According to the latest news released by NASA, the solar sail mission, which aims to test new space travel materials in Earth orbit, is scheduled to launch as soon as April 24. For the mission, a next-generation solar sail technology, known as the Advanced Composite Solar Sail System (ACS3), will be launched from the company's launch centre 1 in Māhia, New Zealand, on an electronic rocket from Rocket Lab. This technology could power future space travel and expand humanity's understanding of the Sun and the solar system.
The solar sail can be propelled using the pressure of sunlight, which causes photons to bounce off the reflected sail to propel the spacecraft. This eliminates heavy propulsion systems, allowing for longer duration and lower cost missions. While previous missions, such as the Planetary Society's famous LightSail 2, have demonstrated that small spacecraft can indeed travel millions of miles with solar sails and change orbits as needed, these missions use metal booms that are not only heavy but can deform unpredictably due to the extreme temperature fluctuations in space.
LightSail 2 is the first small spacecraft to demonstrate solar navigation using solar photons to readjust its orbit, pictured above in the Horn of Africa and the Gulf of Aden in January 2020
In comparison, NASA says the ACS3 system, which is four times larger than LightSail, uses a lighter boom made of carbon fiber-reinforced polymer (CFRP) that is strong enough to taut the solar sail while being flexible enough to fold compactly for launch.
A new lightweight solar sail developed by NASA in the United States
The advanced composite solar sail system demonstration uses a twelve-unit (12U) CubeSat, manufactured by NanoAvionics, to test a new composite boom made of flexible polymer and carbon fiber material that is stiffer and lighter than previous boom designs. The main goal of the mission was to successfully demonstrate the new boom deployed, and once deployed, the team also wanted to verify the performance of the solar sail.
Just as a sailboat turns to catch the wind, solar sails can adjust the track by adjusting the angle of the sail. After evaluating boom deployment, the mission will test a series of operations to change the spacecraft's orbit and collect data for potentially larger missions in the future.
Keats Wilkie, the mission's principal investigator working at NASA's Langley Research Center in the United States, noted that in the past, booms were often made of heavier metal materials or bulky lightweight composite materials, neither of which were suitable for today's small spacecraft. Solar sails require very large, stable, lightweight booms that can be folded compactly. The boom of this sail is tubular and can be flattened like a tape measure and rolled into a small package, while having all the advantages of a composite material, such as not bending when the temperature changes.
Mariano Perez, a quality engineer at NASA Ames, inspects an advanced composite solar sail system spacecraft
After reaching a sun-synchronous orbit about 1000 kilometers from Earth, the spacecraft will begin to deploy composite booms across the diagonal of the polymer sail. After about 25 minutes, the solar sail will be fully deployed, with an area of about 80 square meters, which is approximately the size of 6 parking spaces. Cameras mounted on the spacecraft will capture important moments in the sail and monitor its shape and symmetry during deployment. If the lighting conditions are right, the ship's sails can be seen from Earth. Once fully unfolded and in the right direction, the reflective material of the sail will be as bright as Sirius, the brightest star in the night sky.
Carbon fiber composite structure in an advanced solar sail
Solar sails use booms made of composite materials for deployment and support. Once the satellite is in orbit, the four composite booms on the spacecraft are untied from the spacecraft to form an X-shaped frame. This X-shaped frame is used to support the next four sail segments to be deployed. Since the boom is 7 meters long and the sail is 9 meters on each side, the total area is 81 square meters. The reflective film material of the sail is essential for harnessing solar radiation and generating enough thrust to move the satellite. Since the solar radiation pressure is very small, the actual solar sail must be very large, lightweight, and very compact to fit within the CubeSats and small satellite payload volumes. The ACS3 solar sail system is sized to fit a 12-unit (12U) CubeSat (below).
The solar sail system can be installed on a 12U CubeSat at launch
The ACS3 boom is made of carbon fiber-reinforced polymer material, which is a step forward in thin-layer composites over the past decade. The engineers at the German Aerospace Center were able to manufacture the boom from an ultra-thin composite material reinforced with multidirectional fibers. This makes it possible to create a flexible structure that can be folded or wound around the reel. The spools were placed at the four corners of the cubesats and activated to deploy the booms, each weighing only 900 grams.
These new booms save about 75 percent overall compared to Project Apollo, where all parts were made of metal. What's more, they are 100 times more resistant to thermal deformation in outer space. In addition, they take up less space on the boat because they can roll for compact loading. For a total surface area of 81 square meters, the sail itself weighs only 0.5 grams. By comparison, a peanut kernel weighs about 1 gram! Therefore, the ACS3 program provides an unprecedented means of optimizing weight and size.
The solar sail booms are stiff, lightweight, compact to store, and the carbon fiber construction also makes them less prone to bending at high temperatures
Enabling the solar sailing of the future
Through NASA's Small Spacecraft Technology Program, the successful deployment and operation of the solar sail's lightweight composite boom will prove its capabilities and open the door to larger missions to the Moon, Mars and beyond. This boom design could support a future 500 square meters of solar sail, about the size of a basketball court, and the technology brought by the success of this mission could support 2,000 square meters of sails, about half a football field.
Concept art of an advanced composite solar sail system spacecraft using the sun's energy to travel through space
Since sails use the power of the sun, they can provide constant thrust to support missions that require a unique vantage point, such as those trying to understand the sun and its impact on the Earth. Solar sails have long been a capability required for missions that carry early warning systems to monitor solar weather. Solar storms and coronal mass ejections can cause considerable damage to the planet, overload power grids, disrupt radio communications, and affect aircraft and spacecraft.
In addition to solar navigation, the lightweight design and compact packaging system in the composite boom may make it the perfect material for building habitats on the Moon and Mars, which can serve as a frame structure for buildings or a compact mast to create a communications relay for astronauts exploring the lunar surface.