Two years ago, a NASA spacecraft crashed into a small asteroid millions of miles from Earth to test a technology that could one day prove useful in deflecting an object off a collision course with Earth. The European Space Agency returned to the crash site on Monday and began a follow-up mission to assess the damage caused.
The roughly $400 million (€363 million) Hera mission, named after the Greek goddess of marriage, will study the aftermath of a space collision between NASA’s DART spacecraft and the skyscraper-sized asteroid Dimorphos on September 26, 2022. NASA’s Double Asteroid Reorientation Test Mission was the first planetary defense experiment, and it was a success. Dimorphos was successfully deflected from its usual orbit around a larger companion asteroid called Didymos.
But NASA had to sacrifice the DART spacecraft for the diversion experiment. Because of the destruction, there are no detailed images showing the condition of the target asteroid after the impact. A small Italian CubeSat deployed as DART approached Dimorphos captured blurry long-range images of the impact, but Hera is expected to carry out a full investigation when it arrives in late 2026.
“We are going to have a surprise to see what Dimorphos looks like, which is, first, scientifically exciting, but also important because if we want to validate the technique and validate the model that can reproduce the impact, we need to know the final outcome,” said Patrick Michel, principal investigator on the Hera mission from Côte d’Azur Observatory in Nice, France. “And we don’t have it. With Hera, it’s like a detective going back to the crime scene and telling us what really happened.”
Final Flight Before the Storm
The 1,108-kilogram (2,108-kilogram) Hera spacecraft lifted off on a SpaceX Falcon 9 rocket from Cape Canaveral Space Force Station in Florida at 10:52 a.m. EDT (14:52 UTC) on Monday.
Officials were unsure whether the weather at Cape Canaveral would allow for a launch on Monday, with extensive rain showers and a layer of clouds covering Florida’s Space Coast. However, the conditions were exactly right for a rocket launch, and the Falcon 9 fired its nine kerosene-fueled engines to lift off from pad 40 after an easy countdown.
This was likely the final opportunity to launch Hera before the spaceport was closed by Hurricane Milton, a dangerous Category 5 storm heading for Florida’s west coast. If the mission had not launched on Monday, SpaceX would have returned the Falcon 9 rocket and Hera spacecraft to a hangar, ready to store until the storm had passed.
Meanwhile, a few miles away at NASA’s Kennedy Space Center, SpaceX is securing a Falcon Heavy rocket carrying the Europa Clipper spacecraft to ride out Hurricane Milton in a hangar at Launch Complex 39A. Europa Clipper is the flagship mission of a $5.2 billion mission to explore Jupiter’s most mysterious icy moon. It was scheduled to launch on Thursday, the same day Hurricane Milton could pass over central Florida.
NASA announced Sunday that it would postpone the launch of Europa Clipper until the storm is over.
“The safety of launch team personnel is our highest priority, and all precautions will be taken to protect the Europa Clipper spacecraft,” said Tim Dunn, senior launch director at NASA’s Launch Services Program. “Once we have the `all-clear’ followed by facility assessment and any recovery actions, we will determine the next launch opportunity for this NASA flagship mission.”
Europa Clipper must be launched for Jupiter and its moon Europa by November 6, 2030 to reach it. ESA’s Hera mission similarly had a limited time to launch in October and reach the asteroids Didymos and Dimorphos in December 2026.
Back to the flight
The Falcon 9 completed its mission on Monday, with sequential firings of its first and upper stage engines accelerating the Hera spacecraft to a breathtaking speed of 43,042 km/h, the largest payload injection SpaceX has ever achieved.
SpaceX did not attempt to recover the Falcon 9’s reusable booster during Monday’s flight, because Hera needed all of the rocket’s power to gain enough speed to escape Earth’s gravity.
“Good launch, good orbit, and good payload deploy,” commented Kiko Dontchev, SpaceX’s vice president of launch, on X.
This was SpaceX’s first Falcon 9 launch in nine days, an unusually extended period between missions, after the rocket’s upper stage misfired during a maneuver to steer itself out of orbit following an otherwise successful launch on September 28 with a two-man crew bound for the International Space Station.
Officials said the upper stage engine apparently “overburned” and debris from the rocket fell into the atmosphere just short of the expected Pacific Ocean atmospheric re-entry corridor. The Federal Aviation Administration grounded the Falcon 9 rocket while SpaceX investigated the failure, but the FAA cleared SpaceX to launch the Hera mission because its trajectory would have had the rocket re-enter the atmosphere and away from Earth.
“The FAA has determined that the absence of a second stage reentry for this mission adequately mitigates the primary risk to the public in the event of a reoccurrence of the mishap experienced with the Crew-9 mission,” the FAA said in a statement.
This is the third time the FAA has grounded SpaceX’s Falcon 9 rocket fleet within three months, following another upper stage failure in July that destroyed 20 Starlink internet satellites and caused a Falcon 9 to crash-land a booster for an offshore drone ship. Federal regulators must ensure that commercial rocket launches do not pose a danger to the public.
Dimorphos orbits Didymos as soon as each eleven hours and 23 mins, kind of 32 mins shorter than the orbital duration earlier than DART`s effect in 2022. This alternate in orbit proved the effectiveness of a kinetic impactor in deflecting an asteroid that threatens Earth.
Dimorphos, the smaller of the 2 asteroids, has a diameter of round 500 feet (a hundred and fifty meters), even as Didymos measures about a half-mile (780 meters) wide. Neither asteroid poses a chance to Earth, so NASA selected them because the goal for DART.
The Hubble Space Telescope noticed a particles discipline trailing the binary asteroid machine after DART’s effect. Astronomers diagnosed as a minimum 37 boulders drifting farfar from the asteroids, fabric ejected whilst the DART spacecraft slammed into Dimorphos at a pace of 14,000 mph (22,500 kmh).
Scientists will use Hera, with its suite of cameras and instruments, to look at how the strike through DART modified the asteroid Dimorphos. Did the effect go away a crater, or did it reshape the complete asteroid? There are “tentative hints” that the asteroid`s form modified after the collision, in step with Michael Kueppers, Hera’s venture scientist at ESA.
“If this is the case, it would also mean that the cohesion of Dimorphos is extremely low; that indeed, even an object the size of Dimorphos would be held together by its weight, by its gravity, and not by cohesion,” Kueppers said. “So it really would be a rubble pile.”
Hera may even degree the mass of Dimorphos, some thing DART turned into not able to do. “That is important to measure the efficiency of the impact… which was the momentum that was transferred from the impacting satellite to the asteroid,” Kueppers said.
The main goal of Hera is to bridge information gaps about Didymos and Dimorphos. Precise measurements of DART’s momentum, combined with a greater understanding of the internal structure of asteroids, may help future mission planners determine the optimum way to deflect a hazardous object threatening Earth.
“The third part is to generally investigate the two asteroids to know their physical properties, their interior properties, their strength, essentially to be able to extrapolate or to scale the outcome of DART to another impact should we really need it one day,” according to Kueppers.
Hera will launch two briefcase-sized CubeSats, Juventas and Milani, to work in tandem with ESA’s mothership. Juventas carries a miniature radar to investigate the internal structure of the smaller asteroid and will eventually attempt to settle on Dimorphos. Milani will investigate the mineral compositions of individual stones around DART’s crash site.
The state of the debris field discovered by Hubble a few months after DART’s impact is one source of doubt, and possibly concern, about the environment surrounding Didymos and Dimorphos. However, Kueppers believes this is unlikely to be an issue.
“I’m not really worried about potential boulders at Didymos,” he remarked, citing the relative ease with which ESA’s Rosetta mission maneuvered around an active comet from 2014 to 2016.
Ignacio Tanko, ESA’s Hera flight director, doesn’t share Küpper’s optimism.
“We didn’t hit the comet with a hammer,” said Tanco, who is responsible for keeping the Hera spacecraft safe. “The debris question for me is actually a source of… I wouldn’t say concern, but certainly precaution. It’s something that we’ll need to approach carefully once we get there.”
“That’s the difference between an engineer and a scientist,” Küpper joked.
Initially, scientists wanted to place Hera near the binary asteroid system Didymos before the arrival of DART in order to observe the collision and its effects first-hand. However, ESA member states did not approve funding for the Hera probe in a timely manner, and the space agency did not sign a contract to build the Hera probe until 2020.
ESA first considered a mission like DART or Hera for more than 20 years. Earlier, scientists proposed a mission called “Don Quixote” to redirect the asteroid. But other missions took priority in the European Space Programme. Now, Hera is well on its way to writing the final chapter in the story of humanity’s first planetary defense test.