At the end of this month a small satellite will flyastride the SpaceX Falcon Heavy rocket as part of the world's first demonstration of "green" rocket fuel in space. The satellite flies on AFM-315 fuel, developed by the Air Force 20 years ago as an alternative to hydrazine common to satellites. If successful, AFM-315 can make satellites much more efficient, reduce satellite deployment from weeks to days, and significantly reduce the safety requirements for storing and handling satellite fuel, which will be good for people and the environment. Looking into the future, scientists working on fuel say that it will play an important role in facilitating operations with remote satellites from the earth.
What kind of fuel do the satellites fly on?
Hydrazine is a volatile fuel that will spoilyou day, and maybe life, if you are exposed to it. To refuel the satellite, you will need a lot of security infrastructure, including hermetically sealed SCAPE suits, just to handle this material. AFM-315, on the other hand, is no more toxic than caffeine, so all you need is a lab coat and a pump. “We literally sat in a room with a plastic jug when we refueled the satellite,” said Chris Macklin, Ball Aerospace engineer and project leader at NASA Green Propellant Infusion Mission.
Unlike hydrazine, which has the consistency of water, AFM-315 is viscous. But its fuel density will increase the "mileage" of the satellite by 50%, if compared with hydrazine of similar volume.
Macklin says that one of the biggestThe advantage of AFM-315 is that it does not freeze. AFM-315 is a liquid salt, which means that at extremely low temperatures it undergoes glass transition. It turns the fuel into a brittle, glass-like solid, but does not cause the 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 extremely low, so the fuel does not need to be heated on the satellite - which usually represents an energy-intensive process. Macklin says that this will make energy available to other instruments or systems on the satellite, which will open up new possibilities for missions on other planets.
But despite all its benefits, the AFM-315 pathfrom concept to launch was very long. First developed in the laboratory of the Air Force in 1998 as an alternative to satellite fuel, AFM-315 was used sparingly due to a high ignition temperature twice as high as hydrazine. Exotic and expensive materials were required to prevent damage to the satellite. By the end of the 2000s, the cost of producing propulsion systems capable of withstanding the burning temperature of the AFM-315 was low enough to be used, but no company wanted to risk refueling their satellites with experimental fuel. In order for AFM-315 to take root in the satellite field, Macklin said, he needed to show himself in orbit. This is how the NASA Green Fuel mission was born.
Initially scheduled for launch in 2015year, the mission with green fuel faced delays that hampered the development of the SpaceX Falcon Heavy rocket. On June 24, the satellite is scheduled to launch with Falcon Heavy and other cargo, including the atomic clock tested for navigation in deep space.
Satellite tire with green fuel wasdesigned by Ball Aerospace and equipped with four 1 Newton engines and one 22 Newton engines to be used for testing AFM-315 fuel. During its 13-month mission, the satellite will activate engines to perform orbital maneuvers, such as lowering the orbit, changing position or tilting, to test the effectiveness of the new rocket fuel.
Macklin says customers have already appearedinterested in using green fuel if the demo flight is successful. This means that the satellites will be able to make operational flights around the Earth already 18 months after the demonstration. Looking to the future, Macklin says that AFM-315 may be particularly useful for exploring the cold regions of the solar system, such as the Martian poles.
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