INDIUM - Storage Tests of Indium Ion Emitters
Developed more than 20 years ago, Indium Ion Emitters were first successfully tested on board the Russian MIR station in 1991 and have since flown on a number of satellites as part of a spacecraft potential control (ASPOC) or secondary ion mass spectrometer device. All missions in the past required the presence of a pyro spring cap to protect the Indium Ion Emitters from oxidation during long term storage. This pyro cap is both a risk element as well as a cost item.
For NASA’s Magnetic Micro Scale (MMS) mission, a red cap option has been selected as the baseline design to avoid the spring cap method. In this design, a cap is attached on top of the module connected to a nitrogen supply to allow permanent purging. A similar method is to be used on LISA Pathfinder for the Indium FEEP microthruster. Prior to launch, the red cap is removed.
We have to show by testing that the performance of the LMIS is not affected by prolonged purging.
For emitter sizes 0,5 g (MMS baseline) and 15 g (LISA PF baseline) three emitters were selected, documented for current / voltage characteristics, and put into a purging container. After 6 months of purging one 0.5 g and one 15 g emitter were taken out and tested again.
If the emitters are firing they will be stored in standard atmosphere to simulate worst case exposure (as they have been from that day on) for another 6 months (e.g. in a dust- free box). A comparison between the nitrogen purged emitters with the one being exposed to the atmosphere is of specific interest. After one year (+/- one week) the remaining 4 emitters are being tested and documented, and the 2 modules stored under general ambient conditions are being tested again.
ARC Austrian Research Centers GmbH, Space Propulsion & Advanced Concepts - Dr. Wolfgang Steiger
Austrian Research Centers GmbH - ARC
Space Propulsion & Advanced Concepts
Dr. Wolfgang Steiger