Solar sail technology is based on the pressure of sunlight on large surfaces. By bringing such a sail closer to the Sun, its efficiency is expected to increase. The Mercury Scout project is utilising this advantage to explore Mercury. The solar sail vehicle will map the Mercurian surface at a resolution of up to 1 metre and, by using the highly reflective surface of the sail to illuminate shadowed craters, will be able to search for water deposits.

In contrast to conventional rocket engines, which require fuel, solar sails are much more efficient. The light falling on the sail can move it through space. This concept, which dates back to the 1600s, was first proposed by Johannes Kepler to Galileo Galilei. It was not until the early 21st century that the Planetary Society built Cosmos 1, a solar sail vehicle. The vehicle was launched in June 2005, but failed to reach orbit due to a malfunction. The first such vehicle to be successfully launched was Ikaros, developed by the Japanese Aerospace Exploration Agency JAXA, which successfully demonstrated the feasibility of the technology.

It has been known since 1905 that light is made up of tiny particles called photons. These particles have no mass, but when travelling through space, they have momentum. When a tennis ball strikes a racket, it rebounds off the strings, transferring some of its momentum to the racket. Similarly, photons of light striking a solar sail transfer some of their momentum to the sail, imparting a slight push. As more photons strike the sail, this push becomes more pronounced, gradually accelerating the spacecraft.

Upon reaching Earth orbit, the Mercury Scout will utilise the solar sail as its primary propulsion system. Its objectives include mapping the distribution of minerals on Mercury’s surface, undertaking high-resolution surveys (up to one metre) and searching for ice deposits in permanently shadowed craters. The solar sail was selected due to its significant technical and financial advantages, which will reduce the overall cost of the project and shorten the mission time to Mercury.

In order to propel the Mercury Scout module, the solar sail must have a surface area of approximately 2500 m2 and a thickness of 2.5 microns. The material is aluminised CP1, which is similar to that used in the heat shield of the James Webb Space Telescope. The sail, which consists of four separate quadrants, will unfold on carbon fibre supports and will take 3.8 years to reach Mercury.

Upon arrival, the sail will enter a polar orbit, where it will remain for a further 176 days, mapping the planet’s entire surface. To achieve this, the orbit must be maintained by adjusting the angle of the sail. As with a conventional sailboat, which can sail upwind or downwind by adjusting the angle and position of the sail, a solar sail can be used to create thrust in the desired direction.

In contrast to conventional rocket engines, whose operational lifespan is typically constrained by the availability of fuel, the operational lifetime of a solar sail is solely determined by the rate of deterioration of its constituent materials. This operational lifetime is estimated to be approximately 10 years. Currently, additional coatings are being investigated with the objective of extending the operational lifetime of the sail.

Author: Mark Thompson
https://www.universetoday.com/166341/mercury-is-the-perfect-destination-for-a-solar-sail/#more-166341