RPW INSTRUMENT DESCRIPTION¶

Science Objective¶

RPW will make key measurements in support of the first three, out of four top-level scientific questions, which drive Solar Orbiter overall science objectives:

• How and where do the solar wind plasma and magnetic field originate in the corona?

• How do solar transients drive heliospheric variability?

• How do solar eruptions produce energetic particle radiation that fills the heliosphere?

• How does the solar dynamo work and drive connections between the Sun and the heliosphere?

Here is the summary of the specific RPW Science Objectives.

Solar & Interplanetary Radio Burst

• What is the role of shocks and flares in accelerating particles near the Sun?

• How is the Sun connected magnetically to the interplanetary medium?

• What are the sources and the global dynamics of eruptive events?

• What is the role of ambient medium conditions on particle acceleration and propagation?

• How do variations and structure in the solar wind affect low frequency radio wave propagation?

Electron density & temperature measurements with the Quasi-Thermal Noise spectroscopy

• Precise measurement of both the electron density and temperature, with accuracies respectively of a few % and around 10 %, at perihelion.

• Study the non-thermal character of the electron distributions at perihelion.

Radio emission processes from electron beams: Langmuir waves and electromagnetic mode conversion

• Measurements for the first time in the Solar Wind of both the electric and magnetic field waveforms at high time resolution (up to 500 kSs).

• Study of the mode conversion from Langmuir to electromagnetic waves.

• Study of the energy balance between electron beams, Langmuir waves and e.m. radio waves at several radial distances

Solar wind microphysics and turbulence

• Measure of the waves associated with the plasma instabilities that are generated by temperature anisotropies in the solar wind.

• First DC/LF electric field measurements in the inner heliosphere and over a large radial distance in the solar.

Shocks, Reconnection, Current Sheets, and Magnetic Holes

• Identification & study of the reconnection process in current sheets with thickness down to the ion scales and smaller.

• Determination of the interplanetary shock structure down to the spatial and temporal scales comparable and smaller than the typical ion scales.

• Determination of different particle energisation mechanisms within shocks and reconnection regions.

• Distinguish different radio burst generation mechanisms. Interplanetary Dust

• Determination, in combination with the EPD instrument, the spatial distribution, mass and dynamics of dust particles in the near-Sun heliosphere, in and out of the ecliptic.

To cover its specific Science Objectives, RPW will measure magnetic and electric fields at high time resolution using a number of sensors, to determine the characteristics of electromagnetic and electrostatic waves in the solar wind. More precisely, RPW will:

• Make the first-ever high accuracy, high-sensitivity and low noise measurements of electric fields at low frequencies (below ~1 kHz) in the inner Heliosphere.

• Measure the magnetic and electric fields of the solar wind turbulence with high sensitivity and dynamic range along the spacecraft trajectory.

• Store high-resolution data from scientifically interesting regions such as in-situ shock crossings, in-situ Type III events and others.

• Measure the satellite potential with high temporal resolution permitting to estimate the density fluctuations in the solar wind and allowing higher accuracy particle instrument measurements.

• Measure the quasi thermal noise and Langmuir waves around the local plasma frequency

• Measure for the first type the high frequency magnetic counterpart of Langmuir waves associated with in-situ Type III bursts

• Observe the solar and interplanetary radio burst

• Observe the radio counterpart of dust particle impacts

• Detect on-board in-situ shock crossings and store the corresponding data

• Detect on-board in-situ Type III events and store the corresponding data

Operational Modes¶

Figure below gives the RPW operational modes, which are managed by the Data Processing Unit (DPU).

Fig. 1 RPW operational modes¶

Especially, the DPU shall manage the following modes:

• A “SAFE” mode: RPW is electrically powered by the spacecraft and initializes its DPU Boot Software (DBS). Only Housekeeping (HK) telemetry (TM) is emitted.

• A “STANDBY” mode: When the DPU Application Software (DAS) is started by the DBS upon reception of a telecommand (TC), RPW enters in the STANDBY mode. In this mode, only the DPU and the Power Distribution Unit (PDU) are switched on. RPW waits for a TC to go in the SERVICE mode.

• A “SERVICE” mode: In this mode, RPW switches on all the analyser boards, checks the analyser software integrity before booting them, performs maintenance operations if needed and configures the software and hardware parameters of each analyser. RPW switches ON the Search Coil Magnetometer (SCM) and the Antenna preamplifiers. RPW waits for a TC to go in the science modes

• A “SCIENCE” mode: where the instrument performs scientific measurements and generates related TM packets, including Low Latency.

In the SCIENCE mode, RPW will have capability to run into basically three different sub-modes:

• A “SURVEY_NORMAL” sub-mode, where the science data acquisition is performed continuously in the normal cadence

• A “SURVEY_BURST” mode, where the science data acquisition is performed continuously in a high cadence

• A “SBM_DETECTION” mode where, in parallel to the normal cadence data acquisition, in-situ shocks and Langmuir Waves (LW) events are automatically detected and measured at higher cadence, via dedicated “SBM1” and “SBM2” sub-modes respectively.

The “SURVEY_NORMAL” mode is a nominal cadence mode that will basically run all the time along the orbit, except during time when the “SURVEY_BURST” mode will operate. The “SURVEY_NORMAL” mode is intended to provide all the data for synoptic survey of the plasma conditions in the heliosphere.

The “SURVEY_BURST” mode is a high cadence mode that will be operated by command.

The “SBM_DETECTION” mode will run simultaneously with the normal cadence data flow, and fill internal (circular or no) buffers in order to enable the RPW DPU to perform the selection of in-situ shocks and LW events. The existence of SBM_DETECTION” mode involves therefore that two data flows, one at “normal” cadence, the other one at higher cadence, are continuously recorded by the sub-systems and transmitted to the DPU. The telemetry (TM) data of in-situ shocks and LW events detected by RPW are saved in a dedicated packet store of the Solar Orbiter Solid State Mass Memory (SSMM). The selection of SBM event data to downlink is triggered from ground by command.

Calibration¶