Since 1957, space agencies around the globe have carried out more than 4,900 space launches. This has left 23,000 radar-trackable objects (larger than 10 centimeters) orbiting the Earth, according to the European Space Agency (ESA). About 1,000 of those are operational satellites, but the rest are objects and debris that resulted from satellites breaking up.
Most of this “junk” is nonfunctional spacecraft and mission-related debris, including fragments from disintegration, erosion, collisions, paint flecks and even solidified liquids leaking from spacecraft. When all the smaller, nearly invisible pieces of space junk (less than 1 mm in diameter), are also counted, there are an estimated 170 million objects in orbit.
The debris orbit travels at about 10 km/s. If a 1-cm particle traveling 10 km/s hits a spacecraft or satellite, it releases the same amount of energy as a small car crashing at 40 km/h. This can damage equipment and put astronauts’ lives at risk.
In 2016, for example, what is believed to have been a paint chip a few thousandths of a millimeter in diameter crashed into a window on the International Space Station. It left a 7-mm wide dent in the window.
There have also been collisions between intact satellites. In 2009, for example, Kosmos 2251, a deactivated Russian military satellite launched in 1993, collided with Iridium 33, a commercial U.S. satellite built in 1997. Both satellites were destroyed and close to 2,000 new pieces of space junk started orbiting Earth.
Tracking debris helps prevent collisions. The U.S. Defense Dept., for example, uses its Space Surveillance Network to track more than 27,000 pieces of orbital debris. A newcomer to the tracking business is the German Space Agency. To handle the task, the GSA contracted with the Fraunhofer Institute for High Frequency Physics and Radar Technology to design and build the German Experimental Space Surveillance and Tracking Radar (GESTRA).
It's a ground-based radar facility that uses 256 individually phase-controlled antennas. The 1.3-GHz transmitters and receiving sections can be housed separately for convenience and flexibility. The transmitters are mounted on a three-meter diameter plate that moves in three axes using a positioning subsystem from AlpinaTec, giving it a wide field of view and the ability to focus its power on relatively small areas of the sky. AlpinaTec is a development firm founded by Peter Burger that specializes in industrial automation. The gimbaled antenna must be positioned accurately since even a small error can lead to significantly inaccurate tracking data.
One of the primary challenges for AlpinaTec engineers was safely supplying the moving antenna plate with cables and hoses for air and water, fiber optics, motor controls, signals and high-voltage power despite the limited amount of space available.
Key to meeting this challenge were off-the-shelf, flexible hose and cable e-chain and chainflex guides from igus inc. The antenna plate’s vertical axis of rotation (azimuth),for example, is equipped with side-mounted cable guides with reverse-bend radii (counter-rotating and running into each other). The elevation axis has two vertically suspended energy chains, one running inside the other, with a reverse bend radius so it does not hit the outer shell.
The axis of rotation around the center of the antenna plate (polarization) also contains two reverse energy chains with reverse bend radius for vertical pivoting movements of ± 50°. And vertical height is handled by a vertically hanging extension-link chain while the lifting unit moves the plate from its parking position to the working position.
The GESTRA radar can monitor objects 24/7 that orbit the Earth from 186 to 1,861 miles up. This data is sent to the German Space Situational Awareness Centre in Uedem, where analysts monitor data for potential collisions and for debris that leaves their orbit to enter Earth’s atmosphere.
The next step in the project involves distributing a network of GESTRAs to track objects in near-Earth orbits.
To see the GESTRA being assembled and the igus components, check out the video below: