Saturday, November 22, 2008

Artifical Satellites and Orbital debris( 2 of 9)

Artificial satellites are used in almost every business or even for personal use. From satellite communications, earth science, astronomy, urban planning, to tracking packages and monitoring weather patterns and natural disasters, satellites are becoming increasingly essential to the modern way of business and life. For example, enhanced 911, in which the emergency station finds the location of the caller, depends upon GPS satellites for most mobile phones. And weather tracking and imaging, vital to air and water traffic and a great help to everyone else, is greatly dependent upon the images that weather satellites provide. So, far from abandoning space after the final moon landing in 1972, space use has only been expanded. In 2007 alone, there were 68 orbital launches and 22 spacewalks worldwide, 19 of those to maintenance artificial satellites. The US and the world have come to depend upon these orbiting satellites, necessitating the tracking and use of thousands of them.
Space debris is considered a problem because of the collisions between spacecraft, especially satellites, and debris. Figure 1 shows the distribution of observable debris (>3.9 inches) in Earth’s orbit, while Figure 2 shows the distribution of satellites in Earth’s orbit. This comparison shows the correlation between the most commonly used orbits and the amount of debris they possess. While spacecraft are made out of extremely durable material, the main problem lies in the large velocities that objects have in orbiting the earth. In space, a .4 inch aluminum sphere in an average orbital velocity of about 16.1 miles/sec has the equivalent velocity of a bowling ball moving at 300 miles/hour. (NASA, n.d.) So while a great deal of the mass of the satellite may be due to the shielding, it usually is not enough to protect against larger debris. And that debris has an especially dehabilitating effect on artificial satellites with their more delicate elements such as memory chips, solar cells and observational lenses that are easily corrupted. So a collision between debris and a satellite is always disastrous to both the information payload on the satellite and the usefulness of the satellite afterwards.

Figure 1 is from the NASA Orbital Debris Program Office Education Package (2005)
Figure 2 is from NASA’s J-Track 3-D (November 16, 2008.) (please click to enlarge)

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