DRACO acquired this image of Didymos' brightness and moonlet Dimorphos. The image is a composite of 243 individual frames. Experts in navigation cameras doubted whether DRACO could identify the asteroid at this distance (20 million miles from DART) because the Didymos system is still dim. After combining 243 DRACO pictures, the team was able to find Didymos and pinpoint its location.
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“This first set of images is being used as a test to prove our imaging techniques,” said Elena Adams, the DART mission systems engineer at the Johns Hopkins Applied Physics Laboratory (APL) in Laurel, Maryland.
“The quality of the image is similar to what we could obtain from ground-based telescopes, but it is important to show that DRACO is working properly and can see its target to make any adjustments needed before we begin using the images to guide the spacecraft into the asteroid autonomously.”
DART will eventually rely on its capacity to view and interpret photographs of Didymos and Dimorphos, once it too can be seen, in order to navigate the spacecraft toward the asteroid, particularly in the last four hours before impact, despite the fact that the team has previously done a number of navigation simulations using non-DRACO images of Didymos. As soon as DART reaches Dimorphos, it will need to steer itself to a safe collision without any more assistance from Earth.
“Seeing the DRACO images of Didymos for the first time, we can iron out the best settings for DRACO 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 refine where DART is aiming by getting a more precise determination of Didymos’ location.”
The DART crew will undertake three trajectory correction manoeuvres over the next three weeks to lower the spacecraft's margin of error. After the last manoeuvre on Sept. 25, the navigation team will know the target's location within 2 kilometres 24 hours before impact. DART will then navigate independently to the asteroid moonlet.
DRACO has seen Didymos on August 12, 13, and 22.
Johns Hopkins APL administers NASA's DART mission as a Planetary Missions Program Office project. DART is the world's first planetary defence test mission, impacting Dimorphos to alter its orbit. The DART mission will show that a spacecraft can autonomously travel to a kinetic impact with a relatively minor asteroid and establish this is a realistic approach to deflect an asteroid on a collision path with Earth if one is ever identified. DART will arrive in 2022.
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