In a development that could help slow the proliferation of space junk, the orbit of a communications satellite has for the first time been altered using solid iodine as a propellant. The Beihangkonshi-1 smallsat made the maneuver earlier this month using a self-contained NPT30-I2 electric propulsion system developed by French startup Thrustme.
Built by Spacety Luxembourg and launched on November 6, 2020 atop a CZ-6 Long March 6 rocket from Taiyuan, China, Beihangkonshi-1 is a technology demonstrator satellite that's designed to test multi-beam, multi-channel automatic surveillance-broadcast communication systems as a way to provide continuous global aircraft tracking, as well as communication and intervention for air traffic control systems.
That's a pretty standard sort of small satellite, but it suffers from the same problem as other bread loaf-sized spacecraft, which is that they are too small to carry the heavy, complex propulsion systems that conventional satellites use for station keeping, attitude control, and end-of-life disposal.
To overcome this, Thrustme, a spin-off company from the École Polytechnique and the French National Centre for Scientific Research (CNRS), with the support of ESA, has developed a modular ion thruster system that is much smaller and simpler than conventional systems, as well as having the ability to operate using onboard algorithms.
The NPT30-I2 electric propulsion system dispenses with liquid propellants in favor of a plug of iodine, which is solid at room temperature. Aside from not needing any valves or plumbing to move the propellant about, solid iodine doesn't slosh like liquids do, is much denser than liquids, and can be configured into any needed geometry for storage.
The reason why iodine was chosen is familiar to any high-school chemistry student. When iodine crystals are heated, they don't melt and then boil, Instead, they directly flash into a purple gas. This is not only an impressive school lab experiment, it's also very useful for space propulsion.
The ion propellant comes pre-loaded in the NPT30-I2. When the engine is brought on line, the plug is heated and sublimates into gas. The iodine molecules are then given an electric charge and accelerated by a grid, producing up to 1.1 mN of thrust and a specific impulse of up to 2,400 seconds.
The new bolt-on system could be used to make CubeSats that reenter the Earth's atmosphere at the end of their missions, meaning less space junk. They could also be boosted to higher altitudes for longer missions. This could be especially useful for the project constellations of CubeSats that will one day be used for agricultural monitoring or internet access.
Source: ESA
