RPC detection of Rosetta thrusters firing
This plot of measurements by the Rosetta Plasma Consortium's (RPC) Langmuir Probe (LAP) reveals a set of three firings of Rosetta's thrusters on 10 November. When the spacecraft's thrusters are fired (for reaction wheel offloading, in this case), a portion of the gas released is ionized by the solar UV radiation, creating a plasma cloud easily detected by the Langmuir probes of the RPC. The instrument team knew the time slot for the wheel offloading, but not the exact timing. From the LAP data they can see that three thruster firings were performed within a few minutes, and it is possible to accurately time them.
At each firing, a sudden jump is seen in the probe potential, decaying at a slower rate as the cloud disperses. The scale at the left is in volts, showing the potential of one of the RPC probes with respect to the spacecraft. The three peaks reach different heights - this is possibly a sampling effect since the sample rate at the time was set to one sample per second.
Acknowledgment: the plot was provided by Anders Eriksson, the principle investigator for Rosetta's RPC-LAP at the Swedish Institute of Space Physics, Uppsala.