At the end of this month, a small satellite will fly SpaceX Falcon Heavy as part of the world's first demonstration of "green" rocket fuel in space. A summer satellite on AFM-315 fuel, developed by the Air Force 20 years ago as an alternative to hydrazine common for satellites. If successful, AFM-315 can make satellites more efficient, reduce the placement of satellites from weeks to days and significantly reduce the safety requirements for storage and handling of satellite fuel, which will be beneficial for people and the environment. Looking to the future, scientists working on fuels say that it will play an important role in facilitating operations with distant satellites from the earth.
What kind of fuel do the satellites fly?
Hydrazine is a volatile fuel that will ruin your day and maybe your life if you are exposed to it. In order to refuel the satellite, you will need a lot of security infrastructure, including tight SCAPE overalls for the whole body, only to handle this material. On the other hand, AFM-315 is no more toxic than caffeine, so all you need is a lab coat and a pump. "When we refueled the satellite, we literally sat in a room with a plastic jug," said Chris Macklin, Ball Aerospace engineer and project manager at NASA Green Propellant Infusion Mission.
Unlike hydrazine, which has the consistency of water, AFM-315 is sticky. However, its fuel density will increase the "course" of the satellite by 50%, compared with hydrazine of similar volume.
Macklin says one of AFM-315's biggest advantages is that it does not freeze. AFM-315 is a liquid salt, which means that it changes the glass at extremely low temperatures. Turns the fuel into a brittle, glass-like solid, but does not cause fuel to expand, like frozen water or hydrazine. This attribute prevents cracking of fuel lines and storage tanks under load. In addition, its glass transition point is very low, so the fuel does not have to be heated on the satellite – which is usually an energy-consuming process. Macklin says that thanks to this energy will be available to other instruments or systems on the satellite, which will open new opportunities for missions on other planets.
But despite all its advantages, the path of the AFM-315 from concept to launch was very long. Developed for the first time in the Air Force Laboratory in 1998. As an alternative to satellite fuel, the AFM-315 was sparingly used due to the high flashpoint twice as high as hydrazine. Exotic and expensive materials were necessary to prevent damage to the satellite. At the end of 2000, the cost of producing propulsion systems capable of withstanding the AFM-315 combustion temperature was so low that it could be used, but no company wanted to risk refueling its satellites with an experimental fuel. For AFM-315 to take root in the satellite field, Macklin said, he had to appear in orbit. This is how the NASA Green Fuel mission was born.
Initially planned launch in 2015, the Green-Fuel Mission faced delays that hampered the development of the SpaceX Falcon Heavy rocket. On June 24, the satellite is to launch Falcon Heavy and other charges, including the atomic clock tested for navigation in space.
The Green Satellite Bus was developed by Ball Aerospace and is equipped with four Newton 1 motors and one 22 Newtons engine that will be used to test AFM-315 fuel. During the 13-month mission, the satellite will launch engines to perform orbital maneuvers, such as lowering the orbit, changing position or inclination, in order to check the effectiveness of the new rocket fuel.
Macklin says that there are already customers interested in using green fuel if the demonstration flight is successful. This means that satellites will be able to conduct operational flights around the Earth as early as 18 months after the demonstration. Looking to the future, Macklin says that the AFM-315 can be particularly useful for researching cold areas of the solar system, such as the Martian poles.
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