Hypervelocity Asteroid Intercept Vehicle
A Hypervelocity Asteroid Intercept Vehicle (HAIV) is a spacecraft being developed by NASA to deflect dangerous Near Earth objects (NEOs) such as comets and asteroids that threaten colliding with Earth. HAIVs focus on utilizing powerful explosives, such as nuclear bombs, to achieve deflection by detonating on the surface of the NEO to change its trajectory away from Earth. This method of asteroid impact avoidance is intended to be used on dangerous NEOs detected within a short time frame (less than 5 years) before a possible impact event with Earth. The idea came about when asteroid detection  improved. Since then, scientists and engineers have made a well thought out design for an HAIV. History. Over the years, certain events brought up the idea of planetary defense from NEOs. These events lead to the development of the HAIV that NASA intends to use. Project Icarus. In 1967, Professor Paul Sandorff at the Massachusetts Institute of Technology asked his graduate students to come up with a plan to deflect 1566 Icarus, an asteroid about 1 km wide. An asteroid was observed to have an orbit bringing it into a close approach pass by Earth in the coming year, curiosity  however motivated Sandorff to task his students to come up with a solution to the thought-experiment 'what if it were on an impact trajectory?' As the students were in a position of nothing being known about the density nor spin rate of the asteroid at the time, the team needed to propose a deflection solution that would not be held back by these unknowns. Eventually the team landed upon a conservative mission architecture that would work with 73 days remaining until impact. It consisted of launching a repeated series of the, then in-development, Saturn V rocket vehicle to  deliver 6 to 7 somewhat hypothetical 100-megaton nuclear explosive devices which would detonate about "50 to 100 feet" in proximity to the asteroids surface. With the first explosive Saturn-Icarus 1 physics package arriving at the asteroid with 13 days before Earth-impact remaining, the second Saturn-Icarus 2, arriving with 10 days remaining and so on. It is reported that analysis by Sandorff of the Project Icarus study, with an unspecified criteria and with the use of then estimated Saturn V launch success rates, that the project had a 71% chance of completely protecting the Earth and an  86% chance of reducing the damage a full impact would cause. Though Project Icarus was never tested, it laid the foundation for future research on nuclear explosive device deflection techniques. Chelyabinsk meteor. In 2013, a meteor about 30 meters in diameter and weighing about 13,000 metric tons had an impact event over Russia. Once in Earth's lower atmosphere it burned up and exploded. This relatively small meteor damaged over 7200 buildings and injured over 1400 people. It brought renewed attention towards asteroid defense. The NASA Suomi NPP satellite was able to track the plume afterwards, giving scientists more data  on asteroids. Design. After detecting many of the asteroids in the Solar System and observing their composition through meteorite remains, NASA has identified multiple large asteroids that may collide with Earth. To combat these NEOs, NASA has come up with the following design for an HAIV. The vehicle is split into two major parts; the leader craft and the follower craft. Leader craft. The leader craft is initially attached to the follower craft, but before impact the two craft are spread out by an extendable pillar known as the AstroMast Boom. Furthermore, it contains the primary guidance systems including normal  cameras and Lidar (light based radar). The purpose of this craft is to make an initial crater in the target NEO where the follower craft may detonate in. Doing this helps direct the explosive energy of the follower craft, hopefully applying enough force to change the orbit of the NEO. Follower craft. The follower craft contains the following: Once the leader craft impacts the NEO and makes a crater, the follower craft detonates its NED soon after. It also relays back whether the detonation was a success or failure which can be confirmed by observation from the Earth. Obstacles. There  are numerous factors that have slowed the development of the HAIV. These include but aren't limited to budget, law, and irregular NEOs. Budget. Initial test missions have cost between US$600 million to $1.8 billion, to test the feasibility of the guidance. A full mission may cost much more than this amount, especially in the case of a NEO detected with a short time till collision with Earth. With recent cuts to NASA's funding, it is unsure whether an HAIV mission will ever occur. Law. The use of nuclear explosive devices is an international issue and will  need to be addressed by the United Nations Committee on the Peaceful Uses of Outer Space. The 1996 Comprehensive Nuclear-Test-Ban Treaty technically bans nuclear "weapons" in space. However it is unlikely that a nuclear explosive device, fuzed to be detonated only upon interception with a threatening celestial object, with the sole intent of preventing that celestial body from impacting Earth would be regarded as an un-peaceful use of space, or that the explosive device sent to mitigate an Earth impact, explicitly designed to prevent harm to come to life would fall under the classification of a "weapon