Meteor Defence Force
What NEC is doing to prevent devastating asteroid strikes
In 2013, a 20-metre-wide asteroid flew into the Earth’s atmosphere above the city of Chelyabinsk, Russia. Thousands witnessed the bright streak flash across the sky before it exploded in the air, 30 kilometres above ground. The blast released the same amount of energy as 500,000 tons of TNT. While the asteroid did not hit the earth’s surface, the explosion created a shockwave that injured 1,500 people and damaged 7,200 buildings across six cities.
Now, imagine the devastation if this seemingly tiny space rock had hit the ground, millions could have been killed and many others affected. Before we start panicking about the next meteor strike, let’s take comfort that the international space community is keeping a close watch on any celestial bodies around our planet, and there’s a way to prevent these disasters.
Hayabusa2 – NEC’s answer to planetary defence
International space agencies closely track the path of any space rock close to Earth. Based on its composition and trajectory, they can assess if a collision will occur. To avoid an asteroid strike, they will set up a robust plan to divert its path from our planet.
This is where NEC’s Hayabusa2 comes into the cosmic picture. The asteroid surveyor returned to Earth from its seven-year maiden mission in December 2020. It brought back surface material samples from asteroid Ryugu, providing the Japanese Space Agency JAXA valuable insights into its composition. Hayabusa2 also delivered an impressive three-dimensional mapping of the entire asteroid with the help of the state-of-the-art laser altimeter LIDAR.
Understanding the material composition of asteroids and their shapes and dimensions can help agencies decide on the best method to prevent a collision with the earth. It could be something as simple as a propulsion device attached to the asteroid's surface to steer it – a slight push is enough to move the asteroid considerably over time, as there is no friction in space – avoiding a disaster.
LIDAR – The super asteroid scanner
Perhaps the most impressive ‘weapon’ that the Hayabusa2 is equipped with is the LIDAR laser altimeter. LIDAR measures the distance to the surface of, say, an asteroid by projecting a laser beam at it and detecting the returning light. By taking these precise measurements while circling an asteroid, it is able to accurately map out its entire 3D dimensions.
The LIDAR beam also takes measurements of how much light bounces off the rocks, or the rocks’ reflectivity. Differences in reflectivity are a vital piece of information that helps to distinguish the different types of matter packed together on the surface.
What’s unique about LIDAR’s laser is that it travels in a dead-straight line without becoming diffused or diminishing in brightness, even over long distances. In December 2020, LIDAR was put to the challenge when the Hayabusa2 tested a two-way laser link with Earth. The beam was successfully transmitted and received, travelling a total of six million kilometers — more than fifteen times the distance between Earth and the moon.
The “sampler horn” – An ingenious mechanism for collecting space rock samples
There’s very little space agencies know about asteroids until a surveillance spacecraft actually gets there. The surface may be very uneven and rocky, or soft and unstable. To collect a sample, it might not always be feasible to use the simple “shovel technique”. To do that, though, you need a surface covered in sand; and because asteroids have such a weak gravitational field, the spacecraft could end up rising off the ground, endangering the entire mission.
NASA’s asteroid explorer OSIRIS-REx, tried a different technique. It collected samples by releasing a burst of nitrogen gas from the end of its sampling arm and capturing the sand stirred up. But that approach works only if the surface is sandy and not littered with boulders.
The NEC-developed “sampler horn” equipped on the Hayabusa2 uses the same concept as NASA, but instead of gas, it shoots a spherical projectile made of rare metal, which breaks the surface and sends fragments flying. The resulting cloud of debris ends up in the catcher. So whether the asteroid's surface is sandy or rocky, it does not pose a problem.
The Hayabusa2 journeys on…
The Japanese ion-powered spacecraft set off on its current journey in December 2020. It isn’t scheduled to arrive at its next destination until 2031. This eleven-year odyssey will test the limits of Hayabusa2’s capabilities – never before has a Japanese space explorer braved the unforgiving environment of outer space for so long.
Its destination? A mysterious asteroid called 1998 KY26, which, based on its trajectory, might be a threat to Earth. When the Hayabusa2 reaches close enough to observe the asteroid in detail, it could determine the density and hardness of the rock and the minerals that make it up. This would help scientists on Earth draw up a suitable plan in time to divert the asteroid’s course.
Until then, the Hayabusa2 boldly journeys on into the abyss of space. While all of us on Earth can look up into the dark night and be assured that our planet is being watched over by the keen laser eyes of our space explorer.