This paper describes the technical excellence of the Sardinia Radio Telescope (SRT) design, development status, and the scientific plans foreseen by the Italian Space Agency (ASI) for deep space tracking, radio science, and related scientific opportunities such as near-Earth objects (NEO) and space debris monitoring. SRT, when functioning as a ground tracking station, will eventually provide operational support to spacecraft at four frequencies simultaneously: X-band uplink and downlink as well as Ka-band uplink and downlink. In order to pursue all of its space science objectives, ASI is also considering an agreement with the Italian National Institute for Astrophysics to share a quota of the observing time of the other smaller Italian radio telescopes at Medicina and Noto, where many successful experiments have been conducted with the Ulysses and Cassini missions as well as many other encounters and detections.

Traditional astronomy has focused on properties of the steady-state universe. Recent discoveries of strong, isolated radio pulses have, however, invigorated interest in transient phenomena. These radio transient events are rare, necessitating long observing times to give reasonable statistics. The National Aeronautics and Space Administration/Jet Propulsion Laboratory (NASA/JPL) Deep Space Network (DSN) tracks spacecraft continuously with several large antennas having low system noise temperature. The DSN also returns substantial predetection bandwidth from the antennas (400 MHz at X-band), currently processing only a fraction of that band for spacecraft tracking. This unused wideband capability is ideal for study of the radio transient sky. Here we describe and show initial performance results of a prototype receiver to search for such transients. This prototype is implemented as a firmware change in an operational DSN tracking receiver and can thus run in parallel with operational spacecraft tracks using existing spare receiver hardware. An operational version of this system could be deployed throughout the DSN to acquire data over extended periods and substantially improve the statistics of rare radio transient events.

In the postprocessing of open-loop radio science receiver (RSR) data, the frequency of a received signal is reconstructed and its amplitude estimated. Three types of algorithms can be used for the signal detection: a digital phase lock loop (PLL), fast Fourier transform (FFT) alone, or FTT with an optimization. One optimization, referred to as spectral analysis, is compared with the PLL and FFT detection methods especially for the case of signal with high-frequency dynamics. The reconstruction procedure is an important first step of processing radio science experimental data since its accuracy influences the resulting science observations. The comparisons deduce that the spectral analysis is superior for the cases of high dynamics signals.

Spacecraft-to-ground bistatic radar provides a straightforward method for surveying planetary surfaces on scales of importance to landers and rovers. Centimeter wavelengths, currently in use for deep-space telecommunications, interact with surface structure of similar to somewhat larger scales. For the quasi-specular component of scattering and for surfaces uniformly illuminated by monochromatic signals from an orbiting or flyby vehicle, the echo Doppler dispersion is proportional to the root mean square (rms) surface slope. When the specular condition occurs within 10°-20° of the Brewster angle, the surface dielectric constant can be derived from relative echo power measured simultaneously in orthogonal polarizations and the Fresnel reflection laws. Cross spectra, computed from outputs of the orthogonally polarized receivers, may be used to calculate a complete description of the polarization properties of the scattered fields. Application to planetary studies requires accurate amplitude and phase calibration of the polarization channels, including correction for any leakage between the two receiving paths, such as from imperfectly isolated antenna feeds. We illustrate these techniques using Mars Express results from “Stealth” (Medusae Fossae), a region on Mars that has not previously been detected by Earth-based radar, and from a long profile including Acidalia Planitia. Single-location Stealth observations support previous conclusions that the surface is rough and porous (dielectric constant ≈ 1.4). But the longest experiment (in which the specular point was followed for an hour) yields relatively high dielectric constants (2.8), suggesting that the model is incomplete. The surface of Acidalia Planitia has low dielectric constants ( ≈2.6) over 60-90 W at 50 N and higher values (≈3.6) as the specular point moves south and crosses the equator.