VISIONARY

NASA’s DART Targets Twins

Bfyo jorhn FA. Krsosts eroid Defense

Taking a page from a science fiction movie DART would slam into the space rock about script, NASA has approved a mission to de - nine-times faster than a bullet—six kilome - flect an asteroid to further planetary de - ters per second—allowing Earth-based fense. The mission, dubbed the Double observatories to see the crash and shift Asteroid Redirection Test (DART), takes aim in the orbit of Didymos B around its larger at an intermediate-size object that could twin. “We intend to… change the orbital cause regional damage if it collided with period of Didymos… seven minutes or Earth. “DART would be NASA’s first mission more… and we will be able to see that from to demonstrate what’s known as the kinetic the ground,” predicted Cheryl Reed, DART’s impactor technique—striking the asteroid to project manager at the Johns Hopkins *1 shift its orbit—to defend against a potential University Applied Physics Laboratory future asteroid impact,” said Lindley John - (JHUAPL). son, planetary defense officer at NASA headquarters. To acquire the know-how The sudden impact would change the needed to tackle potential threats, NASA mutual orbit of the two objects, but cause created the Planetary Defense Coordination only a minor shift in the heliocentric orbit Office (PDCO) in 2016 to ramp up the track - of the system. Although the Didymos twins ing and characterization of potentially haz - pose no threat, in principle, even a small ardous objects and coordinate a response. nudge to a menacing asteroid could change In concert, the U.S. space agency approved its speed and trajectory enough to miss our the promotion of DART from concept devel - planet. opment to the preliminary design phase in June 2017. “DART is a critical step in demonstrating we can protect our planet from a future aster - Weighing 500 kilograms, the refrigerator- oid impact,” explained DART investigation size DART spacecraft would target a binary team coleader, Andy Cheng at JHUAPL. asteroid system called Didymos (Greek for “With DART, we can show how to protect “twin”) composed of a larger asteroid, Didy - Earth from an asteroid strike with a kinetic mos A, about 780 meters in size, and Didy - impactor by knocking the hazardous object mos B, its 160-meter wide sidekick. Only into a different flight path that would not Didymos B would be in DART’s crosshairs as threaten the planet.” the twins make a distant approach (10.9 million kilometers) from Earth in 2022 and About 100 tons of cosmic 2024. After launch, DART would fly to the material falls onto the Earth daily, binary system using its targeting system to mostly in the form of harmless dust zero in on Didymos B, most likely in 2024. “A and small meteorites that break up in binary asteroid is the perfect natural labora - the atmosphere. tory for this test,”said Tom Statler, program scientist for DART at NASA. “The fact that Most of the 1,000 or so near-Earth asteroids Didymos B is in orbit around Didymos large enough to cause a global disaster have 4 3

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1. More information is needed to defend against intermediate-size 2. An artist's concept of the DART mission to intentionally strike the

D asteroids that could cause severe regional damage to our planet. Image binary asteroid system called Didymos (Greek for “twin”) and test planetary A credit: ESA - P.Carril defense. Image Credit: ESA that could cause severe regional damage Evolutionary Xenon Thruster-Commercial (NEXT-C) to our planet. “Since we don’t know that solar electric propulsion system, a more advanced much about their internal structure or compo - and powerful version of the ion thruster used on sition, we need to perform this experiment on a the Dawn spacecraft. Electric propulsion provides real asteroid,” said Andy Cheng at Johns Hopkins greater flexibility to DART’s mission timeline and University Applied Physics Laboratory (JHUAPL). launch window, as well as decreases launch costs. DART could ride as a shared payload on a com - Autonomous Navigation and Ion Thrusters mercial rocket carrying a communications satellite The DART (Double Asteroid Redirection Test) and be inserted into a geostationary transfer orbit spacecraft features a simple single string design before thrusting its ion engine toward Didymos. and thruster-only control, but carries sophisti - cated instruments and propulsion technologies. Originally, the DART project, a joint effort between On board, a high-resolution imager derived from NASA and the JHUAPL, was a complementary part the New Horizons LORRI camera, called the of the Asteroid Impact and Deflection Assessment Didymos Reconnaissance and Asteroid Camera (AIDA) mission in collaboration with the European for Op-Nav (DRACO), would support navigation Space Agency (ESA) and the German Aerospace and pinpoint the impact site in geologic context. Center. ESA agreed to build a separate Asteroid As a technology demonstration mission, DART Impact Mission (AIM) spacecraft to orbit the aster - would also integrate advanced technologies such oid pair and observe DART’s impact. However, in as electric propulsion and autonomous naviga - late 2016, the AIM probe was defunded by ESA to tion. Precise, self-directed navigation is required help pay for ExoMars and other projects. Euro - to ensure the accuracy of the kinetic impact. pean space officials are still weighing a future role In addition, the autonomous system for a scaled-back, cheaper version of the AIM mis - would test fuel management logic soft - sion called AIMlight. Despite AIDA’s abrupt finale, ware to tweak the timing of course DART gained approval from NASA as a solo mis - corrections and optimize the sion, though it is not a specific budget item in the

limited fuel onboard. Fiscal Year 2018 budget. If fully funded, however, A D

DART would be the first off-world demonstration A S

DART would steer to its of planetary defense, just in case the sky really T R

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