NASA’s deep space exploration robots are typically engineering marvels built to last. You have the Voyager probes at the end of the solar system, operating dutifully decades after launch. The Parker solar probe dances around the sun and carries an epic heat shield that will hopefully keep it running for years to come. and Lucy although it had some problemsis currently on a mission to visit a handful of space rocks near Jupiter – a journey that will span the next 12 years.
Then you have DART.
DART (Double Asteroid Redirection Test) was not intended for decades of solar system science. The spacecraft launched in November 2021 and, well, just crashed up onto an asteroid on Monday. It is now completely destroyed – but its death was the purpose of its existence.
DART is NASA’s test run for a planetary defense system designed to push incoming asteroids away from Earth by literally hurling spacecraft into them. asteroids ranging in size from refrigerators to cars, collide with our planet more often than you might think. Fortunately, these impacts are generally not too threatening, since most of the rock in Earth’s atmosphere burns up. But almost 66 million years ago, as you may recall, dinosaurs were wiped out by a massive space rock called Chicxulub.
The goal of the DART mission was simple: NASA wanted to understand if we could crash into an asteroid to prevent such a catastrophe from also wiping out humans. So, as proof of principle, the spacecraft hit a small asteroid called Dimorphos orbiting a larger asteroid, Didymos.
On Monday, the DART spacecraft autonomously navigated towards and collided with Dimorphos when the rock was about 7 million miles from Earth — its closest point to our blue planet. The target asteroid is about the size of the Washington Monument, and upon impact, the team behind DART hoped the rock’s trajectory and speed would be slightly altered.
To put it bluntly, this particular floating rock never posed a threat to our planet. But if DART managed to throw Dimorphos off course a bit, we know we might one day have a viable tactic to repel asteroids, that are actually dangerous. The take-home message is that this is basically a technology demonstration — a way for NASA to glean valuable insights into how we might one day actually deflect a scary asteroid onto a collision course with Earth.
Target acquired: Dimorphos
Crossing our solar system is a gray space rock about half a mile wide known as Didymos, holding a companion asteroid by tether with a gentle gravitational pull. This second, smaller fragment, orbiting Didymos, was the target of DART: Dimorphos.
The scientists behind DART chose Dimorphos for the test because its orbit around Didymos mimics how potentially threatening near-Earth asteroids orbit the Sun. Asteroids are gravitationally bound to our star, which could put them on a collision course with Earth. But the orbit of Dimorphos is not tied to the Earth or the Sun, but to Didymos. This makes it a perfect proving ground for NASA – they tried to crash DART into the tiny rock to see how it changes orbit around its larger companion.
NASA predicted the crash would be strong enough to alter Dimorphos’ orbital period by a few minutes. More specifically, calculations show what effects Dimorphos will bring closer to Didymus.
Now that impact is complete, the agency will begin reviewing data on the spacecraft’s trajectory and final moments, as well as Dimorphos’ new trajectory, to determine if those calculations were correct. “Most of the time we try to change the speed of the incoming object by about a centimeter per second. That’s not very fast, but if you do it enough seconds in advance, you could cause it to miss Earth entirely,” according to the mission brief from Johns Hopkins University’s Applied Physics Laboratory.
This approach — one of many ideas to save humanity from asteroids — is known as “kinetic impactor deflection.” According to the team, this was the first time the method had been used intergalactically.
“This technique is considered the most technologically advanced approach to contain a potentially dangerous asteroid,” Lindley Johnson, NASA’s Planetary Defense Officer, said in a statement. “It will help planetary defense experts refine computer models of asteroid kinetic impactors and provide insights into how we might deflect potentially dangerous near-Earth objects in the future.”
How it works is pretty intuitive.
Quick, throw something at it!
Let’s say your buddy is skateboarding extremely fast and heading towards your dog. One (chaotic) way for you to save your dog is to run into your skateboarding friend. When you collide with your friend, the energy you build up changes direction and reduces his speed. You’ve just become a kinetic impactor tasked with throwing your skateboarding buddy off course and rescuing your dog.
DART is expected to work similarly, but it’s not trying to protect any canines, it’s just trying to throw the skateboarder off course. The spacecraft, which is about the size of a school bus, entered Dimorphos at a speed of about 4.1 miles per second. That’s about 14,760 miles per hour (23,760 kilometers per hour).
Upon impact, NASA says the small asteroid or small moon’s orbital velocity should change by a fraction of a percent, resulting in a few minutes slower orbital period.
Though Dimorphos poses no threat to Earth, Earth-based telescopes can easily catalog the impact of the bump because, at only about 7 million miles, the impact was close enough for scientists to observe changes in the rock’s orbit around its companion. Such observations will ultimately help scientists perfect future planetary defense weapons based on valuable information gleaned from DART’s prototype.
The technical data of the brave spaceship
DART was pretty easy. It was a relatively inexpensive metal box with two extendable, expandable solar arrays for power, a single camera, and a smaller satellite or CubeSat deployed just prior to impact. The limited number of tools made sense since the spaceship was doomed to die on a suicide mission.
Here are some details about the DART spacecraft:
Costs: $308 million.
Weight: 1,345 pounds (610 kg) at launch / 1,210 (550 kg) pounds at impact.
Carton dimensions: 3.9 x 4.3 x 4.3 feet (1.2 x 1.3 x 1.3 meters).
Dimensions of the solar system: 27.9 feet (8.5 meters).
Additional instrumentation: DRACO camera and a CubeSat.
Engine: Ion Engine Technology/Xenon Engines.
While the DART spacecraft’s payload was extremely light, the programming of the team behind the course was highly sophisticated. That’s because the plucky little vehicle behaved autonomously throughout the mission.
Until the end, DART
The spacecraft’s tools might be few, but they were the key. The Didymos Reconnaissance and Asteroid Camera for Optical Navigation, or DRACO, was an ultra-high-resolution camera that measured the size, shape, and geological composition of nearby asteroids.
DART also had a metal-oxide semiconductor and image processor that helped the spacecraft pinpoint Dimorphos’ exact position and send real-time information back to Earth via an antenna attached to the machine.
In addition, DART was equipped with a navigational toolkit with state-of-the-art directional coding, including the Star Tracker, NASA’s personal favorite tool to ensure it hit Dimorphos at just the right moment – ding, ding: the 7 million miles (11 million kilometers) Checkpoint. Ten days before DART hit its target, it sent out a CubeSat. This offshoot will preserve the history of kinetic impact, though DART is now just a pile of rubble somewhere in the cosmos.
But until the end, DART did its duty. NASA was able to capture the juicy details of the collision before, during and after impact.
“In its final moments,” states the overview from Johns Hopkins University, “DART’s DRACO camera will help characterize the impact site by providing high-resolution, scientific images of Dimorphos’ surface.”
Then: boom. “Pour one for the dinosaurs,” DART said. Probably.
This article was originally posted when DART was launched in November 2021.