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INSTITUTET FÖR RYMDFYSIK UPPSALA
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Swedish Institute of Space Physics (59o50.272'N, 17o38.786'E)
Student project at IRF Uppsala

Project work (15 c)/Examensarbete (15 hp) [BSc thesis]

Photoemission and surface contamination on Rosetta

Student: Ava Gramin, Uppsala University
Supervisors: Fredrik Johansson, Elias Odelstad, Anders Eriksson
Period: Winter 2016/2017

Background

The ESA (European Space Agency) spacecraft Rosetta orbited comet 67P/Churyumov-Gerasiminko for more than two years, 2014-2016. The Swedish Institute of Space Physics in Uppsala designed, built and operated one of the instruments on-board, the dual Langmuir probe LAP, to study the ionized gas (plasma) close to the comet. The principal operational mode of LAP is to measure the current to any of two 50 mm spheres mounted on booms protruding several meters from the spacecraft. The current is carried by charged particles, so the local properties (e.g. density and temperature) of the space plasma can be deduced from this measurement. However, other sources of current also contribute, particularly photoelectrons emitted from the probe itself and surrounding parts on the spacecraft. While this partly contaminates the plasma measurements, it also gives an opportunity to improve the knowledge of photoemission in space, which is crucial not only for Langmuir probe data interpretation but also for the broader topic of spacecraft-plasma interaction and spacecraft charging studies. Another potential problem is contamination of the probe surfaces, due to condensation of gaseous matter from the spacecraft or the comet itself.

Project

The overall goal is to characterize surface contamination of the LAP probes. Changes in observed photoemission current from the LAP probes, after compensation for variations in solar UV flux, indicate changes of probe surfaces. This is particularly if different changes are seen on the two LAP probes, which have different exposure to e.g. exhaust plumes from the thruster rockets on Rosetta. As the LAP operational modes have changed during the mission, systematic effects of which mode we are running must be constrained and/or compensated for.

Results

To come!

[Rosetta]
ESA's comet hunter Rosetta, with the two Langmuir probes from IRF Uppsala at the end of the booms protruding from the spacecraft. Each probe is a sphere of 50 mm diameter. [Background image credit: ESA]

http://www.space.irfu.se/exjobb/2016_ava_gramin/index.html
last modified on Thursday, 17-Nov-2016 20:55:09 CET