The US space association NASA plans to launch a Double Asteroid Redirection Test (DART) on 24 November 2021 from Vandenberg Space Force Base, California. The spacecraft will be launched from the SpaceX Falcon9 rocket. Through this mission, NASA is planning to build advanced technologies to protect Earth from hazardous asteroid collisions. The idea of the DART mission is based on the mission of developing a defense system against asteroid collisions. The main reason for this mission is the warning of scientists and astronauts that asteroids can cause severe damage to Earth without a proper defense system. The primary example that was pointed out was the extinction of dinosaurs due to an asteroid collision 65 million years ago.
DART is one of NASA’s largest planetary defense strategies. Planetary defense contains the measures required to detect the potential asteroid and comet collisions with Earth. They aim to prevent collisions and to avoid the possible effects of a potential impact.
Asteroids
Asteroids, also known as minor planets, are the rock remnants from the formation of the solar system around 4.6 billion years ago. There are around 1,113,527 known asteroids in the solar system. Most asteroids orbit around the Sun and are located between Mars and Jupiter.
Asteroids are often irregularly shaped though some are spherical. There are around 150 asteroids with a small companion moon called moonlet, and there are binary and triple asteroid systems which are two or three same-sized asteroids that orbit around each other. Asteroids are classified into three types which are C-, S-, M- types. The C- type or chromite type contains silicon and clay rocks and are dark in color. They are one of the oldest objects in the solar system. The S- type or stony type contains silicate and nickel-iron, and the M- type contains nickel-iron.
Didymos—The Ideal Target for DART’s Mission
The target of DART is a binary asteroid system called Didymos. However, it is not in a direct path to collide with Earth, so it is not a threat. It is similar in size to an asteroid that could be potentially dangerous for Earth. This binary asteroid system contains two asteroids. The primary body is called Didymos, which means twin in Greek, is around 780m in diameter, and the secondary body or the moonlet is called Dimorphous. Dimorphous is around 160m in size and orbits around the larger asteroid. The DART plans to impact Dimorphous directly and change its orbital path by several minutes.
When viewed from Earth, the Didymos system is an eclipsing binary which means when Dimorphous orbits around the larger one it appears in front of and behind Didymos. The DART will impact the asteroid in 2022 when the distance between the asteroid and Earth is 11 million kilometers; this will enable the scientists to observe the impact and subsequent actions through telescopes on Earth.
Double Asteroid Redirection Test (DART) Mission
The DART, a planetary defense-driven test, was built and developed at John Hopkins Applied Physics Laboratory (APL) and other NASA centres, including JPL, GSFC, JSC, GRC, and LaRC. The mission, which is in Phase C, is the first demonstration of the kinetic impactor technique capable of changing the motion of an asteroid in space. The kinetic impactor deflection is achieved by deliberately crashing into the moonlet Dimorphous at 6.6 km/s with the help of an onboard camera named DRACO (Didymos Reconnaissance and Asteroid Camera for Optical navigation) and autonomous navigation software. DRACO is a high-resolution camera that supports navigation of the spacecraft, measures the size and shape of the asteroid, and determines the impact site and geologic context. Even though the collision will only change the speed of the moonlet by one percent, it will be able to change the orbital period of Dimorphous around Didymos by several minutes. The DART project will show that a spacecraft can successfully navigate itself to an impact on the target and will measure the effect of that impact on the natural asteroid. The mission will help NASA prepare for asteroids that might be dangerous to Earth.
When launched, the spacecraft will deploy Roll-Out Solar Arrays (ROSA), which will provide the solar power necessary for the functioning of its electric propulsion system. After the separation from the launch vehicle, the spacecraft will have a year-long cruise and will intercept Dimorphous in late September 2022, around 11 million kilometers away from Earth. The change in the momentum of the asteroid after the impact will be observed and measured using ground-based telescopes and planetary radar.