Monthly Archives: September 2011

Chinese Researchers Unveil Plan to Divert Asteroid Apophis

Diagram displaying orbital parameters

Asteroid Apophis (Formal designation 99942 Apophis) will be making an extremely close pass to Earth in 2029. The trajectory of Apophis is such that the asteroid will pass through a “keyhole” area of space near Earth, which will cause the asteroid to make a second pass near Earth in 2036.

While the orbital trajectories of the 2029 Apophis encounter with Earth are well known, the details of the 2036 pass are a bit uncertain. Given a window of only seven years between the 2029 and 2036 passes, scientists and engineers will have to work quickly if the chance of a collision between Apophis and Earth is relatively high in 2036.

A recent scientific paper authored by Shengping Gong (Tsinghua University, Beijing) outlines a possible plan of action to divert Apophis.

Given that orbital keyholes are only a few hundred meters wide, the team believes a very small deflection relatively soon would cause Apophis to avoid the keyhole and a second close encounter with Earth.

Aside from sending Bruce Willis and Ben Affleck on a Space Shuttle to blow up Apophis, there are numerous methods that could be used to deflect an incoming asteroid. Some methods border on science-fiction and others are quite ingenious.

Scientists and engineers have suggested placing probes in orbit around Apophis to “steal” its momentum, others have suggested “painting” part of an incoming asteroid a different color to take advantage of solar radiation, and some have suggested the equivalent of a tugboat in space to tow the asteroid. One other method, which is the method suggested by Gong and team, is to use a solar sail to place a small spacecraft on a collision course with Apophis. If the impact velocity is around 90km/s there should be enough energy to move Apophis enough to alter its trajectory.

The close approach of 99942 Apophis to the Earth and Moon on Friday, April 13, 2029.
Image Credit: Wikimedia

No single method to divert an asteroid is perfect, as each of the methods have differing advantages and drawbacks. Based on the calculations presented in Gong’s paper, the main advantage of their proposed plan is that a 10 kg sail colliding with Apophis in 2028 ( a year before the 2029 encounter), would deflect it enough to prevent a second encounter between Apophis and Earth in 2036.

One of the major drawbacks to Gong’s plan is that much like a hot-air balloon or a sailing ship, using a solar sail to place a spacecraft on a collision course with Apophis is fairly risky. The solar wind has variations that could send a craft off-course. One other issue is that a very large sail would be require, which could be easily damaged, or could malfunction.

Another possible issue with Gong’s plan is that the physical properties of Apophis are relatively unknown. Sending an object on a collision course with the asteroid could have consequences if the asteroid breaks apart instead of having its trajectory slightly adjusted. There are also questions of whether or not tweaking the trajectory of Apophis could still end up causing a collision with Earth.

In short, there are many techniques that could be used, if the need arises to alter the trajectory of an incoming asteroid. Each technique has benefits and drawbacks which need to be weighed against what, if any, benefits there would be to altering the trajectory of an incoming asteroid.

If you’d like to learn more about Apophis, visit NASA’s Near Earth Object Program at:

You can read the full paper at:

Source:Utilization of H-reversal Trajectory of Solar Sail for Asteroid Deflection

Earth’s Moon

Photographed by the Expedition 28 crew aboard the International Space Station, this image shows the Moon, the Earth's only natural satellite.
Image Credit: NASA

Shown at center, this image features Earth’s moon, with the limb of Earth transitioning into the troposphere (orange).
The troposphere is the lowest and densest component of Earth’s atmosphere.

The sharp boundary between the orange and blue regions is the tropopause. Silvery-blue noctilucent clouds can also be seen far above Earth’s troposphere.

Source:NASA Image of the Day Gallery

NASA UARS Satellite Reentry

Check out this YouTube video from Analytical Graphics, Inc. AGI’s animation shows UARS in its current orbit, along with its potential debris area, breakup model and the estimated debris region.

The Upper Atmosphere Research Satellite (UARS) will deorbit sometime during the afternoon of Friday, Sept. 23, Eastern Daylight Time. NASA has reported that the satellite will not be passing over North America during atmospheric re-entry.

If you’d like to learn more about AGI, visit:

You can read more about NASA’s Upper Atmosphere Research Satellite mission at:

Source: YouTube/AGI , NASA UARS mission page

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