Young stars are expected to be surrounded by protoplanetary disks. To date, such stars have only been observed at optical wavelengths in silhouette against bright nebulae using, the Hubble Space Telescope. Their inner regions are optically inaccessible since they are opaque to visible photons.
The VLA 40-50 GHz system, when completed on all antennas and
supported by a wide-band data transmission system will have three
times the angular resolution of the Hubble Space Telescope and 36
times the sensitivity of the present 40-50 GHz system (a factor of
over a thousand improvement in observing time!). The VLA will be the
only
instrument able to penetrate the inner regions of protoplanetary
disks. The disks are optically thick to optical wavelengths, and they
cannot be resolved at longer wavelengths. Present estimates suggest
that roughly 100 protoplanetary disks with angular extent exceeding
exist within 200 pc of the Sun with total flux densities
of 1 mJy at 
7mm wavelength. Such a source could be imaged with
a
signal-to-noise ratio of 10:1 in 12 hrs with the A-configuration.
Technical requirements essentially match those of §3.3.