China's aerospace sector has been developing at an incredible clip. They have been building rockets capable of reaching the money, stealth fighters,
a global position system able to rival the American GPS, and hypersonic technologies. China even became the first nation to return to the moon's
surface not once, but twice, including one on the lunar farside. A feat neither of the Cold War super powers accomplished. China isn't resting on
its laurels either.
China's Shenyang Institute of Technology flew a cubesat with a demonstrator for a solar sail onboard. The solar sail was the first, subscale
demonstration of that technology by the Chinese. The Chinese have been working on flexible structure deployment systems since 2011 and the SIASAIL-1
was the first demo of that technology along with the basic solar sail tech. Solar sails have the potential to be an expensive delivery system for
the solar system.
Solar sails operate by being very low mass relative to its surface area and reflecting the light from the sun. Solar sails are huge, but low mass
mirrors in essence. Light has momentum and when reflected, the photon bounces off and pushes the sail. The acceleration is minuscule: at best around
1 mm/s^2. However, so long as the sun is shining on the sail, the solar sail can constantly accelerate. This means over time, a solar sail can
actually accelerate to speeds faster than a chemical rocket.
The real beauty of a solar sail, though, is there is no fuel and it can be used over and over without needing to replenish the spacecraft. So long as
it has sufficient reflective surface, it can still accelerate and deliver cargo. Over time, the sail will be torn and degrade, but the spacecraft
could act as a reusable delivery system throughout the solar system, at least the inner solar system, for decades.
One of the beautiful alternate potential uses of solar sails would be to hover over the poles of the earth. At sufficient height and with sufficient
efficiency, a solar sail could just hover above one of the poles of the Earth, using the acceleration imparted by reflecting sunlight to cancel out
the effects of gravity from the Earth. This would keep a satellite directly above that point and allow for a constant surveillance of the poles.
To be sure, the US has known about solar sails for decades. The NASA mission to Haley's Comet that was considered and then cancelled had looked at
using a solar sail (an ion drive was selected before cancellation though as the solar sail was considered too new and risky at the time). The
Planetary Society with its COSMOS-1, Light Sail-1 and Light Sail-2 have been largely developing the technology. Until now.
China has taken a keen interest and started spending money on it. It will be interesting to see if China follows through. If so, it could allow for
a reusable interplanetary transportation system suitable for cargo and would be a unique capability. China has a long way to go before the technology
is useful, but the longest journeys are begun by the first steps.