COPS is dedicated to measuring the neutral gas parameters around comet 67P/Churyumov-Gerasimenko, more precisely, the total density and the radial flow velocity. Therefore, COPS consists of two sensors. The first sensor is the so-called Nude Gauge. It is a common pressure gauge which allows direct measurement of the total gas density. Besides its high scientific value this sensor was a designated safety device during the Rosetta mission. If the total pressure exceeded a particular limit, the other sensors onboard the spacecraft shut down in order to avoid damage of the high voltage power supplies. The second sensor is the so-called Ram Gauge. It measures the molecular flow from the comet and hence provides information about the dynamics of cometary gases.
COPS Nude Gauge operation was very reliable all during the mission, whereas the Ram Gauge used up some of the microtips which led to an intermittent operation on lower electron emission for part of the mission.
Calibration measurements taken with the COPS-FS Nude and Ram Gauge at the CASYMIR calibration facility:
The next figure shows the measured pressure values on the Rosetta spacecraft between March 2004 and March 2010. This curve can be explained with three different outgassing mechanisms:
The thruster firing can be observed with COPS. The image below shows the six burn sequences generated by a reaction wheel offloading: