Sails of the next century

Imagine solar sailing ships plying the trade routes between the planets, powered by light from the sun. David Whitehouse reports on a futuristic vision of space propulsion

Later this week, a group of hopeful people will gather for a conference at Nasa's Jet Propulsion Laboratory in Pasadena, California. The location is ironic; the method of space transport that they will be discussing doesn't involve jets at all. It uses the motive power of the sun's light to propel spacecraft of the future.

The conference title, "Solar Sails", revives a technology which has foundered in recent years. In the 1980s, George Bush asked a US event-planning committee to commemorate the 500th anniversary of Christopher Columbus's departure from Europe for the Americas. One bright idea was to launch a group of spacecraft using chemical rockets on Columbus Day, 1992, and let them race to Mars powered only by light pressure.

The idea never materialised. Yet the idea of solar sails is a robust one. Light applies a slight pressure on any illuminated object. In 1924, space pioneers Fridrikh Tsander and Konstantin Tsiolkovsky noted that in the vacuum of space, a large thin sheet of reflective material could work as a propulsion device requiring no propellant; sunlight would literally push it along.

For a highly reflective sail, the solar flux could produce a force of about nine Newtons for every square kilometre (one Newton is the force needed to give a one-kilogram mass an acceleration of one metre per second every second). That seems minimal - but it's actually quite reasonable, because it is continuous.

In 1973, Nasa sponsored a study for a solar-sailing probe to tow a platform of scientific instruments to intercept Halley's Comet. A team from JPL designed a number of solar sails. Their recommended sailcraft had a central mast and booms that would spread and support an aluminium-coated plastic sheet 850 square metres in size and two micrometres thick. Making one side of the sheet reflective and the other dark would set up a force imbalance that could be used for manoeuvring. It would weigh five tonnes and need little highly advanced technology. But it would have needed launching in 1985 to meet the comet.

Instead, others in Nasa decided that the Halley's Comet interceptor should be driven by a solar-powered electric propulsion system. Both studies were soon rendered academic when the project was cancelled by Congress.

In 1979, the World Space Foundation, a non-profit-making organisation of space enthusiasts (including many JPL scientists), took up the idea again. Two years later, the world's first solar sail, a half-scale prototype, was exhibited. By 1983, a full-size prototype was completed.

A spacecraft pulled by a solar sail - a large metal sheet, microns thick, that converts the momentum of sunlight into thrust - would be a very useful space vehicle. A sail of four square kilometres deployed from the Space Shuttle in Earth orbit could take a cargo-bay of payload to Mars before returning to Earth for more. An ordinary rocket motor would get the equipment there sooner, but would need up to three times as much fuel. It would also have to be lifted out of the Earth's "gravity well".

A "sunjammer" solar sail vehicle could carry any amount of cargo; the only difference would be to the journey time. Permanent bases on other planets such as Mars would be delighted to receive such provisions. Sunjammers could therefore form a bridgehead and lifeline for such colonists.

The Voyager 2 spaceprobe, now heading out of our solar system, will take some 80,000 years to travel the 4.3 light years (about 25 million million miles) to the nearest star - though it is not heading in the right direction. A conventional solar sail could perhaps reduce this to about 15,000 years because it would keep accelerating while the sun was behind it. In interstellar space, there would be nothing to slow it down. That time seems an eternity when compared with an individual's lifespan, but some scientists have suggested that we could speed sunjammers up by firing lasers or microwave beams at them.

Studies indicate that a solar sail 3.6 kilometres in diameter, trailing a one-tonne probe, could be powered by a 65 billion-watt laser fired from Earth orbit. Such energies are far higher than any yet obtained, but could conceivably be developed during the next century. Although the laser light would be a tight beam, it would tend to spread out over vast distances of space. For this reason, a large Fresnel lens 1,000 kilometres wide, located at a stationary point between Saturn and Uranus, would be used to focus the laser beam on the receding probe. Three years of such acceleration would give it a velocity 10 per cent that of light, meaning that it would reach the nearest star system - the Alpha Centauri group - in about 40 years.

Such ideas, although fascinating, are still deep in the realm of speculation. Other propulsion technologies may be better at propelling the first exploration trips to the stars, but it is not too fanciful to think of future space mariners plying the trade routes between the planets on sails of gossamer that ride the sunlight.

Surprisingly, perhaps, Tennyson saw it - or something like it - in the last century: For I dip't into the future/ far as human eye could see./ Saw the vision of the world,/ and all the wonder that would be,/ Saw the heavens fill with commerce,/ argosies of magic sails,/ Pilots of the purple twilight,/ dropping down with costly bales.

The writer is the BBC's science correspondent.

Suggested Topics
footballLIVE City face Stoke, while Warnock returns to Palace dugout
Life and Style
3D printed bump keys can access almost any lock
gadgets + techSoftware needs photo of lock and not much more
Paul McCartney backs the
Arts and Entertainment
Inside the gallery at Frederick Bremer School in Walthamstow
tvSimon Usborne goes behind the scenes to watch the latest series
Life and Style
Silvia says of her famous creation: 'I never stopped wearing it. Because I like to wear things when they are off the radar'
fashionThe fashion house celebrated fifteen years of the punchy pouch with a weighty tome
Arts and Entertainment
Gregg Wallace in Summer's Supermarket Secrets
tv All of this year's 15 contestants have now been named
i100Steve Carell selling chicken, Tina Fey selling saving accounts and Steve Colbert selling, um...
Life and Style
A picture taken on January 12, 2011 shows sex shops at the Paris district of Pigalle.
newsThe industry's trade body issued the moratorium on Friday
Arts and Entertainment
Could we see Iain back in the Bake Off tent next week?
tv Contestant teased Newsnight viewers on potential reappearance
ebooksAn evocation of the conflict through the eyes of those who lived through it
The slice of Prince Charles and Princess Diana's wedding cake and the original box from 29 July 1981
newsPiece of Charles and Diana's wedding cake sold at auction in US
The Ukip leader has consistently refused to be drawn on where he would mount an attempt to secure a parliamentary seat
voicesNigel Farage: Those who predicted we would lose momentum heading into the 2015 election are going to have to think again
Arts and Entertainment
Cara Delevingne made her acting debut in Anna Karenina in 2012
film Cara Delevingne 'in talks' to star in Zoolander sequel
Mario Balotelli pictured in his Liverpool shirt for the first time
Travel Shop
the manor
Up to 70% off luxury travel
on city breaks Find out more
Up to 70% off luxury travel
on chic beach resorts Find out more
sardina foodie
Up to 70% off luxury travel
on country retreats Find out more
Latest stories from i100
Have you tried new the Independent Digital Edition apps?
Independent Dating

By clicking 'Search' you
are agreeing to our
Terms of Use.

iJobs Job Widget
iJobs General

C# .NET Web Developer (ASP.NET, JavaScript, jQuery, XML, XLST)

£40000 - £50000 per annum + Benefits + Bonus: Harrington Starr: C# .NET Web De...

Clinical Negligence Solicitor

Highly Competitive Salary: Austen Lloyd: HAMPSHIRE MARKET TOWN - A highly attr...

Network Engineer (CCNP, CCNA, Linux, OSPF, BGP, Multicast, WAN)

£35000 per annum: Harrington Starr: Network Engineer (CCNP, CCNA, Linux, OSPF,...

Commercial Property Solicitor - Bristol

Highly Attractive Package: Austen Lloyd: A VERY HIGH QUALITY FIRM A high qual...

Day In a Page

Ukraine crisis: The phoney war is over as Russian troops and armour pour across the border

The phoney war is over

Russian troops and armour pour into Ukraine
Potatoes could be off the menu as crop pests threaten UK

Potatoes could be off the menu as crop pests threaten UK

The world’s entire food system is under attack - and Britain is most at risk, according to a new study
Gangnam smile: why the Chinese are flocking to South Korea to buy a new face

Gangnam smile: why the Chinese are flocking to South Korea to buy a new face

Seoul's plastic surgery industry is booming thanks to the popularity of the K-Pop look
From Mozart to Orson Welles: Creative geniuses who peaked too soon

Creative geniuses who peaked too soon

After the death of Sandy Wilson, 90, who wrote his only hit musical in his twenties, John Walsh wonders what it's like to peak too soon and go on to live a life more ordinary
Caught in the crossfire of a cyber Cold War

Caught in the crossfire of a cyber Cold War

Fears are mounting that Vladimir Putin has instructed hackers to target banks like JP Morgan
Salomé's feminine wiles have inspired writers, painters and musicians for 2,000 years

Salomé: A head for seduction

Salomé's feminine wiles have inspired writers, painters and musicians for 2,000 years. Now audiences can meet the Biblical femme fatale in two new stage and screen projects
From Bram Stoker to Stanley Kubrick, the British Library's latest exhibition celebrates all things Gothic

British Library celebrates all things Gothic

Forthcoming exhibition Terror and Wonder: The Gothic Imagination will be the UK's largest ever celebration of Gothic literature
The Hard Rock Café's owners are embroiled in a bitter legal dispute - but is the restaurant chain worth fighting for?

Is the Hard Rock Café worth fighting for?

The restaurant chain's owners are currently embroiled in a bitter legal dispute
Caribbean cuisine is becoming increasingly popular in the UK ... and there's more to it than jerk chicken at carnival

In search of Caribbean soul food

Caribbean cuisine is becoming increasingly popular in the UK ... and there's more to it than jerk chicken at carnival
11 best face powders

11 best face powders

Sweep away shiny skin with our pick of the best pressed and loose powder bases
England vs Norway: Roy Hodgson's hands tied by exploding top flight

Roy Hodgson's hands tied by exploding top flight

Lack of Englishmen at leading Premier League clubs leaves manager hamstrung
Angel Di Maria and Cristiano Ronaldo: A tale of two Manchester United No 7s

Di Maria and Ronaldo: A tale of two Manchester United No 7s

They both inherited the iconic shirt at Old Trafford, but the £59.7m new boy is joining a club in a very different state
Israel-Gaza conflict: No victory for Israel despite weeks of death and devastation

Robert Fisk: No victory for Israel despite weeks of devastation

Palestinians have won: they are still in Gaza, and Hamas is still there
Mary Beard writes character reference for Twitter troll who called her a 'slut'

Unlikely friends: Mary Beard and the troll who called her a ‘filthy old slut’

The Cambridge University classicist even wrote the student a character reference
America’s new apartheid: Prosperous white districts are choosing to break away from black cities and go it alone

America’s new apartheid

Prosperous white districts are choosing to break away from black cities and go it alone