New Fuels Are Being Developed For Satellite Propulsion - Part 1 of 2 Parts

New Fuels Are Being Developed For Satellite Propulsion - Part 1 of 2 Parts

Part 1 of 2 Parts
    Space industries are always looking to find better propellants for satellites. The current commonly used propellant is hydrazine but it is highly toxic. Developing new propellants for satellites to replace hydrazine would make launching and handling of satellites much safer but it would also require change to current systems which be expensive and difficult.
    The number of satellites in Earth orbit has been rapidly increasing with even more scheduled for future launch. Getting those satellites into Earth orbit is only part of the necessary effort. After a satellite has been launched into its chosen orbit, it needs to have a way to propel itself so it can move if it needs to avoid space trash in orbit. It also needs to compensate for the drag effect of thin atmosphere to stay in orbit. Eventually, it should be deorbited to be disposed of and some sort of propellent would be required to accomplish that.
    The current standard propellant for satellites is a hydrazine-based fuel. Exposure to high levels of hydrazine can cause a variety of health problems which include possible damage to liver, kidneys and central nervous system. Hydrazine is violently explosive as required for a propellant. If it spills before a satellite is launched it can be a public hazard.
    Preparing a hydrazine-fueled satellite for launch is a difficult and hazardous activity which requires special precautions for anyone working on it. This includes a garment like a spacesuit to ensure that if something goes wrong and the fuel is spilled, the wearer will not breath any hydrazine. 
     Erikas Kneižys is the Chief Design Officer at NanoAvionics, a spacecraft equipment manufacturer based in Europe. He said “Hydrazine is pretty nasty to work with from a health and safety perspective, so we're seeing a lot more interest in these sorts of new propellants.”
     In 2011, the European Chemicals Agency added hydrazine to its list of “substances of very high concern.” This indicates that the use of hydrazine may be restricted in the near future.
     NanoAvionics specializes in technology for nanosatellites including CubeSats. CubeSats are miniature satellites made from cube-shaped units about four inches on a side. They are typically built from off-the-self components and weigh about two pounds. NanoAvionics say that there has been a three hundred percent increase in the number of small satellites launched between 2016 and 2020. As the number of small satellite launches increases so does the demand for a better propellant for them. Kneižys said “There were basically no products when looking at the CubeSat market and when looking especially at (chemical) propulsion using (clean fuel). So we've seen this niche and started working on it.”
    NanoAvionics has a project named EPSS dedicated to developing a less dangerous propellant based on ammonium dinitramide (ADN) for small satellites. This is a compound composed of nitrogen, oxygen and hydrogen. The new technology involving ADN is referred to as a monopropellant. This process passes the fuel over a catalyst that causes it to decompose. This decomposition produces heat and gas that can propel a satellite. Other small satellite propulsion systems use a bipropellant approach in which two liquids are kept in separate tanks that ignite when they are mixed.
    The use of a bipropellant increases risks during manufacture because the bipropellant fuels could ignite accidentally during handling. Kneižys said, “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.”
    Better propellants would be a great benefit for small satellites but bigger satellites would also be able to make use of such new propellants.
Please read Part 2 next