NASA's solar sail spacecraft is visible in the night sky. Here's how to see it
NASA's Advanced Composite Solar Sail System (ACS3) can be seen with the naked eye as it orbits Earth, and can be tracked with a helpful app.
An experimental NASA solar sail can be seen in the night sky as it orbits the Earth.
NASA's Advanced Composite Solar Sail System (ACS3) launched in April 2024 atop a Rocket Lab Electron rocket. The mission is designed to test solar sail technology to help NASA develop larger spacecraft in the future using this next-generation propulsion system. Solar sails work similarly to nautical sails, but instead of being pushed by wind, they are impacted by the pressure of sunlight as photons bounce off of the reflective material they're made from.
On Aug. 29, the ACS3 spacecraft deployed its 860-square-foot (80-square-meter) solar sail while operating at an altitude about 600 miles (1,000 kilometers) above Earth, which is nearly twice as high as the International Space Station. As the ACS3 spacecraft orbits Earth, it's large surface area means it reflects enough sunlight to be seen from the ground. Under some conditions, the solar sail demonstrator could even appear as bright as Sirius, the brightest star in the night sky. If you want to see it for yourself, you're in luck: NASA has an app that lets you track sighting opportunities from your location.
To most easily see NASA's ACS3 solar sail, you'll want to download the official NASA app from the Google Play Store or Apple App Store.
From there, navigate to the "Featured" tab at the bottom of the app. You should see a section for the Advanced Composite Solar Sail System (ACS3) under "Featured missions."
Once you tap on that mission, you'll be able to then tap on "Sightings." If you've allowed the app to access your location, the app will give you a list of times and dates for when you'll be able to see NASA's solar sail, including in what direction of the sky it will be visible, its celestial altitude and the duration of each sighting.
Satellite tracker Kevin Fetter caught ACS3 on camera on Sept. 5 as it passed near one of the brightest stars in the night sky. "It got bright for a short time as it was passing by the star. Briefly it was just as bright as Vega, the 5th brightest star in the night sky," Fetter told SpaceWeather.com.
Some researchers believe solar sails could advance space travel in the future by allowing the development of spacecraft that are lightweight yet can still travel great distances without the need for carrying heavy fuels.
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Solar sails can theoretically also reach high speeds, as it is believed their unique method of propulsion can grant them infinite acceleration.
Related: NASA spacecraft captures 1st photo of its giant solar sail while tumbling in space
Solar sails could lower the cost of deep space exploration while also enabling missions of long durations, since their fuel supplies never exhaust. If ACS3 can successfully maneuver in orbit and succeed in its mission, it could potentially help develop more advanced solar sail spacecraft.
"The hope is that the new technologies verified on this spacecraft will inspire others to use them in ways we haven't even considered," said Alan Rhodes, the ACS3 mission's lead systems engineer at NASA's Ames Research Center, in an agency statement.
Scientists have already proposed using solar sails to send missions to Saturn's moon Enceladus or Jupiter's moon Europa, while the Breakthrough Starshot initiative has for years suggested that solar sails propelled by lasers could reach Alpha Centauri, the closest star system to our own, in order to search for life.
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Brett is curious about emerging aerospace technologies, alternative launch concepts, military space developments and uncrewed aircraft systems. Brett's work has appeared on Scientific American, The War Zone, Popular Science, the History Channel, Science Discovery and more. Brett has English degrees from Clemson University and the University of North Carolina at Charlotte. In his free time, Brett enjoys skywatching throughout the dark skies of the Appalachian mountains.
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johnfbramfeld 60 square feet does not equal 80 square meters, and the sail is not almost twice as high as the ISS, it is more than twice as high.Reply -
phottomatt
Reread the article, it says 860 square feet not 60, 860sqft = 79.9sqmjohnfbramfeld said:60 square feet does not equal 80 square meters, and the sail is not almost twice as high as the ISS, it is more than twice as high. -
Helio FWIW, my little mag. equations show as max. of 0.44 magnitude. I've seen one report it was about 0 mag. and another stating its maximum is 2.2 mag.Reply
My value is about that of Betelgeuse. -
dev_willis Most nautical sails are not pushed by the wind; they’re pulled by the low pressure area created in front of the sail by the wind flowing over it, similar to an airplane wing. Solar sails do NOT work this way.Reply -
Unclear Engineer
Sort of correct. Quibbles about what is a "push" and what is a "pull" in aeronautics.dev_willis said:Most nautical sails are not pushed by the wind; they’re pulled by the low pressure area created in front of the sail by the wind flowing over it, similar to an airplane wing. Solar sails do NOT work this way.
Solar sails are not just pushed in the direction away from the Sun. By angling the sail to be off-perpendicular to the direction of the incoming light, the reflection effect of the photons to one side can provide a sideways push in any direction required.
Too bad it can't tack up-(solar)-wind though, like a sailboat can go as little as 45 degrees off the direction that the wind is coming from. That is because the photons do not interact to change direction as they pass by close to the sail, unlike the way air molecules flow around a boat's sail. The photons do not act like a cohesive fluid, but more like individual projectiles.
And, of course, solar sails don't have any sort of keel sticking into a different fluid with a different motion on the other side of some interface between the fluids, like a sailboat does. So, there are fewer vectors to work with to get a net "upwind" force on a solar sail spacecraft, compared to a sailboat moving through water with air blowing across the water's surface.
So, in sailing terms, a solar sail can't quite get to a "beam reach" and is basically a "broad reach" and "downwind" sail.
But, a solar sail still does have some maneuvering capabilities. -
dev_willis
Very interesting explanation. Thanks!Unclear Engineer said:Sort of correct. Quibbles about what is a "push" and what is a "pull" in aeronautics.
Solar sails are not just pushed in the direction away from the Sun. By angling the sail to be off-perpendicular to the direction of the incoming light, the reflection effect of the photons to one side can provide a sideways push in any direction required.
Too bad it can't tack up-(solar)-wind though, like a sailboat can go as little as 45 degrees off the direction that the wind is coming from. That is because the photons do not interact to change direction as they pass by close to the sail, unlike the way air molecules flow around a boat's sail. The photons do not act like a cohesive fluid, but more like individual projectiles.
And, of course, solar sails don't have any sort of keel sticking into a different fluid with a different motion on the other side of some interface between the fluids, like a sailboat does. So, there are fewer vectors to work with to get a net "upwind" force on a solar sail spacecraft, compared to a sailboat moving through water with air blowing across the water's surface.
So, in sailing terms, a solar sail can't quite get to a "beam reach" and is basically a "broad reach" and "downwind" sail.
But, a solar sail still does have some maneuvering capabilities.