Upcoming Solar Sail Missions

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.

LightSail 2 Over Australia. Image by The Planetary Society

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.

NEA Scout sail deployed. Image by NASA.

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.

The Solar Sea

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/.

LightSail 2 – One Year After Launch

This past Thursday marked the one-year anniversary of LightSail 2’s launch into orbit. LightSail 2 is a crowdfunded solar sail project managed by the Planetary Society and it’s the first craft propelled entirely by sunlight. The Planetary Society hosted a webinar to celebrate the event. Planetary Society CEO Bill Nye, Chief Operating Officer Jennifer Vaughn, Program Manager Dave Spencer, and Project Manager Bruce Betts all spoke. The presentation was moderated by Planetary Radio host Mat Kaplan. I am pleased to have been one of the mission funders and I was delighted to have had an opportunity to attend the webinar live. I gather the presentation will be viewable soon at https://www.planetary.org/multimedia/planetary-tv/. I found the presentation fascinating and I took three pages of notes. I’ll touch on a few highlights below and in Tuesday’s blog post, but if you’re interested in this project, be sure to check out the full video at the link above. You can learn more about the Planetary Society by visiting http://www.planetary.org.

Screen shot of the live webinar featuring Bill Nye, Dave Spencer, Mat Kaplan, Jennifer Vaughn, and Bruce Betts

The most exciting news from the webinar is that LightSail 2 is still flying one year after launch. It was placed into an orbit about 720 kilometers above the Earth’s surface, which is still low enough to have a very small amount of atmospheric drag. Despite that, the spacecraft has only lost about 10 km of altitude over the course of a year. It’s not certain how long it will be before it de-orbits, but current estimates say LightSail 2 could continue its mission for another year.

Bill Nye opened the presentation by noting it was 17th century astronomer Johannes Kepler who first speculated on the possibility of solar sails after observing the comet that would ultimately be known as Comet Halley. He reasoned that whatever force from the sun could produce the comet’s tail could propel a sailing vessel to other planets. The specific particle that can be used to propel a solar sail is the humble photon. Light has momentum and that momentum can be transferred to the sail for motion.

LightSail 2 has been able to perform so well because it can be turned like a sailboat’s sail. In this case, the craft is turned by momentum wheels aboard the ship. Momentum wheels are just gyroscopes, but tradition suggests that the word “gyroscope” is used principally when applied to navigation. When LightSail 2 is in a position to get a boost from sunlight, it turns so the sail catches all the light. When the light pressure would work against the sail, the craft turns 90 degrees so it presents the sun with the least amount of surface to push against.

Many great photos were shared during the webinar. My favorite was this one showing LightSail 2 over the Nile and the Red Sea. As you’ll notice, there’s a thin blue line at the Earth’s left edge. That’s our atmosphere, which looks very thin and fragile. I also imagine measuring the spectrum of that thin film on a planet in some distant stellar system from a telescope in our solar system. It’s a real technical challenge, but it looks like we may be getting close to a point where we could do that. This is something we’ll need to do in order to determine whether or not an exoplanet is potentially habitable.

LightSail 2 over the Nile and Red Sea. Image from The Planetary Society.
The Solar Sea

One of the things that makes all of this personally exciting is that I first joined the Planetary Society when I was in high school as a result of a letter sent to Star Trek fan clubs by Gene Roddenberry. I first learned of the Society’s interest to make solar sails a reality in the society’s newsletter, The Planetary Report. The idea caught my imagination and in high school, I started to write a novel called The Solar Sea. I didn’t complete it then, but the idea stayed with me and I made several attempts until I wrote a version that pleased me. That version was published in 2008 and you can learn more about it at: http://davidleesummers.com/solar_sea.html

Successful Solar Sailing

The Planetary Society’s LightSail 2 spacecraft launched into orbit on June 25, 2019 and deployed its 32-square meter sails almost a month later on July 23. In the time since sail deployment, it raised its orbit some seven kilometers. Here we see a great shot of the LightSail 2 over Australia.

LightSail 2 image courtesy The Planetary Society

In 1619, astronomer Johannes Kepler noticed that comet tails always point away from the sun and realized that some solar force must produce that effect. Two centuries later, in 1862, James Clerk Maxwell suggested that light has momentum and it was finally demonstrated in 1900. The goal of the LightSail 2 mission was to show that momentum from light could propel a spacecraft. The process of solar sailing is not unlike sailing on the water, only in space, gravity acts like water currents while light acts like wind. As with a sail at sea, the sails must be turned in flight to take the best advantage of the “wind” while the ship moves on the “current.” LightSail 2 accomplishes this via internal reaction wheels. The gif below shows how the sail is turned to take the best advantage of sunlight and raise its orbit.

Josh Spradling / The Planetary Society

The following graph shows the elevation of LightSail2 over the course of the mission. The apogee is the highest point in orbit, the perigee is the lowest point. At LightSail2’s elevation, there are two forces working on the sail besides gravity. The first is light pressure from the sun. The other is atmospheric drag from the Earth. Even though LightSail 2 is in a relatively high orbit, it’s still in the most tenuous parts of the upper atmosphere. The upshot is that the apogee increases because of light pressure, but the perigee decreases because of atmospheric drag. That noted, LightSail 2 has accomplished the mission it set out to do, demonstrate that light can propel a spacecraft.

Image from the LightSail Mission Control Page supported by the Planetary Society

You can keep up to date with the LightSail mission and visit their mission control page by going to http://www.planetary.org/explore/projects/lightsail-solar-sailing/#the-lightsail-2-mission.

It’s worth noting this is a technology in its infancy. That said, with the lessons learned from this mission, there’s promise that solar sails could be used for small unmanned probes in the not-too-distant future, or perhaps they could be used to deflect dangerous asteroids, especially if caught early enough that they only need a small nudge.

In the long run, with much more development and technical innovation, I would like to think solar sails could be used to propel humans across the solar system as I imagine in my novel The Solar Sea. In a little under a week, on Friday October 11, Lynn Moorer will interview me about the novel on her radio show from 12:30-1:00 pm mountain daylight time. If you’re in Las Cruces, you can tune in to 101.5 FM on your radio dial. If you aren’t in Las Cruces, or just don’t listen to shows on the radio, you can stream the show at  https://www.lccommunityradio.org/stream.html. It looks like KTAL Community Radio is building up their archive of past shows, so I’m hoping I can share these interviews with you soon. If you want to read the book before the interview, you can find all the places it’s available by visiting http://www.davidleesummers.com/solar_sea.html.

Celebrating the Future

Early in the morning of June 25, the Planetary Society’s LightSail 2 mission launched aboard a SpaceX Falcon Heavy rocket. Actual deployment of the sail is set for today. These are great accomplishments to celebrate. On a more personal note, my novel Firebrandt’s Legacy received a wonderful review from Midwest Book Review. The reviewer says Firebrandt’s Legacy is “A rip-roaring space adventure!”

Also underway is the annual Smashwords Summer/Winter Sale. It gets its name because where I live in the northern hemisphere, readers are loading up their e-readers for great beach reading and vacations. In the southern hemisphere, it’s the middle of winter where people are spending time in a warm and cozy place reading. So, to celebrate the successful launch of LightSail 2 and a good review in Midwest Book Review, my novels The Solar Sea and Firebrandt’s Legacy are on sale at Smashwords for just $1.00 each this month. Keep reading for the details.


In The Solar Sea, whales around the world changed their songs the day scientists announced the discovery of powerful new particles around Saturn’s largest moon which could solve Earth’s energy needs. The Quinn Corporation rushes to build a solar sail space craft to unlock the secrets of these strange new particles. They gather the best and brightest to pilot the ship: Jonathan Jefferson, an aging astronaut known as the last man on Mars; Natalie Freeman, a distinguished Navy captain; Myra Lee, a biologist who believes the whales are communicating with Saturn; and John O’Connell, the technician who first discovered the particles. Charting the course is the mysterious Pilot who seems determined to keep secrets from the rest of the crew. Together they make a grand tour of the solar system and discover not only wonders but dangers beyond their imagination.

T. Jackson King, the author of Battlestar and Star Glory says, “This story follows the private space industry exploration of the Moon and becomes a kind of Voyage of the Beagle as the solar sail ship Aristarchus visits Mars, Jupiter, then Saturn and its giant moon Titan … Highly enjoyable read. Highly recommended.”

Get the book for $1.00 at: https://www.smashwords.com/books/view/805692


In Firebrandt’s Legacy, Ellison Firebrandt fights the good fight for Earth. Under a letter of marque, he raids the ships of Earth’s opponents, slowing down their progress and ability to compete with the home system. On the planet Epsilon Indi 2, he rescues a woman named Suki Mori from a drug lord, only to find she isn’t so happy about living a pirate’s life. However, when the captain finds a new engine that will make him the most successful pirate of all, Suki is the only one who can make it work. Now Firebrandt must find a way to keep his crew fed and his ship supplied while relying on a woman who barely trusts him and while every government in the galaxy hunts him to get the engine back!

Midwest Book Review says, “A grand space opera filled with high adventure from cover to cover, Firebrandt’s Legacy is highly recommended.”

Get the book for $1.00 at: https://www.smashwords.com/books/view/916916

LightSail 2 Launch

On Monday, The Planetary Society’s experimental solar sail, LightSail 2 is scheduled to launch aboard a SpaceX Falcon Heavy. I’m a member of the society and one of this mission’s Kickstarter backers, so I’m really excited to see this mission getting underway.

Artist’s Concept of LightSail above the Earth, courtesy The Planetary Society

Currently, LightSail 2 is tucked into a package about the size of a loaf of bread called a CubeSat and this CubeSat sits inside a suitcase sized satellite called Prox-1. Prox-1 will be deployed from the SpaceX rocket at an altitude of 720 kilometers, about an hour and twenty minutes after launch. About a week after launch, Prox-1 will open a hatch and the CubeSat will be ejected. At this point, onboard computers will boot up and ground control will start conducting tests. Presuming all goes well, about five days later, solar panels will be deployed and a day after that, the 32-square meter solar sail will deploy.

In solar sail theory, gravity is like the water currents that carry an earth sailboat. Photons from the sun are like the wind. The goal of LightSail 2 will be to show that the sail can orbit the Earth in such away that light pressure can carry it into a higher orbit. To do this, it needs to have the reflective sail facing the sun when being pushed away. Then it needs to turn its reflective surface away when gravity carries it toward the sun. This means that sunlight will give it a push every time the craft goes around the Earth.

As it turns out, the Japanese Space Agency, JAXA has already demonstrated that sunlight can cause a light sail to accelerate. In 2010, they launched a probe toward Venus. Piggybacked on that mission was a solar sail called Ikaros. With no other source of propulsion than sunlight, Japanese scientists saw Ikaros accelerate. The photo above this paragraph shows Ikaros in flight.

I’ve long been fascinated by the concept of solar sails ever since I first read about them in an early edition of The Planetary Society’s newsletter, The Planetary Report. In high school, I came up with the idea for a novel called The Solar Sea. I wrote a few chapters and then set it aside in favor of other projects. I finally returned to the idea almost twenty years later, in 2007. I defined the characters, determined the mystery they were solving, and wrote the book. It tells the story of humanity’s first voyage through the solar system aboard a solar sail spacecraft. In the novel, the astronauts visit Mars, Jupiter, and Saturn. At each stop, they learn more clues to the nature of life in the galaxy. The story expresses my love of astronomy, space exploration, and the solar system. If you’re as fascinated as I am about traveling on a space ship powered only by sunlight, I invite you to take a journey through The Solar Sea.