SANSA demonstrates satellite weightlessness on Earth


Imagine a system that uses complex electronics and magnetism to simulate weightless conditions on Earth, to demonstrate how satellites can be oriented – in outer space. That may sound like science fiction, but a visiting engineering student at SANSA is making this fantasy a reality.

Satellites in low-Earth orbit can use magneto-torquer rods for positioning. SANSA is working on a model of magneto-torquer rods to demonstrate the phenomenon here on Earth.

In order to orient satellites in low-Earth orbit, special electromagnetic  components called magneto-torquer rods are used, but their working principle can be rather complex to explain. SANSA wanted to create an experiment that could demonstrate how a specialised version of a magneto-torquer rod could operate in space, and here is where French exchange student Gaetan Laurent enters the picture.

Laurent, who is an Aerospace Engineering student from France, joined SANSA for a three-month internship. He is a member of the French Air Force Academy, and worked with Danie Gouws (SANSA’s Applied Science and Technology Manager), on this magneto-torquer rod concept experiment.

Gouws explains that a magneto-torquer rod is a ferromagnetic core or rod with many windings of electrically conductive wire wrapped around it to form a coil. As electrical current flows through the wire, the coil induces a magnetic field that interacts with Earth’s own magnetic field called the geomagnetic field. The two fields can interact to control the rotation of satellites in different directions in space.

“Because they depend on Earth’s magnetic field to generate a torque, magneto-torquer rods are limited to use in satellites with an altitude lower than 2000km,” says Gouws.

It can be difficult to demonstrate this phenomenon without the benefit of being weightless in low-Earth orbit, so SANSA wanted to construct an experiment to demonstrate it effectively on Earth. For this to happen, a mock satellite would have to be levitated to simulate the weightless conditions of outer space. 

Laurent placed a strong, rare earth magnet inside a small model of a satellite, and placed the satellite model below a strong electromagnet. Using a magnetic sensor that can detect how far away the satellite model is from the electromagnet, Laurent could switch the electromagnet on and off at a very high rate depending on the distance of the model satellite from the electromagnet. 

He then constructed an electronic circuit that supplied power to the electromagnet to attract the satellite model. He created the circuit so that as the satellite model approached the electromagnet, the magnetic sensor would detect the model and switch off the electromagnet depending on how close the model is. This makes the satellite model fall back to Earth due to gravity, but this switching on and off happens so rapidly (50 000 times a second) that the satellite model effectively levitates.

Having achieved levitation to illustrate weightlessness, Laurent moved on to place another small magnet on the body of the satellite model. “An external magneto-torquer rod, when activated, interacts with the small magnet on the model satellite to stabilise a spinning levitated satellite and demonstrate the ability of a torque rod to change the orientation of the model satellite,” says Gouws.

Laurent has returned to France to finalise his BEng, but the project continues at SANSA within the Applied Science and Technology unit.

Vaneshree Maharaj