Solar system science imposes some of the more demanding constraints on the correlator, total power system, and prime focus systems. All elements of the proposed project will have a significant impact on solar system science, as we now summarize:
Filling in the frequency coverage with new wide-bandwidth feeds and receivers is extremely important. The 2.4 and 33 GHz bands will significantly augment the VLA's ability to support planetary radar experiments. The VLA will be able to participate in bistatic-mode observations with the newly upgraded 2.4 GHz transmitter at Arecibo, and with a new 30 GHz transmitter at Goldstone. The completion of the 40-50 GHz system will be particularly important for probing the outer layers of the terrestrial planets. The increased continuum sensitivity will enable much greater numbers of background sources to be exploited as probes of the IPM.
To take advantage of the wide bandwidth ratios for solar imaging experiments, we require the ability to re-tune and re-establish phase-lock on timescales sec. In addition, at least one dichroic system is desirable, pairing the 2.4 GHz/8.4 GHz bands or the 4.9 GHz/15 GHz bands, for example.
An exciting prospect for solar physics is performing broadband imaging spectroscopy of solar radio bursts over roughly an octave of bandwidth: e.g., 300-600 MHz. To do so requires a broadband feed located at the prime focus. For solar observations, the feed does not need to be high performance.
A robust total power system is required for both solar and planetary radar observations. The demands are not stringent for the planetary radar case. They are quite demanding for the solar case, however. During solar flares may increase by orders of magnitude over a timescale of seconds. Therefore an accurate, linear (over a dynamic range of 30 dB), and fast (0.1 s) total power system is needed. A robust total power system is also needed in support of a super-compact array configuration (E configuration), which will be used extensively for mosaicing.
A new correlator is required to process broadband continuum signals, to support an enhanced spectral line capability, and to support more flexible observing modes. In the case of solar observations, a new correlator is needed in support of broadband imaging spectroscopy. Transient bursts occur on timescales of several 10s of ms over relative bandwidths of . Imaging with 128 or 256 channels with a time resolution of, e.g., 20 ms, produces an enormous number of baseline-channels per second ( !) if the full array is employed. It is anticipated that a subarray of perhaps 9-10 antennas will suffice, in which case the number of baseline-channels per second is reduced by a factor of 8-10. Alternatively, a ``burst mode'' could be employed wherein only short periods of interest are recorded to a large buffer with full temporal and spectral resolution. It is likely that imaging spectroscopy performed by a subarray of antennas would be complemented by continuum imaging in other bands by the remaining antennas.
In the case of planetary bistatic radar observations, the spectral resolution required to resolve the Doppler-broadened radar signal most objects is 5 Hz. On the other hand, observations over a wide bandwidth are required to obtain an accurate measurement of the baseline due to the thermal source emission. These competing requirements suggest correlator modes which support two spectral line observing modes simultaneously, one with high spectral resolution and the other with coarser resolution.
A super-compact configuration with good surface-brightness sensitivity is needed for the study of largescale transient solar phenomena (eruptive prominences and CMEs), for the study of comets, and for mosaicing fields of interest at high frequencies.
An extended VLA configuration is highly desirable for the study of planets, minor bodies, and the IPM. Bistatic radar in the S band with the A+ configuration will permit comparisons with similar measurements in the A configuration in the 8.4 GHz band with matched angular resolution. In addition, the A+ configuration would allow the Galilean satellites to be resolved.