September 262022, NASA’s Double Asteroid Redirection Test (DART) made history when it encountered the asteroid Didymos and impacted its moon, Dimorphous.
The objective was to test the “Kinetic Impact” method, a defense against potentially dangerous asteroids (PHA) where a spacecraft collides with them to modify their trajectory. Based on follow-up observations, the test was successful as DART managed to shorten Dimorphos’ orbit by 22 minutes. The impact also caused the moon to grow with a visible tail!
However, as Hollywood likes to remind us, there are scenarios where a planet-killing asteroid closes in on Earth before we can do anything to stop it. And there’s no shortage of near-Earth asteroids (NEAs) that could become potential threats one day.
That’s why space agencies around the world are getting into the habit of monitoring them and knowing how far they pass from Earth. According to a new study by a group of satellite experts, it may be possible to build a fast-response kinetic impactor mission that could encounter and deflect a PHA shortly before it collides with Earth. .
The study, recently published in Acta Astronautics, was conducted by Adalberto Domínguez, Víctor M. Moreno and Francisco Cabral – three researchers affiliated with the Spanish satellite developer GMV. This company specializes in guidance, navigation and control (GNC) and attitude orbit control (AOCS) systems with commercial, military, research and space exploration applications. In the interest of their article, the research team presented GMV’s recent work on a CNG system for a Kinetic Impact mission.
How to deflect an asteroid
In recent years, space agencies have studied several strategies to deflect asteroids that pose a threat of collision with Earth. As Domínguez explained to Universe today per email, three are considered the most promising: the Nuclear Standoff, the Gravity Tractor, and the Kinetic Impactor.
While the nuclear option involves detonating a nuclear device in the vicinity of an asteroid, the gravity tractor involves a craft flying around an asteroid to deflect its course. Only the kinetic impactor, said Dominguez, is feasible to deflect PHAs:
“The applicability of the nuclear showdown remains to be demonstrated, and their target would be asteroids with a diameter of the order of several kilometers. These asteroids are no longer a threat these days, as the vast majority are monitored. Moreover, the 1967 Outer Space Treaty prohibits nuclear explosions in space. The Gravity Tractor targets more interesting asteroids on the order of hundreds of meters. There is a large percentage of asteroids of this size yet to be discovered, and the impact could involve the destruction of an entire city. Nevertheless, the gravity tractor would take several years to move away from this asteroid.
For the purposes of their study, Dominguez and his colleagues focused on developing a CNG system for a kinetic impactor. This is vital for any robotic mission, especially when autonomy is required. One of the most cutting-edge aspects of the DART mission was the autonomous guidance system it was testing, known as Small-body Maneuvering Autonomous Real-Time Navigation (SMART Nav). This system guided DART on its final approach to Dimorphos, as mission controllers could not issue heading corrections at this point.
A KI mission intended to deflect an asteroid at the last moment will also require autonomy, in particular because of its speed of movement. By the time it hits the asteroid, the spacecraft will need a relative speed of between 3 and 10 km/s – 10,800 km/h and 36,000 (6,710 and 22,370 mph). Dominguez said:
“Another additional difficulty is that we know next to nothing about the asteroid we are targeting. objects with a size of about a hundred meters Imagine the difficulties associated with the problem of the impact of an object with an unknown dynamics and shape, at a speed of km/s and without the possibility of making corrections from the ground.
This, says Dominguez, makes the GNC the most important element of the critical subsystem since it is responsible for targeting the asteroid and applying course corrections at the last second. These corrections present the additional difficulty of being calculated and executed on the spot, that is to say as the mission progresses rapidly. To ensure that their GNC design could perform such calculations, the team studied the algorithms commonly used by spacecraft (navigation, image processing, etc.) in their analysis and tested their performance. The former, Dominguez said, comes in two varieties:
“Guidance algorithms can be divided into two main groups: proportional navigation and predictive feedback. Proportional navigation algorithms use knowledge of the current position of the target and impactor to calculate the maneuver needed to achieve impact. Proportional navigation is equivalent to the guidance employed by a missile, corrections are applied every second (continuous maneuvers) to correct the trajectory of the spacecraft.
Meanwhile, predictive feedback guidance relies on past and present information to predict the future state of the spacecraft and impactor. In this case, the corrections are only applied at certain times during the mission, such as when the spacecraft is only one hour away from performing the impact maneuver.
Ultimately, they identified two main problems with proportional algorithms, which led them to incorporate predictive algorithms into their concept.
“First, to be applied directly, it requires choke thrusters,” Dominguez said. “Secondly, it requires a system that allows constant maneuvering. These two facts usually imply degradation in fuel consumption and performance. With the use of a predictive guidance system, system stress can be significantly reduced. Additionally, most of the current state of the art only employs proportional navigation. DART used this type of navigation system. We wanted to show that other approaches can also provide great results and could be used. »
After simulating how these factors would affect a KI mission, the team found that their spacecraft was very accurate, with an impact error of just 40 meters (131 feet). According to asteroid monitors, an object measuring 35 meters (~115 feet) or more in diameter is considered a potential threat to a city or town. Meanwhile, the largest PHAs tracked regularly by NASA, ESA, and other Earth defense organizations measure between 2 and 7 km (1.25 and 4.35 mi). Regarding the guidance system alone, their simulations reached an error of less than one meter (~3.3 feet).
“This is an excellent result for the stage of development of our GNC concept, as we envision errors beyond those that would be present in a true kinetic impactor, and navigation could be significantly optimized by improving image processing and filtering in order to increase the chances of a successful impact,” Dominguez concludes. “The scheme we have proposed opens the door to the development of a kinetic impactor mission.”
In the future, he and his colleagues hope to optimize the variables of their kinetic impactor and compare its performance and applicability to other designs. In the end, it’s all about preparation, planning and knowing that we have methods in place in case of a worst-case scenario.
While regular monitoring of near-Earth asteroids is the most important part of planetary defense, it’s good to have contingency plans in place. One day, kinetic impact missions designed for long-range, last-minute intercepts could be the difference between Earth’s survival and an extinction-level event.
This article was originally published on Universe today by MATT WILLIAMS. Read the original article here.
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