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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 became accurate and since then, scientists and engineers have come up with a well thought out design for an HAIV.
Contents
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 the approximately 1 km wide asteroid 1566 Icarus. An asteroid which 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 of, 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 a 86% chance of reducing the damage a full impact would cause. Though Project Icarus never was tested, it laid the foundation for all future 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 then exploded. NASA expected the meteor to burn up without any issues, but was not the case. This relatively small meteor damaged over 7200 buildings and injured over 1400 people. The Chelyabinsk meteor brought renewed attention towards asteroid defense and the remains of the meteor gave scientists more data on asteroids.
Design
After detecting many of the asteroids within our 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 crafts 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 600 million to 1.8 billion and these were 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".
Irregular NEOs
Sometimes NEOs are difficult to track. They could have an irregular orbit or be spinning, making it hard for the leader craft to make an initial crater. If the HAIV doesn't make proper contact, the NEO's orbit may not change and go on to collide with Earth. NASA is currently working out how to combat this problem for the HAIV, in contrast the project Icarus technique of MIT would not be hindered by these complications.