Network Requirements

Given these strong logistic, financial, and scientific motivations for remote observing, we may then explore the network requirements to make remote observing feasible. The primary issue involves the large size of modern astronomical images. The optical instruments in use at the Keck Telescope have frames that are currently 8 Megabytes in size, soon to become a factor of 4 larger. Although actual integration times depend on the scientific program, and range from less than a second to an hour, the quality of ground based optical and infrared astronomy observations is very sensitive to weather conditions, including clouds and atmospheric turbulence. Hence, even though observing sessions are planned in detail in advance, careful ``quick look'' analysis of each image is important in defining what to do next, how long the next exposure should be, whether to switch to brighter objects due to poor sky conditions, how to modify the program to cope with unexpected failures of non-critical telescope or instrument components, etc. An operating mode such as this clearly requires a means of viewing or retrieving the images at the remote observing site with a minimal amount of delay. The public Internet connection between Hawaii and California was in 1995 (and still is today) insufficient for these purposes.

Beyond the network requirements for rapid image data transfer, telescope instrument control software generally employs minimal bandwidth. Due to stringent requirements on robustness and ease of use, long software development times, and the wide variety of astronomical instrument characteristics, instrument software interfaces are rarely more complex than a single interactive window. In some cases that window may even be the user's web browser, as recently groups have been experimenting with front-end instrument control interfaces based on Sun Microsystems' Java language (e.g., [9]).

Finally, previous remote observing projects have demonstrated the need to maintain a strong communications link between the remote astronomer and any on-site technical or operations personnel. Not only does the astronomer require adequate communications to direct the course of the observing run, but the on-site staff also value the contact and stimulation that interaction with scientists brings. There are a range of solutions for this issue, spanning a range of bandwidth requirements, from a simple text-based ``chat'' window, to full audio/video-conferencing systems. Regardless, it is crucial that the communications link not interfere with the accurate transmission of scientific data.