Next Monday, NASA will broadcast its first attempt to modify the orbit of an asteroid, a capability that will be necessary if we discover an asteroid that poses a collision threat to Earth. Planetary defense efforts are focused on a vehicle, called DART, to test the double asteroid redirection, which will target a small asteroid called Dimorphos orbiting the largest 65803 Didymos, forming a binary system. If all goes according to plan, DART will orient itself for a head-on collision slowing the Dimorphos, changing its orbit around Didymos. NASA has repeatedly emphasized that there is no way for any asteroid or any material released by impact to pose a threat to Earth.
Ars will be in the mission control center at the Johns Hopkins Applied Physics Laboratory (APL) for the planned collision, which will also be broadcast live on NASA’s YouTube channels. While we’ll know right away if the collision happened as planned, it could be several months before we’re sure the Dimorphos’ orbit has been successfully adjusted.
To prepare you for Monday’s festivities, we’ve compiled a background on the DART mission and planned follow-up notes.
DART and its ultimate approach
The DART spacecraft itself weighs just over 600 kilograms, which is notable primarily because of its lack of instruments. Its solar panels include an experimental concentrated solar cell that takes up less space to generate the same amount of power as devices in space, and the main transmitter is testing a new antenna configuration. Its ion engine is also a next-generation evolution of previous NASA instruments.
But all the action is handled by a single camera, the Didymos Camera for Reconnaissance and the Asteroid Camera for Optical Navigation, or Draco, a 2560×2160-pixel monochrome camera. DRACO and transmitters can send an image to Earth every second. During its final approach to Didymos, DART will be far enough away that back and forth transmissions will take more than a minute. As such, the final approach and targeting of the asteroid will be handled by an onboard navigation system called SMART Nav (Real-time Autonomous Small Object Navigation).
Currently, Dimorphos are too small for DRACO to dissolve, and will remain that way until approximately an hour and a half before impact. As described by Evan Smith, deputy mission system engineer at DART, the system will switch to onboard navigation in about four hours before impact, and SMART Nav will track the largest Didymus and use that for navigation until about 50 minutes before impact, or about half an hour after it has resolved. Within 2.5 minutes before impact, the ion engine will be turned off, and DART will crash at about 6 kilometers per second.
Although Dimorphos are only about 120 meters wide, they will completely fill the landscape of DRACO starting about two minutes before impact. “We don’t know what Dimorphos looks like,” said Nancy Chabot, a planetary scientist at APL. “This will be the first time we even see what this asteroid looks like.” According to Chabot, in the final image, sent back before the impact, it will resolve features that are no more than tens of centimeters wide.
And then, if all goes well, the transfers will stop.