The Radio and Plasma Waves (RPW) experiment is unique amongst the Solar Orbiter instruments in that it makes both in-situ and remote-sensing measurements. RPW will measure magnetic and electric fields at high time resolution using a number of sensors/antennas, and it will determine the characteristics of electromagnetic and electrostatic waves in the solar wind from almost DC to 20 MHz. RPW has heritage from Stereo and BepiColombo Mercury Magnetospheric Orbiter (MMO) and consists of:
- The Low Frequency Receiver (LFR): LFR covers both in-situ electric and magnetic measurements from DC to about 10 kHz and will provide both waveform and power spectra in this frequency range. Highlevel processed data (polarization and propagation properties of the observed waves), with various data rate possibilities (continuous or cyclic transmission, adaptable frequency bandwidth, as well as adaptable frequency and time resolutions) will also be provided by LFR.
- The Thermal Noise and High Frequency receiver (TNR-HFR): TNR-HFR will determine properties of the ambient electron population from measurements of the local thermal noise around the plasma frequency and remotely detect solar radio emissions. It will provide, at various temporal resolutions, electric power spectra from 4 kHz up to 20 MHz and magnetic power spectral densities from 4 kHz up to 500 kHz.
- The Time Domain Sampler (TDS): TDS will perform digitization of the electric and magnetic field waveforms in the frequency range from 100 Hz to 250 kHz. These will be pre-processed and a selection of potentially interesting events will be stored in internal memory and later transmitted to the ground.
These three sub-systems (LFR, TNR-HFR, TDS) are connected to two different sensor units: a set of electric antennas (ANT) and a search coil magnetometer (SCM), both of which will be optimized to perform correctly for DC as well as high frequency measurements. The ANT sensor design is optimized to measure both DC/low frequency electric fields and higher frequency radio and thermal noise emissions. A biasing unit (BIAS, as described below) will allow DC electric measurements. ANT consists of a set of three identical antenna monopoles deployed from two corners and one side of the spacecraft. After deployment, the three monopoles are 120° apart, in a plane perpendicular to the spacecraft-Sun axis. Each monopole consists of a rigid deployable boom and a deployable antenna sensor. The rigid deployable boom provides a larger spacing of the antenna sensor from the spacecraft and ensures that the antenna sensor will be fully illuminated and therefore well coupled to the local plasma potential through a photoelectron sheath. This is required for good DC/LF measurements.
The BIAS will drive a constant current to the electric antennas allowing reliable DC/LF electric field and satellite potential measurements by minimizing the impedance in the coupling to the plasma.
The SCM is an inductive magnetic sensor consisting of a core of a high permeability material (ferrite or permalloy) around which a main coil with several thousand turns and a secondary coil with a few turns are wound. The SCM is located on the instrument boom. These subsystems have a common DPU that handles commands, data and communication with the spacecraft. Together with an LVPS, the four sub-systems will be integrated in a main electronic box (MEB) that will be located inside the spacecraft.