The age of the solar sail is arriving sooner than expected

NASA has launched the latest attempt to test solar sail propulsion technology. 

The Advanced Composite Solar Sail System (ACS3), consisting of a CubeSat the size of a microwave oven and a solar sail, took off on board a Rocket Lab Electron rocket from Launch Complex I on the Mahia Peninsula in New Zealand. After reaching 600 miles above the Earth, the ACS3 deployed its sail.

The ACS3’s solar sail is made of a reflective polymer and is held by a boom made of carbon fiber composite material. Previous solar sail tests have used metal booms that have tended to warp due to the temperature extremes of space. The sail is 680 square feet in area.

The ACS3’s goal is modest, to use the solar sail to raise and lower the spacecraft’s orbit. But the technology might lead to sailing ships of the heavens, which use the pressure of sunlight to fly the solar system and even to visit other star systems.

A spacecraft that uses a solar sail has both advantages and disadvantages over those propelled by rockets.

A spacecraft propelled by a solar sail has three main advantages. First, it saves the mass of engines and rocket fuel. Second, it can theoretically fly forever if the solar sail remains intact and undamaged. Finally, while such a spacecraft would accelerate very slowly, the acceleration would be constant. In the fullness of time, it would build up incredible speeds.

The disadvantages of solar sails include that they are less effective the farther away from the sun they get, they tend to be large and hard to manage and susceptible to damage by even the smallest of space debris, natural or human-made.

Still, a working solar sail system creates a range of possibilities for cheap planetary missions.

A recent study published in Phys.org suggested that a probe propelled by a solar sail could reach Mars in just 26 days. By contrast, probes using conventional rockets take between 7 to 9 months. A combination of aerobraking and a conventional rocket would be used to insert the probe into an orbit around Mars.

The University of California at Berkeley proposed sending fleets of probes using solar sails to visit near-Earth asteroids and comets. The Berkeley Low-cost Interplanetary Solar Sail, or BLISS, project envisions swarms of these tiny craft sailing to these objects and taking high-resolution images of them.

Near-Earth objects are of interest for two reasons.

First, asteroids and comets whose orbits intersect Earth’s could provide valuable resources that fuel space-based industries. The kind of solar-sail-propelled probes that the BLISS envisions could discover where these objects are and their orbits.

Second, these objects could be a danger to Earth and every living thing dwelling on it. Over 60 million years ago, an asteroid hit the Earth and put an end to the age of the dinosaurs. A similar object could do the same to the human species. The detection of Earth-approaching objects and the measurement of their orbits and the likelihood they might collide with our planet could give us time to prepare to divert an object on its way to end humankind.

What about using light sails to send probes beyond our solar system, say to the Alpha Centauri system? Space.com recently discussed two studies for just such a mission.

Breakthrough Starshot, envisions using lasers on Earth to accelerate a probe the size of a microchip to 20 percent of the speed of light. The probe would reach the vicinity of Alpha Centauri in just 20 years. Two studies discuss the sort of materials that a solar sail would be constructed of and the shape of the sail that would ensure it would survive long enough to accelerate the probe so that it might cross interstellar distances within a human lifespan.

The idea of solar sails has been the subject of science fiction and speculation for many decades. Aside from test flights such as ACS3, the technology has yet to be seriously used. 

If solar sail spacecraft ever depart to interstellar destinations, they will impart the romance of the golden age of sailing the Earth’s oceans to space travel. They will be like the clipper ships and galleons that once transported cargo and people all across the world before the advent of coal, diesel and then nuclear power.

Mark R. Whittington, who writes frequently about space policy, has published a political study of space exploration entitled “Why is It So Hard to Go Back to the Moon?” as well as “The Moon, Mars and Beyond,” and, most recently, “Why is America Going Back to the Moon?” He blogs at Curmudgeons Corner.