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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.
Next: The ACTS Satellite
Up: OVERVIEW
Previous: Remote Observing
Patrick Shopbell
3/17/1998