated ion-propulsion engines. The challenge to this mission to generate adequate power using a power solar sail and thin photovoltaic cells is severe. At Jupiter's distance from the Sun, the efficiency of generating power from photovoltaic cells is only 4% that at Earth's distance. This spacecraft's mission is to fly to Jupiter and the Trojan asteroids.

Mourning for Icarus / Draper 1898
Photo: Staszek99/Wikimedia

Icarus flew too close to the Sun and died because wings and wax were a very poor choice for a close encounter with the Sun. His father Daedalus invented this zero emission flying technology to help himself and his son escape imprisonment on Crete and he told Icarus to avoid getting close to the Sun. Japan's IKAROS mission has achieved a breakthrough in noncarbon propulsion for spacecraft and can fly where Icarus could not. IKAROS has opened up a new, inexpensive and near zero carbon footprint option with which to continue exploration of our solar system. JAXA's power solar sail technology is a win-win for both astronomers and the solar power industry.

Sources: 1, 2, 3, 4, 5, 6, 7, 8

This article may be posted and copied elsewhere on blogs and in not-for-profit contexts with the requirement that this copyright notice is clearly visible. For use in for-profit business, please contact the author.