NASA’s DART spacecraft recently got its first look at Didymos, the double-asteroid system that includes its target, Dimorphos. DART will intentionally collide with Dimorphos, Didymos’ asteroid moonlet, on September 26. While the asteroid poses no threat to Earth, this is the first time a spacecraft has been used to deflect an asteroid for planetary defence.
This image of the light from Didymos and its orbiting moonlet Dimorphos is a composite of 243 images taken on July 27, 2022 by the Didymos Reconnaissance and Asteroid Camera for Optical Navigation (DRACO).
The Didymos system is still very faint from this distance—about 20 million miles away from DART—and navigation camera experts were unsure whether DRACO would be able to spot the asteroid yet. The team was able to reveal Didymos and pinpoint its location after combining the 243 images DRACO took during this observation sequence.
“This first set of images is being used to prove our imaging techniques,” explained Elena Adams, DART mission systems engineer at the Johns Hopkins Applied Physics Laboratory (APL) in Laurel, Maryland.”The image quality is comparable to what we could obtain from ground-based telescopes, but it is critical to demonstrate that DRACO is functioning properly and can see its target before we begin using the images to guide the spacecraft into the asteroid autonomously.”
Although the team has already run a number of navigation simulations using non-DRACO images of Didymos, DART’s ability to see and process images of Didymos and Dimorphos, once they can be seen, will ultimately be used to guide the spacecraft toward the asteroid, particularly in the final four hours before impact. DART will need to self-navigate at that point in order to successfully impact Dimorphos without human intervention.
“Seeing Didymos’ DRACO images for the first time allows us to iron out the best DRACO settings and fine-tune the software,” said Julie Bellerose, the DART navigation lead at NASA’s Jet Propulsion Laboratory in Pasadena, California. “In September, we’ll fine-tune DART’s objectives by obtaining a more precise determination of Didymos’ location.”
The DART team will perform three trajectory correction manoeuvres over the next three weeks, each of which will further reduce the margin of error for the spacecraft’s required trajectory to impact. The navigation team will know the position of the target Dimorphos within 2 kilometres after the final manoeuvre on September 25, approximately 24 hours before impact. DART will then be on its own to navigate itself to its collision with the asteroid moonlet.
DRACO then observed Didymos during planned observations on August 12, August 13, and August 22.