Duke University Trinity College of Arts & Sciences
ASTEROID IMPACT: ANALYZING WHAT IT TAKES TO DETECT AND PREVENT A COSMIC ASSUALT Levi Rhoades
Math 89s: Mathematics of the Universe
Professor Hubert Bray
Introduction Even though Bruce Willis does exist in society. The suave, courageous, and intuitive version of Bruce Willis who is able to deflect massive asteroids away from planet Earth is unfortunately still nonexistent. Space object collision is a topic that has recently resurfaced in the public view because of the 2013 meteor which exploded at a height of around 30 kilometers over Chelyabinsk, Russia injuring 1,500 people and causing millions in property damage. NASA is currently allocated around 0.4% of the United State’s total budget and only 0.05% of this funding is dedicated to the NEO (near earth object) program which tracks and plans for asteroid collisions (Powell). A student at Duke University, JJ Liao, examined in his previous paper the cost efficiency of properly funding an asteroid defense program and concluded it would cost between 50 and 100 million dollars a year (JJ). This passages to the topic of the genuine likeliness of a global Armageddon by NEO, and since Bruce Willis can’t save the world; what precautions have human’s taken as a species to prepare for, protect against, and deflect any asteroids or comets that could potentially collide with Earth? This essay will focus on the detection and responses to an extinction type space object colliding with the planet that are funded by the United State’s government while providing special consideration to a novice but procedural overview of the impact of orbital mechanics when addressing this problem.
The first step to saving mankind would be to detect the celestial satellite set to impact. Uncovering these rocks as early as technologically possible is a key component to survival because of both composition and response. The current method for finding and tracking asteroids includes the WISE (Wide-field Infrared Explorer) which emits infrared bands at four different wavelengths to perform an all sky astronomical survey. The WISE system has helped to discover tens of thousands of new asteroids as well as new star clusters, but researchers still estimate that it has only discovered 2% of the NEO population of interest (Near). In addition to the WISE system, the Canadian Space Agency launched NEOSat (near earth object surveillance satellite) in 2013 which can hunt for more hidden NEOs in space. However, a more simple and effective way to detect new asteroids is available to anyone with a telescope. Backyard amateur observations of objects in anomalous motion returned about 80 new NEO’s during the month of March, 2014. On average observations through a telescope with the human eye return about 500 more NEOs a year according to private researchers at space.com.
Detecting composition would help better prepare scientists and politicians to appropriating defense mechanisms for the entity. Asteroids fall under three types: C (carbonaceous), S (silicaceous), M (metallic). C-type accounts for 75% of all observable asteroids and is dark in color and dominantly found on the outer rim of asteroid belts. S and M type asteroids are less common and dominate the inner regions of belts, however all types can vary in size, speed and color. Specifically, if the asteroid is classified as size “planetismal” (less than a 100 meters in diameter) then it is likely a collection of loose rubble bound together by gravity and formed by debris after collisions with other asteroids. If the asteroid is larger, then it is classified as a “protoplanet” which has a spherical and solid outline usually with a chemically differentiated interior (Shoemaker). These composition distinctions bear weight when considering how to best diminish the threat of impact because a collection of smaller asteroid rubble cannot be effectively destroyed or deflected by impact mechanisms such as a HAIV (hyperactivity asteroid intercept vehicle) or nuclear blast (Near). In addition, metallic comets require more force to change velocity than carbon based rocks.
Nuclear Explosive Device
The responses to asteroid collision are what fuel the scripts of blockbuster films, and captures the minds of daydreamers everywhere. There are dozens of theories on how to deflect or destroy an asteroid, however this paper will only focus on those considered and funded by the United State’s government. Using a nuclear detonation to vaporize or change the course of the objects orbit to avoid hitting Earth is the most funded approach. In 1967 students at the Massachusetts Institute of Technologycalculated the nuclear megatonnage needed to divert a 1.4 km wide asteroid off of a collision course with Earth given 18 months notice in a project nicknamed Icarus. It was concluded that multiple rockets loaded with 100 megatons of nuclear energy would be needed to change the velocity of the rocket enough to miss colliding with the surface (Shoemaker). However Dr. Wie of Iowa State University examined the same simulation and concluded that using a HAIV was the only method to deliver a force strong enough to divert course. The HAIV would increase speed gradually as it moved towards the asteroid until it preformed a kinetic impaction in which a large crater would form exposing more vulnerable center of the asteroid composed of soft x-rays and neutrons. Then the rockets would be fired to strike this crater and disable the threat. Dr. Wie expressed his confidence in this method in 2014, “For example, according to their computer models, with a warning time of 30 days a 1,000-foot-wide (300 m) asteroid would be neutralized by using a single HAIV, with less than 0.1 percent of the destroyed object's mass potentially striking Earth” (Planetary).
Furthering the nuclear method is the standoff approach which is particularly effective against smaller asteroids which are composed of loose rock pieces held together by gravity. A head on nuclear explosion would likely scatter some rocks into unpredictable orbits and not contact enough surface area of the larger rocks to have a palpable impact on their trajectory. However detonating a bomb at a 20 meter or greater stand off height would circumvent the splitting of already fractured material (Preparing). However because the standoff method uses less force it would need to be employed very prematurely in the progress of the asteroid or would require a greater multitude of blasts for a rock with a short travel period.
Currently the nuclear warhead B53 is the only publically known weapon possessed by the United States with a great enough energy yield to be effective against an asteroid of size protoplanet or greater. The Comprehensive Nuclear-Test Ban treaty of 1996 also bans the use of all nuclear weapons. However, it is likely that these prohibitions would be temporarily uplifted if a large scale collision was inevitable and could cause a significant loss of life.
Kinetic Impact/Gravity Tractor
Another option for redirecting the celestial body includes using a large unmanned space craft to change an orbit through impact or explosive deflection. In the kinetic impact model, an object with extremely high mass and low brittleness would be sent onto a collision course with the asteroid attempting to rebound it from its current course. A NASA analyst in 2007 stated why he believes that kinetic impactions are the future of asteroid protection, “Non-nuclear kinetic impactors are themost mature approachand could be used in some deflection/mitigation scenarios, especially for NEOs that consist of a single small, solid body” (Lincoln). The European Space Agency is currently running simulations for a 2020 mission which would see two aircraft (AISA, and Don Quijote) perform the first asteroid deflection although funding is limited. One of the limitations of the kinetic impact model is the cost efficiency because the spacecraft requires enormous amounts of size and fuel and cannot be recovered after the mission.
The asteroid gravity tractor is the final U.S. research-funded response although it is by far the most expensive and immature program of all defense systems. Essentially a rocket with an extremely heavy mass would locate and begin to orbit the asteroid, and because these two bodies are mutually attracted to each other due to gravity the rocket could begin to counteract this force by flying away from the asteroid and pushing with the rocket’s ion thrusters. Over a long period of time, researchers estimate years, the asteroid would accelerate towards the spaceship diverting its course from an Earth impact.
The Future of Development/Orbital Mechanics
In a case study by Dr. Izzo, Dr. Yam, and Dr. Olympio of the ESA they analyzed the orbital mechanics required to properly deflect an asteroid named Epcoch headed towards collision in the year 2030. The following equation shows variables accounted for during the shift of the asteroid Epcoch which was set to a collision with earth following its current orbit:
∆r = 3a µ vast,te (te − t0)(vast,t0 · ∆V)
In this model ∆r is the deflection distance, ∆V is the change in velocity, a is acceleration and te is the time Epcoch is experiencing relative to the time the Earth is experiencing Epcoch. The change in deflection ∆r is vested primarily in the amount of force applied to the object (Lu). In spite of this asteroids sometimes fly as groups of smaller rubble and are prone to fracture, so these calculations can only be attributed to ideal conditions. Another factor that researchers are considering on the impact of deflection is the color of the asteroid. Asteroids of lighter colors such as type S or M will over time emit more and more photons than a similar type C rock. These photons, while small carry some momentum and overtime can affect the orbit of the asteroid. This is another instance of detection being so important to the process of defense.
The future of asteroid defense advances can best be attributed to the vision of former astronaut Ed Lu. Dr. Lu is the founder of the B612 foundation and has donated 50 million dollars towards asteroid detection research in the fiscal year of 2016. This figure is on par with what my colleague J.J. Liao estimated was required for defense and is also 10 times more than NASA was spending on the same project in 2010 (JJ, Powell). B612 hopes to launch a new infrared telescope into space named Sentinel which could detect objects as small as 30 meters across. This improvement in detection is due to Dr. Lu’s distrust in nuclear deflection or obliteration. Dr. Lu argues that detecting a collision headed celestial rock years in advance would afford mankind with the luxury of trying several different more stable and gradual approaches such as a tractor beam or the gradual thrust method. He is also voiced his concerns on twitter that an asteroid heading for earth could become weaponized through the strategic deflection or collapsing of the rock so as to target impacts in specific countries.
Asteroid defense and exploration is a topic that should be taken seriously and regarded with a moderate sense of urgency. Although no human has been killed by an asteroid or its impact in the last 1000 years, the blast above Chelyabinsk proved once again to the public that we do not have the solar system mapped out completely, and that many NEO’s have slipped through the cracks of documentation because of insignificant funding and muted necessity (Powell). The current primary methods of defense include nuclear strikes, kinetic impaction, and gravity tractors all of which are untested and relatively juvenile in their production. As space exploration develops in the rest of the 21st century, asteroids both in mining and defense will become an integral tool in the development of the knowledge of the cosmos. When considering man-made interaction with an asteroid it is important to consider its size, type, and color as well as document its acceleration, time in space, and velocity to consider the applied force of its movement. Asteroids are are region of space like many others that mankind is still very in the dark about. However, since so many are flying so close it might not be a bad idea to go learn something about them considering Bruce Willis may not be around that much longer.
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