The purpose was to test the “Kinetic Impact” method, a means of defense against potentially dangerous impacts. asteroids (PHAs) where a spacecraft collides with them to alter its trajectory. Based on follow-up observations, the test was successful as DART achieved shorten the orbit of Dimorphos by 22 minutes. The impact also caused the little moon to grow a visible tail!
However, as hollywood He loves to remind us that there are scenarios where 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.
Hence, space agencies around the world are in the habit of monitoring them and how close they pass to Earth. according to a new study by a group of satelite Experts, it would be possible to build a fast-response kinetic impact mission that could find and deflect a PHA shortly before it collided with Earth.
The study, which recently appeared in Astronautical Act, It was carried out 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 and Orbit Control Systems (AOCS) with commercial, military, research and space exploration applications. For the sake of their article, the research team presented GMV’s recent work on a GNC system for a Kinetic Impact mission.
How to deflect an asteroid
In recent years, space agencies have investigated multiple strategies to deflect asteroids that pose a threat of collision with Earth. As Dominguez 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 ship that flies around an asteroid to divert its course. Only the kinetic impactor, Dominguez said, is feasible to deflect the PHAs:
“The applicability of the nuclear confrontation has yet to be proven, and its target would be asteroids with a diameter on the order of several kilometers. Those asteroids are not a threat today, since the vast majority are monitored. Also, the Outer Space Treaty of 1967 banned nuclear detonations in outer space. The gravity tractor targets more interesting asteroids on the order of hundreds of meters. There are a large percentage of asteroids of this size yet to be discovered, and the impact could destroy an entire city. However, it would take the gravity tractor several years to deviate from this asteroid.”
For the sake of their study, Dominguez and his colleagues focused on developing a GNC system for a kinetic impactor. This is vital for any robotic mission, particularly where autonomy is required. One of the most innovative aspects of the DART mission was the autonomous guidance system it was testing, known as Small Body Maneuvering Real-time Autonomous Navigation (SMART Nav). This system guided DART during its final approach to Dimorphos, as mission controllers were unable to correct course at this point.
A KI mission designed to deflect an asteroid at the last minute will also require autonomy, mainly because of how fast it will travel. By the time it hits the asteroid, 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). Dominguez said:
“Another added difficulty is that we hardly know anything about the asteroid we are targeting. This requires that the CNG adapt to any possibility. In addition, the size of the asteroids involved introduces difficulties in navigation since we are talking about objects with a size of around one hundred meters. Imagine the difficulties associated with the problem of impacting an object with unknown dynamics and shape, at a speed of km/s and with no possibility of making any corrections from the ground.”
This, says Domínguez, makes the GNC the most important critical element of the subsystem, since it is in charge of pointing at the asteroid and applying course corrections at the last second. These corrections have the added difficulty of being calculated and executed in situ, that is, while the mission is developing rapidly. To make sure that their GNC design could run such calculations, the team investigated 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:
“Orientation 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 the impactor to calculate the maneuver required to achieve the impact. Proportional navigation is equivalent to the guidance used by a missile, corrections are applied every second (continuous maneuvers) to correct the trajectory of the spacecraft.
Meanwhile, the predictive feedback guidance is based on past and present information to predict the future state of the spacecraft and impactor. In this case, the fixes are only applied at certain times in the mission, such as when the spacecraft is only an 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 of all, to be applied directly, it requires adjustable propellants,” Dominguez said. “Secondly, it requires a system that allows constant maneuvering. These two events generally imply a deterioration in fuel consumption and performance. With the use of a predictive guidance scheme, stress on the system can be greatly reduced. Also, most of the current state of the art only employs proportional navigation. DART employed this type of navigation scheme. We wanted to show that other approaches can also provide excellent 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 a hit 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 town or city. Meanwhile, the the largest PHAs regularly tracked 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 achieved an error of less than one meter (~3.3 feet).
“This is a great result for the development stage of our GNC concept, as we are considering larger errors than would be present in a real kinetic impactor, and navigation could be noticeably optimized by improving image processing and filtering. to increase the chances of a successful impact”, concludes Domínguez. “The scheme we proposed opens the door for the development of a kinetic impact mission.”
In the future, he and his colleagues hope to optimize the variables of their kinetic impactor and compare its performance and applicability with other concepts. At the end of the day, it’s all about preparation, planning, and knowing that we have methods in place in case the worst-case scenario happens.
While regular monitoring of near-Earth asteroids is the most important part of planetary defense, it’s good to have contingency plans in place. Someday, kinetic impact missions designed for last-minute, long-range interceptions could be the difference between Earth survival and an extinction-level event.