Solar Winds: sail to the stars

I look out from the port during the summer to see the lake spotted with the sails of the intrepid enjoying the peace of Mother Nature's push. I watch our favourite swashbuckler Jack Sparrow order his men onto the yardarm to unfurl the canvas as he strikes out on a new adventure. There's a certain romance to this age-old system of propulsion, a system which doesn't use fuel to produce the force necessary to move the vehicle but which harnesses the power of the wind. It is an interesting concept. Instead of burning a substance to release its inherent energy, we are tapping into the energy of an existing force. It could be hydro-electricity; it could be a wind mill farm; it could be a solar panel but it is all an attempt to make use of what already exists.

Such are the things of dreams but dreams can come true; they can happen to you. In science fiction circles, a story line has been presented where a space ship doesn't fire up its rocket engines; it unfurls its sails and rides the solar winds. I remember reading about such a farfetched idea when I was young, my nose buried in a sci-fi novel which sometimes included an artist's rendering of just what such a contraption would look like. This seemed so unbelievable; how could anybody think this was possible?

As strange as this sounds, all this starts with light. For those of you who may have forgotten your physics one oh one, light is made up of individual particles called photons. These particles exert a certain force, a very small force mind you but a force nevertheless. Scientists have known for a long time that such a force could possibly be harnessed as a system of propulsion much in the same way a sail captures the force of the wind. The sun is constantly shining light everywhere and the stream of particles emanating from the sun is called the solar wind (http://en.wikipedia.org/wiki/Solar_wind). It is this "wind" that causes the various disturbances here on Earth like upsetting our power systems or communications, producing the northern (and southern) lights and pushing the tails of comets away from the sun.

Knowing this, scientists came up with the idea that a sail, obviously a very light sail, could conceivably be pushed by the solar wind. The image of a sailing ship is a good one and while the phenomenons (phenomena?) are totally different, the idea is essentially the same. Normally we think of propulsion in terms of a fuel as when the combustion engine of our car burns fuel to produce energy to displace it or a rocket which burns fuel to provide thrust. As with a sailing ship, we are using a force of something passing by us to push a sail and hence, push our vehicle. But who would have thought that light could push a sail and hence push a vehicle?

NanoSail-D2
Never heard of it, right? Hey, this is the stuff of science fiction; it is indeed exciting and we all need to get on-board and catch up with the latest from this NASA initiative.

Back on November 19, 2010 NASA's Fast, Affordable, Science and Technology Satellite, or FASTSAT, was launched from the Kodiak Launch Complex on Kodiak Island, Alaska. This satellite is a proof of concept called a "microsatellite platform" or a satellite which enables researchers to conduct low cost experiments. One of the many experiments on-board was NanoSail-D2, a device no larger than a breadbox which was to study the deployment of a solar sail. (see video of solar sail unfurling)

On January 17, 2011 NanoSail-D2 was successfully ejected from FASTSAT and according to its official web site, the sail was deployed. Unfortunately, NASA subsequently lost track of the device and the conjecture is that the battery running the device was drained. Without power, it is no longer sending out any signal. (artist's rendering of the device) However, there is a contest to snap pictures of the unfurled sail in orbit. The size of the sail is stated to be the size of a small tent and the orbit will approximately last for the next 100 days.

IKAROS
However, NanoSail is not the first to attempt to use a solar sail; that distinction goes to this Japanese satellite. Launched in May 2010, this interplanetary spacecraft deployed its sail in June 2010. A 20-meter sail made of polyimide resin just 0.0075 mm thick was unfurled in space (see diagram). The craft rotated 25 times per minute, and extended four "arms" of material folded origamilike, which unraveled and started generating power.

The craft is now using a solar sail for its propulsion; there is no rocket. It has already "set sail" for Venus and after doing a fly-by, it will continue to the far side of the Sun onto Jupiter where it will pass by that planet and the Trojan asteroid.

According to the official blog (Google translation of Japanese), IKAROS is currently 120 million kilometres from Earth. Signals take 14 minutes to traverse that distance!

Final Word
Considering how weight is such an important factor in anything involving space - the cost of getting all those pounds / kilograms off the ground - this new kind of propulsion system would have an enormous impact of the design of future spacecraft. Instead of costly motors and fuel, a solar-sail craft could devote more of its payload to scientific experiments. A craft with a propulsion system consisting of only solar sails would start at a snail's pace however, with no air resistance in space, momentum would rapidly build. Scientists have estimated that a mission to Pluto which currently takes 10 years could be done in five.

I read about this and saw drawings when I was a child. The future has arrived and here are two projects which have turned fantasy into fact.


References

Wikipedia: Solar Sail

Wikipedia: Solar Wind

Wikipedia: NanoSail-D
NanoSail-D was a small satellite which was to have been used by NASA's Ames Research Center to study the deployment of a solar sail in space. It was a three-unit CubeSat measuring 30 by 10 by 10 centimetres (12 × 3.9 × 3.9 inches), with a mass of 4 kilograms (8.8 lb). The satellite was lost shortly after launch due to a problem with the rocket carrying it, however a replacement, NanoSail-D2, was launched in 2010 to complete its mission.
...
NanoSail-D2 was built as a ground spare for NanoSail-D. Following the launch failure, it was launched in 2010 aboard a Minotaur IV rocket. It was ejected from the FASTSAT satellite on 6 December 2010, and successful ejection confirmed on 19 January 2011. NASA has requested to amateur radio operators to listen for Beacon signal from NanoSail-D.

NanoSail-D2 Mission Dashboard

NASA: Small Satellite Missions

Twitter: NanoSail-D

NanoSail-D2: video of sail unfurling

Wikipedia: FASTSAT
Fast, Affordable, Science and Technology Satellite or FASTSAT is a NASA satellite that was launched from the Kodiak Launch Complex in Kodiak, Alaska on November 20, 2010 on a Minotaur IV rocket. The mission's objective is to demonstrate the capability to build, design and test a microsatellite platform to enable researchers to conduct low-cost scientific and technology experiments on an autonomous satellite in space.

YouTube video: Minotaur 4 rocket launches FastSat, NanoSail-D (7 satellites total) from Kodiak, Alaska
November 19, 2010

Wikipedia: IKAROS
IKAROS (Interplanetary Kite-craft Accelerated by Radiation Of the Sun) is a Japan Aerospace Exploration Agency experimental spacecraft. The spacecraft was launched on 21 May 2010 aboard an H-IIA rocket, together with Akatsuki (Venus Climate Orbiter) and four other small spacecraft. IKAROS is the first spacecraft to successfully demonstrate solar-sail technology in interplanetary space.

JAXA Space Exploration Center: IKAROS Project

2011-01-26

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