LightSail 2: A solar sail spacecraft could reach Mars in only 26 days

They measured the speed at which solar sails could reach Mars and the interstellar medium, which is also known as the heliopause — the point at which the influence of solar wind is no longer felt.

They simulated two different trajectories from Earth, known as direct outward transfer and inward transfer methods, for each of these journeys.

The direct outward transfer method for the trip to Mars and the heliopause involved the solar sail deploying and departing from a polar orbit around Earth.

For the inward transfer method, the solar sail spacecraft would be flown by a traditional rocket to a location roughly 0.6 astronomical units (AU) from the Sun. The solar sail would then deploy and begin its journey to Mars or the heliopause.

The researchers found that the direct outward transfer method allowed a solar sail spacecraft to reach Mars in 26 days. A spacecraft using the inward transfer method would reach the red planet in 126 days, though 103 of those days were the time it would take the conventional rocket to reach the deployment location.

For the journey to the heliopause, the inward transfer method took 5.3 years, while the outward transfer method took 4.2 years.

The outward transfer method requires 103 days of travel before deployment, but it reaches the heliosphere faster due to the fact that the solar sail reaches its maximum speed at 300 days. Using the outward transfer method, it would take two years to reach its maximum speed.

Sailing on sunlight

A big part of the reason the solar sails in the scientists' simulations would be able to get to these distant locations at such high speed is down to the material they are made out of — aerographite.

In an interview with Universe Today, study lead author Julius Karlapp, a research assistant at the Dresden University of Technology, said, "With its low density of 0.18 kilograms per cubic meter, aerographite undercuts all conventional solar sail materials."

"Compared to Mylar (a metallized polyester foil), for example, the density is four orders of magnitude smaller," he continued. "Assuming that the thrust developed by a solar sail is directly dependent on the mass of the sail, the resulting thrust force is much higher. In addition to the acceleration advantage, the mechanical properties of aerographite are amazing."

Of course, despite their incredible speeds, solar sails would only be able to carry very small payloads to Mars or deep space — the Breakthrough Starshot mission, for example, hopes to one day send a very light camera to our nearest star system, Alpha Centauri within 20 years.

"Solar sail propulsion has the potential for rapid delivery of small payloads (sub-kilogram) throughout the solar system," Dr. René Heller, an astrophysicist at the Max Planck Institute for Solar System Research and a co-author on the study, told Universe Today.

"Compared to conventional chemical propulsion, which can bring hundreds of tons of payload to low-Earth orbit and deliver a large fraction of that to the Moon, Mars, and beyond, this sounds ridiculously small," Heller continued. "But the key value of solar sail technology is speed."

Since it successfully demonstrated a working solar sail, the Planetary Society has been collaborating with NASA and other organizations on future light sail missions. NASA expects to launch its Solar Cruiser mission, which will study the Sun using a solar sail spacecraft, in February 2025.