One of Finland's smaller companies, Aurora Propulsion Technologies, is testing a radical new satellite de-orbiting technology this summer. Plasma brake technology was invented by astrophysicist Pekka Janhunen, one of the company's founders.

The plasma brake is solid, light and relatively cheap. In the size of an old-fashioned cassette, it can be attached to the satellite before launch, but it may be possible in the future to adapt it to satellites weighing up to 600 kg, thanks to a robotic arm mounted on another spacecraft.

Safely removing satellites from orbit is critical to reducing space debris occurring by collisions between orbiting objects. A plasma braking unit that can safely de-orbit satellites from orbits up to 1,000 km altitude will weigh just 2 kg and cost a small fraction of competing technologies. The company doesn't claim to have the only solution for exiting orbit, but says the plasma brake comes at one-tenth the competitive cost. Mechanical engineer Roope Takala, CEO of Aurora Propulsion Technologies, estimates a possible selling price of around €30,000 per unit.

The technology uses aluminum or titanium metal micro multiple tethers that detach from the satellite to provide orbital exit in the ionosphere layer. When a negative charge is applied to the tethers, the electric field generated creates a barrier against the positively charged particles in the plasma of the ionosphere.

Braking effects, or Coulomb friction, work best between 400 and 800 km above the Earth's surface, the most effective altitude at which enough positively charged particles will interact with the electric field and create friction. The interaction between the counterwind of the plasma through which the satellite passes at a speed of 8 km/sec and the negatively charged released tether causes the satellite to slow down and lose altitude.

The friction from a single 300 m long rope is enough to take a 4.5 kg satellite out of orbit about 200 km in 9-13 months. Longer, multiple tethers will curb larger satellites. On May 3, the company said it had successfully deployed two bonds to conduct a trial run of the current copy of its patented plasma brake design during the AuroraSat-1 mission launched from New Zealand.

According to the company, in the next few weeks, the demonstration satellite, known as The Flying Object, will be deployed in low Earth orbit to validate its registered next-generation propulsion technologies that enable collision avoidance and orbital exit. Aurora's satellite was sent into low Earth orbit to demonstrate that the company's resistojet thrusters and plasma brakes can provide "efficient propulsion and de-orbit capabilities for small satellites."

In the future, the technology will be deployed only when the satellite reaches the end of its working life. “After all, why slaughter a milking cow,” CEO Takala says with a laugh. "The business drive will always be to keep the satellites up there and productive for as long as possible." Unlike similar devices that use atmospheric friction to slow down satellites, the microtether is thinner than a human hair, making them safe for other spacecraft as they won't cause any damage. Coulomb drag is also stronger than atmospheric drag. This difference in decelerating forces becomes larger as orbital height increases. In addition to all the control electronics, the AuroraSat-1 includes a twin Aurora plasma brake module with two aluminum microteam spools that can be opened independently for testing purposes.

In the near future, efficient de-orbiting will become an integral prerequisite for the launch of the first design of any satellite. The company expects international legislation designed to limit space debris also applies to smaller satellites and other space junk. Current regulations governing end-of-life requirements for exiting orbit are set by the UN; these only apply to satellites of 500 kg and above that do not burn completely during their descent into the atmosphere and pose a potential danger to life when striking the Earth. The US Federal Aviation Authority is proposing new international regulations that would require even the smallest satellites to be equipped with a means to safely return them to Earth at the end of their useful life. The arrangements, called Designed for Demise (or Death)D4D, will require satellites of any size to have pre-launch de-orbit technology by design so that new launches do not increase space junk in Earth orbit in the future.

Levent Aslan

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