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Monday, May 03, 2021

Space Fence? Traffic Cop for Low Earth Orbit.

 With all the communications things going up wonder this.  Worried about the loss our clear skies, but also just getting in each others way.   Its getting crowded up there.   Will a "Space Fence' Work?

A Traffic Cop for Low Earth Orbit

By Keith Kirkpatrick   Communications of the ACM, May 2021, Vol. 64 No. 5, Pages 15-17  10.1145/3453703

On Earth, avoiding collisions is a key priority for traffic cops, air traffic controllers, and the parents of toddlers. It is no different in space—and perhaps even more critical—given that objects orbiting the Earth are moving at more than 17,000 m.p.h., which means that even very small objects less than a centimeter in diameter have caused damage to the International Space Station, the Space Shuttle, and satellites.

In fact, the U.S. National Aeronautics and Space Administration (NASA) estimates there are more than 500,000 such objects orbiting the Earth that are larger than a marble, and at least a million smaller pieces of debris that cannot be tracked. Based on the growing number of commercial and government launches of spacecraft, satellites, and even space stations, the number of objects that will need to be catalogued, tracked, and managed is expected to grow significantly in the coming years. And the solutions to this issue are fraught with both technical and political challenges.

A key organization charged with tracking and notifying the operators of space objects of a potential course collision is the 18th Space Control Squadron (SPCS), part of the U.S. Air Force's Space Surveillance Network (SSN), which currently tracks 27,000 objects in low Earth orbit (up to 2,000km above the Earth's surface), medium Earth orbit (2,000km to 3,600km up), and geosynchronous equatorial orbit (located 35,786km above the Earth).

The 18th SPCS is co-located with the Combined Space Operations Center at Vandenberg Air Force Base in Santa Barbara County, CA, and is charged with handling conjunction assessments (the close physical encounters of two tracked objects in space), collision avoidance, and reentry assessment for satellites and other objects returning to Earth from space.

Object tracking is handled via a network of sensors and telescopes located around the world and in space, and utilizes two-line element (TLE) position datasets (which incorporate the parameters required to uniquely identify an orbiting element at a given point in time), which can then be fed into models that take into account atmospheric drag, gravitational drag caused by the Earth's shape, the Earth's spin, and various other factors in order to predict the motion of each orbiting object over time.

The Space Surveillance Network also incorporates the Haystack Ultrawideband Satellite Imaging Radar (HUSIR), which is located in the Lincoln Laboratory of the Massachusetts Institute of Technology (MIT). HUSIR, the highest-resolution, longest-range sensor in the world, simultaneously generates X- and W-band images that can provide valuable information about the size, shape, and orientation of Earth orbiting objects. HUSIR was incorporated into the SSN in 2014.

In March 2020, additional object tracking capability known as the Space Fence, designed to provide higher resolution for tracked objects, was declared operational. Located on Kwajalein Island in the Republic of the Marshall Islands near the Equator in the Pacific Ocean, the Space Fence uses an S-band radar system to track objects primarily in low Earth orbit (though it is also capable of tracking objects in higher orbits), and allows the tracking of objects below the previous size limitation of 10cm.

While the Space Fence technology permits greater visibility of smaller objects orbiting the Earth, it requires a significant amount of compute power to project the paths of these objects, according to Mike Gruntman, a professor of Astronautics at the University of Southern California's School of Engineering.  .... "

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