Young stars are expected to be surrounded by proto-planetary disks. To date, they have only been observed in the optical in silhouette against bright nebulae using, e.g., the Hubble Space Telescope. Their inner regions are inaccessible since they are completely opaque to photons at visible wavelengths.
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 resoltion of the Hubble Space Telescope and 36 times the sensitivity of the present 40-50 GHz system (a factor of 1300 improvement in observing time!). The VLA will be the only instrument able to penetrate the inner regions of proto-planetary disks. The disks are optically thick to shorter wavelengths, and they cannot be resolved at longer wavelengths. Present estimates suggest that roughly 100 proto-planetary disks exist within 200 pc of the Sun with flux densities of 1 mJy/beam (). Such a source could be imaged with a signal-to-noise ratio of 20:1 in 12 hrs.
Technical requirements essentially match those of §1.3.3.