Deflecting an asteroid impact – The Technical Feasibility

Asteroid Deflection Strategy

Asteroid deflection strategies have been a topic of interest for those enamoured with space studies for ages galore. From NASA scientists to ordinary people they’ve garnered everyone’s attention. Simply defined, asteroid deflection strategies are the “planetary defense” methods[ref][/ref] using which these near-earth objects (NEOs) are diverted thereby preventing catastrophic occurrences on earth, ranging from tsunamis to impact winters (by placing large quantities of dust into the stratosphere, blocking sunlight)[ref][/ref]. While the probability of such an event occurring any time soon is deemed scant, certain recent events such as Shoemaker-Levy 9 have created enough headlines to get people wondering.

Spotting an incoming asteroid

About 90% of NEOs greater than 1 kilometer in diameter have been surveyed by NASA. On a scale of 1 to 10, a 1 kilometer diameter asteroid is deemed to be the least destructive while a 10 kilometer diameter asteroid is considered catastrophic enough to extinguish all life on earth. These survey programs funded by the NASA have been christened “Spaceguard”. Their aim is to attempt to detect and document all asteroids including and exceeding 140 meters in diameter by 2028.

Deflection strategies

Nuclear attack

Asteroid Nuclear Deflection

This is often considered the easiest and quickest method. This can be done in one of two ways. A nuclear explosion can be instituted around, on or beneath the surface of an asteroid with the resulting blast evaporating part of the object and throwing it off course. This is a form of nuclear pulse propulsion[ref][/ref]. However, one can never be certain whether the NEO has been broken into small enough pieces to completely avoid harm. Fracturing a 10 kilometer asteroid into a six kilometer and four kilometer asteroid is great, but they might still be on target for our lovely little planet and carry worldwide devastation in tow[ref][/ref]. An alternative method is to have a series of small bombs explode alongside the asteroid but at a distance enough to not fracture the object. The relatively small forces from any number of nuclear blasts could be enough to alter the object’s trajectory enough to avoid an impact[ref][/ref]. A key factor however is to do so well in advance so as to have the maximum impact.

Kinetic energy effect

Asteroid Deflection Kinetic Energy

This works through the impact of a gigantic, non-explosive object, such as a spacecraft or another NEO, a collision with which to alter the course of the asteroid. This strategy is being pioneered by the European Space Agency using a carrier craft and an impactor that can be released on command.

Using a gravitational tractor

Asteroid Deflection Gravitational Tractor

Proposed by Edward T. Lu and Stanely G. Love, this method involves altering the natural course of an asteroid slowly over a period of time sometimes spanning years. The idea is to have a gigantic heavy unmanned spacecraft hover over an asteroid and divert it from its orbit through the simple mechanics of gravitational attraction. The spacecraft would attract the asteroid towards itself and thus deflect it from its original path. While slow, this method has the advantage of working irrespective of the asteroid composition or spin rate – rubble pile asteroids would be difficult or impossible to deflect by means of nuclear detonations while a pushing device would be hard or inefficient to mount on a fast rotating asteroid[ref][/ref].

Attach a rocket

Based upon a proposal of theoreticians at Johns Hopkins University, attaching a rocket to an asteroid would propel it off of its path enough to avoid an impact with earth. Another method is termed the Madmen approach, in which a series of disassembles are docked on to the asteroid which then use the asteroid to create small pebbles which are ejected away from the asteroid. The presumed advantage is that it would take only weeks or months to reduce asteroid mass and velocity using this method and it would act as a safe alternative to chemical and nuclear explosives.


It would be safe to say that it would be in humanity’s interest for several countries to have contingency plans and alternative methods ready in the unlikely event of an asteroid attack occurring anytime soon. Russia has some nascent plans in store while the European Space Agency plans to test its kinetic energy method on a non-threatening asteroid in 2015. In addition, NASA’s constant documenting of NEOs along with the search for effective deflection strategies should let us sleep easy at night.

Apophis! – Earth’s death knell?

Image of Apophis
Image of Apophis as a snake in Egyptian Mythology

Egyptian mythology has a character called Apophis which was an ancient spirit of evil and destruction, a demon determined to plunge our world into eternal darkness. Astronomers reason that the name befits a menace that is currently hurling towards Earth from outer space.

Scientists for the past few years have been monitoring a 390 metre wide asteroid which is currently classified under the “Potentially Hazardous Objects” category because of its calculated collision course with the planet. Governments have already been alerted to take necessary actions to avoid any catastrophe that might arise if this rock collides with our planet.

According to an estimate by NASA, an impact from Apophis, which is scheduled to take place on April 13 2036, would generate over 100,000 times the energy released in the nuclear blast over Hiroshima. Thousands of square kilometres from the impact site would receive the direct effect of the impact and the rest of the earth will see the effects of huge amounts of dust released into the atmosphere.

Image of 99942 Apophis
99942 Apophis – Courtesy Wikipedia

Scientists insist on every Near Earth Objects meetings that there is very little time left to decide and act since the technology required to thwart an asteroid would take decades to design, test and build.  Meteorite experts say that it is a question of when and not if such an object will collide with Earth. A meteorite of the size of 1 km and above will cause mass extinction to species inhabiting our planet including us. The possibility of such collisions is in every hundred million years and it seems we are already overdue for a big collision.

Apophis has been a concern since December 2004 after astronomers projected the orbit of the asteroid into the future and found that the odds of it hitting the Earth is alarming. It was predicted that if it missed Earth in its first approach to Earth in 2029, then the next approach in 2036 might most certainly end in a collision. The object currently has an Aphelion of 1.0987 AU, Perihelion of 0.74604 AU, Semi-major axis of 0.92241 AU, Eccentricity of 0.19121 and Orbital period of 323.58 d or 0.89 a. It has an Average orbital speed of    30.728 km/s, Mean anomaly of 339.94°, Inclination of 3.3315°, Longitude of ascending node of 204.43° and Argument of perihelion of 126.42°.

Image of Radar Image of Apophis
2005 Arecibo Radar Image of Apophis – Courtesy NASA

Currently Apophis is placed at 4 out of 10 in the Torino Scale which measures the threat posed by an NEO where 10 is a certain collision that causes global catastrophe marking it the highest for any asteroid in recorded history. However, the collision in 2029 was eventually ruled out as more data poured in.

Astronomer Alan Fitzsimmons of Queen’s University, Belfast said that Earth’s gravity will deflect the asteroid on 2029 and that there is a small possibility of the asteroid moving through a region in space called the keyhole. If that happens, the chances of a collision during its next pass in 2036 will be even higher.

There is no shortage of ideas as to how to deflect asteroids like these. Even dangerous technologies like nuclear powered spacecraft is under consideration. The Advanced Concepts Team at the European Space Agency is leading the effort in designing a range of satellites and rockets to nudge these potentially hazardous objects. According to Prof Fitzsimmons, the advantage of nuclear propulsion is the amount of power it generates though it has not been tested so far. Solar electric propulsion, another promising idea is already being used by several spacecrafts giving us hope that projects like these would work.

Another interesting method favoured by ESA is the proposed Don Quijote mission which intends to send two spacecrafts at the asteroid. One of them called Hidalgo is supposed to collide with the asteroid and the other called Sancho is supposed to measure the deflection caused by the collision. The test launch is supposed to take place in 2013. Another idea is to use explosives on the asteroid but no astronomer has so far supported the idea since if the explosion takes place close to impact, we might have several fragments hitting us than one thereby increasing the area of damage.

Image of Apophis Path of Risk
The path of risk where Apophis may impact in 2036 – Courtesy Wikipedia

Currently we cannot rule out the possibility of the 2036 impact. However, we need to get our next chance in making an observation of this object which unfortunately will not come until 2013 when we can use radar observations and work out possible future orbits of this asteroid more accurately. NASA argues that the final decision of what needs to be done has to be made at that stage.

Astronomers like Fitzsimmons and Yates say that the preparation should start before 2013 itself. In 2029, we will know for sure whether the object will hit us or not. However, if the worst case scenario turns out to be true and if Earth is not prepared, then it will be too late. Hence we cannot wait until 2029 and start preparing now itself.