This coming Monday, NASA will broadcast its first attempt to change the orbit of an asteroid, which will be important if we detect an asteroid that threatens to collide with Earth. Planetary defense efforts are focused on a craft called DART for the Double Asteroid Redirect Test, which will target a small asteroid called Dimorphos that orbits the larger 65803 Didymos, forming a binary system. If all goes according to plan, DART will be headed for a head-on collision that slows Dimorphos down and changes its orbit around Didymos. NASA has repeatedly emphasized that there is no way that either the asteroid or any material ejected from the collision would pose a threat to Earth.
Ars will be at the mission control center at the Johns Hopkins Applied Physics Laboratory (APL) for the planned collision, which will also be streamed live on NASA’s YouTube channels. Although we will know immediately whether the collision went as planned, it may be several months before we know for sure that Dimorphos’ orbit was successfully changed.
To get you ready for Monday’s festivities, we’ve gathered information about the DART mission and planned follow-up observations.
DART and its final approach
The DART spacecraft itself weighs just over 600 kg and is notable primarily for its lack of instruments. Its solar panels include an experimental concentrated solar cell that takes up less space to generate the same amount of energy as existing space-based equipment, and its main transmitter is testing a new antenna configuration. Its ion engine is also a next-generation evolution of the previous NASA craft.
But all the action is controlled by a single camera, the Didymos Reconnaissance and Asteroid Camera for Optical Navigation, or DRACO, a 2,560×2,160 pixel monochrome camera. DRACO and the transmitter are capable of sending an image to Earth every second. During its final approach to Didymos, DART will be far enough away that a round-trip transmission will take more than a minute. Thus, the final approach and targeting of the asteroid will be controlled by an onboard navigation system called SMART Nav (Small Body Maneuvering Autonomous Real-Time Navigation).
Dimorphos is currently too small for DRACO to resolve and will remain so for about an hour and a half before impact. As described by Evan Smith, DART’s deputy mission system engineer, the system will switch to on-board navigation about four hours before impact, and SMART Nav will track the larger Didymos and use it for navigation about 50 minutes before impact. or it may resolve after about half an hour. 2.5 minutes before impact, the ion engine will shut down and DART will collide at about 6 kilometers per second.
Although Dimorphos is only 120 meters wide, it will completely fill DRACO’s view about two minutes before impact. “We don’t know what Dimorphos looks like,” said Nancy Chabot, a planetary scientist at APL. “This is the first time we’ll see what this asteroid looks like.” According to Chabot, in the last image sent one second before impact, it will resolve features that are only ten centimeters wide.
And then, if all goes well, the transmissions will stop.
