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
Start your day with The Independent, sign up for daily news emails
i100 In this video, the late actor Leonard Nimoy explains how he decided to use the gesture for his character
Robert De Niro has walked off the set of Edge of Darkness
news The Godfather Part II actor has an estimated wealth of over $200m
Arts and Entertainment
Fearne Cotton is leaving Radio 1 after a decade
radio The popular DJ is leaving for 'family and new adventures'
Robbie Savage will not face a driving ban
football'Mr Marmite' faced the possibility of a 28-day ban
Life and Style
Nearly half of all young people in middle and high income countries were putting themselves at risk of tinnitus and, in extreme cases, irreversible hearing loss
health Nearly half of all young people in middle and high income countries are at risk of tinnitus
It was only when he left his post Tony Blair's director of communications that Alastair Campbell has published books
people The most notorious spin doctor in UK politics has reinvented himself
ebooksA special investigation by Andy McSmith
Arts and Entertainment
arts + ents
Life and Style
Arts and Entertainment
James Franco and Zachary Quinto in ‘I Am Michael’
filmJustin Kelly's latest film tells the story of a man who 'healed' his homosexuality and turned to God
Arts and Entertainment
Public Service Broadcasting are going it alone
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

Sauce Recruitment: Retail Planning Manager - Home Entertainment UK

salary equal to £40K pro-rata: Sauce Recruitment: Are you available to start a...

Ashdown Group: Front-End Developer - London - up to £40,000

£35000 - £40000 per annum: Ashdown Group: Creative Front-End Developer - Claph...

Recruitment Genius: Product Quality Assurance Technologist - Hardline & Electric

£18000 - £24000 per annum: Recruitment Genius: The role in this successful eco...

Ashdown Group: QA Tester - London - £30,000

£28000 - £30000 per annum: Ashdown Group: QA Tester - London - £30,000 QA Tes...

Day In a Page

HIV pill: Scientists hail discovery of 'game-changer' that cuts the risk of infection among gay men by 86%

Scientists hail daily pill that protects against HIV infection

Breakthrough in battle against global scourge – but will the NHS pay for it?
How we must adjust our lifestyles to nature: Welcome to the 'Anthropocene', the human epoch

Time to play God

Welcome to the 'Anthropocene', the human epoch where we may need to redefine nature itself
MacGyver returns, but with a difference: Handyman hero of classic 1980s TV series to be recast as a woman

MacGyver returns, but with a difference

Handyman hero of classic 1980s TV series to be recast as a woman
Tunnel renaissance: Why cities are hiding roads down in the ground

Tunnel renaissance

Why cities are hiding roads underground
'Backstreet Boys - Show 'Em What You're Made Of': An affectionate look at five middle-aged men

Boys to men

The Backstreet Boys might be middle-aged, married and have dodgy knees, but a heartfelt documentary reveals they’re not going gently into pop’s good night
Crufts 2015: Should foreign dogs be allowed to compete?

Crufts 2015

Should foreign dogs be allowed to compete?
10 best projectors

How to make your home cinema more cinematic: 10 best projectors

Want to recreate the big-screen experience in your sitting room? IndyBest sizes up gadgets to form your film-watching
Manchester City 1 Barcelona 2 player ratings: Luis Suarez? Lionel Messi? Joe Hart? Who was the star man?

Manchester City vs Barcelona player ratings

Luis Suarez? Lionel Messi? Joe Hart? Who was the star man at the Etihad?
Arsenal vs Monaco: Monaco - the making of Gunners' manager Arsene Wenger

Monaco: the making of Wenger

Jack Pitt-Brooke speaks to former players and learns the Frenchman’s man-management has always been one of his best skills
Cricket World Cup 2015: Chris Gayle - the West Indies' enigma lives up to his reputation

Chris Gayle: The West Indies' enigma

Some said the game's eternal rebel was washed up. As ever, he proved he writes the scripts by producing a blistering World Cup innings
In Ukraine a dark world of hybrid warfare and murky loyalties prevails

In Ukraine a dark world of hybrid warfare

This war in the shadows has been going on since the fall of Mr Yanukovych
'Birdman' and 'Bullets Over Broadway': Homage or plagiarism?

Homage or plagiarism?

'Birdman' shares much DNA with Woody Allen's 'Bullets Over Broadway'
Broadchurch ends as damp squib not even David Tennant can revive

A damp squib not even David Tennant can revive

Broadchurch, Series 2 finale, review
A Koi carp breeding pond, wall-mounted iPads and a bathroom with a 'wellness' shower: inside the mansion of Germany's 'Bishop of Bling'

Inside the mansion of Germany's 'Bishop of Bling'

A Koi carp breeding pond, wall-mounted iPads and a bathroom with a 'wellness' shower