WASHINGTON — NASA is ready to launch its first mission devoted to planetary defense, a spacecraft that will collide with the moon of a small asteroid to test the ability to deflect it.
The Double Asteroid Redirection Test (DART) spacecraft is scheduled to launch at 1:21 a.m. Eastern Nov. 24 on a SpaceX Falcon 9 from Vandenberg Space Force Base in California. At a Nov. 22 media briefing, project officials said the spacecraft and rocket are ready for launch, with a 90% chance of acceptable weather.
DART will fly to the near Earth asteroid Didymos, which has a moon called Dimorphos, about 160 meters across, orbiting it. DART will collide with Dimorphos at a speed of more than 24,000 kilometers per hour in September 2022, changing its orbital period by an estimated 10 minutes.
The purpose of DART is to test the kinetic impactor technique for changing the trajectory of an asteroid. That could be used to deflect an asteroid on course to impact the Earth, although NASA officials emphasized throughout the lead-up to the DART launch that there is no known asteroid that poses an impact threat to the Earth for at least 100 years.
The mission is a “first-of-its-kind experiment,” said Thomas Zurbuchen, NASA associate administrator for science, at a Nov. 22 prelaunch briefing. “What we’re trying to learn is how to deflect a threat that would come in.”
Project officials compared the mission to ramming a golf cart into a football stadium filled with rocks. “We’re going to give it a nudge. We’re going to hit it hard, but we’re hitting it with a very small vehicle. It doesn’t take a lot,” said Ed Reynolds, DART project manager at the Johns Hopkins Applied Physics Laboratory (APL). “When we’re looking at what does it take to deflect an asteroid away from Earth, given enough time, you can do big things with small vehicles.”
The flight portion of the DART mission is short, with impact on Dimorphos about 10 months after launch. Most of the action will take place in the final days and hours as DART approaches the binary asteroid. Its single instrument, a camera called DRACO, will return images at a rate of one per second on that final approach.
“You’ll go from just a little point for the longest time, and then it’s in the last hours that you begin to resolve a moon,” Reynolds said. “Each time we get a new picture it’s going to get better and better and better. Those last pictures are going to be right up against the asteroid, and then it’s going to be complete silence.”
“At that point the mission is only half done,” Tom Statler, DART program scientist at NASA Headquarters, said at a Nov. 21 science briefing. “We still have to watch what the asteroid does as a result of that impact.”
Groundbased telescopes will observe Didymos and Dimorphos for months after the impact to measure the change of the rotation period of Dimorphos. “We expect to get initial results about the change of Dimorphos’s orbit within a few weeks of DART’s impact next year,” said Andy Rivkin, DART investigation team lead at APL. Those results will be refined by additional observations over the following several months.
While DART will be destroyed in the impact, another spacecraft will attempt to observe it. About a month before impact, DART will release LICIACube, an Italian cubesat that carries cameras that will observe Dimorphos before, during and after DART’s impact. Simone Pirrotta, project manager for LICIACube at the Italian space agency ASI, said the goal is for LICIACube to fly within 55 kilometers of Dimorphos and collect images that will be transmitted back after the flyby.
DART will be on its own for its final approach. The spacecraft will operate autonomously in the final hours of the mission. Since it will not be able to see Dimorphos as a separate object until about an hour before impact, it will target the moon on its own using a technology called SMART Nav originally developed for missile defense applications.
DART is not solely a planetary defense mission. NASA is also using DART to test several advanced technologies that could be used on future missions. Those include a NEXT-C ion thruster, Roll-Out Solar Array and the Radial Line Slot Array antenna.
“All of these technologies are going to be flown on DART and proven on DART so they can enable the next generation of deep science missions,” said Betsy Congdon, DART mechanical systems engineer at APL.
Planetary defense, though, is the primary purpose of the mission, and plans to have it crash into an asteroid have helped increase interest in it, even within NASA. “How cool? We’re smashing into an asteroid,” said Omar Baez, senior launch director for NASA’s Launch Services Program, at the prelaunch briefing. “I can’t believe we’re doing that.”
