What kind of testing does the ESA Propulsion laboratory carry out?
An eerie bluish glow is the tell-tale sign that the Laboratory is in the midst of testing. Ion thrusters produce a distinctive exhaust plume of ionised plasma – and much of the Laboratory's work involves characterising engine performance as they fire.
Test firing is carried out within specialised vacuum chambers. Laboratory personnel seek to measure the precise level of thrust an engine produces, the rate of propellant flow and the amount of electric charge driving the firing, and what happens if current or propellant levels are changed – how controllable is the engine?
The Laboratory has a certified ability to obtain these measurements. As well as possessing general ISO (International Organization for Standardization) 9001 quality management accreditation, the facility has specific ISO 17025 accreditation for measuring thrust, mass flow and electrical parameters related to propulsion system operations, along with related calibration processes.
Another test the Laboratory performs is endurance firings: because ion thrusters in particular deliver low initial acceleration they often need to operate for extended periods of time to yield full benefit. So ion thrusters have to be run continuously in the Laboratory for hundreds or even thousands of hours at a time.
A thruster's exhaust plume is also a rich source of performance data. Diagnostic systems record the plume's electrical charging and chemical make-up. Meanwhile high-speed, high-resolution cameras monitor the plume visually, including the degree of divergence it exhibits leaving the thruster nozzle, reflecting the rate that propellant ion have been accelerated.
Besides testing complete electric propulsion engines of various types – including Hall effect thrusters, resistojets, FEEP engines as well as high to medium ion engines and micro-propulsion - the Laboratory is also able to check the performance of individual subsystems such as propellant feeding systems, power supply and conditioning units, anodes and cathodes as well as neutralisers whose task it is to prevent a potentially dangerous electrostatic charge building up while the thruster is fired.
The Laboratory supports the work of ESA's Propulsion and Aerothermodynamics division, reflecting its overall range of activity. Its chemical propulsion testing includes work on 'cold gas thrusters' powered solely by internal gas pressure. It also involves research on means of increasing propellant feeding efficiency and avoiding 'water hammer' – pressure waves generated when propellant starts to flow through empty fuel lines – which can sometimes be sufficiently intense to damage the satellite.
Its single most exotic area of research is known as 'in-situ propulsion production' – looking for ways of extracting carbon dioxide from the Martian atmosphere to use as rocket fuel. The aim is to cut the mass needed for the planned Mars Sample Return mission which will not only touch down on Mars but subsequently need to be able to take off again.
Last update: 9 October 2012