Once a satellite is in position on Earth, it needs a method of propulsion to make sure it can move if necessary, avoiding space debris, compensating for drag over time, and even deorbiting at the end of its mission.
The current standard propellant for satellites is hydrazine-based fuel, which is highly toxic. Exposure to high levels of hydrazine can cause a number of health problems, including damage to the liver, kidneys, and central nervous system. If hydrazine is spilled while a satellite is still on the ground, its violent and explosive nature can become a public safety concern.
Preparing a hydrazine-powered satellite for space is a dangerous task that requires special precautions for anyone involved, including clothing or spacesuit that ensures that if something did go wrong, those handling the fuel would not breathe the gas . “They look a bit like a Michelin man,” said Dr. Norbert Frischauf, a partner at space consultancy SpaceTec Partners in Belgium.
Therefore, it is not surprising that engineers are looking for new and cleaner ways to launch and power satellites that use non-toxic fuels. “Hydrazine is quite unpleasant to work with from a health and safety perspective, so we are seeing a lot more interest in these types of propellants,” said Erikas Kneižys, director of design at NanoAvionics, a manufacturer of spacecraft-based equipment. Europe and US.
In 2011, the European Chemicals Agency added hydrazine to its list of “substances of very high concern” , meaning that its use could soon be restricted.
CuboSats
NanoAvionics specializes in technology for nanosatellites, including CubeSats , which are miniature satellites made of 10 cm cube-shaped units , built with ready-to-use components and weighing around 1 kg each. As satellites as small as these have become more common, NanoAvionics says there has been a 300% increase in small satellite launches between 2016 and 2020 and the demand for clean propellants suitable for them is likely to increase.
“There were basically no products when you looked at the CubeSat market and especially chemical propulsion using clean fuel,” Kneižys clarifies. “So we’ve seen this niche and started working on it.”
Through a project titled EPSS, NanoAvionics has developed a less harmful propellant based on ammonium dinitramide or DNA, a compound of nitrogen, oxygen and hydrogen, specially designed for small satellites. The system has been integrated into a pilot satellite and has undergone an in-orbit demonstration.
The new system is what’s known as a monopropellant, which works by passing fuel over a catalyst that causes it to break down, producing heat and gases that power the spacecraft. Other systems use a bipropellant, in which two liquids are kept separate and generally ignite when mixing.
Using a bi-propellant increases the risk during manufacturing, Kneižys exposes, as the two substances can accidentally come into contact and ignite earlier than expected. “In our monopropellant, you have to go miles to make sure it burns, so it’s relatively benign and stable compared to (most) bipropellant systems.”
But it’s not just the smallest satellites that could benefit from the non-toxic propellant.
HyproGEO , a project coordinated by the aerospace company Airbus, has also developed a non-toxic propulsion system, this time focused on satellites in geostationary orbit around the Earth. Orbiting at 36,000 km, these satellites appear to remain at a fixed point on the Earth’s surface and are generally used for things like communications and transmission.
“It takes a lot of energy to get there,” says Dr. Frischauf of SpaceTec Partners, a member of the HyproGEO consortium.
Right now, that energy is provided primarily by hydrazine-based propellants. But HyproGEO has developed a hybrid powertrain that uses hydrogen peroxide instead. Fuel, which is 98% hydrogen peroxide, compared to the roughly 6% solution you would use to bleach your hair, is highly acidic, but still less dangerous to work with than hydrazine. It also breaks down into oxygen and water, preventing the release of fumes that are harmful to humans.
Geostationary satellites are designed to last a decade or more, so the thruster, which is also used to maneuver them once they are in orbit, must be just as robust. “You have to make sure that it will continue to work after 15 years, so it should be a simple system , because if it is complicated there is always the risk that something will break,” says Frischauf.
Hybrid
HyproGEO’s solution was to use hybrid propulsion, which involves running hydrogen peroxide over a catalyst to produce very hot oxygen, as well as water vapor. That oxygen can provide the propulsion on its own, or it can be used to ignite another substance for an added boost . “When you control the flow of oxygen, you can control the thrust of the engine,” says Frischauf.
The team, which successfully developed a test engine to store the new booster, showed that it broke down as expected and then designed a rocket engine with the fuel. Since that work was completed in 2018, the Norwegian defense company Nammo has used the HyproGEO hybrid engine to launch a rocket 107 km from the Earth’s surface in just three minutes, a timescale similar to that of suborbital rockets. using traditional propulsion systems.
Using these new propellants not only benefits people working with today’s toxic fuels, it also makes the entire infrastructure more efficient and cheaper. Kneižys says that the EPSS system designed by NanoAvionics costs about a third of the products that use traditional propellants.
With all those benefits, what is holding back these new thrusters? For one thing, hybrid powertrains have not been able to count on long durations to put satellites into geostationary orbit, a problem that HyproGEO managed to overcome.
And the industry already has procedures in place for dealing with traditional fuels like hydrazine – transitioning to something new requires disrupting those systems, Frischauf says. “You always need a little push, a little push to ensure that new technology can prevail.”
Original article
This article was originally published in Horizon, the EU Research and Innovation Magazine
