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| INSTITUTET FÖR RYMDFYSIK |
UPPSALA |
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| Swedish Institute of Space Physics |
(59°50.272′N, 17°38.786′E) |
Student project at IRF Uppsala
Project work /
Projektarbete (15 hp)
Examensarbete /
Master thesis (30 hp)
Numerical modeling of Rosetta Langmuir probe measurements
Student: Fredrik Johansson,
Uppsala University
Supervisor:
Anders Eriksson
Period: Autumn 2012 - spring 2013
Background
Rosetta is an ESA spacecraft, launched March 2, 2004 for arrival at its target comet in 2014. At the Swedish Institute of Space Physics in Uppsala, we have built an instrument called LAP (Langmuir probe) to study the ionized gas (plasma) close to the comet. The basic Langmuir probe principle is simple: we use a metal sphere exposed to space to measure the current that flows due to collection of charged particles as a function of the voltage we apply to the sphere. The more particles in the plasma, the higher the current, resulting in a density measurement. However, despite having the sphere at the tip of a boom extending away from the spacecraft, perturbations due to the presence of the spacecraft and its emission of photoelectrons are inevitable and needs to be studied.
SPIS, the Spacecraft-Plasma Interaction System, is an ESA-sponsored open source code package allowing detailed simulation of spacecraft-plasma interactions. Previous versions of SPIS have not been able to simulate the current flowing to a small Langmuir probe on a big spacecraft within our practical constraints on computer power and run time. We now participate in the SPIS-Science development project, validating a new version of SPIS which actually can be useful for this kind of problem.
Project
The main task is to use SPIS to simulate Langmuir probe bias sweeps on Rosetta in various space environments. The project relates to some previous student projects:
- Alexander Sjögren and
Christian Hånberg used SPIS to simulate the potential structure around Rosetta. The spacecraft model used by them can be modified for use in this project as well.
- Thomas Nilsson simulated the similar Langmuir probe on Cassini.
- Andreas Johlander studied Langmuir probe bias sweeps from most of the LAP data set 2004-2010.
The project included:
- Gathering background information on Rosetta and the SPIS code
- Re-run previous simulations of the Rosetta s/c potential measurements
- Simulate Langmuir probe sweeps using new features in SPIS
Results
- Presentation at the 19th SPINE meeting, ESTEC, March 19-21, 2013
- First report (15 hp project)
- Final report (30 hp project)
Rosetta
with the LAP probes at the end of two booms. When the spacecraft
turns, the probes move around in the cloud of photoelectrons emitted
by the solar panels and the spacecraft itself.
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