Beneath this eerie green light and tendril-like cables sits a newly developed gridded ion engine thruster that will eventually be used to power the HENON Cubesat on its mission as the European Space Agency (ESA)’s first standalone deep space CubeSat.
The golden cables are taped to the inside of one of the seven vacuum chambers found inside ESTEC’s electric propulsion laboratory, where the ion engine is being tested to understand what parameters will give it the best lifetime and operational performance during its long journey.
The engine, shown producing a plume of blue light, has been originally developed by TransMIT GmbH and is going through industrialisation by Mars Space Ltd, UK. It is a Gridded Ion Engine, similar to that currently flying on the BepiColombo mission, though utilizing an RF discharge to enable significant miniaturization for Cubesat applications.
At the time, the QinetiQ-built engine was the most powerful and high-performance electric propulsion system ever flown. BepiColombo’s thrusters were about the same size as a dinner plate while the ones built for HENON are roughly the same diameter as a wine glass.
Powered by electricity generated from the CubeSat’s solar panels, the engine uses charged xenon gas atoms. A beam of these charged atoms, or ions, is expelled from the spacecraft to propel it forward, seen in the image as faint blue light pouring from the circular silver engine in the centre of the photo.
“So you can see our 3.5 cm diameter radio frequency ion engine that we are developing,” explains Alexander Daykin-Iliopoulos, from Mars Space Ltd, the lead test engineer working on the propulsion system. “Inside the vacuum chamber, we’ve got the MSL thruster accompanied by a novel neutralizer, designed to emit the same number of electrons as the thruster ejects ions to prevent the spacecraft charging up. The new neutralizer also allows us to save more than half the amount of propellant used in-flight.”
Reducing the amount of fuel needed over the CubeSat’s lifetime is one of the most critical factors in accommodating all the equipment into a shoe-box sized spacecraft that could be comfortably carried under your arm. The efficiency of the ion engine and the fuel utilised requires 10 to 20 times less volume and mass than more conventional propulsion systems, allowing more science instruments to be carried onboard the spacecraft.
“If we told people we are going to run a car on the highway for over one million kilometres without it needing to stop for fuel or be serviced they would think it was impossible, but this is in effect what we are doing,” says Davar Feili, an electric propulsion thruster engineer supporting Neil Wallace, who is leading the electric propulsion subsystem for HENON from ESA’s side. “The challenges don’t stop with the thruster efficiency either, as the engine is also required to run for at least 10 000 hours.”
The CubeSat launches with all the fuel it will need to power its 2-3 year lifespan. Part of the tests being done here in the ESTEC laboratories are to optimise the operations of the thruster to make it as efficient as possible, from the amount of gas flow needed to make enough charged ions, to the specific voltages required to power it. All the components onboard also need to be tested to last that long without any maintenance or refuelling in that time. The vacuum chamber the engine is currently inside simulates the vacuum of space, where the engine will operate for its entire lifetime.
At present testing is focused on the thruster and neutralizer, with control of the gas flow and power supplies provided by the electric propulsion facility, but in just a few weeks flight equivalents of the power supply and gas flow equipment, also being developed for the HENON mission, will be delivered to the laboratory, coupled to the engine and tested for the first time.
The HENON mission is being developed under ESA’s General Support Technology Programme (GSTP), which supports in-orbit demonstrations of new technologies to ensure that future ESA missions will have the right technologies available to use at the right time.