Next Monday, NASA will release its first attempt to alter an asteroid’s orbit, a capability that will be essential if we detect an asteroid threatening to collide with Earth. The planetary defense effort is focused on a craft called DART, for Double Asteroid Redirection Test, which will target a small asteroid called Dimorphos that orbits the larger 65803 Didymos, forming a binary system. If all goes as planned, DART will head into a head-on collision that will slow Dimorphos, altering its orbit around Didymos. NASA has repeatedly stressed that there is no way the asteroid or any other material released by the collision could pose a threat to Earth.
Ars will be at the Johns Hopkins Applied Physics Laboratory (APL) Mission Control Center for the planned collision, which will also be streamed live on NASA’s YouTube channels. Although we know immediately if the collision occurred as expected, it may be several months before we are certain that Dimorphos’ orbit has been successfully altered.
To prepare you for Monday’s festivities, we’ve prepared a history of the DART mission and planned follow-up sightings.
DART and its final approach
The DART spacecraft itself weighs just over 600 kg and is mainly distinguished by its lack of instruments. Its solar arrays include an experimental concentrating solar cell that takes up less space to generate the same amount of power as existing space hardware, and its primary transmitter is testing a new antenna configuration. Its ion engine is also a next-generation evolution of NASA’s previous hardware.
But all the action is handled by a single camera, the Didymos Reconnaissance and Asteroid Camera for Optical navigation, or DRACO, a 2560×2160 pixel monochrome camera. DRACO and the transmission equipment are able to send an image back to Earth every second. On its final approach to Didymos, DART will be far enough away that round-trip transmissions will take over a minute. Thus, the final approach and targeting of the asteroid will be ensured by an on-board navigation system called SMART Nav (Small-body Maneuvering Autonomous Real Time Navigation).
At present, Dimorphos is so small that DRACO is unable to resolve it, and it will remain so until about an hour and a half before impact. As described by Evan Smith, DART’s Assistant Mission System Engineer, the system will switch to on-board navigation approximately four hours before impact, and the SMART Nav will follow the larger Didymos and use it for navigation until approximately 50 minutes before the collision, or about half an hour after it can be resolved. At 2.5 minutes before the collision, the ion engine will be shut down and DART will collide at approximately 6 kilometers per second.
Even though Dimorphos is only about 120 meters in diameter, it will completely fill the view from DRACO about two minutes before the collision. “We don’t know what Dimorphos looks like,” said APL planetary scientist Nancy Chabot. “It will be the first time we see what this asteroid looks like.” In the final image, sent a second before impact, it will resolve features that measure only tens of centimeters in diameter, according to Chabot.
And then, if all goes well, the transmissions will stop.
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