Slow down and speed up for satellites


Satellites must be able to de-orbit when they have completed their mission. A plasma brake could be an answer.

The small Finnish company Aurora Propulsion Technologies is testing a radical new technology for deorbiting satellites this summer. Plasma brake technology was invented by astrophysicist Pekka Janhunen, one of the company’s founders.

The plasma brake is compact, lightweight and relatively inexpensive. The size of an old-fashioned cassette, they can be installed on a satellite before launch, although in the future it may be possible to adapt them to satellites weighing up to 600 kg using a robotic arm mounted on another spacecraft.

The safe deorbiting of satellites is essential to mitigate the generation of space junk by collisions between objects in orbit. A plasma brake unit capable of safely deorbiting satellites from orbits up to 1,000 km altitude would weigh only 2 kg and cost a fraction of competing technologies. The company doesn’t claim to have the only deorbiting solution, but it does claim that the Plasma Brake costs one-tenth the cost of the competition. Aurora Propulsion Technologies CEO, mechanical engineer Roope Takala, estimates a likely selling price will be around €30,000 per unit.

Image credit: Aurora

The technology uses metal micro-tethers made of aluminum or titanium, which are unwound from the satellite to be de-orbited from the ionosphere. When a negative charge is applied to the microtethers, the electric field generated acts as a barrier to positively charged particles in the plasma of the ionosphere.

Braking effects, or Coulomb drag, work best between 400 and 800 km above the Earth’s surface, the altitudinal sweet spot where there are enough positively charged particles to interact with the electric field around micro- tethers and generate drag. The interaction between the plasma headwind that the satellite passes through at 8 km/second and the negatively charged uncoiled microtether causes the satellite to slow down and lose altitude.

The drag from a single tether 300m long is enough to deorbit a 4.5kg satellite about 200km in 9-13 months. Longer and multiple tethers will slow down larger satellites. On May 3, the company said it successfully deployed two tethers to demonstrate the current iteration of the patented plasma brake design on its AuroraSat-1 mission, launched from New Zealand.

According to the company, over the next few weeks its demonstration satellite, known as The Flying Object, will deploy into low Earth orbit to validate its proprietary next-generation collision avoidance and de-orbit propulsion technologies. . Aurora’s satellite will deploy to low Earth orbit to demonstrate how the company’s resistojet thrusters and plasma brakes can “provide effective propulsion and deorbit capabilities for small satellites.”

Going forward, the technology will only be deployed once the satellite has reached the end of its lifespan. “After all, why slaughter a dairy cow,” CEO Takala laughs. “The driving force of the business will always be to keep the satellites up there and productive for as long as possible.” Unlike similar devices that use atmospheric drag to decelerate satellites, the Micro Tether is thinner than a human hair, making it safe for other spacecraft as it won’t cause them any harm. Coulomb drag is also stronger than atmospheric drag. This difference in the deceleration forces is all the greater as the orbital altitude increases. AuroraSat-1 includes a dual Aurora Plasma Braking Module, which for testing purposes has two independently deployable aluminum micro-tether coils, in addition to all control electronics.

In the near future, efficient de-orbiting will become a prerequisite for launch and will be an integral part of the initial design of any satellite. The company expects international legislation to limit space waste to extend to small satellites and other space debris. Current regulations governing end-of-life requirements to deorbit are set by the UN; these only apply to satellites of 500 kg and above, which would not completely burn up on their descent through the atmosphere, which could pose a danger to life when they crash into Earth. The US Federal Aviation Authority is proposing new international regulations that would require even the smallest of satellites to be equipped with a means of returning them safely to Earth at the end of their useful life. Called Designed for Demise (or Death), the D4D regulations will require satellites of any size to have a means of de-orbiting the technology designed into the satellite’s pre-launch, so that new launches never contribute to space junk in orbit. close to Earth in the future.

“We are confident that this technology will be a game-changer in the field of deorbiting, especially in orbits where deorbiting by aerodynamic drag is impossible,” says Takala.


Electric sail on the solar wind

Plasma braking tests in low Earth orbit will pave the way for a new form of space propulsion: the electric sail or e-sail. The electronic sail, invented by Pekka Janhunen, could propel a small craft to the heliopause – the outskirts of our solar system, in as little as 10 years, turning it into the fastest man-made object of all. time. It took 35 years for Voyager-1, a conventionally powered probe, to reach the same point.

Where the Plasma Brake operates in low Earth orbit, the Electric Sail can only be deployed once a spacecraft has exited Earth’s magnetosphere. The sail will be formed by unrolling several 25-micron-thick, 20 km-long threads or micro-threads and rotating the spacecraft to keep them extended. The wires are then positively charged using an electron gun powered by a solar panel, creating a positively charged electric field of a hundred meters around each nanowire.

Our Sun emits a constant stream of charged particles as well as light. The new propulsion system takes advantage of what happens when negatively charged particles from the Sun in the solar wind encounter the positively charged electric umbrella-like structure of micro-tethers attached to a small spacecraft. Each encounter adds infinitesimal thrust to the electronic sail, which builds up over time, adding speed as the spacecraft moves through space.

The beauty of the system is that it’s lightweight, as it requires no chemical propulsion other than that needed to propel the probe past the magnetosphere, the researchers said.

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