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The Challenge and Promise of Interstellar Propulsion
The prospect of interstellar travel has been a dream of humanity for a long time. The recent rapid technological advances made interstellar travel a possibility, providing possible solutions for the difficulties that come with travelling between stars or planetary systems, such as large distances and power supply limitations. One of the biggest limitations for interstellar travel is the fuel source. Long distances between stars make the fuel storage and efficient use of fuel a difficult problem for spacecraft manufacturers and developers. A solar sail, a form of spacecraft propulsion using radiation pressure exerted by sunlight, is a promising way of providing propulsion for interstellar travel.
Solar Sails and Laser-Driven Acceleration
The further the spacecraft travels from the Solar System, the less intense the sunlight becomes, gradually making the solar sail obsolete. To resolve this issue, laser beam-powered propulsion has been proposed: the giant sails are pushed by lasers or masers to a significant fraction of the speed of light.
At the moment, researchers have already deployed several solar sails in space. In theory, an advanced solar sail could reach around 13% of the speed of light, as well as being able to withstand a wide range of temperatures, perform a gravitational slingshot move around the sun. Solar sails are ultra-thin, light, and durable, which makes them ideal for interstellar travel. However, a laser-propelled solar sail is expected to reach about 25% of the speed of light. The array of lasers is planned to be installed on Earth and fire continuously at the sail for several minutes, which will propel the spacecraft to 60,000 kilometers per second.
Technological Barriers and Needed Breakthroughs
The leading researchers and investors in the field of laser-powered solar sail design and construction are waiting for the breakthroughs in the laser industry, including fiber laser systems, which are the most promising technology among other laser systems. The 100-gigawatt array of lasers is around a million times more powerful than today’s biggest continuous lasers, which put out several hundreds of kilowatts. The array may be composed of several lower-powered lasers; however, they will need to be finely tuned and brought into phase with each other for the light waves produced by lasers to add and not cancel each other out. This technology has not been developed yet and requires the most work from laser manufacturers.
The solar sail itself must be worked on, as the material that can be potentially used in its construction needs to be extremely durable in order to withstand the powerful acceleration caused by the laser array for several minutes. The materials that have been tested so far are able to withstand such high forces for less than a second.
The projects that utilize solar sails plan to complete the technology and launch satellites and spacecraft in the next 20 years, which will put fiber laser manufacturers under pressure to develop the needed technology. In turn, researchers in the field of space technologies need to be on the lookout for new and developing companies that offer promising solutions for laser-powered solar sails.