Double Asteroid Redirection Test (DART)
The Double Asteroid Redirection Test (DART) is a pioneering space mission aimed at testing planetary defense techniques against potential asteroid threats. Developed collaboratively by NASA and the Johns Hopkins University Applied Physics Laboratory, DART's primary objective was to assess the viability of the kinetic impactor method, which involves crashing a spacecraft into an asteroid to alter its trajectory. Launched on November 24, 2021, DART targeted the asteroid Dimorphos, which orbits a larger asteroid named Didymos, both of which posed no threat to Earth.
On September 26, 2022, DART successfully collided with Dimorphos, resulting in a change to its orbit that exceeded initial expectations, reducing its orbital period by thirty-three minutes. The mission was significant not only for demonstrating effective asteroid deflection techniques but also for providing valuable data on near-Earth objects (NEOs). DART's success has paved the way for future investigations, including a follow-up mission by the European Space Agency's Hera spacecraft, which aims to further explore the effects of the DART impact on the Didymos system. Overall, DART marks a crucial step in advancing human understanding and preparedness for potential asteroid impacts.
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Double Asteroid Redirection Test (DART)
Double Asteroid Redirection Test (DART) was the first space mission to test humanity’s planetary defense capabilities. It was developed jointly by the US National Aeronautics and Space Administration (NASA) and the Johns Hopkins University Applied Physics Laboratory (APL). The mission involved sending a spacecraft crashing into an asteroid to see if this impact could change the speed and path of a near-Earth object (NEO), a technique called kinetic impactor. To test this theory, scientists aimed the DART spacecraft at Dimorphos, an asteroid orbiting a larger asteroid called Didymos. Neither Dimorphos nor Didymos posed any threat of colliding with Earth. The craft launched in November 2021 and made impact with its intended target on September 26, 2022. A subsequent investigation revealed that the collision altered Dimorphos’s path, shortening its orbit around Didymos by thirty-three minutes. The test far exceeded NASA’s hope of being able to shorten it by seventy-three seconds. The project cost an estimated $313.9 million.
Background
Large asteroids and other NEOs can cause tremendous damage when they hit another object. Small asteroids enter Earth’s atmosphere on a regular basis, usually breaking up before they reach the surface. Occasionally, sizable asteroids have exploded in the atmosphere, causing damage on the ground. For example, an object exploded in the atmosphere above the Podkamennaya Tunguska river in rural Siberia in Russia in June 1908. The incident, commonly referred to as the Tunguska event, involved either an asteroid or comet only about 98.4 feet (30 m) in diameter but affected an area of about 830.1 square miles (2,150 sq km). A slightly smaller object, an asteroid about 65.6 feet (20 m) in diameter, exploded in the atmosphere above the Russian city of Chelyabinsk. The explosions damaged thousands of buildings across six cities. More than one thousand injuries but no deaths were reported. While these incidents had significant effects, the objects were relatively small and never made an impact.
The most consequential incident of an asteroid entering Earth’s atmosphere occurred more than sixty-five years ago when an asteroid with a diameter of at least 3.7 miles (10 km) struck the Gulf of Mexico. Scientists credit the incident, commonly referred to as the Chicxulub event, with the dinosaurs’ extinction.
Whether an explosion in the atmosphere or an impact event, NEOs pose a grave threat to life on Earth. With the passage of the NASA Authorization Act in 2005, NASA began the NEO Observation Program to locate and track NEOs with a diameter of at least 459 feet (140 m). This program led to the creation in 2016 of the Planetary Defense Coordination Office (PDCO), which is tasked with detecting smaller NEOs as well as developing strategies and technologies to prevent foreign objects from entering Earth’s atmosphere. NASA and other space agencies had already begun research and development related to asteroid deflection before the establishment of the PDCO. Construction of DART, PDCO’s first space mission, began in 2018. DART launched November 24, 2021.
Overview
DART’s primary mission was to test the kinetic impactor technique on an asteroid. The technique had been used previously when NASA launched the Deep Impact space probe in 2005. It delivered an impactor that hit a comet, allowing scientists to study its composition. Rather than detonate explosives, an impactor functions as a high-speed projectile like a bullet. Scientists at NASA and the APL selected the Didymos asteroid system about 6.8 million miles (11 million km) from Earth for its tests and planned impact to occur the last week of September 2022. Scientists selected the Didymos asteroid system because its position allows telescopes on Earth to take especially accurate measurements.
Astronomers discovered the Didymos asteroid system in the 1990s and first observed the moonlet Dimorphos in 2003. Didymos measures 2559 feet (780 m) in diameter. Dimorphos, DART’s target, has a diameter of about 525 feet (160 m). DART was much smaller than these bodies with a dimension of 3.9 x 4.3 x 4.3 feet (1.2 x 1.3 x 1.3 m). Two roll-out solar arrays (ROSA) powered the craft’s electric in-space propulsion system. Each ROSA extended 27.9 feet (8.5 m). When its solar arrays were fully deployed, DART resembled a paragliding refrigerator. Having a total mass of 610 kilograms, the craft weighed about 1340 pounds on Earth.
DART was carried by a Falcon 9 rocket developed and built by private manufacturer SpaceX. The Falcon 9 rocket launched on November 24, 2021, from Vandenberg Space Force Base in Lompoc, California. The rocket deployed DART about an hour after launch, sending it into orbit around the Sun on its ten-month journey. Scientists planned for DART to reach the Didymos asteroid system between September 25 and October 2, 2022. DART made impact on September 26, flying at a speed of 14,760 miles (23,760 km) per hour. It displaced at least 1,100 US tons (1 million kilograms) of ejecta, or debris.
Guidance, navigation, and control (GNC) for DART was achieved using the Didymos Reconnaissance and Asteroid Camera for Optical navigation (DRACO) imager aboard the craft as well as an autonomous optical navigation system. DART also carried a device developed by the Italian Space Agency (ASI) called Light Italian CubeSat for Imaging of Asteroids (LICIACube), which detached fifteen days before DART’s scheduled impact so that it could record the collision with Dimorphos and collect data of its effects. The device helped determine how significantly DART shortened Dimorphos’s orbit but also recorded how the moonlet responded to the disruption. The data helps scientists better understand the composition and behavior of NEOs.
Following the success of the DART mission, scientists continued plans to further investigate the Didymos asteroid system to expand planetary defense capabilities. The European Space Agency (ESA) organized a mission involving its Hera spacecraft that launched in October 2024. Among the mission’s stated objectives, the ESA explicitly intended for Hera to make observations about how the DART mission affected the asteroid system.
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