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article imagePossible satellite collision puts focus on space debris cleanup

By Karen Graham     Jan 29, 2020 in Science
Two decades-old inactive satellites currently in low Earth orbit are in danger of possibly colliding on Wednesday evening above the U.S., according to space debris tracking service LeoLabs, raising concerns over the "Kessler Effect."
LeoLabs is a tracking service that uses radar to calculate the collision risk of satellites in low-Earth orbit. Founded in 2016, and based out of Menlo Park, California, the company has a worldwide network of phased-array radars that track objects in LEO in high definition.
On January 27, LeoLabs announced they had identified a potential conjunction, or close approach, between the Infrared Astronomical Satellite (IRAS) and the Gravity Gradient Stabilization Experiment (GGSE) 4 satellite in LEO.
All the scientific jargon means LeoLabs predicted that on January 29, there was a 1-in-100 chance the two satellites could collide with each other at 6:39 p.m. ET about 900 kilometers (560 miles) above the city of Pittsburgh.
However, in an update on January 28, LeoLabs changed its prediction on a collision downward, to about 1-in-1,000, estimating that the two spacecraft will pass between 13 and 87 meters of each other, according to Space News.
Distribution of space debris around Earth
Distribution of space debris around Earth
ESA
Two defunct satellites involved
The Infrared Astronomical Satellites (IRAS) space telescope was launched in 1983 as a joint project of NASA, Britain and the Netherlands, and its mission lasted only 10 months. It weighs about a ton and is the size of a truck with measurements of around four meters by three meters by two meters (12 feet by 11 feet by seven feet).
The other spacecraft is the experimental US satellite, GGSE-4, launched by the US Air Force in 1967. It is not that big, weighing only 85 kilograms (190 pounds), however, it does has an unusual shape. The satellite is 60 centimeters (two feet) wide but 18 meters (60 feet) long, and it flies vertically.
LeoLabs had to take into account the uncertain orientation of the GGSE-4 satellite in doing their calculations and came up with a probability of impact at between one and five percent.
Space Shuttle Endeavour had a major impact on its radiator during STS-118. The entry hole is about ...
Space Shuttle Endeavour had a major impact on its radiator during STS-118. The entry hole is about ​1⁄4 inch, and the exit hole is twice as large.
NASA
If they do hit, they could create around a thousand pieces of debris larger than 10 centimeters, and more than 12,000 fragments bigger than one centimeter, aerodynamicist Dan Oltrogge told AFP.
"We will know because especially for low Earth orbit, there is much radar coverage, and we would see fragmentation happening, we would see objects separating off," he said -- though it won't be visible to the naked eye.
The Kessler effect
Since we began launching satellites into space during the 1950s, we have left behind an ever-growing amount of space debris. According to NASA, the agency is monitoring approximately 20,000 objects as big or bigger than a baseball and 50,000 objects as big as a marble. Additionally, there are an estimated 600,000 pieces of space junk ranging from 1 cm to 10 cm floating, and on average one satellite is destroyed each year.
These pieces of space junk are traveling at 17,500 miles per hour and can exert powerful kinetic energy capable of significant damage upon impact. Knowing this can happen, and looking at the bigger picture, NASA scientist Donald J. Kessler proposed a scenario in 1978 called the Kessler syndrome (also called the Kessler effect, referring to a collisional cascading or ablation cascade).
Launched in 2002  Envisat is the largest Earth observation satellite ever built. The spacecraft stop...
Launched in 2002, Envisat is the largest Earth observation satellite ever built. The spacecraft stopped functioning in 2012.
ESA
Simply put, Kessler theorized that an increase in the number of objects in low-Earth orbit would lead to conditions where collisions between objects could cause a cascade where each collision generates space debris that increases the likelihood of further collisions.
Kessler surmised that one implication of this cascading effect is that the distribution of debris in orbit could render space activities and the use of satellites in specific orbital ranges unfeasible for many generations. And according to Popular Mechanics, with enough impacts, the amount of debris created would reach a critical mass, blanketing our planet in a fog of debris and making it nearly impossible to safely launch spacecraft from Earth.
Jonathan McDowell, an astronomer at the Harvard-Smithsonian Center for Astrophysics, reminds us that "People need to care about this because we depend on space for a lot of things nowadays, so even if you never go to space you're using space technology, with things like GPS, Internet, and satellite communications. So there's a lot of concern," according to CTV News Canada.
More about defunct satellites, collision course, lowearth orbit, Kessler effect, Space debris
 
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