PDS_VERSION_ID = PDS3 LABEL_REVISION_NOTE = " 2006-12-27 SOC:Carcich Initial version; 2014-02-23 SOC:Carcich Corrected quoted number of modes " RECORD_TYPE = STREAM OBJECT = INSTRUMENT INSTRUMENT_HOST_ID = "NH" INSTRUMENT_ID = "SWAP" OBJECT = INSTRUMENT_INFORMATION INSTRUMENT_NAME = "SOLAR WIND AROUND PLUTO" INSTRUMENT_TYPE = "PLASMA INSTRUMENT" INSTRUMENT_DESC = " ######################################################################## ######################################################################## REQUIRED READING: - McComas et al. (2008) [MCCOMASETAL2008] - Weaver et al. (2008) [WEAVERETAL2008] ######################################################################## ######################################################################## The SWAP description was was adapted from the New Horizons website, Weaver et al. (2008) [WEAVERETAL2008], and McComas et al. (2008) [MCCOMASETAL2008]. Instrument Overview ======== Specifications -------- NAME: SWAP (Solar Wind Around Pluto) DESCRIPTION: Low energy plasma instrument PRINCIPAL INVESTIGATOR: Dave McComas, SwRI ENERGY RANGE: 30 eV - 7.7 keV FIELD OF VIEW: 270 deg x 10 deg (Note 1) ANGULAR RESOLUTION: N/A ENERGY RESOLUTION: 1eV (<2keV); 9% (>2 keV) Note 1: deflection angles up to +15 deg additional Description -------- Solar Wind Around Pluto (SWAP) instrument is designed to measure the properties of solar wind ions for the New Horizons mission to Pluto. The SWAP instrument is an electrostatic instrument. The SWAP electro-optics control the energy band pass of ions entering the instrument. The electro-optics have three parts: the Retarding Potential Analyzer (RPA), the Electrostatic Analyzer (ESA), and the deflector (DFL). The RPA consists of four grids with the inner two having a positive voltage, which repels ions with energies less than the corresponding potential energy (qV). The Electrostatic Analyzer has two parts, which are concentrically spaced, an inner dome and an outer spherical shell (at ground). For any given settings of the RPA and ESA voltages, only ions with a limited range (bandpass) of energies pass through the ESA to reach the detector. The deflector is used to adjust the field of view. SWAPs ESA and RPA voltages are used together to select the E/q (energy) passband. When the RPA is off, the passband is determined solely by the ESA voltage, which provides an 8.5% FWHM resolution. At increasing RPA voltages for a given ESA voltage, the passband is cutoff in a variable shark-fin shape, allowing roughly two decades decreased sensitivity. Finally, differentiating adjacent RPA/ESA voltage combinations, or deconvolving multiple combinations, provides high-resolution differential measurements of the incident beam's flux as a function of energy. Differences in the ion energy as small as 1-2 eV are distinguishable at typical solar wind energies of ~1000 eV which is a resolution on the order of 0.1%. See the Required Reading documents listed above, and provided with this data set, for further details of this instrument and its capabilities. Scientific Objective ======== The Solar Wind Analyzer around Pluto (SWAP) instrument will measure charged particles from the solar wind near Pluto to determine whether Pluto has a magnetosphere and how fast its atmosphere is escaping. Calibration ======== See /DOCUMENT/SWAP/SWAP_CAL.* and Section 4 of McComas et al. (2008) [MCCOMASETAL2008], also available as a preprint at this URL: http://www.boulder.swri.edu/pkb/ssr/ssr-swap.pdf as of 20.April, 2007. Operational Considerations ======== SWAP data are affected by spacecraft attitude and thruster firings. Values for those parameters concurrent with each observation, along with housekeeping information, are included in the observation's data file. The SWAP experiment detects atmospheric escape from Pluto as a change in the solar wind caused by the interaction of the Pluto atmosphere with the solar wind. In certain scenarios, a factor of 10 variation in the solar wind may occur over a period of days. It is therefore critical to measure the solar wind for several solar rotations in order to characterize the most likely external solar wind properties during the actual encounter period. Detectors & Electronics ======== See the instrument description and specifications above. Operational Modes ======== The SWAP instrument uses six modes: OFF; BOOT; LVENG; LVSCI; HVENG; HVSCI. For a description of these modes see Tables IV & V in the Space Science Reviews paper McComas et al. (2008) [MCCOMASETAL2008], also available as a preprint at this URL: http://www.boulder.swri.edu/pkb/ssr/ssr-swap.pdf Science Data Collection ----------------------- Science data are collected in the HVENG and HVSCI modes. HVENG was used extensively during commissioning for initial HV ramp-up. HVSCI is the primary SWAP science mode. In HVSCI, the optical power supply voltages are stepped every 0.5 seconds. During each 0.5-second period at a single pair of RPA/EPA voltage settings, approximately 100 milliseconds are allowed for the optical power supply settling time and 390 milliseconds are allocated to counting events. An overall cadence comprising 128 0.5-second steps defines the 64-second science-acquisition frames and hence all science activities. Two methods of sweeping during each 64 second period, called the coarse-fine and coarse-coarse sweeps, are user selectable. A typical coarse-fine sweep comprises a 32-second coarse sweep which covers the entire energy range with 64 logarithmically-spaced optical power supply voltages, followed by a 32-second (also 64 0.5-second steps) fine sweep. A coarse-coarse sweep comprises two 32-second coarse sweeps performed in one 64-second period. For both sweep types, the optical power supply voltages are set from one of several user-selectable tables. For the coarse-fine sweep, the peak value of the event counter during the coarse sweep is located to set the center voltages of the fine sweep so that a finer resolution sweep around that peak response can be performed. The following graphics describe very roughly of what happens during a typical coarse-fine sweep; more detailed plots are avaiable in the documents referred to earlier. In all three graphics, the abscissa is time covering one 64-second coarse-fine sweep. The legend inside each plot gives a descripting, the range, and the untis of the ordinate. In the first 32 seconds on the left of the plots, the ESA and RPA voltages go rapidly through a large range in a coarse sweep that covers the entire energy range of the instrument. At around ten to fifteen seconds into that coarse sweep, there is a rise in count rate indicated by the peak. Based on the timing and voltages corresponding to that peak, the SWAP instrument sets the ESA and RPA voltages and changes them more slowly through the fine sweep during the second 32 seconds on the right of the plots, and there is a peak observed at much higher resultion during that time. _____________________________________________________________________________ | * | Output Count rate (0-600Hz) * * | * * | * * | * * | * * | * * | * * * | * * * * | * * ** * | _**********_____*************************************______________********__| 0s 32s 64s _____________________________________________________________________________ | * | * Input ESA Voltage (0-4000V) | * | * | ** | ** | *** | **** ______________ | ***** * --------------____________| ****** * | _________________________**********__________________________________________| 0s 32s 64s _____________________________________________________________________________ | ****** | * Input RPA Voltage (0-2000V) | * | * | * | * ______ | ** * ------_______ | ** * ------______ | *** * ------___| ******* * | ________________________***********__________________________________________| 0s 32s 64s One result of this is that there will be gaps in the apparent energy resolution when the data from coarse and fine sweeps are compared against each other. Measured Parameters ======== SWAP counts events which represent the interactions between the SWAP electro-optics and solar wind particles. The energy of any detected event is determined by the energy bandpass in effect at the time of that event, which in turn is determined by the ESA and RPA settings (voltages). SWAP sweeps its energy bandpass over the instrument's energy range, sorts events into energy and time bins, and returns either real-time science or summary data based on those events. Indirectly through calibration, the SWAP instrument measures the bulk properties of the solar wind (speed, density or flux, temperature), and analysis of changes in these parameters during Pluto encounter will provide an indication of the nature of any atmospheric particles that are escaping Pluto. See the SWAP SSR paper for more detail. " END_OBJECT = INSTRUMENT_INFORMATION OBJECT = INSTRUMENT_REFERENCE_INFO REFERENCE_KEY_ID = "MCCOMASETAL2008" END_OBJECT = INSTRUMENT_REFERENCE_INFO OBJECT = INSTRUMENT_REFERENCE_INFO REFERENCE_KEY_ID = "WEAVERETAL2008" END_OBJECT = INSTRUMENT_REFERENCE_INFO END_OBJECT = INSTRUMENT END