NASA's solar sail spacecraft visible with naked eye. Here's how to spot it

NASA's experimental Advanced Composite Solar Sail System (ACS3) can be spotted with the naked eye as it orbits Earth. Here's how you can track it with Nasa's application

The National Aeronautics Space Agency (Nasa) launched the experimental Advanced Composite Solar Sail System (ACS3) in April 2024, which has now fully deployed its giant solar sail in orbit. The shining probe can be seen in the night sky from many places on earth. 

The mission aims to test solar sail technology as Nasa plans to build larger spacecraft in the future to use next-gen propulsion systems, driven by nothing but sunlight. 

These solar sails work just like nautical sails where wind drives the sail, but in this case, it’s the sunlight, as photons bounce off of the reflective material of the sail.

 

The ACS3 operates at an altitude of 600 miles (1000 kilometres) above Earth, nearly double the height of the International Space Station. The spacecraft orbits Earth with its large surface of 860-square-foot (80-square-metre) reflecting enough sunlight to be seen from the ground. In certain conditions, it can appear as bright as Sirius, which is the brightest star in the night sky.

Kevin Fetter tracked ACS3

Kevin Fetter, a satellite tracker, witnessed the ACS3 on camera on September 5, when it was passing though the brightest stars in the night sky. Fetter told SpaceWeather.com that, "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." 

Solar Sails is a great fuel alternative to carry out deep space missions

According to the Nasa website, “solar sails use the pressure of sunlight for propulsion, angling toward or away from the Sun so that photons bounce off the reflective sail to push a spacecraft.” The future spacecraft, therefore, no longer need heavy propulsion systems, enabling longer duration and lower-cost missions.
 

“Although mass is reduced, solar sails have been limited by the material and structure of the booms, which act much like a sailboat’s mast. But NASA is about to change the sailing game for the future,” reads the blog on Nasa website.

Researchers believe solar sails could advance space travel in the future allowing the development of spacecraft that are lightweight yet can still travel great distances without carrying heavy fuels. Solar sails can theoretically reach high speeds as it is believed their unique methods of propulsion grant them infinite acceleration. 

These sails can play a vital role in reducing space exploration costs while enabling missions of long durations, as their fuel supplies never exhaust. If ACS3 can successfully manoeuvre in orbit, it can succeed in its mission and can potentially help in developing more advanced solar sail spacecraft.

The ACS3 mission's lead systems engineer at NASA's Ames Research Center, Alan Rhodes, mentioned in the agency statement that, "The hope is that the new technologies verified on this spacecraft will inspire others to use them in ways we haven't even considered."

Scientists proposed using solar sails in order to conduct missions to bodies like Saturn's moon Enceladus or Jupiter's moon Europa. The Breakthrough Starshot initiative has suggested for years that solar sail propelled by lasers could reach Alpha Centauri, the closest star system to our own, in order to search for life.

How to Watch ACS3?

If you can watch the giant spacecraft as it crosses your location in the sky, you are in luck. Nasa has arranged sighting opportunities from your location. 

To watch Nasa's ACS3 solar sail, people need to download the Nasa application from the Google Play Store or Apple App Store. 

On the application, you can navigate 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."

Then click on 'Sightings' at the top of the mission option. Make sure to give location access to the application. It will show you dates and times when you can see Nasa's solar sail. You can also check the direction of the sky where you can witness the sighting of ACS3.