An iodine-ion engine has been tested in space for the first time. And successfully, report researchers of the Parisian École Polytechnique and its affiliate ThrustMe Wednesday in Nature. Iodine engines in satellites have been dreamed of for decades, but they have now been successfully demonstrated in space for the first time aboard China’s Beihangkongshi-1 satellite.
Ion motors use electrically charged (ionized) gas that is accelerated in an electric field and then spewed out. By spitting out that gas at high speed, a satellite can be powered. That ion propulsion is not strong enough to launch a satellite, conventional rocket engines are used for that, but it is a very efficient way to control a satellite that is already in orbit.
Read more about the principle of the iodine engine: Into space with an iodine engine
Until now, xenon has almost always been used for this purpose. But that gas is expensive, scarce and must be stored under high pressure. Iodine is a lot cheaper and can be stored in solid form. Then the engine can remain smaller and lighter.
In 2019, the same group of researchers launched their first test system. It was consciously only working half way: it could only emit uncharged iodine gas. The thrust is still far from high enough, so electric charging and acceleration are essential. “That test was important to test the storage of the iodine in space,” said Dmytro Rafalskyi, technical director of ThrustMe and lead author of the study, via video call.
The iodine is stored in solid form and only sublimated to gas when used. “The solid shape allows the iodine to break due to vibrations during launch. It can also come loose from the walls of the storage due to weightlessness. Then it takes a very long time until it has warmed up far enough to sublimate.” The solutions that the researchers devised for this, such as packaging the iodine in porous ceramics, were successfully tested in 2019.
Pipeless system
A lot has happened since then, because storage was not the only challenge. Iodine sublimates easily, but the reverse process is also fast. This can cause the new fuel supply lines to be blocked by solid iodine. The researchers therefore developed a system without pipes. Corrosion, due to reactions of the hot gas with other materials in the engine, also proved to be a challenge. After much testing, the group found the right materials and coatings to prevent this. “We now know for sure that this works for low-altitude flights. But more research is needed to validate that it is also good enough for extended use deep in space,” the researcher admits.
The way now seems clear for the iodine-ion engine. ThrustMe has sold over ten engines in the past year, the same as they demonstrated in space. The company is now working on their production line to scale up to hundreds of engines per year, Rafalskyi said. In upcoming missions, the engine will also be used in satellites up to 200 kilograms, ten times more than the test satellite.
A version of this article also appeared in NRC in the morning of November 18, 2021
#corrections #cheaper #engine