Bruce Willis and Space Rocks
Armageddon is, in my (apparently very underrepresented) opinion, a fairly decent movie. Although the love story is exceedingly dull and the physics are just trash, I enjoyed the ensemble cast and dumb fun of oil drillers fighting an asteroid, even if the reasoning behind it makes little to no sense. However, given that the situation in the movie (the asteroid hurtling towards us, not Bruce Willis sacrificing himself) will certainly come to pass at some point in the future, it's important to take a deeper look at it. Although sending Steve Buscemi up into space with a nuke may not be a viable plan, finding a legitimate one, preferably involving as little Buscemi as possible, is an important goal for humanity. So, should a species-killing asteroid find itself on the road to Earth, we'll need to have a game plan.
What's probably the simplest and most reasonable plan we could actually use is a lot less exciting than blowing the rock apart with nukes. For this plan, we'll need to use a 'Gravity Tractor' method, as proposed by NASA in the past. In order for this plan to work, however, we'd need years, and perhaps even decades, of advance warning before the asteroid's impact. Given these issues, we'll assume that in this hypothetical scenario, NASA has finally received some much-needed funding to spot and identify asteroids long before their potential impact with the Earth.
This method requires us to launch an (unmanned) spacecraft to the incoming asteroid. The spacecraft, unlike those proposed in a kinetic impact scenario, would never actually come into contact with the asteroid. Instead, it would need to travel alongside the asteroid over an extended period of time, during which it would either orbit or hover with the asteroid. The idea behind the Gravity Tractor is that the spacecraft, even one much smaller than its target, would continuously thrust in a specific direction while traveling with the asteroid, and, should it maintain this thrust for a long enough period of time, the asteroid will be affected by the gravitational field of the spacecraft.
The gravitational field generated by the spacecraft's continuous direction could eventually be used as a sort of tow line for the asteroid, with which the spacecraft could tow it away from its current trajectory, and hopefully into a new orbit around the sun which would not involve slamming into the earth and killing all humans. The toughest aspects of getting this plan to work would involve technical problems, for the most part. One major issue would be preventing the thrust generated by the spaceship's propulsion from impacting the asteroid and effectively pushing it directly the opposite way we intend. However, scientists have come up with a solution to this issue-- If the thrusters are simply angled slightly away from the spaceship, in order to avoid hitting the asteroid, the Gravity tractor could still work, albeit at a slower speed.
Although the gravity tractor seems like science fiction, it is actually a quite viable plan to change an asteroid's orbit away from Earth, and is one of many being considered by various space agencies around the world. With enough funding, a spacecraft heavy enough and with an adequate amount of fuel could tow asteroids away from the danger zone, and would be a pretty incredible way of moving various space objects where we want them to go. However, the gravity tractor would need a whole lot of advance warning to be successful. Considering that we haven't even started constructing or planning the use of one, decades would likely be required just to bring the idea to fruition, and decades more would be needed to tow the asteroid out of its dangerous orbit. As such, likely the most important thing of all for space agencies to be working on concerning the plan is a more expansive, reliable and complete mapping and identification of asteroids that pose a threat. To do so, they'll need a whole lot more money, but in the end, our lives may depend on it.
What's probably the simplest and most reasonable plan we could actually use is a lot less exciting than blowing the rock apart with nukes. For this plan, we'll need to use a 'Gravity Tractor' method, as proposed by NASA in the past. In order for this plan to work, however, we'd need years, and perhaps even decades, of advance warning before the asteroid's impact. Given these issues, we'll assume that in this hypothetical scenario, NASA has finally received some much-needed funding to spot and identify asteroids long before their potential impact with the Earth.
This method requires us to launch an (unmanned) spacecraft to the incoming asteroid. The spacecraft, unlike those proposed in a kinetic impact scenario, would never actually come into contact with the asteroid. Instead, it would need to travel alongside the asteroid over an extended period of time, during which it would either orbit or hover with the asteroid. The idea behind the Gravity Tractor is that the spacecraft, even one much smaller than its target, would continuously thrust in a specific direction while traveling with the asteroid, and, should it maintain this thrust for a long enough period of time, the asteroid will be affected by the gravitational field of the spacecraft.
The gravitational field generated by the spacecraft's continuous direction could eventually be used as a sort of tow line for the asteroid, with which the spacecraft could tow it away from its current trajectory, and hopefully into a new orbit around the sun which would not involve slamming into the earth and killing all humans. The toughest aspects of getting this plan to work would involve technical problems, for the most part. One major issue would be preventing the thrust generated by the spaceship's propulsion from impacting the asteroid and effectively pushing it directly the opposite way we intend. However, scientists have come up with a solution to this issue-- If the thrusters are simply angled slightly away from the spaceship, in order to avoid hitting the asteroid, the Gravity tractor could still work, albeit at a slower speed.
Although the gravity tractor seems like science fiction, it is actually a quite viable plan to change an asteroid's orbit away from Earth, and is one of many being considered by various space agencies around the world. With enough funding, a spacecraft heavy enough and with an adequate amount of fuel could tow asteroids away from the danger zone, and would be a pretty incredible way of moving various space objects where we want them to go. However, the gravity tractor would need a whole lot of advance warning to be successful. Considering that we haven't even started constructing or planning the use of one, decades would likely be required just to bring the idea to fruition, and decades more would be needed to tow the asteroid out of its dangerous orbit. As such, likely the most important thing of all for space agencies to be working on concerning the plan is a more expansive, reliable and complete mapping and identification of asteroids that pose a threat. To do so, they'll need a whole lot more money, but in the end, our lives may depend on it.
This is a very nice description of the "gravity tractor" idea! The one thing I would have liked to see added would be some actual calculations to show that this idea could actually work. The tractor is trying to accelerate the asteroid (i.e. change its velocity). You could either assume some acceleration and ask how long would the tractor need to significantly alter the asteroid's trajectory. Or you could assume a given amount of time, and ask how big the acceleration would need to be.
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