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February 13, 2013

Carbon nanotube sheets for solar sails for 5.6% of lightspeed

Multiwall carbon nanotube sheets have been made with a mass of ~27 milligrams per square metre and about the strength of kevlar. Adam Crowl of Crowlspace examines this a bit more. Nextbigfuture covered the dry spinning of carbon nanotubes into sheets back in 2007.

The self-supporting MWNT sheets initially form as a highly anisotropic aerogel that can be densfied into strong sheets that are as thin as 50 nm. The areal density of the sheet is 30 mg/m and there is no fundamental limit on
sheet width or length. The measured gravimetric strength of orthogonally oriented sheet arrays exceeds that of the highest strength steel sheet.

In theory that means a suitably steered solar-sail made of CNT sheet could send itself away from Earth’s orbit and reach a final speed of 42*sqrt(57-1) km/s ~ 315 km/s. If it swooped past Jupiter then swung in hard for the Sun, scooting past at 0.019 AU, then it would recede at ~2,200 km/s (0.73 % of lightspeed).

A spaced out grid of carbon nanotubes with doping to have 100% reflectivity could achieve 5.6% of lightspeed.

Atomic layer deposition for solar sails almost as good as carbon nanotubes

Beneq has successfully scaled up its proprietary continuous ALD (atomic layer deposition) process to a 500 mm (half of meter. 20 inches) wide web using the R2R (roll to roll) manufacturing method.

The material developed for the proposed Drexler solar sail was a thin aluminum film with a baseline thickness of 0.1 micrometres (100 nanometers), to be fabricated by vapor deposition in a space-based system. Drexler used a similar process to prepare films on the ground. As anticipated, these films demonstrated adequate strength and robustness for handling in the laboratory and for use in space, but not for folding, launch, and deployment. Vapor deposition aluminum at 100 nanometer thickness would mass less than 0.1 grams/meter.



A lot of small solar sails could also form a matter beam that would hit the pusher plate of a larger and heavier spacecraft. This would allow a large and heavy spacecraft to achieve the speeds that the solar sails could reach.

Ikaros

Japan's JAXA successfully tested IKAROS in 2010. The goal was to deploy and control the sail and for the first time determining the minute orbit perturbations caused by light pressure. Orbit determination was done by the nearby AKATSUKI probe from which IKAROS detached after both had been brought into a transfer orbit to Venus. The total effect over the six month' flight was 100 m/s.

IKAROS has a diagonal spinning square sail 20 m (66 ft) made of a 7.5-micrometre (0.0075 mm) thick sheet of polyimide. A thin-film solar array is embedded in the sail. Eight LCD panels are embedded in the sail, whose reflectance can be adjusted for attitude control. IKAROS spent six months traveling to Venus, and then began a three-year journey to the far side of the Sun

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