The concept of a solar sail seems to be right out of a science fiction novel. However, this could become a reality as soon as 2014, when a NASA research team; ‘In-Space Demonstration of a Mission-Capable Solar Sail’, plans to launch a solar sail and prove the feasibility and significance of this technology.
Historic Inspiration Behind Solar Sails
It all began with the imagination of German astronomer Johannes Kepler, who had observed what he thought to be solar breeze. He was inspired by this and believed that ships and sails could be built to glide through space using the heavenly air.
Later in 1873, a new observation was made by James Clerk Maxwell, who stated that the sun exerted pressure via photons that bounce off a reflective surface. It is this phenomenon that is being analyzed for use in solar sail designs today.
Another discovery in 1974 when NASA’s Mariner 10 spacecraft on a mission to Mars ran low on attitude control gas. NASA's scientists decided to use the Sun’s pressure to aid the Mariner 10. They angled the spacecraft’s solar arrays towards the Sun, gaining radiation pressure for attitude control. This was successful and the possibility of a solar sail.
With all these lessons, NASA began experimenting with solar sails that can be pushed through space by the power of sunlight.
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Could this be what Spacecrafts look like in the future? Powered by Solar Sails? Image Credit: Photos.com
Mechanics Behind Solar Sails
Primarily, a solar sail-powered spacecraft requires three key components - continuous force exerted by sunlight, a large ultrathin mirror, and a separate launch vehicle.
The solar sail-powered spacecraft uses the sunlight as its propellant and the sun as its engine unlike any other conventional spacecraft. Sunlight has electromagnetic radiation and exerts a certain force on objects it comes in contact with.
NASA scientists have discovered that at one astronomical unit (AU), which is equal to 93 million miles (150 million km), sunlight can produce about 1.4 kW of power. When 1.4 kW is divided by the speed of light, it gives the force exerted by the sun, which is about 9 Newtons (N)/square mile (i.e., 2 lb/km2 or 0.78 lb/mi2). The general belief among the NASA scientists is that the continuous force of the sunlight on a solar sail could propel a spacecraft to speeds five times faster than that of conventional rockets.
The solar sail-powered spacecraft has to be lightweight as well as highly reflective with the capacity to handle extreme temperatures. The material used by NASA is an aluminized, temperature-resistant material called CP-1, which is said to be 100 times thinner than an average sheet of stationery.
Photons from sunlight will bounce off the reflective material, and push the sail along by transferring momentum to the sail. The constant pressure exerted on the sail produces a constant acceleration for the spacecraft. The solar-sail spacecraft is constantly accelerated and over time achieves a greater velocity than conventional.
In case the solar sail veers away from the sun, NASA has an alternative - an onboard laser is designed to take over and provide the necessary propulsion for the sail.
For the entire solar sail spacecraft to be launched, another also has to be launched so the the solar sail spacecraft can be deployed into space.
The Sunjammer
NASA has dubbed their innovative solar sail spacecraft - the Sunjammer in honor of a 1964 Arthur C. Clarke story called ‘The Sunjammer’, in which he had coined the phrase ‘solar sailing’.
On NASA’s request the Sunjammer was built by L’Garde Inc. of Tustin, California. L’Garde Inc. has been involved in many NASA projects before as well.
When the sail of the Sunjammer is deployed, it will approximately measure 124 ft (a third of an acre) on one side - When collapsed it is merely 70 pounds in weight, which is 10 times lesser than the weight of the largest sail ever flown in space. The solar sail spacecraft is attached to a 175-pound disposable support module, and thus can be easily packed into a secondary unit on a rocket bound for low-Earth orbit.
NASA is working on several flight experiments to ensure the success of this project. Attitude controls, assessment of sail stability, ability to trim, navigation sequence are some of the issues being looked into.
The Sunjammer is planned for launch in 2014 by SpaceX, a rocket and spacecraft company started by Elon Musk (of Tesla Motors and Paypal), on top of its Falcon 9 rocket.
The Sunjammer has captured many a scientists’ imagination as it is could possibly be the first fuel-less spacecraft, thereby making it very affordable than any other. It will also be the first ‘green’ space propulsion system.
Future Possibilities
If the Sunjammer’s space odyssey is a success, it will open doors to several other versatile space missions such as flying an advanced space-weather warning system that could more rapidly and accurately alert satellite operators and utilities on Earth of geomagnetic storms caused by coronal mass ejections from the sun.
Another use of the solar sail technology would be to remove some of the 8,000 plus pieces of debris orbiting Earth, which would be a very economical solution as well.
The other possible applications are as follows:
- To conduct station-keeping operations
- To hover at high latitudes above Earth for communications and observation
- Deorbit old satellites
- Conduct deep space propulsion
- Drive numerous propellant-less, deep-space explorations and supply ferrying missions.
Private space companies are keen to harvest resources from asteroids and hence will be looking towards the success of this launch.
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