The URAP Instrument

The URAP Experiment consists of six sub-instruments that are designed to provide the ideal frequency and time resolution for studying the various wave phenomena that Ulysses was expected to encounter. These six sub-instruments are:

  • Radio Astronomy Receiver (RAR)
  • Plasma Frequency Receiver (PFR)
  • Waveform Analyzer (WFA)
  • Fast Envelope Sampler (FES)
  • A resonance sounder (SND)
  • A DC electric field capability

A more complete description of each of the instruments can be found in Stone et al. (Astronomy & Astrophysics Supplement Series, vol. 92, pp. 291-316, 1992).

The RAR consists of four superheterodyne radio receivers, which cover two bands (1.25 to 48.5 kHz and 52 to 940 kHz) and can be connected to three electric field antenna configurations. Specifically, two of the receivers are connected to the spin-axis monopole and two receivers are connected to either the spin-plane dipole antenna or to the summation of signals from the spin-plane and spin-axis antennas. The summation configuration is used to facilitate determining the direction to a remote radio source. The spin plane antenna consists of a pair of wire booms, each 35 m long, which form a dipole of 72 m tip-to-tip length. The spin-axis monopole is a 7.5 m boom, whose effective electrical length is less than 4 m.

The PFR receivers cover the range from 0.57 to 35 kHz with continuous, logarithmically-spaced frequency steps, large dynamic range, and good time resolution. One of the two PFR receivers is connected to the spin-plane dipole, the other to the spin-axis monopole.

The WFA provides spectral analysis in the range from 0.08 to 448 Hz for both electric and magnetic fields.

The FES provides snapshots of one or two receiver inputs acquired through one of several broad-band filters. These snapshots contain 1024 data points and can cover intervals as short as 1 sec, thereby providing millisecond time resolution.

The resonance sounder uses the RAR and WFA instruments to sound the local medium and to measure the plasma frequency and other resonances in the frequency range 1-48.5 kHz.