PDS_VERSION_ID = PDS3 LABEL_REVISION_NOTE = "2012-07-03 Second LAP delivery; 2015-05-05 Updated archiving contact and REFERENCE_KEY_ID" RECORD_TYPE = STREAM OBJECT = INSTRUMENT INSTRUMENT_HOST_ID = RO INSTRUMENT_ID = RPCLAP OBJECT = INSTRUMENT_INFORMATION INSTRUMENT_NAME = "ROSETTA PLASMA CONSORTIUM - LANGMUIR PROBE" INSTRUMENT_TYPE = "PLASMA INSTRUMENT" INSTRUMENT_DESC = " Instrument Overview =================== The Langmuir probe instrument (RPC-LAP) is part of the set of Rosetta orbiter instruments known as the Rosetta Plasma Consortium (RPC). The purpose of the LAP is to provide measurements of several plasma parameters in the parts of space visited by Rosetta, primarily the cometary environment. LAP uses two Langmuir probes to access primarily the following plasma parameters: - Plasma (electron) density (ne) - Electron temperature (Te) - Spacecraft potential (Vsc) - Plasma drift speed (v) - Plasma fluctuations and waves up to 8 kHz (dn/n, E) Not all parameters can be derived in all regions, and the methods for deriving a particular parameter can vary from region to region. This catalog file gives a brief overview. For more details, please see the instrument description in Space Science Reviews (full reference at end of this file). Scientific objectives ===================== 1. By monitoring the development of plasma density, electron temperature and flow speed from the onset of cometary activity to the perihelion, LAP will significantly improve our view of cometary outgassing and the formation and structure of the cometary plasma environment. 2. By studying time and space variations of the fluid parameters of the inner coma, LAP will pave the way for a detailed understanding of this region, including the diamagnetic cavity where no in-situ observations have previously been made. 3. By its ability to measure plasma density structures, LAP can investigate dynamic features in the cometary environment that can be compared to and linked to comet surface events as observed by other Rosetta orbiter instruments. 4. By measuring density fluctuations and electric field variations from zero frequency up to 8~kHz, LAP will be able to investigate the stability and dynamics of the cometary plasma environment in different stages of cometary activity. This is of particular interest on and inside the contact surface (diamagnetic cavity boundary), which defines the inner limit of penetration of magnetic fields and plasma of solar wind origin into the cometary plasma environment. 5. By analysing LAP data together with data from other RPC instruments, it will be possible to investigate a broad range of problems no single RPC instrument could cover on its own. Examples are interactions between low frequency waves and plasma particles (LAP-ICA-IES), MHD waves and contact surface properties (LAP-MAG), and wave-wave interactions (LAP-MIP). Measurement principles ====================== A spherical Langmuir probe is a conceptually simple device, but is nevertheless able to provide data on a multitude of plasma parameters. The use of two probes extends these possibilities further, particularly when coupled to versatile electronics. LAP implements several measurement principles: - Bias voltage sweeps: yields ne and Te in dense (a few hundred electrons per cm3 and more) plasmas; photoemission saturation current in tenuous plasmas (below a few hundred cm-3); spacecraft potential (actually spacecraft-to-probe potential) in all plasmas. - Probe current variations: yields plasma density fluctuations (dn/n) in dense plasmas; electric field variations in low density plasmas. - Electric fields and spacecraft potential: Yields spacecraft potential, from which the plasma density can be derived in low density plasmas, and electric wave fields. For a full description of the measurement modes, see the published instrument descriptions ERIKSSON2007A and ERIKSSON2008A, provided in the DOCUMENT directory. RPC-LAP characteristics in brief ================================ + Two spherical probes of radius 25 mm + Mounted at the tips of two booms of length 2.24 m and 1.62 m, respectively + Probe surface coating: titanium nitride + Each probe can individually operate in bias voltage or bias current mode + Bias voltage range +-31 V + Bias current range +-44 nA + One high-rate (18.75 kHz, 16 bit) and one low-rate (57.8 Hz, 20 bit) ADC for each probe + Current measurement range +-0.2 mA in low gain mode + Current measurement range +-0.01 mA in high gain mode + Voltage measurement range +-40 V + Analog anti-aliasing filters at 20 Hz, 4 kHz or 8 kHz + Flexible digital filters in flight software + Internal offset determination and calibration by possibility to sweep over open probe or internal resistor + One of the probes (Probe 2) can be used by RPC-MIP in its long Debye length mode LAP Sensor Locations ==================== The LAP sensors, known as LAP1 and LAP2, probe 1 and probe 2, or P1 and P2, are mounted at the tips of the two spacecraft booms, of length 2.24 m and 1.62 m. In the spacecraft coordinate system, the probes and the hinges at the boom roots are located in the following positions: Unit x [m] y [m] z [m] ------------------------------------- Probe 1 -1.19 2.43 3.88 Hinge 1 -1.19 0.85 2.30 Probe 2 -2.48 0.78 -0.65 Hinge 2 -1.19 0.65 0.30 In this system, the solar panels extend in the y directions, while the +z direction is the nominal comet pointing direction. The booms are mounted on the -x surface, where the Rosetta lander (Philae) is carried during the cruise to the comet. ==================== Operations ========== LAP has a wide variety of possible operational modes. An overview of the various possible settings is provided in the instrument descriptions ERIKSSON2007A and ERIKSSON2008A in the DOCUMENT directory. The latter of these references give examples of how the variety of LAP operational settings are condensed into 'macros', fully defining the instrument operations from the time the macro is started. See also the section on LAP operational modes in the EAICD. RPC-LAP key people ================== PI: Anders Eriksson, Swedish Institute of Space Physics, Uppsala TM: Lennart Ahlen, Swedish Institute of Space Physics, Uppsala Software: Reine Gill, Swedish Institute of Space Physics, Uppsala Archiving: Erik P G Johansson, Swedish Institute of Space Physics, Uppsala References ========== ERIKSSON2007A and ERIKSSON2008A in the DOCUMENT directory." END_OBJECT = INSTRUMENT_INFORMATION OBJECT = INSTRUMENT_REFERENCE_INFO REFERENCE_KEY_ID = ERIKSSONETAL2007 END_OBJECT = INSTRUMENT_REFERENCE_INFO END_OBJECT = INSTRUMENT END