On September 26thIn 2022, NASA’s Dual Asteroid Redirection Test (DART) made history when it met the asteroid Didymus and collided with its amorphous moon.
The goal was to test the “kinetic impact” method, a defense against potentially dangerous asteroids (PHAs) in which a spacecraft slams into them to change its trajectory. Based on follow-up observations, the test succeeded since DART managed to shorten Dimorphos’ orbit by 22 minutes. The impact also caused Little Moon to grow a visible tail!
However, as Hollywood likes to remind us, there are scenarios in which a planet-killing asteroid gets too close to Earth before we can do anything to stop it. And there is no shortage of near-Earth asteroids (NEAs) that could become potential threats one day.
This is why space agencies around the world make it a habit to monitor them and how close they are to Earth. According to a new study by a group of satellite experts, it will be possible to build a fast-response kinematic impact mission that can rendezvous and deflect a PHA shortly before it hits the ground.
The study that appeared recently in space acta, Adalberto Dominguez, Victor Moreno and Francisco Cabral – three researchers affiliated with Spanish satellite developer GMV. This company specializes in Guidance, Navigation and Control (GNC) and Orbit Attitude Control Systems (AOCS) systems with commercial, military, research and space exploration applications. For their paper, the research team presented GMV’s recent work on the GNC system for the motor impact task.
How to deflect an asteroid
In recent years, space agencies have investigated multiple strategies for deflecting asteroids that pose a threat of collision with Earth. As explained by Dominguez L the universe today By email, three of them are considered the most promising—nuclear standoff, gravity tug, and kinetic collision.
While the nuclear option is to detonate a nuclear device near an asteroid, gravity involves a ship flying around an asteroid to deflect its trajectory. Dominguez said that only a kinetic collider can deflect a PHA:
“The applicability of nuclear confrontation is yet to be proven, and its target will be asteroids several kilometers in diameter. These asteroids do not pose a threat at present, since the vast majority of them are monitored. Moreover, the Outer Space Treaty of 1967 Prohibited nuclear explosions in outer space. The gravity tractor targets the most interesting asteroids within hundreds of metres. There is a large percentage of asteroids of this size to be detected, and the impact could mean the destruction of an entire city. However, Earth’s gravity would require several years to deflect this asteroid.”
For their study, Dominguez and colleagues focused on developing a GNC system for a kinetic collider. This is vital to any robotic task, particularly when autonomy is required. One of the most sophisticated aspects of the DART mission was the autonomous guidance system it was testing, known as Small-Body Maneuvering Real-time Navigation (SMART Nav). This system guided DART through its final approach to Dimorphos, as mission controllers were unable to issue course corrections at this point.
A KI mission designed to deflect an asteroid at the last moment requires autonomy, mainly because of the speed at which it will move. By the time the asteroid hits, the spacecraft will need a relative velocity of between 3 and 10 km/s – 10,800 km/h and 36,000 (6,710 and 22,370 mph). Said Dominguez:
Another difficulty is that we hardly know anything about the asteroid we are targeting. This requires that the General National Congress must adapt to any possibility. Moreover, the implied size of the asteroids causes navigation difficulties because we are talking about objects about a hundred meters in size. Imagine the difficulties associated with the problem of impacting a body with unknown dynamics and shape, at a speed of km / s and without the possibility of making any corrections from the ground.
This, Dominguez says, makes the GNC the most important component of the subsystem because it is responsible for targeting the asteroid and applying last-second trajectory corrections. These corrections have the added difficulty of being computed and implemented on site – that is, when the job is rapidly unfolding. To ensure that their GNC design could perform such calculations, the team investigated algorithms commonly used by spacecraft (navigation, imaging processing, etc.) in their analysis and tested their performance. Dominguez said that the former comes in two forms:
Routing algorithms can be divided into two main groups: relative navigation and predictive feedback. Relative navigation algorithms use knowledge of the target’s current location and impacts to calculate the maneuver needed to achieve the impact. Relative navigation is equivalent to the guidance used by the rocket, and corrections are applied every second (continuous maneuvers) to correct the spacecraft’s trajectory.”
Meanwhile, predictive feedback guidance relies on past and present information to predict the future state of the spacecraft and collision. In this case, the corrections are only applied at certain moments in the mission, such as when the spacecraft is only an hour away from performing the collision maneuver.
In the end, they identified two major problems with relativistic algorithms, which led them to incorporate predictive algorithms into their concept.
“First, to be applied directly, it requires throttle-capable thrusters,” Dominguez said. Secondly, it requires a system that allows for continuous maneuvers. These two facts generally indicate a deterioration in fuel consumption and performance. By using the predictive steering scheme, system pressure can be significantly reduced. Moreover, most of the current state of the art uses only relative navigation. DART used this type of navigation scheme. We wanted to show that other methods can also deliver great results and can be used.”
After simulating how these factors affect the KI mission, the team found that their spacecraft was extremely accurate, with a collision error of just 40 meters (131 feet). According to asteroid monitors, an object with a diameter of 35 meters (about 115 feet) or more is considered a potential threat to a town or city. Meanwhile, the largest PHAs regularly tracked by NASA, the European Space Agency and other Earth defense organizations measure between 2 and 7 kilometers (1.25 and 4.35 miles) wide. For the guidance system alone, their simulations achieved an error of less than 1 meter (~3.3 ft).
“This is a great result of our GNC concept development phase, as we are studying errors larger than those that would be present in a real kinetic collider, and navigation can be significantly improved by improving image processing and filtering in order to increase the chances of a successful forcing,” Dominguez concludes. “The scheme we proposed opens the door for the development of a kinetic collider mission.”
In the future, he and his colleagues hope to improve the variables of the motor stimulus and compare their performance and applicability with other concepts. At the end of the day, it’s all about preparation, planning, and knowing we have methods in place should a worst-case scenario occur.
While regular observation of near-Earth asteroids is the most important part of planetary defense, it’s a good idea to have contingency plans in place. Someday, kinetic impact missions designed for long-range and last-minute interceptions could be the difference between Earth’s survival and an extinction level event.
This article was originally published the universe today by Matt Williams. Read the original article here.
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