Future solar powered orbital lasers could send small spacecraft to distant solar system destinations such as the Kuiper Belt or the Oort Cloud. This laser can be ground based or placed in orbit, with solar power providing the electricity for the orbiting laser. Solar sail propulsion is redefined as Light Sail propulsion when the photons are generated by a high energy laser. NASA and other space agencies have solar sail propelled missions on their agendas, essentially establishing solar sailing as a standard method of spacecraft propulsion. The success of the LightSail 2 mission paves the way for a future of solar sail propelled CubeSats operating in Earth orbit, Cis-Lunar space, and lunar orbit. The third stage has occurred since August of 2021 with increasing solar activity (increasing extreme ultraviolet radiation) resulting in an increasing rate of orbital decay of the LightSail 2 spacecraft. The second stage was from May to August of 2021 (also during solar minimum), when the spacecraft’s gyro was properly calibrated which resulted in optimum solar sail surface area exposed to the sun causing a small increase in spacecraft altitude per orbital period. The first stage (from July 2019 to May of 2021), occurred during solar minimum where the spacecraft experienced a slow decay in its orbit due solely to atmospheric drag effects. This has caused an increasing rate of orbital decay, with the LightSail 2 spacecraft expected to burn up in the atmosphere in the Northern Hemisphere sometime between Fall and Winter months of 2022.Īccording to Bruce Betts, LightSail 2 Program Manager, the altitude profile of the spacecraft occurred in 3 major stages. This increase in altitude of the upper atmospheric molecules drags the lower atmospheric molecules with it, resulting in a significant increase in atmospheric density per altitude. Increased solar activity since August of 2021 has heated up the upper atmosphere of the Earth, causing the atmosphere to expand. Since the LightSail 2 was initially placed in Low Earth Orbit (LEO) by a Falcon Heavy rocket, the spacecraft experiences a steady drag force caused by the high atmospheric density of LEO altitude air molecules. Even though the thrust generated by solar photons is very tiny, it is continuous, with the spacecraft experiencing constant acceleration. This momentum exchange generates a force (thrust) that propels the spacecraft into a higher orbit.
When the photons of sunlight reflect off the Mylar sail of the LightSail 2, they exchange momentum with the spacecraft. Even though photons have no mass, they have momentum due to their energy content. Light is made up of particles called photons that are made up of energy according to Einstein’s famous equation E = mc 2. Solar Sail propulsion is based on the physics of light. LightSail 2 uses the technique called laser ranging to determine the increase in spacecraft orbital altitude by measuring how long it takes a ground-based laser beam to reflect off a small array of mirrors located at the bottom of the CubeSat. The spacecraft is powered by 4 solar arrays with 8 rechargeable lithium-ion batteries that keep the CubeSat functioning during ecliptic periods. The LightSail 2 is a 78 cm length CubeSat that is attached to a 32 square meter solar sail. The LightSail 2 made history by becoming the first spacecraft to change its orbital altitude by thrust generated by the pressure of sunlight. In this latest suggestion, engineers propose making a sail from two layers made up of the compounds molybdenum disulfide and silicon nitride, both of which can be fabricated into sheets and have the kinds of optical properties to balance minimal absorption and emission of light as it stretches out.Ī second paper has tackled the problem not from a materials perspective, but a structural one designed to handle the strain of increased photon pressure a laser array would impose.On July 22, 2022, the Planetary Society held a Webinar event celebrating the three year anniversary of the solar sail deployment of the Society-built LightSail 2 spacecraft. But none have really focused on the trade-off between keeping the absorption low and the momentum high over a specific distance required to accelerate the craft. As the sail accelerates, for example, the wavelengths of radiation hitting it will appear to shift slowly towards the red end of the rainbow, setting limits on the kinds of material that won't absorb too much infrared and overheat.įinding the right material to make the sails tough, lightweight, and capable of handling the heat produced by gigawatts of stretched out laser light has been the subject of previous investigations.
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