The world faces many terrestrial crises right now, so it’s easy to forget that giant space rocks may one day threaten the very existence of entire civilizations. Yes, the threat of asteroid strikes is a remote one, but nevertheless something humanity may have to face one day, and one day soon.
NASA takes the issue seriously, and has staffed its Planetary Defence Coordination Office since 2016. In service to these efforts, it’s also developing a mission to research how dangerous androids may be deflected. The Double Asteroid Redirection Test, or DART, is set to launch within the next year.
DART aims to change the path of an asteroid through kinetic impact, or, in layman’s terms, by smashing into it. The craft will target Didymos, a binary asteroid system consisting of Didymos itself and the smaller asteroid Dimorphos in orbit around it. The asteroid will pass near Earth, at a distance of 11 million kilometres, without being on a collision trajectory, making it a good candidate for humanity’s first attempt at asteroid deflection.
Didymos, the larger asteroid of the pair measures 780 meters in diameter, while Dimorphos is significantly smaller at just 160 meters across. The DART craft will aim to hit Dimorphos head on, and in doing so, reduce its orbital period around Didymos. This change in the orbit will be measured from observatories on Earth in order to gauge the success of the mission.
The main body of the DART spacecraft measures just 1.2 x 1.3 x 1.3 meters, and the craft as a whole weighs approximately 500 kg. DART is intended to impact Dimorphos at a speed of 6.6 km/s. In doing so, it will alter the orbital period by 4.2 minutes, from 11.9 to 11.8 hours. The change in the orbital period is expected to be on the order of 10 minutes or so. It may not sound like a big change, but the hope is that over millions of kilometers, it will add up to a significant shift in the original trajectory of the asteroid system.
The DART mission will also serve to trial several innovative technologies. New to the project are the Roll Out Solar Arrays, or ROSA. These flexible solar panels can be rolled up for launch, and deployed once the craft is in space. They’re also lighter and more compact than traditional arrays, while also being stiffer as well. The twin roll-out panels will each span 8.5 meters when fully unfurled. Similar technology was recently deployed to the ISS, which has had roll-out panels laid over its original rigid solar panels to improve the power budget of the aging space station. The ROSA arrays will also feature a small section to trial Transformational Solar Array technology, which uses reflective concentrators combined with high-efficiency solar cells to potentially provide triple the power available from a typical solar array.
Propulsion is via NASA’s NEXT-C xenon-fueled gridded ion thruster. This uses electric fields to accelerate ions to huge velocities on the order of 40 km/s in order to generate thrust for the spacecraft. While the thrust generated is small, on the order of a few hundred milliNewtons, the ion thruster is very fuel efficient. Thus, it can be run for a long time to slowly accelerate the craft to great speed. We’ve featured a run down on the technology before, which promises to be useful on a variety of long-range space missions.
In order to target the asteroid and hit it square and true, the DART mission needs a top-notch navigation system. The craft thus features the Didymos Reconnaissance and Asteroid Camera for Optical, or DRACO. This device is for terminal navigation to ensure DART makes a good solid impact with the asteroid. The high-resolution camera feeds into the SmartNAV autonomous guidance system which will control the space craft in its final four hours of flight towards the asteroid. Having the spacecraft guide itself is important, as with the distances involved, the round trip delay for commands from Earth would be 1.5 minutes. Thus, the craft must fly itself to its target.
The DART mission will also carry LICIACube, a small cube sat built by the Agenia Spaziale Italiana (ASI). Five days prior to impact, LICIACube will be deployed in order to image the impact of DART into Dimorphos. The aim is to capture shots of the impact site itself, as well as the cloud of ejected material in the immediate wake of the impact. This should provide plenty of material for analysis as to the effectiveness of the DART mission at redirecting the asteroid.
It’s an interesting approach to the problem of asteroid deflection. Hitting asteroids with relatively small spacecraft nice and early in their approach is something that should be readily achievable with current technology, as DART will demonstrate. It’s also less desperate and drastic than other ideas involving the last-ditch use of nuclear weapons to turn away or destroy incoming objects.
At present, there are no major asteroids expected to hit Earth in the near future. However, that’s not to say there aren’t plenty of asteroids floating around out there. The Planetary Defense Coordination Office had detected over 19,000 near-Earth asteroids by the start of 2019, and 30 new objects are detected on average each week. These detection and tracking efforts are key to planetary defense. The earlier we’re aware of an object heading towards Earth, the more time we have to plan a mission to deal with it, and more options are on the table. Let the asteroid get too close, and the amount of energy needed to deflect it away from Earth becomes much greater, and the task much harder.
While the effect of DART will be small, it’s only humanity’s very first attempt to redirect an asteroid. The brave people of Earth will be able to rest easier, knowing that great minds are tackling the difficult problem of how to protect us from the big rocks from above.
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