How, Exactly, Did NASA Smash Its DART Spacecraft Into an Asteroid?
NASA’s $308 million spacecraft crashed into a deep space asteroid, and the scientific community couldn’t be happier with the results.
Marking the end of an approximately 10-month-long mission, NASA’s Double Asteroid Redirection Test (DART) spacecraft successfully impacted the moonlet Dimorphos after traveling over seven million miles. NASA’s Planetary Defense Coordination Office (PDCO) reported that this mission was the first milestone in assessing the Earth’s ability to redirect potentially devastating alien objects, opening the door to future deep space reconnaissance missions.
Image of asteroid Didymos (left) and its moonlet, Dimorphos, 2.5 minutes before the DART spacecraft made impact. Image used courtesy of NASA/Johns Hopkins APL
The true novelty of DART was not observed until its final four hours. At this point, dubbed the “terminal phase,” DART began to self-correct its own trajectory thanks to the electronics in its payload. A combination of multiple subsystems enabled the success of the DART mission, each of which will be analyzed here in more detail.
DRACO: Helping DART Keep its Eye on the Target
Acting as the eyes for the mission, the Didymos Reconnaissance and Asteroid Camera for Optical navigation (DRACO) was the sole instrument onboard the DART spacecraft. DRACO, as its long-form name implies, is a specialized, high-resolution camera designed to provide immediate feedback to DART, so the spacecraft could accurately steer itself toward Didymos, as well as measure the dimensions of the asteroid pair.
A 3D rendering of the DRACO instrument with structures for mounting to the DART payload. Image used courtesy of the Johns Hopkins Applied Physics Laboratory
DRACO's images were processed onboard the payload to assist with navigation in the terminal phase while also being downlinked using a high-gain radial line slot antenna. Since DRACO's course corrections were made as early as possible to preserve fuel, DRACO’s field of view was quite small at only 0.29 degrees to allow for significant magnification. Despite this narrow view, DRACO captured high-quality images of Dimorphos all the way until impact.
SMART Nav: Real-time Control for Deep-space Missions
Perhaps the most exciting component of the DART mission’s success was the Small-body Maneuvering Autonomous Real-time Navigation (SMART Nav) algorithms. SMART Nav independently guided DART to the surface of Dimorphos with no human intervention using the same computational power as a 21-year-old PlayStation 1.
In the terminal phase of the DART mission, the DART spacecraft traveled at about 4 miles per second. The round-trip travel time for light is approximately 90 seconds, making terrestrial control of DART impractical and inefficient. NASA developed the SMART Nav algorithms to control the DART spacecraft in real-time using the onboard electronics exclusively. After receiving image data from DRACO, SMART Nav not only detected the asteroid pair but estimated its trajectory and the most efficient method for DART to reach Dimorphos.
SMART Nav block diagram used to process DRACO images and calculate the most efficient steps to impact Dimorphos. Image used courtesy of Johns Hopkins Applied Physics Laboratory
The real beauty behind SMART Nav is how much it can accomplish in a simple, robust system without any human input. With more computational power, NASA could have implemented more advanced navigational algorithms in DART. Without the protection of the atmosphere, however, cosmic radiation drastically impacts electronic circuits, especially as the number of transistors increases and their size decreases.
ROSA: Breaking the Tradeoff Between Size and Power
To supply DART’s onboard electronics with sufficient power for months on end, NASA used Roll-out Solar Arrays (ROSA). For long-term missions, it is usually more energy-efficient to equip a spacecraft with an energy harvesting device such as solar panels versus carrying a form of energy storage. Traditional solar devices, however, are large, rigid, and cannot be readily deployed without human intervention. ROSA achieved a better tradeoff for both launch and energy efficiency while supplying up to 30 kW per array.
ROSA system after deployment on a spacecraft. Image used courtesy of Redwire
When launched, ROSA’s solar cells were rolled up like a carpet inside the payload for easier transportation. Once the launch was completed, ROSA was then deployed. During deployment, composite boom structures passively extended from the payload, extending the solar cells with them to provide a wide cross-sectional area for energy harvesting. The composite booms didn't require motors to deploy, instead using stored strain energy in the composite itself to extend the solar cells—further reducing the number of failure points in the system.
ROSAs have already been installed on the International Space Station (termed iROSAs), with future integration in solar technologies such as concentrators on the horizon.
The Future of Planetary Defense
Getting DART to Dimorphos was only the first step for the PDCO. After the success of the DART mission, numerous teams across the globe are observing the asteroid pair to help determine the effectiveness of DART in altering the orbit of the moonlet and to generate models for future planetary defense missions.
DART’s companion satellite LICIACube (Light Italian CubeSat for Imaging Asteroids), which detached from DART 15 days before impact, has already produced images of the asteroid following DART’s collision.
The DART mission not only verified the effectiveness of its subsystems in deep space travel but also showed how NASA scientists might protect the Earth from catastrophic collisions.