Because Dimorphos is such a small space rock, DART will need to hit a bull’s-eye when the asteroid system reaches its closest point to Earth along its orbit around the sun, some 6.8 million miles away. It’s a complex orbital choreography involving a precise launch time off Earth and intermittent firings of a dozen tiny onboard thrusters that will refine DART’s path to collide with Dimorphos.
“From an engineering point of view, this is really hard,” said Andy Rivkin, the DART investigation team lead at Johns Hopkins Applied Physics Laboratory, which is managing the mission. DART’s single shot at striking Dimorphos will rely on a fully automated process that begins four hours before impact and uses an onboard navigation system called SMART Nav.
“They had to build an algorithm that does it by itself; there’s no joysticking it in,” he said.
Tom Statler, a DART program scientist at NASA, agreed.
“In one sense, DART is fairly simple. There’s only one instrument on board,” he said, referring to the spacecraft’s camera. “But on the other hand, the precision of the navigation is really beyond what we’ve done before.”
Ten days before impact, DART will deploy a small satellite built by the Italian Space Agency called LICIACube, which carries two cameras. This traveling companion will witness DART’s self-destructive mission from 34 miles away and measure the amount of debris kicked up from the impact. The DART spacecraft’s onboard camera, called DRACO, will snap photos of the asteroid as it approaches, streaming them back to Earth up until 20 seconds before impact.
To test whether DART has succeeded, scientists at NASA and the Applied Physics Laboratory will measure how much Dimorphos’s orbit around Didymos changes after the spacecraft’s impact. To ground-based telescopes, the asteroids are tiny dots of light. After impact, the scientists will track the duration of Dimorphos’s orbit by measuring the time between flickers of reflected light that signal that Dimorphos has crossed in front of Didymos, then passed behind it half an orbit later.
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