How diffractive solar sails could stop a killer asteroid at 100 km/s
Asteroids don't come with a warning label that they might one day hit Earth. While we don't know of any currently on course to do so, we are finding thousands of new ones each year, and there's always a chance that one could.
Asteroid strikes pose a significant threat to Earth, as we have yet to receive any warning signs of incoming celestial bodies. Thousands of new asteroids are discovered each year, and there's always a chance that one could collide with our planet. The recent DART mission successfully employed a kinetic impactor to alter the trajectory of a small asteroid, but this method has limitations.
The DART probe approached the asteroid from behind, requiring multiple orbital maneuvers and years of preparation. Researchers from Beihang University have proposed an alternative solution using diffractive solar sails to defuse an asteroid head-on. The energy transferred during an impact increases with the square of velocity, meaning that an impactor traveling at 100 km/s could deliver 230 times the energy per kilogram of impactor mass compared to the DART test.
However, reversing direction to enter a clockwise orbit requires substantial energy. Traditional chemical rockets are not capable of this task, but solar sails could potentially achieve the necessary trajectory change. Solar sails harness solar radiation pressure, allowing spacecraft to travel without fuel. Italian engineer Giancarlo Vulpetti developed an "H-reversal trajectory" that utilizes solar sails to reverse a craft's angular momentum and enter a retrograde orbit.
However, conventional solar sails are inefficient for this purpose due to their limited thrust orientation. To overcome this limitation, researchers explored diffractive solar sails, which use microstructured optical gratings to diffract light sideways without altering the sail's orientation. Simulations demonstrated that reflection-type diffractive sails are more effective in achieving the desired trajectory to impact an asteroid at high velocity.
The researchers tested this concept on a famous asteroid, Apophis, simulating a diffractive-reflective sail configuration capable of delivering a 100 km/s impactor within 200-300 days from launch. This method could potentially reduce mission time compared to traditional reflective solar sails. While we hope we won't need to employ this technology, it's reassuring to know that alternative deflection techniques are being researched and developed.
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