NASA’s DART About to Move An Asteroid

On Monday, a NASA spacecraft will deliberately crash itself into an asteroid to change its orbit just a bit. The Double Asteroid Redirection Test is just that, a test to see if it is possible to divert an asteroid’s trajectory. This asteroid poses no threat to Earth, but NASA wants to find out if this kinetic energy method would work if the day comes when it’s needed.

DART was launched from Vandenberg Space Force Base, CA on November 23, 2021 PST (November 24 EST) headed to the asteroid Didymos and its tiny moon Dimorphos 7 million miles away. The plan is for DART to ram itself into Dimorphos while scientists on Earth measure whether its orbit around Didymos changes.

NASA TV will provide live coverage Monday evening as DART zeroes in on Dimorphos. When the screen goes blank and there’s a loss of signal, cheers will ring out rather than alarm because it means the impact was successful.

Tom Statler, DART Program Scientist at NASA, told reporters today that “we’re doing this test when we don’t need to, on an asteroid that isn’t a danger, just in case we ever do need to if we discover an asteroid that is a danger.”

He also commented on the significance of the mission more broadly.

“We are moving an asteroid. We are changing the motion of a natural celestial body in space. Humanity has never done that before. This is stuff of science fiction books and really corny episodes of Star Trek when I was a kid. And now it’s real. It’s kind of astonishing that we are actually doing that and what that bodes for the future.”

A tiny Italian cubesat, LICIAcube, is along for the ride. It will separate from DART before impact and collect images of those last moments, though it will take some time to get them back due to slow data rates. NASA’s Hubble Space Telescope in Earth orbit, James Webb Space Telescope at the Sun-Earth Lagrange Point-2 (SEL-2), and the Lucy spacecraft on its way to the Trojan asteroids will take a look, too. They will not see the impact itself, but might detect the brightness of ejecta spewed out into space.

The measurements to detect the change in Dimorphos’s orbit will come from ground-based telescopes and radars over a period of time. How much time is a matter of debate.

Statler said there’s a “friendly rivalry” between the optical observers and radar observers on the science team as to who will detect it first. “I don’t want to get into the middle of that debate, but I would be surprised if we had a firm measurement of the period change in less than a few days and I would be really surprised if it took more than three weeks.”

That will not be the last chance to see what happened, however. The European Space Agency is launching the HERA mission in 2024 that will visit the double asteroid pair and perform a post-impact survey in 2026.

Protecting Earth from asteroids and comets — Near Earth Objects (NEOs) — that might cause regional or global catastrophes is called planetary defense. Lindley Johnson is NASA’s Planetary Defense Officer and heads the Planetary Defense Coordination Office (PDCO) at NASA Headquarters. At today’s briefing, Johnson said changing an asteroid’s trajectory through imparting kinetic energy is just one method. Gravity tractors and ion beam deflection are others. NASA has no plans to launch missions to test those methods, however. For now, the focus is DART.

The spacecraft is using a navigation system called SMART Nav to find its way to Didymos, which is quite small, about one half mile (780 meters) in diameter. Dimorphos is smaller still, approximately 525 feet (160 meters) in diameter. DART’s DRACO camera has already found Didymos, but will not be able to see Dimorphos until the last hour before impact. Scientists discovered Didymos and Dimorphos in 1996, but little is known about their shape and surface characteristics.

Images from DRACO will be transmitted down to mission control at the Johns Hopkins Applied Physics Laboratory (APL) in Laurel, MD, which is managing the mission for NASA, via NASA’s Deep Space Network. The last image is expected to be taken about 2.5 seconds before impact.

Asked what happens if DART misses Dimorphos, Johnson said he is “highly confident” it won’t, but if it does the most important question will be to figure out why. That means getting as much data as possible from the spacecraft. Elena Adams, DART Mission Systems Engineer at APL, added that “missed impact” is one of 21 contingencies her team is prepared to deal with.  If it happens “we’re going to sit down back in our seats and we’re going to start preserving all the data … and conserving propellants and start looking for the object to come back to.”

APL is still commanding trajectory corrections now, but 4 hours prior to impact the spacecraft becomes autonomous. However, Adams said mission control still will be able to issue commands if necessary. For example, if the image of Dimorphos is too faint, they can increase the camera’s exposure time. The one-way travel time for signals is 38 seconds.

DART is PDCO’s first flight project.

The office primarily is tasked with finding NEOs that could threaten Earth, a concern highlighted by the 2013 Chelyabinsk meteor that exploded in mid-air over Chelyabinsk, Russia, injuring more than 1,000 people largely by flying glass from windows broken by the shock wave.

An asteroid impact is thought to have killed the dinosaurs 65 million years ago when an impact threw debris high into the atmosphere, cooling the planet and extinguishing cold-blooded animals. The 1908 Tunguska incident that flattened trees for about 2,000 square kilometers (770 square miles) in Siberia also is attributed to an air-blast from an incoming asteroid or comet.

In 1998, Congress directed NASA to locate 90 percent of hazardous asteroids 1-kilometer (0.6 miles) or more in diameter within 10 years. That size asteroid is thought to have caused the extinction of the dinosaurs. NASA accomplished that task and in 2005 Congress set another goal of locating 90 percent of hazardous asteroids 140-meters or more in diameter within 15 years. That is a more difficult task since they are much smaller and dark. The 15 years have already elaposed and while progress has been made, there is a long way to go.

Johnson said today what’s needed is a space-based infrared telescope dedicated to searching for asteroids, the Near Earth Object Surveyor or NEO Surveyor.  The program had trouble winning support for years, but the recent Decadal Survey on Planetary Science and Astrobiology strongly endorsed it. Nevertheless, NASA proposed delaying it for two years, from 2026 to 2028, in its FY2023 budget request, which is currently pending in Congress. House and Senate appropriators urged NASA to keep the launch date in 2026 or at least launch it before 2028 and added money to that end. What will be in the final appropriations bill remains to be seen. In any case, NEO Surveyor is going through its Preliminary Design Review this week, so progress is being made.