Last week, the Planetary Society’s LightSail 2 mission celebrated the one-year anniversary of its launch date. The project has made great strides in demonstrating that solar sails are a practical method of propulsion. LightSail 2 was able to raise its orbit using sunlight as the only source of propulsion. The craft can be steered using momentum wheels so it can maximize the light received when moving away from the sun and minimize the light received when going toward the sun. It also set the record for the highest acceleration achieved by a solar sail to date.
As it turns out, the LightSail 2 mission hasn’t been completely trouble free. Two of the solar panels it uses to energize its momentum wheels and power systems like the onboard camera did not deploy correctly and are in a tipped position, so they don’t receive sunlight equally. This is seen in the shadow on the sail in the above image. Also, one of the sail booms appears to be bent. You can see what appears to be a gap in the left hand part of the sail and a structure visible through the gap. My takeaway is that despite these issues, LightSail 2 has done remarkably well.
I was pleased to learn that NASA has an upcoming solar sail mission and it’s investigating another one. The upcoming mission is the Near-Earth Asteroid Scout Mission or NEA Scout. Like LightSail 2, it will be a small solar sail deploying from a CubeSat. It’s currently scheduled for 2021 and the plan is for the craft to visit the asteroid 1991 VG. The larger goal of the mission is to better understand the larger Near Earth Asteroids that might be a threat to life on Earth. Another goal of this mission is to show that solar sails can be used to send scientific payloads to objects at low cost compared to craft that burn conventional fuel. This would be a somewhat larger solar sail than LightSail 2’s 32 square meter area. NEA Scout would deploy a 68 square meter solar sail. In the image below, we see the NEA Scout sail deployed in the lab along with some of the people working on it, to give an idea of the scale.
Another mission being considered is NASA’s Solar Cruiser. This would be a 1200 square meter solar sail used to provide views of the sun not easily available with current technology. It would measure the Sun’s magnetic field structure and the velocity of coronal mass ejections which at times can interfere with utility grids on Earth. This craft could be very useful as an advance warning system for at-risk infrastructure on Earth.
It’s exciting to see solar sails being scaled up into new projects. There have even been discussions of using solar sails for interstellar missions. A rocket can never go faster than its exhaust velocity. However, a solar sail can continue to accelerate as long as it gets light on its sails. It’s not yet practical to build a solar sail to propel a payload big enough to carry humans, but I suspect if the technology keeps being developed, it will get there one day. This dream is what I captured in my novel The Solar Sea. If you would care to join me on an imaginary voyage through the solar system using one of these sails pushed by light, visit: http://davidleesummers.com/solar_sea.html.
Greg Long in Australia recently posted a review of the novel, so I’m especially pleased to have shared the photo of LightSail 2 above. You can read Greg’s review at: https://greole.com/blog/2020/06/review-the-solar-sea-by-david-lee-summers-davidleesummers-sciencefiction/.