NASA fights against the threat of asteroids

The world is currently facing many earthly crises, so it’s easy to forget that giant space rocks could one day threaten the very existence of entire civilizations. Yes, the threat of asteroid strikes is distant, but nonetheless something that humanity may have to contend with someday, and someday soon.

NASA takes the problem seriously and has staffed its Planetary Defense Coordination Office since 2016. Serving these efforts, it is also developing a mission to research how dangerous androids can be deflected. The Double Asteroid Redirection Test, or DART, is expected to launch within the next year.

DART aims to change the trajectory of an asteroid by kinetic impact or, in layman’s terms, crashing into it. The spacecraft will target Didymos, a binary asteroid system made up of Didymos itself and the smaller asteroid Dimorphos orbiting it. The asteroid will pass close to Earth, at a distance of 11 million kilometers, without being on a collision course, making it a good candidate for humanity’s first attempt at asteroid deflection.

Didymos, the largest asteroid of the pair, is 780 meters in diameter, while Dimorphos is significantly smaller at just 160 meters in diameter. The DART craft will aim to strike Dimorphos head-on and in doing so reduce its orbital period around Didymos. This change of orbit will be measured from observatories on Earth in order to measure the success of the mission.

The main body of the DART spacecraft measures only 1.2 x 1.3 x 1.3 meters, and the spacecraft as a whole weighs around 500 kg. DART is intended to impact Dimorphos at a speed of 6.6 km / s. In doing so, it will change the orbital period from 4.2 minutes, from 11.9 to 11.8 hours. The change in orbital period should be of the order of about 10 minutes. It may not seem like a big change, but the hope is that over millions of miles this will add up to a significant change in the original trajectory of the asteroid system.

The DART mission will also be used to test several innovative technologies. The new features of 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 are also lighter and more compact than traditional arrays, while also being more rigid. Twin Rolling Panels will each measure 8.5 meters when fully extended. Similar technology was recently deployed on the ISS, which had deployment panels installed on its original rigid solar panels to improve the energy budget of the aging space station. The ROSA panels will also include a small section for testing Transformational Solar Array technology, which uses reflective concentrators combined with high efficiency solar cells to potentially deliver triple the power available from a typical solar panel.

Propulsion is via NASA’s NEXT-C xenon-powered grid ion thruster. This uses electric fields to accelerate the ions to enormous speeds of the order of 40 km / s in order to generate a thrust for the spacecraft. While the thrust generated is low, on the order of a few hundred milliNewtons, the ion thruster is very fuel efficient. So, it can be run for a long time to slowly accelerate the craft to high speed. We have already presented an overview of the technology, which promises to be useful in various long-range space missions.

In order to target the asteroid and hit it straight and true, the DART mission needs a top notch navigation system. The machine thus has the Didymos Reconnaissance and Asteroid Camera for Optical, or DRACO. This device is intended for terminal navigation to ensure that DART makes a good solid impact with the asteroid. The high-resolution camera powers the SmartNAV autonomous guidance system which will control the spacecraft in its final four hours of flight to 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 machine must fly itself towards its target.

The DART mission will also carry LICIACube, a small seated cube built by Agenia Spaziale Italiana (ASI). Five days before the impact, LICIACube will be deployed to image the impact of DART in Dimorphos. The goal is to capture images of the impact site itself, as well as the cloud of material ejected in the immediate wake of the impact. This should provide a lot of material for the analysis of the effectiveness of the DART mission in redirecting the asteroid.

This is an interesting approach to the asteroid deflection problem. Hitting asteroids with relatively small spacecraft in a nice and early fashion is something that should be easily achievable with current technology, as DART will demonstrate. It’s also less desperate and drastic than other ideas involving the ultimate use of nuclear weapons to hijack or destroy incoming objects.

Currently, no major asteroids are expected to hit Earth in the near future. However, that doesn’t mean that there aren’t a lot of asteroids floating there. The Planetary Defense Coordination Office had detected more than 19,000 near-Earth asteroids as of early 2019, and 30 new objects are detected on average every week. These detection and tracking efforts are essential to planetary defense. The sooner we are aware that an object is heading towards Earth, the more time we have to plan a mission to deal with it, and the more options are on the table. Let the asteroid get too close, and the amount of energy needed to divert it from Earth becomes much greater and the task much more difficult.

Although the effect of DART is small, this is only humanity’s very first attempt to redirect an asteroid. It will be easier for the good people of Earth to rest, knowing that great minds are grappling with the difficult problem of how to protect us from the big rocks above.