Rosetta Langmuir probe performance

Abstract: Several Langmuir probe voltage sweeps by a model of the ESA spacecraft Rosetta was simulated in a plasma with solar wind parameters using the ESA open source software SPIS 5. The simulations were carried out to in- vestigate the features of the spacecraft’s environment in the solar wind and the effect of photoemission from the spacecraft surface on the measurements made by the Langmuir probes on board Rosetta. We report a best fit to an existing probe sweep result in the solar wind near the Earth at 1 AU from 9 Nov 2009 for a 4 million particle simulation in SPIS of an 8 V positively charged spacecraft with the following parameters: Tph = 2 eV, Te = 12 eV, Ti = 5 eV, ne = 5 cm−3. We also report that the spacecraft is shielding the Langmuir probes on Rosetta from plasma electrons, and particularly low energy electrons. In one instance, this blocking is shown to lead to an over- estimation of solar wind electron temperature by 12% and underestimate the plasma density by 24% by the Langmuir Probe for a +10 V charged spacecraft in ne= 5 cm−3, Te = 12 eV solar wind. Two models used in lit- erature on photoemission, one for isotropical emission from a plane and the other for radial emission from a point, was used and compared. We report a clear preference to the approximation of a Maxwellian energy distribution of photoelectrons emitted radially from a point source model with our sim- ulation result on the Langmuir Probe aboard Rosetta. We also report the solar aspect angle dependence on the plasma potential and plasma density result, which are in overall agreement with Rosetta measurements from the second Earth fly-by.